Biological Electrical Signals PDF

Biological Electrical Signals M O Ababneh, FCAI A. Professor, IU  Measurement Systems It is a process by which the quantity being measured provides an input to a measurement system, which in turn processes this input to yield an out put in the form...

Biological Electrical Signals M O Ababneh, FCAI A. Professor, IU  Measurement Systems It is a process by which the quantity being measured provides an input to a measurement system, which in turn processes this input to yield an out put in the form of reading or display.  Biological Signals Electrical According to their physical entity are divided into Non-Electrical ELECTRICAL SIGNALS Generated as a result of Electrical actions, which are happened in plasma cell membrane, ECG, EEG, EMG, … NON-ELECTRICALS Movements, deflections, pressure, voltage, volume or flowing changes. e.g.: Expenditure of the heart…  What Is Biological Signals ? ⚫ A Bio-signal is; any signal in human beings that can be continuously measured and monitored. - ECG (electrocardiogram) - EEG (Electroencephalogram) - EMG (Electromyogram) - EOG ( Electrooculogram) - Galvanic Skin Response - MEG (Magneto Encephalography)  Electrical Signals In modern measuring instruments the transducer usually produces an electrical current or voltage. This current or voltage is a signal. ⚫ Signals in clinical measurements are usually voltage signals or ‘biological potentials’. ⚫ Electrical signals can be described in the following ways: 1 - As a voltage varying in time. 2 - As periodic- a signal that varies with a repeating pattern in time, at regular intervals:  Electrical Signals 3 - As Analogue or Digital. 4 - As Series of Frequency Components.  Detection of Signals ⚫ This can be done using proper electrodes.  Signals Processing 1 - Amplification: ⚫ Gain ⚫ Frequency response. ⚫ Upper cut-off frequency. ⚫ Lower cut-off frequency. ⚫ Bandwidth. ⚫ Input impedance. ⚫ Output impedance. 2 - Filtering. 3 - Spectral analysis. 4 - Analogue to digital conversion. 5 - Averaging to Remove Noise. Display of Signals  Initiation of Electrical Potentials 1 - Cardiac Pacemaker. 2 - The Nerve Stimulator & TENS. 3 - Electroconvulsive Therapy. Electric Current M O Ababneh, FCAI A. Professor, IU  Most electrical effects are produced by the movement of charge. Any movement of electric charge forms an electric current. The current flowing in a conductor can be measured as the number of coulombs passing any given point per second. The unit of current is the ampere (amp – SI symbol A), where; 1 Ampere (A) = 1 coulomb s 1 Milliampere (mA) = 1 × 10−3 A 1 Microampere (A) = 1 × 10−6 A  When a current flows through a conductor it produces magnetic lines of force around the conductor. This effect was discovered by Oersted and later applied by Michael Faraday to give rise to the development of electric motors and generators.  Definition of the Ampere If two conducting wires are close to each other they will produce a force between them due to their magnetic fields, which depends on the size of the current in the wires. The Ampere is defined as the current which, if flowing in two parallel wires of infinite length, placed 1 metre apart in a vacuum, will produce a force on each of the wires of 2 × 10⁷ newtons per metre.  Currents flow easily in Conductors, which commonly include metals and electrolyte solutions. Materials which do not conduct current are Insulators. There are some materials with intermediate conducting properties (Semiconductors), e.g. Silicon, which have revolutionised electronic technology.  Electrical Potential If a positive electrical potential exists at a point, any positive charge at that point will possess potential energy and will tend to move away from it to a point at lower potential. Electrical potential is analogous to height in a gravitational field, where a mass possesses potential energy due to its height, and always tends to move downhill. The electrical potential of the earth is taken as a Reference Point for Zero Potential, and is usually referred to simply as earth. Potential is measured in Volts (V). Charge will only move between points separated by a potential difference (also measured in volts).  Potential Difference (Voltage) Potential Difference (Voltage) When a potential difference is applied across a conductor it produces an electric current. A current is a flow of positive charge from the higher potential to the lower. One volt can be defined as a potential difference producing a change in energy of 1 joule when 1 coulomb is moved across it.  Electric Circuits The flow of electric current in circuits is a critical concept. Consider a simple circuit. An electric current flows from positive to negative and lights the lamp. However, as electrons are the only mobile form of charges in a conductor, this current is actually formed by a movement of electrons in the opposite direction.  Ohm’s Law Electrical resistance is the electrical property of a conductor which opposes the flow of current through it. Electrical resistance is measured in Ohms (). Ohm’s law states that the current flowing through a resistance is proportional to the potential difference across it. The potential difference across the resistance = V volts, the current = I amps and the resistance has a value of R. So V = I R volts  Direct Current (DC) & Alternate Current (AC) The terms DC and AC are normally used to describe the electricity supply to a circuit or system, and are applied to either voltages or currents. DC describes current which only flows in one direction (i.e. the polarity always remains the same). Generally DC is supplied by a battery (or power adaptor).  AC describes a supply in which the current reverses direction cyclically. AC is the normal mains supply, and has this form because of the way in which electricity is generated and distributed. An AC voltage is described by its Amplitude (peak value) and Frequency. The amplitude of mains voltage in the UK is 340 V, and it has a frequency of 50 Hz.  Usually mains voltage is quoted as 240 V, which is the root mean square (RMS) value. The RMS value for an AC voltage is the DC voltage or current which would have the same heating effect. This is used to compare AC and DC because the heating and lighting effects (power dissipation) of a current are not dependent on the direction of flow. It is obtained mathematically by squaring the value of the Voltage/Current, averaging this squared value over time and then taking the square root value.  AC currents and voltages are important because they can be used to carry information. In this case they are usually referred to as signals. Often electrical currents and signals are a combination of DC and AC.  Impedance & Reactance The response of many circuit elements to DC and AC can be very different. Some devices may have a very low ability to resist the flow of AC but offer a high resistance to DC, or vice versa.  Resistance is ameasure of a device’s ability to resist DC current. It is represented by R and measured in Ohms. Reactance describes a device’s ability to resist the flow of AC. The reactance of a device will be dependent on the frequency of AC applied. It is normally represented by X and is measured in Ohms. Impedance for a device is obtained by mathematically combining its reactance and resistance. It is normally represented by Z and is measured in Ohms. Note that impedance will also vary with frequency, because of the reactive component. Symbols Representing Circuit Elements  Resistance Resistance opposes the flow of both AC and DC alike. A resistor in a circuit can be used to reduce currents or voltages. Often multiple resistors are used in a circuit. These can be combined in order to calculate the values of currents and voltages produced in different parts of the circuit.  Series Resistance A series arrangement is ‘end to end’. This is shown in Combination of these values is by simple addition.  Parellel Resistance A parallel arrangement is ‘side by side’.  Wheatstone Bridge Circuit This circuit consists of a ring of four resistances supplied by a DC voltage across diagonally opposite corners of the ring A and C. The values of the resistances are balanced using a variable resistor R1, such that points B and C are at exactly the same potential. This occurs when R1/R3 = R2/R4  When this condition is fulfilled, if a galvanometer, G, is connected between B and D no current will be detected and the bridge is balanced or zeroed. The bridge circuit is very sensitive to any variation in the value of the resistances, and if one of them changes a current will be detected on G.  Capacitance Capacitance describes the property of a device enabling it to store electric charge. A capacitor consists of two conducting plates separated by a thin layer of insulating material (or dielectric). When a voltage is applied across the plates, there is an initial surge of current as charge moves onto the plates, but when the plates have become charged no more current flows. The amount of charge stored depends on the size of the capacitance, which is measured in Farads (F).  This in turn depends on the size of the capacitor plates, the separation of the plates and the dielectric material used. The physical size of a capacitor depends on the materials used and the working voltage, but a capacitance of 1 Farad would be impractical in most circuits, being the size of a briefcase, and thus more practical units of microfarads (F) and picofarads (pF) are used.  In a circuit a capacitor has the useful property of being able to pass AC signals, since electrostatic forces between the capacitor plates transmit AC current changes, but to block DC, since there is no direct contact between the plates. The resistance of a capacitor (to DC) is therefore very high since it is effectively an open circuit. However the reactance of a capacitor (to AC) is low and decreases with frequency. This enables it to be used to bypass unwanted AC signals to earth in cases of electrical interference. The frequency dependence of capacitors also means that they are useful components in filters.  Parallel Capacitors Combination of these values is by simple addition. Thus to calculate total capacitance CT, where C1 = 16 F and C2 = 32 F: CT = C1 + C2 = 16 + 32 = 48 F  Series Capacitors Figure PH60 shows series capacitors of value C1 = 16 FTo calculate the total resistance CT: 1/CT = 1/C1 + 1/C2 = 1/16 + 1/32 = 3/32 Thus, CT = 10.7 F. Inductance An inductor is made by forming a conductor into coils, This construction has the effect of producing a concentrated magnetic field through the axis of the inductor and around it, whenever a current flows.  When a voltage is applied across the terminals of an inductor, current does not flow immediately but increases slowly in step with the build up of the magnetic lines of force. Similarly, if the voltage is switched off, the current does not fall to zero immediately but dies down slowly, since as the magnetic field collapses it maintains the current flow for a while.  The build-up and collapse of the magnetic field around an inductor tends to slow down changes in current flow, whenever the applied potential difference varies. The unit of inductance is the Henry (H). An inductance has a relatively low resistance to DC, However, when AC is applied to an inductance, the continually varying current meets a comparatively high reactance. Inductors therefore tend to block AC but pass DC. Inductances are used as components in filters and to ‘smooth out’ spikes and surges in power supplies.  Defibrillator Circuit A circuit using both Capacitance and Inductance is the defibrillator circuit. Its operation consists of two phases, charging and discharging. These phases are controlled by the switch S1. When charging (Figure PH63a) S1 connects the capacitor to the DC power supply, which charges it to deliver  the required amount of energy or number of joules set by the operator. The energy stored by a charged capacitor depends on its capacitance (C) and the applied voltage (V), since Energy stored = 1/2CV2 joules For C = 100F and V = 2000V: Energy stored = 0.5 (100 × 10−6)(2000)2 = 200 J  On discharge (Figure PH63b) S1 connects the capacitor to the patient circuit, which enables the stored charge to be delivered to the patient via the switch (S2) on the paddles. The inductor (L) in the discharge circuit has the effect of slowing down and spreading out the delivered pulse of energy to the myocardium, which makes it more effective than the shorter sharper spike waveform that would be delivered without the inductance.  Transformer A transformer consists of two inductors wound around the same former. The close physical relationship between the two coils means that current changes in one circuit (the primary winding) will induce currents in the second coil (the secondary winding) via the coupling effect of the magnetic field (Figure PH64). The degree of couplingwill depend on the number of turns in the primary winding (N1) and the secondary winding (N2), and the quality of the former. If an AC voltage V1 is applied across the primary, the voltage produced across the secondary (V2) will be given by V2 = V1 × N2/N1  A transformer can thus be used to step up or step down AC voltages in circuits. Transformers are commonly used in distributing the electrical power supply from the national grid to domestic users. An alternative use for transformers is in transferring signals between circuits and in devices such as microphones or loudspeakers.  Diode A diode is a semiconductor (silicon or germanium) device which only enables current to flow through it in one direction. It is often used to convert AC toDC (Figure PH65) in order to provide a DC power supply from the AC mains. This is commonly found in the mains adaptors used as a substitute for equipment batteries. Diodes are also used in protective circuits and to process signals in measurement systems.  Transistor Transistors are also semiconductor devices. These are used to amplify small current signals, enabling small electrical signals of a fewmicroamps to be converted tomuch greater signals of tens of milliamps. The basic transistor consists of a tiny slice of semiconductor material with connections to three regions: base, collector and emitter (Figure PH66). A common configuration allows a small signal fed into the base to produce an amplified signal in the collector circuit. In the early days of transistor electronics a circuit would be constructed using a few separate transistors. In modern electronicsmany thousands or even millions of transistors may be incorporated into a single semiconductor chip, which in turn is simply a single component in a more complex device such as a computer.  Electrical safety The hazards associatedwith the use of electrical equipment are: Electric shock – macroshock Electric shock – microshock Diathermy hazards Burns Fire and explosion  Electric shock (macroshock) Electric shock (macroshock) occurs with the external application of a voltage to the skin, causing an electric current to pass through the body tissues. Commonly electric shock occurs from the ACmains supply. Themains supply in the UK consists of a live line carrying the generated voltage (240 V RMS) and a neutral line, which acts as a return for the current supplied. The neutral line is earthed at the generator. In an intact mains circuit the current supplied in the live line is equal to the return current in the neutral line.  Electric shock occurs from themains supply, when the body forms a circuit between the live mains line and a local earth connection or the neutral mains line. Earthed circuit – The local earth connection may occur via the floor or ground (Figure PH67). Alternatively earthing may take place by inadvertent contact with earthed metalwork such as an anaesthetic machine or operating table (Figure PH68). Isolated circuit – In the absence of an earth connection, an individual or circuit is said to be electrically isolated or floating. However, current can still flow if contact with an alternative return path such as the neutral supply line is made (Figure PH69).  The effects of electric current flowing through body tissues depend on the following factors: Whether the current is AC or DC The magnitude of the current The tissues the current passes through The current density  AC or DC current DC produces a single muscle spasm on contact, which often throws the victim clear. Arrhythmias can be precipitated, but DC shock is also used to cardiovert arrhythmias. Prolonged exposure to low DC currents can produce chemical burns. AC will cause muscle spasm due to tetanic effects, which are maximal at mains frequency (50 Hz). When contact is made through the hand, muscle spasm may cause the individual to grip the contact uncontrollably, Electric Current M O Ababneh, FCAI A. Professor, IU  Defibrillator Circuit A circuit using both Capacitance and Inductance is the defibrillator circuit. Its operation consists of two phases, charging and discharging. These phases are controlled by the switch S1. When charging S1 connects the capacitor to the DC power supply, which charges it to deliver.  Defibrillator Involved charging of a bank of Capacitors to approximately 1000 volts with an energy content of 100-200 joules, then delivering the charge through an inductance such as to produce a heavily damped sinusoidal wave of finite duration (~5 milliseconds) to the heart by way of paddle electrodes. Enabling the application of the device to arrhythmias such as Atrial Fibrillation, Atrial Flutter, and Supraventricular Tachycardia's in the technique known as “Cardioversion”.  MONOPHASIC DEFIBRILLATION Monophasic defibrillators are devices that send a shock in a single direction from an electrode on one side of the patient’s chest to a second electrode on the other side. This technology is known as monophasic waveform defibrillation and it has been used since the invention of defibrillators.  MONOPHASIC DEFIBRILLATION In a monophasic defibrillator, the delivered current is typically very high, at 360 joules, thus requiring large internal components to allow for the generation and storage of the required amount of electrical current to be delivered through the paddles or electrodes. As such, monophasic defibrillators used to be bulky machines not suited for placement in the community or operation by bystander-responders.  BIPHASIC DEFIBRILLATION Biphasic defibrillators utilize a bi-directional current flow and a less powerful shock than monophasic defibrillators. The technology was adopted from automatic implantable cardioverter- defibrillators or ICDs. This bi-directional current flow is known as biphasic waveform defibrillation. There are many advantages to this type of shock delivery system, as can be expected in the majority of technological advances.  BIPHASIC DEFIBRILLATION Electricity is sent from one electrode to the other in the first phase of this waveform, followed by a return back to the originating electrode in the second phase. Biphasic technology requires a much lower current to achieve successful termination of fibrillation. Evidence has demonstrated a higher efficacy with regards to successful defibrillation than with monophasic technology.  BIPHASIC DEFIBRILLATION Because of the lower current, the same components that contributed to the bulky, heavy size of monophasic defibrillators were able to be reduced in size tremendously, leading to the advent of the Automated External Defibrillator. Current biphasic AEDs are about the size of a lunch box, making it realistic for the majority of shopping centers, warehouse stores, super centers, malls, schools, and other social centers of gathering or commerce to be equipped with publicly-accessible devices.  Beyond Monophasic and Biphasic Defibrillation The constant advance of technology has yielded AEDs which are fully automated, provide clear verbal instruction to the operator, are able to determine if the patient is in a Shockable Rhythm (Ventricular Fibrillation/Ventricular Tachycardia), and which will not allow the operator to deliver a shock if the patient’s heart is not in a shockable rhythm. Thus, it is impossible for a layperson who may have little-to-no formal cardiovascular training to harm a patient by delivering defibrillation. Today’s AEDs will only “charge,” and allow the rescuer to emit a “shock,” if the patient is in a recognizable lethal rhythm.  Furthermore, by allowing for a lower current delivery, the most common risk associated with defibrillation of electrical skin burns at the electrode sites is dramatically decreased with biphasic technology. The other common risks, including the risk of stroke from a traveling blood clot, are also dramatically lowered proportionately to the amount of trauma to the body. This should not serve to in any way discount the significantly-positive impact on survival rates that occurred in countless cases as a result of the advent of the monophasic external defibrillator, to which an untold number of victims of ventricular fibrillation owe their lives.  Transformer A transformer consists of two inductors wound around the same former. The close physical relationship between the two coils means that current changes in one circuit (the primary winding) will induce currents in the second coil (the secondary winding) via the coupling effect of the magnetic field.  A transformer can thus be used to step up or step down AC voltages in circuits. Transformers are commonly used in distributing the electrical power supply from the national grid to domestic users. An alternative use for transformers is in transferring signals between circuits and in devices such as microphones or loudspeakers.  Diode A diode is a semiconductor (silicon or germanium) device which only enables current to flow through it in one direction. It is often used to convert AC to DC in order to provide a DC power supply from the AC mains. This is commonly found in the mains adaptors used as a substitute for equipment batteries. Diodes are also used in protective circuits and to process signals in measurement systems.  Transistor Transistors are also semiconductor devices. These are used to amplify small current signals, enabling small electrical signals of a few micro amps to be converted to much greater signals of tens of milliamps. The basic transistor consists of a tiny slice of semiconductor material with connections to three regions: Base, Collector and Emitter.  A common configuration allows a small signal fed into the base to produce an amplified signal in the collector circuit. In the early days of transistor electronics a circuit would be constructed using a few separate transistors. In modern electronics many thousands or even millions of transistors may be incorporated into a single semiconductor chip, which in turn is simply a single component in a more complex device such as a computer. MEDICAL GAS PIPELINE SYSTEM M O Ababneh, FCAI A. Professor. IU  COMPONENTS A medical gas distribution system includes a central supply, piping extending to locations where the gas may be required, and terminal units at each use point. Hoses that extend from terminal units to the anesthesia machine or other equipment, are not part of the piped system.  Supply Source May be Located Outdoors (with the control panel protected from the weather) in an enclosure used only for this purposes. In a room or enclosure within a building. Access to the central supply area should be restricted to individuals familiar with and responsible for the system.  Two cylinder banks (units) are present. Each bank must contain at least an average day's supply with a minimum of two cylinders Larger amounts may be necessary in areas remote from suppliers. The cylinders are connected to a common manifold (header) that converts them into one continuous supply. A check (non-return) valve is placed between each cylinder lead and the header to prevent loss of gas from the manifolded cylinders if there is a leak in an individual cylinder or lead.  The primary (duty, running) supply is the portion supplying the system at any time, while the other bank is the secondary (standby) supply. When the primary supply is unable to supply the system, the secondary supply automatically becomes the primary supply. A reserve supply is often added. The reserve is used for emergencies or when maintenance or repair is needed.  The Reserve System Size Depends on the Rate at Which Gas is Used The reserve system size depends on the rate at which gas is used. A precaution against gas supply disruption is to place the reserve supply in a different area from the primary and secondary supplies and for the reserve supply to enter the facility by a different route.  Further safety may be achieved by separating the primary and secondary supplies so that the secondary supply can be accessed if the primary supply fails. A pressure-reducing (operating) regulator is installed in the main supply line upstream of the pressure relief valve. The pressures at which gases are piped vary, depending on the country.  In most countries, gases other than nitrogen and instrument air are normally piped at 345 to 380 kPa (50 to 55 psi). Nitrogen and instrument air are usually delivered at 1100 kPa (160 psi). The plant permits pressures up to 2068 kPa (300 psi). All final line regulators must be duplexed with suitable valving to permit service without completely shutting down the piped gas system.  OXYGEN Oxygen may be stored either as a cryogenic liquid at low pressures or as compressed gas in cylinders. Gaseous Supply Oxygen may be supplied from compressed gas cylinders (usually G and H cylinders) that are transported between the distributor and the central supply area or from cylinders that are fixed at the site and refilled by the distributor.  When large amounts of oxygen are required, it is less expensive and more convenient to store it as a liquid. Liquid oxygen containers are refilled from supply trucks without interrupting service. Alternatively, filled liquid containers may be transported between the supplier and the facility. Liquid oxygen containers are installed at ground level so that they are readily accessible to supply trucks. The containers should be located where exposure to potential ignition sources is minimal.  To prevent the liquid from evaporating, it must be kept at or below its boiling point (-182.7) by keeping it in special insulated vessels. These containers vary in size and shape. Are constructed like Thermos bottles with outer and inner metal jackets separated by insulation and a layer that is near vacuum to retard heat transfer from the exterior. Each container should have a contents indicator and low liquid level alarm. Gaseous Oxygen is drawn off as required and passed through a heater to bring it up to ambient temperature and raise its pressure. Although the tank is well insulated, a small amount of heat will be continuously absorbed from the surroundings, causing the liquefied gas to evaporate.  Liquid oxygen produces 861 liters of Gas at about STP for every liter of refrigerated liquid which is boiled and heated up to that temperature. Liquid Oxygen (up to 1500 L) is stocked inside the container at about −160°C, much lower than the critical temperature (−118°C) of Oxygen and at a pressure of 5-10 atmospheres. Liquid Oxygen sits at the bottom of the vessel whilst gas sits at the top at a pressure of 10.5 bar. More Recently, a differential pressure gauge, which measures the pressure difference between the bottom and top of the vessel, has been used instead. This alerts the distributor at times of low supply.  As liquid Oxygen evaporates, its mass decreases, reducing the pressure at the bottom. If there is lesser demand, the pressure inside the vessel rises and to prevent this safety relief valve opens at 1700 kPa and blows the gas to the atmosphere. Conversely, the pressure in the vessel will tend to fall if there is a high demand. After passing through the superheater, the Oxygen vapour is passed through a series of pressure regulators to reduce the pressure down to the distribution pipeline pressure of 410 kPa. Fresh supplies of liquid Oxygen are pumped from a tanker into the vessel when required. The Amount of this Uncontrolled Evaporation is Normally Less than the Demand for the Piped System. If there is no flow from the container to the pipeline system, the pressure in the container will slowly increase until the safety relief valve opens and oxygen is vented to atmosphere. If a liquid system is left standing unused for a long period of time, a significant amount of oxygen will be lost. Using liquid containers is economical Only when there is a fairly constant demand. Having the proper size container will minimize oxygen loss from venting.  Most of the time, the Oxygen is kept cold by the latent heat of vaporization as gaseous Oxygen is removed and the temperature falls. As the temperature falls, the pressure within the tank also falls. To maintain pressure, liquid oxygen must be removed from hot water the tank and passed through a vaporizer (evaporator, vaporizing column, gasifier), which supplies heat. This consists of a coil, tube, or mesh that is heated by using electricity. A third possible Oxygen source to feed the Oxygen pipeline is a supply system with Oxygen concentrators.  Pressure Relief Valves Each central supply system must have a pressure relief valve set at 50% above normal line pressure downstream of the line regulator(s) and upstream of any shutoff valve. This relief valve prevents pressure build-up if a shutoff valve is closed. The valve should close automatically when the excess pressure has been relieved.  Shutoff Valves Permit specific areas of the piping system to be isolated in the event of a problem as well as for maintenance, repair, testing, or expansion without the whole system being turned OFF. There are two types of shutoff valves: Manual : Must be installed where they are visible and accessible at all times. Service Shutoff Valves: Are designed to be used only by authorized personnel. They are in locked cases or have their handles secured and tagged to prevent accidental closing.  Manual Valves are Installed in Boxes with Frangible or Removable Windows A quarter-turn valve with an indicating handle has become standard. Each valve should be marked to indicate its function, gas, and area controlled as well as a caution that it should be closed only in an emergency. A shutoff valve is required at the outlet from the supply source. This allows the entire supply source to be isolated.  The main supply line must be equipped with a manual shutoff valve near the entry into the building unless the source shutoff valve is accessible from within the building. It should be at a location well known and readily accessible to those responsible for maintaining the system but where any attempt to tamper with it would be noticed. Each riser must be equipped with a manual shutoff valve adjacent to the connection to the main supply line. Each branch (lateral) line except those lines supplying anesthetizing locations and other vital life support and critical areas (such as postanesthesia care, intensive care, and coronary care units) must have a service shutoff valve where the lateral branches off the riser. A manual shutoff valve is required immediately outside each vital life support or critical care area and must be readily accessible in an emergency.  Emergency Oxygen Supply Connector When the central Oxygen supply is located outside the building it serves and there is not a connected Oxygen reserve sufficient for an average day's supply inside the building, a fitting for connecting a temporary auxiliary supply source for emergency or maintenance situations is required. Inlet must be located on the building's exterior and be protected. The pipe from this fitting attaches to the main supply line immediately downstream of the main line shutoff valve. The inlet should be located where a supply vehicle will have year-round access. In-building emergency reserves may be used in place of the emergency Oxygen supply connector.  Alarms A master alarm system monitors the central supply and the distribution system for all medical gas systems. To ensure continuous responsible observation, master signal panels must be located in two separate locations, wired in parallel to a single sensor for each condition. A centralized computer system may be substituted for one of the master alarms. MEDICAL GAS PIPELINE SYSTEM M O Ababneh, FCAI A. Professor. IU  Alarms A master alarm system monitors the central supply and the distribution system for all medical gas systems. To ensure continuous responsible observation, master signal panels must be located in two separate locations, wired in parallel to a single sensor for each condition. A centralized computer system may be substituted for one of the master alarms. Area Alarms Systms Critical life support areas such as operating room suites, postanesthesia care units, intensive care units, coronary care units, and the like must have an area (local) alarm system to indicate if the pressure increases or decreases 20% from normal line pressure. In anesthetizing locations, the alarm will be upstream of the shutoff valves to the individual rooms. An appropriately labelled warning signal panel for area alarms must be installed at the nurses' station or other suitable location that will provide responsible surveillance.  Local Alarms Local alarms are installed to monitor the function of the central medical and instrument air systems as well as the vacuum and anesthetic gas scavenging systems.. The signals may be located on or in the control panel of the machinery being monitored, within a monitoring device, or on a separate alarm panel.  Alarm Conditions & Response General Requirements Each alarm must be labelled for the gas and area monitored. Signals should be both audible and visual. Some systems allow the audible signal to be audio paused (temporarily silenced). The visual signal should continue until the problem is corrected. Each panel should contain a mechanism to test the alarms. Alarms should be designed to function during electrical power failure.  Clear, concise instructions should be given to the persons monitoring the alarms to ensure that signals are reported promptly to the proper parties. It is important to update alarms when source equipment is updated or replaced.  Alarm Conditions An Alarm Should Signal When the main supply reaches an average day's supply, When the reserve supply or in-building emergency reserve begins to supply the system, When the reserve supply is reduced to one average day's supply, When the pressure in the reserve supply is below that required to function properly, When the secondary supply becomes the primary supply, When the pressure in the main line increases or decreases from normal operating pressure, When the dew point has been exceeded in the medical air or instrument central supply system.  Pressure Gauges A pressure gauge must be installed downstream of each pressure regulator. It is important that the gauge be on the downstream side of a zone valve so that when the valve is closed, this will be indicated by the pressure gauge. Pipeline pressure gauges are present on all anesthesia machines. This allows the anesthesia provider to keep a continual check on pipeline pressure in that location. If a significant decrease or increase in pressure occurs, the anesthesia provider should notify the proper personnel and consider using gas from the cylinders on the machine.  Periodic Testing & Preventive Maintanance A planned preventive maintenance program can prevent potentially hazardous conditions and unexpected loss of service, reduce the economic burden from leaks, and reduce emergency repairs. Maintenance should be performed at least as frequently as recommended by the pipeline manufacturer and more frequently if required by heavy use or local conditions.  Inspection and testing should be performed on a regular basis and the results recorded in a permanent log. If test buttons are provided at area panels, audible and visual alarm indicators should be tested monthly. All hoses and station outlets in the anesthetizing locations and postanesthesia care units should be checked at least monthly for wear, damage, and proper function. Terminal units should be checked for easy insertion, locking, unlocking, and connector removal; leakage, wear, and damage; contamination; gas specificity; labelling; flow; and pressure.  It is Good Practice to Check Alarms Regularly It is good practice to check alarms regularly. Gauges in area and master alarm panels should be monitored daily for proper pressure. The test button on alarm panels should be pressed monthly to verify audible and visual signals. Burned out bulbs should be replaced, and the testing should be documented. All master alarm signals should be tested at least annually to verify proper operation. These signals are required to be wired so that if a wire gets cut, it will alarm. If removing the wire from the sensor does not activate an alarm, it is not properly wired.  Important Features of Liquid Oxygen Plant Oxygen is the second largest constituent element of the atmosphere. It comprises around 20.8% of the atmosphere. It is highly reactive, colorless, tasteless and odorless gas. In its liquid form, Oxygen is pale blue and is very cold. Though it is non-flammable but it supports combustion. It is a strong oxidizer and sustains burning processes. Being highly reactive, Oxygen reacts with all organic materials and metals except noble gases. Any substance that burns in air will burn furiously in Oxygen. Liquid Oxygen (LOX) is generated in a liquid Oxygen plant based on cryogenic distillation process. Important features of a liquid Oxygen plant are described in the following sub-headings: Important features of liquid Oxygen Liquid Oxygen is a cryogenic liquid.  Liquefied gases having normal boiling point below -90 degrees Celsius are called cryogenic liquids. Liquid Oxygen has a boiling point of -183 degree Celsius. Any equipment used for handling or holding Oxygen must be built with materials having high ignition temperatures and non-reactive with Oxygen under the service conditions. Oxygen cylinders or tanks must be constructed in line with American Society of Mechanical Engineers (ASME) codes and must design to withstand the process temperatures and pressures. Liquid Oxygen needs special equipment for handling and storage. As the temperature difference between LOX and the surroundings is substantial, it is mandatory to keep liquid Oxygen insulated from the surrounding heat. Though Oxygen is a gas but it is often stored as a liquid.  Liquid storage is economical as well as less bulky than the high-pressure gaseous storage of equivalent storage. Cryogenic storage comprises of a cryogenic storage tank, one or more vaporizers and a pressure control system. How liquid Oxygen is manufactured? An air separation unit is used for producing Oxygen by liquefying atmospheric air. Oxygen is, then, separated by continuous cryogenic distillation. The oxygen is, then, removed and stored as a cryogenic liquid. A liquid Oxygen plant is based on this process. However, Oxygen can also be produced non- cryogenically using selective adsorption processes to generate gaseous products.  The ASU manufacturing process starts with the main air compressor and is finished at the output of the product storage tanks. During the process, air is compressed and sent through a cleanup system where impurities such as moisture, Carbon Dioxide and Hydrocarbons are eliminated. Then, the air is passed through heat exchangers where it is cooled to cryogenic temperatures. Afterwards, the air is made to go inside a high pressure distillation column where it is physically separated into a vaporous of Nitrogen at the top of the column and a liquid form of crude Oxygen at the bottom. The crude Oxygen is removed from the column and is directed to a low pressure column, where it is distilled until it meets commercial specifications. Then, the liquid Oxygen directed to a cryogenic tank for storage. Specifications  Bulk Liquid Oxygen Supply Failure Received from the Department of Anesthesiology, University of Alabama School of Medicine, Birmingham, Alabama. Anesthesiology January 2004, Vol. 100, 186–189. WE report an oxygen supply tank failure at our institution that occurred during the morning of a busy operating room schedule when medical center oxygen use was maximal.  The bulk Oxygen supply at our facility consists of three cryogenic Oxygen storage tanks: a primary tank, A ; a secondary tank, B ; and a reserve tank, C Tanks A and B are physically situated next to each other. The reserve tank (C) is located approximately 1 block (approximately 305 m) away and normally serves as the primary oxygen source for our hospital’s second large inpatient bed facility. Valves, piping, and regulators between the primary tank and primary reserve were installed in compliance with the National Fire Protection Association’s guidelines and commonly accepted installation practices.  The tank failure and resulting major liquid oxygen spill were caused by the separation of a brazed joint between the stainless steel primary tank A and a brass pipe fitting. The resulting sudden release of approximately 8,000 gallons of liquid Oxygen from tank A precluded the initial use of the adjacent secondary tank B. Tank B was inaccessible because of massive ice and vapor cloud formation, which initially made it impossible to determine whether the tank was stable and functional. As the pressure in the primary tank rapidly decreased, an automatic switch-over valve opened tank B to provide Oxygen to our medical center. With uncertainty regarding the integrity of the reserve system (because of inability to immediately assess the secondary tank), an adjacent valve was immediately closed to isolate both tanks until the damage could be assessed.  Our hospital engineers reacted almost immediately, closing the valves to isolate both the primary tank A and secondary tank B. At the same time, valves were opened to bring the reserve tank C online as the alternate supply source. Fire and police officials were notified of the situation, and personnel in critical areas (intensive care units, operating rooms, and chiefs-of-staff) also were simultaneously notified. Reserve Oxygen E-cylinders were collected and distributed to critical areas within the medical center. Our bulk Oxygen supplier was notified, and a supply tanker was dispatched to provide additional liquid Oxygen. Fortunately, we never experienced total loss of pipeline supply pressure. However, in the operating rooms, the pipeline pressure was noted to be decreased from 55 to 48 psi gauge. This decreased pressure was thought to be most likely a result of relatively high friction losses as the Oxygen was routed through regulators near the distant reserve tank C to the main hospital and operating room facility. Forty-five minutes after the failure, the secondary tank B was determined to be functional and was put back into service. The valves to the reserve tank C were then closed.  The failure of our primary Oxygen supply tank could have caused complete Oxygen pipeline system failure if the secondary tank had been damaged concurrently. The redundancy in our system with the remote reserve tank provided a continuous supply during the event. Very soon after the failure occurred, the low liquid Oxygen volume alarms were activated at the engineering control center. Because of the design of our alarm system, however, these alarms alone would not have given enough advance warning to prevent loss of pipeline pressure. The inability of our alarm system to provide timely warning in this situation was due to the rapid rate at which the liquid Oxygen was lost. These alarms were set to communicate when the level fell below a preset threshold value and were not designed to give engineers ongoing, quantitative information on the level of liquid Oxygen within the tank.  Typical alarm systems do not provide this quantitative information. Furthermore, if the main and reserve tanks had not been situated in a location that was readily visible, then engineers might have believed that the low Oxygen level alarm was simply a result of normal use. The rapid response time to this system failure at our facility was at least partially because of easy visibility of the tanks and the quick reaction of our engineers, who were at the bulk Oxygen storage facility at the time of the failure. The failure of the liquid Oxygen pipeline that caused this event was determined to be due to both electrolysis of the stainless steel-to-brass joint and thermal expansion damage. The primary tank A and piping were 12 yr. old at the time of the event. After the event, the joint was replaced with a stainless steel-to-stainless steel welded joint. The repaired primary tank was subsequently tested and put back in service as the primary supply within 10 h.  Also note that…100 kPa = 1000mbar = 760mm of Hg = 1030cm of H2O = 14.7psi = 1atmosphere. What is Critical Temperature ? It is the temperature above which a gas cant be liquified, no matter how much pressure is applied; O2 -119º C, so it is a gas in room temp. N2O 36.5º C, so it is a gas + liquid mixture @ room temp; if temp >36.5º,then it exist only as gas.  RULES FOR SAFE USE OF CYLINDERS The maximum amount of Oxygen that can be stored inside a health care facility is 20000 cubic ft. Design banks of cylinders. Each have its on pressure reducing regulator. Must contain a minimum of two cylinders Connected to a common manifold. Check valve in between each cylinder lead & header. SUPPLY Primary supply [duty/running] actually is the portion supplying the system. Secondary supply automatically becomes the primary, when the latter fails [switch over done by manifold change over device] Reserve Supply For larger systems When operating supply fails /emergencies/maintenance. Activating switch is there for activating reserve supply. Oxygen Stored as liquid @ low pressures & < --148⁰C. [when large amounts are required] OR as compressed gas in G or H cylinders. Electrical Safety Dr. M O Ababneh, FCAI A. Professor. IU The anesthetist are in daily contact with a large amount of equipment which is powered by mains supply electricity, monitoring, ventilators, suction, defibrillators and diathermy equipment…  There are Two major hazards from electrical appliances in the operating room: Burns and Arrhythmias. There are three types of electrical currents: Macro shock, Micro shock, and Electrocautery Currents.  Electrical Supply ❖ Mainly electricity is supplied as an Alternating Current, which oscillates at a frequency of 50 Hz. ❖ It travels from the substation to its destination in Two conductors – the Live and the Neutral wire. The live wire is at a potential of 240 V, whilst the neutral wire is connected to the earth at the substation and is thus kept at approximately the same potential as earth. ❖ If a connection is made between the live wire and earth, electricity will flow through that connection to earth. The problems arise when this connection is a patient or member of staff.  How Does The Electricity Damage The Body ? Electricity can cause morbidity or mortality by one of three processes: Electrocution; Burns; Ignition of a flammable material, causing a fire or explosion.  Electrocution The effects produced by electrocution are dependent upon 4 factors: The amount of electricity that flows (current); Where the current flows (current pathway) and its density; The type of current (direct or alternating); Current duration.  Current In electrical terms, It means the flow of electrons. It is measured in the SI unit ampere (A); 1 A represents a flow of 6.24 × 1018 electrons (1 coulomb of charge) past a specific point In 1 sec. Thus, the current will be greatest If the voltage is high or the resistance Is low.  Current Pathway & Density The effect of the size of current and current pathway can be considered together as current density. This is the amount of current flowing per unit area. For example, a 50 Hz alternating current flowing between each hand would have the following effects: 1 mA Tingling sensation. 15 mA Muscle tetany, pain and asphyxia. 75 mA Ventricular fibrillation.  Type of Current Direct and alternating currents have different effects on the body; Alternating current at 50 Hz is the most dangerous. Current Duration Finally, damage caused by electrocution Is dependent upon the duration of time for which the current flows. The shorter the duration, the higher the current required before damage is done.  Burn When an electric current passes through any substance having electrical resistance, heat is produced. Whether or not this produces a burn depends on the current density. Skin (especially when dry) has a high electrical resistance compared with the moist tissues beneath. Thus, electrical burns are generally most marked on or near the skin.  Fires & Explosions Sparks caused by switches or plugs being removed from wall sockets can ignite inflammable vapors. This is prevented by the use of spark proof switches and electric socket outlets which prevent the plug from being withdrawn whilst the switch is turned on.  How Might Electricity Flow Through the Body ? There are Two ways by which the body can form part of an electrical circuit : Resistive or Capacitive Coupling.  Resistive Coupling The body can act as a connection if it comes into contact with the source of electricity and the earth directly or by touching an earthed object such as drip stand. There are two potential sources of this electricity – Faulty equipment and Leakage currents. Faulty equipment may allow contact with a live wire If it touches the equipment casing. Leakage currents arise because electrical equipment is at a higher potential than earth.  Capacitive Coupling The body can also form a connection between an electrical source and earth by acting as one plate of a capacitor If Direct Current is applied to a capacitor, current flows for only the very brief period until the positive plate is charged to the same potential as the electrical source. Thereafter, the current ceases. If Alternating Current Is applied across a capacitor, its plates change polarity at the same rate as the alternating current. The capacitor will then continually charge and discharge and the electrons rush back and forth from plate to plate causing a current to flow In the circuit.  Macro Shock Macro shock has the potential for both burns and cardiac arrhythmias. Currents pass through the extremities mostly through the muscles. A current flowing from arm to arm, or arm to leg, must pass through the thorax. In the thorax the current is split between the chest wall and the great vessels, which obviously deliver the current directly to the myocardium. Commonly electric shock occurs from the AC mains supply. The mains supply consists of a live line carrying the generated voltage (240 V) and a neutral line, which acts as a return for the current supplied. The neutral line is earthed at the generator. In an intact mains circuit the current supplied in the live line is equal to the return current in the neutral line. Electric shock occurs from the mains supply, when the body forms a circuit between the live mains line and a local earth connection or the neutral mains line.  Earthed circuit – The local earth connection may occur via the floor or ground. Alternatively earthing may take place by inadvertent contact with earthed metalwork such as an anaesthetic machine or operating table. ◼ Isolated circuit – In the absence of an earth connection, an individual or circuit is said to be electrically isolated or floating. However, current can still flow if contact with an alternative return path such as the neutral supply line is made. The effects of electric current flowing through body tissues depend on the following factors: ◼ Whether the current is AC or DC. ◼ The magnitude of the current. ◼ The tissues the current passes through. ◼ The current density.  AC or DC Current ◼ DC produces a single muscle spasm on contact, which often throws the victim clear. ◼ Arrhythmias can be precipitated, but DC shock is also used to cardiovert arrhythmias. ◼ Prolonged exposure to low DC currents can produce chemical burns. ◼ AC will cause muscle spasm due to tetanic effects, which are maximal at mains frequency (50 Hz). ◼ When contact is made through the hand, muscle spasm may cause the individual to grip the contact uncontrollably, Several factors in the operating room place the patient at unusual risk for electrocution. The patient is unclothed and frequently wet. The patient is on a large metal table, frequently electrically operated, to which he or she may be connected by large wet towels. The patient is surrounded by electrical devices, and is directly connected to several of them. These electrical devices are exposed to spilled fluids and operator abuses that increase the potential for short circuits. Finally, the anesthetized patient is unable to respond to or withdraw from an electric shock.  Micro Shock Micro shock refers to currents delivered directly to the myocardium via intracardiac electrodes or catheters. Because the current is delivered to a very small area, only a very small current is required to reach the fibrillation threshold. The maximum leakage allowed In OR equipment is 10 A. Very small currents (50 a) through the ventricular endocardium can produce ventricular fibrillation.  Surgical Diathermy Surgical diathermy equipment uses the heating effects of high frequency (kHz–MHz) electrical current to coagulate and cut tissues. There are two basic types – monopolar and bipolar.  Monopolar Diathermy Monopolar diathermy generates electrical energy at 200 kHz to 6 MHz. The energy is applied between two electrodes (neutral and active). The neutral electrode has a large conductive surface area producing a low current density with no measurable heating effect. The active electrode has a very small contact area resulting In a very high current density. The heating effect beneath the active electrode is considerable producing deliberate tissue damage. Cutting diathermy employs a sine waveform whilst coagulation uses a modulated waveform.  Bipolar Diathermy Bipolar diathermy operates with a much lower power output. The output is applied between the points of a pair of specially designed forceps producing high local current density. No current passes throughout the rest of the body.  Accidents with Diathermy Accidents may result from; Electrical burns, Fires and explosions Or by their effect on pacemakers.  Burns Electrical burns may be due to inadvertent depression of the foot switch. Keeping the forceps in a protective quiver and the installation of a buzzer which is activated when the switch is depressed may prevent this. Burns may also result from poor contact between the neutral plate and the patient resulting in increased current density. Some diathermy machines produce an audible warning if the plate is not plugged in or the lead is broken. If the electrical circuit Is completed via the operating table, or other points through which the patient may be earthed, a burn may result at this site Fires & Explosions Fires and explosions may be caused by sparks igniting flammable materials, e.g. skin cleaning solutions, bowel gas.  Pacemakers Unipolar diathermy can inhibit or permanently damage pacemakers. If diathermy is essential, the bipolar variety should be used. However, bipolar diathermy should be applied well away from the pacemaker and Its wiring. How can we prevent electrocution ? General measures; Equipment design; Equipotentiality; Isolated circuits; and Circuit breakers.  General Measures These include adequate maintenance and regular testing of electrical equipment, ensuring the patient is not in contact with earthed objects A common way of reducing the risk of a large current injuring the anesthetist in the operating theater is to wear antistatic shoes and to stand on the antistatic floor.  Equipment Design There are Three Classes of electrical insulation which are designed to minimize the risk of a patient or anesthetist forming part of an electrical circuit between the live conductor of a piece of equipment and ground.  Class 1 Equipment Fully Earthed The main supply lead has three cores (live, neutral and earth). The earth is connected to all exposed conductive parts, and in the event of a fault developing which short-circuits current to the casing of the equipment, current flows from the case to earth and blows a fuse.  Class 2 Equipment Double-Insulated This has no protective earth. The power cable has only live and neutral conductors and these are double-insulated. The casing is normally made of non-conductive material.  Class 3 Equipment Low Voltage This relies on a power supply at a very low voltage produced from a secondary transformer situated some distance away from the device. Spinal & Epidural Equipment's M O Ababneh, FCAI A. Professor, IU  Spinal Needle Multi-angle grinded tip with special bending Extra thin wall Atraumatic Atrau com® Has specifically administered deflection, multi-angle sharpened tip structure, extra thin wall, atraumatic, minimum CSF loss and minimal traumatization features. -Specifically administered deflection, multi-angled sharpened tip structure. -Atraumatic. -Minimum CSF loss. -Minimum traumatization  Quincke In 1891, Quincke published a paper describing a standardised technique of lumbar puncture for the release of cerebrospinal fluid (CSF) for diseases associated with increased intracranial pressure. The next major development in the history of spinal anaesthesia was the work of Augustus Karl Gustav Bier. In 1898. The Quincke spinal needles have a Luer lock connection on the hub, and is designed with an A-bevel cutting sharp tip. Short bevelled, cutting tip. Insertion results in the needle cutting parallel to the dura fibres  Quincke Quincke-Babcock Needle (1914) Gaston Labat designed a spinal needle that was made of unbreakable nickel. It was a medium-gauge cannula with a short, sharp bevel and matching stylet, with the tip ground to match the bevel of the cannula. Quincke Point The quincke tip can easily penetrate the tissues. - The unique harmony of the stylet and the cannula prevents tissue entry into the cannula, the tangled tip prevents damage to the tissues. - Crystal clear needle hub allows the flow of liquids to be observed and CSF loss to be minimized. - The thin structure of the needle wall provides a thin and comfortable flow of liquid. Whitacre Needle (1951) In 1955, Brace produced a needle with a medium length, sharp, cutting bevel.  Pencil Point Pencil Point Perfect tapered elliptical tip allows easy access to the desired area without cutting and damaging tissues. Whitacre Designed to spread the dural fibres and help reduce the occurrence of post-dural puncture headache. Yields a distinct "pop" as the pencil point penetrates the dura.  Whitacre Whitacre pencil point spinal needle for spinal anaesthesia with transparent hub and stylet. – The hub of the stylet is colour-coded according to the diameter of the needle. – The hub of the needle is transparent to visualise CSF reflux and its ergonomic design ensures easy handling. – The stylet is designed to allow rapid reflux of CSF. The lug on the hub of the stylet indicates the position of the distal eye. The lug also helps to easily reposition the stylet in the needle, if dural puncture fails. – Some needles are supplied with an introducer. The spinal needle is inserted through this introducer to reduce the risks of kinking of the thin spinal needle.  Sprotte Jürgen Sprotte (born:1945) Sprotte Needle (1987) Sprotte As the fibres of the dura run parallel to the long axis of the spine, if the bevel of the needle is parallel to them, it will part rather than cut them, and therefore leave a smaller hole.  Epidural Needle Though Ralph L. Huber (1915–2006), a Seattle dentist was the inventor of this needle in 1940, it is known in the name of Edward Boyce Tuohy (1908–1959), a 20th-century U.S anesthesiologist who first popularized it in 1945.  References The incidence of post-dural puncture headache (PDPH) after the use of a standard spinal needle (Quincke) is dependent on the size of the needle. In young female patients, the mean incidence of PDPH is approximately 15% when using a 25G needle and around 5% when using a 26G needle. A significant reduction in PDPH from 6.3% to 2.5% is seen if using a 27G needle instead of a 26G needle in obstetric patients. The incidence can be further reduced by puncturing the dura parallel to the dural fibres. Newer spinal needles with special tip design (modifications of the original pencil point Whitacre needle) have lowered the incidence of PDPH to an acceptable level. In 1987, Sprotte et al. introduced the 'atraumatic' spinal needle (a modified pencil point needle) and reported that the incidence of PDPH could be reduced to less than 1%. However, a higher failure rate was reported and related to the dimensions and placement of the sideport of this needle. The modern Whitacre needles, with a smaller sideport closer to the tip, are superior to the Sprotte® needle and their use has reduced the incidence of significant PDPH to less than 1%.  The epidural needles: Reports PULSEOXIMETRY Dr. M O Ababneh, FCAI A. Professor, IU  Introduction The maintenance of optimal O2 delivery is the core concern during anaesthesia. “Oxygen lack not only stops the machine but wrecks the machinery ”– J.S. Haldane. Monitoring of oxygenation using pulse-oximeter avoids many catastrophes.  Definition A Non-invasive technology to monitor Oxygen saturation of haemoglobin.  History MATHEES - Father of Oximetry 20 papers in1934 –1944. HERTZMAN 1937 – Use of photoelectric finger plethysmography. 1975 – Concept of pulse oximetry – Japan. YELDERMAN & NEW -1983 – Nellcor pulse oximeter.  History ABSORBTION SPECTRO PHOTOMETRY BEER LAMBERT LAW LAMBERT’S LAW states that when a light falls on a homogenous substance, intensity of transmitted light decreases as the distance through the substance increase. BEER’S LAW states that when a light is transmitted through a clear substance with a dissolved solute, the intensity of transmitted light decreases as the concentration of the solute increases.  History Substances have a specific pattern of absorbing specific wavelength. –Extinction coefficient. Uses two lights of wavelengths 660nm – Deoxy Hb absorbs ten times as oxy-hb. 940 nm – Oxy-Hb is greater. Absorption. Lab oximeters use 4 wavelengths to measure 4 species of haemoglobin.  Design of Pulse-Oximeter 2 WAVELENGTHS 660nm [red] & 940nm [infra red] The ratio of absorbencies at these two wavelengths is calibrated empirically against direct measurements of arterial blood oxygen saturation (SaO2) in volunteers, and the resulting calibration algorithm is stored in a digital microprocessor within the pulse oximeter. LED & PHOTODETECTOR Newer types of LED is based on aluminium gallium arsenide system. Signal processed in the micro processor. Senses only the pulsatile flow.  Oxygen Desaturation Saturation is defined as ratio of O2 content to Oxygen capacity of Hb expressed as a percentage. Desaturation leads to Hypoxemia – a relative deficiency of O2 in arterial blood. PaO2 < 80mmHg – hypoxemia  Oxygen Desaturation Oxygen saturation will not decrease until PaO2 is below 85mmHg. At SaO2 of 90% PaO2 is already 60mmHg. Rough guide for PaO2 between saturation of 90%-75% is PaO2 = SaO2 - 30. SaO2< than 76% is life threatening.  Types of Hypoxemia 1. Hypoxic hypoxemia  PaO2  SaO2 – Normal Hb 2. Anaemic hypoxemia Hb, Normal PaO2 & SaO2 3. Toxic hypoxemia SaO2, Normal PaO2  PaO2 [mmHg] SaO2 [%] Normal 97 to ≥80 97 to ≥95 Hypoxia < 80 < 95 Mild 60 - 79 90-94 Moderate 40 – 59 75 – 89 Severe 80    No Reflex change 60-80   No  Direct change than true O2 saturation. 10-20% in heavy smokers. At 660nm its absorption similar to oxyhaemoglobin, so over reads. For every 1% COHB 1% increase in pulse-oximeter reading. ▪ Methemoglobinemia – absorbs equal amount of red &infra red light - Cause SpO2 to move towards 85%.  Limitations ✓ Endo / exogenous dyes interfere -Indocyanine green, Indigocarmine, Methylene blue ✓ Blue, Black, Green nail polishes ✓ Diathermy leads to disturbance in monitor - Can be corrected by placing grounding plate near surgical field  Problems False positives and negatives. Burn injury. Pressure injuries.  Other Types of Oximetry Reflectance oximetry. Sense back scattered light. LED placed to the side of photo diode. Dis adv - noise interference & more costly. Adv - signal in low perfusion is better. ❑ Masimo signal extraction technology ❑ Mixed venous blood O2 saturation Non-invasive brain oximetry - Senses regional O2 saturation in brain [rSO2] - Sensor in forehead emits light of specific wavelength & measure the reflected light ❑ Transcutaneous oximetry  Case Study Consider Mrs. W., a patient scheduled to undergo an endoscopy. A complete blood count (CBC) shows her total hemoglobin level is normal – 15 mg/dl. A pulse oximeter shows that her oxygen saturation level is 97%. To determine her overall oxygen-carrying capacity, multiply 1.34 ml (the amount of oxygen each gram of hemoglobin carries) by the hemoglobin level and then by the SpO2. 1.34 x 15 x 0.97. The total amount of oxygen carried in Mrs. W.’s hemoglobin is 19.50 ml/dl (hemoglobin oxygen content), which falls within the normal range of 19-20 ml/dl.  Mr. B., who’s had shortness of breath for two days. His lungs are clear, and although he has not specific pulmonary symptoms, he looks malnourished and is anaemic. A spot check with a pulse oximeter shows a SpO2 of 97%, the same as Mrs. W., you discover that Mr. B.’s hemoglobin oxygen content is 14.30 ml/dl, far below normal values. Because Mr. B. has fewer hemoglobin molecules, the total amount of oxygen available to his tissues is low, resulting in shortness of breath. What hemoglobin he does have is full of oxygen, producing normal and misleading SpO2.  These two cases illustrate a major cautionary note: Never let normal SpO2 readings let you into a false sense of security! Always interpret SpO2 values in the context of the patient’s total hemoglobin level. Take Home Massage Remember at SaO2 of 90%, PaO2 is already 60mmHg SaO2 < than 76% is life threatening  Capnography M O Ababneh, FCAI A. Professor, IU  Carbon dioxide (CO2 ) is the most abundant gas produced by the human body. CO2 is the primary drive to breathe and a primary motivation for mechanically ventilating a patient. Monitoring the CO2 level during respiration (capnography) is noninvasive, easy to do, relatively inexpensive, and has been studied extensively. Capnography has improved over the last few decades thanks to the developement of faster infrared sensors that can measure CO2 at the airway opening in real-time. By knowing how CO2 behaves on its way from the bloodstream through the alveoli to the ambient air, physicians can obtain useful information about ventilation and perfusion. There are two distinct types of capnography: Conventional, time-based capnography allows only qualitative and semi-quantitative, and sometimes misleading, measurements, so volumetric capnography has emerged as the preferred method to assess the quality and quantity of ventilation.  Benefits of volumetric capnography Improves, simplifies, and complements patient monitoring in relation to metabolism, circulation, and ventilation (V/Q) Provides information about the homogeneity or heterogeneity of the lungs Trend functions and reference loops allow for more comprehensive analysis of the patient condition. Multiple clinical applications, such as detection of early signs of pulmonary emboli, COPD, ARDS, etc. Helps you optimize your ventilator settings is easy to do and is relatively inexpensive In short, volumetric capnography is a valuable tool to improve the ventilation quality and efficiency for your ventilated patients.  The Three Phases The alveolar concentration of CO2 is the result of metabolism, cardiac output, lung perfusion, and ventilation. Change in the concentration of CO2 reflects response in any or a combination of these factors. Volumetric capnography provides continuous monitoring of CO2 production, ventilation/perfusion (V/Q) status, and airway patency, as well as function of the ventilator breathing circuit itself. Expired gas receives CO2 from three sequential compartments of the airways, forming three recognizable phases on the expired capnogram.  A single breath curve in volumetric capnography exhibits these three characteristic phases of changing gas mixtures - they refer to the airway region in which they originate: Phase I - Anatomical dead space. Phase II - Transition phase: gas from proximal lung areas and fast emptying lung areas Phase III - Plateau phase: gas from alveoli and slow emptying areas Using features from each phase, physiologic measurements can be calculated.  Phase I – Anatomical dead space The first gas that passes the sensor at the onset of expiration comes from the airways and the breathing circuit where no gas exchange has taken place = anatomical + artificial dead space. This gas usually does not contain any CO2. Hence the graph shows movement along the X-axis (expired volume), but no gain in CO2 on the Y-axis. A prolonged Phase I indicates an increase in anatomical dead space ventilation (VDaw). Presence of CO2 during Phase I indicates rebreathing or that the sensor needs to be recalibrated.  Phase II – Transition phase Phase II represents gas that is composed partially of distal airway volume and mixed with gas from fast emptying alveoli. The curve slope represents transition velocity between distal airway and alveolar gas – providing information about perfusion changes and also about airway resistances. A prolonged Phase II can indicate an increase in airway resistance and/or a Ventilation/Perfusion (V/P) mismatch.  Phase III – Plateau phase Phase III gas is entirely from the alveoli where gas exchange takes place. This phase is representative of gas distribution. The final CO2 value in Phase III is called end-tidal CO2 (PetCO2 ). A steep slope in Phase III provides information about lung heterogeneity with some fast and some slow emptying lung areas. For example, obstructed airway results in insufficiently ventilated alveoli, inducing high CO2 values and increased time constants in this region.  Slope of Phase III The slope of Phase III is a characteristic of the volumetric capnogram shape. This slope is measured in the geometric center of the curve, which is defined as the middle two quarters lying between VDaw and the end of exhalation. A steep slope can be seen, for example, in COPD and ARDS patients.  Insight into the patient‘s lung condition The volumetric capnogram can also be divided into three areas: Area X - CO2 elimination Area Y - Alveolar dead space Area Z - Anatomical dead space The size of the areas, as well as the form of the curve, can give you more insight into the patient‘s lung condition regarding: Dead space fraction – VDaw /VTE Alveolar minute ventilation – V‘alv  Area X – CO2 Elimination Area X represents the actual volume of CO2 exhaled in one breath. Adding up all of the single breaths in one minute gives you the total elimination of CO2 per minute. If cardiac output, lung perfusion, and ventilation are stable, this is an assessment of the production of CO2. The value displayed on the ventilator can be affected by any change in CO2 production, cardiac output, lung perfusion, and ventilation. It indicates instantly how the patient’s gas exchange responds to a change in ventilator settings. Monitoring trends allows for detection of sudden and rapid changes in V‘CO2. Decreasing V‘CO2 Hypothermia, deep sedation, hypothyroidism, paralysis, and brain death decrease CO2 production and induce a decrease in V‘CO2. Decreasing V‘CO2 can also be due to a decrease in cardiac output or blood loss, and may also suggest a change in blood flow to the lung areas. Pulmonary embolism, for example, exhibits V‘CO2 reduction and a slope reduction in Phase II. Area X – CO2 Elimination Increase in V‘CO2 is usually due to Bicarbonate infusion or an increase in CO2 production that can be caused by: Fever Sepsis Seizures Hyperthyroidism Insulin therapy Area Y - Alveolar dead space Area Y represents the amount of CO2 that is not eliminated due to alveolar dead space. Increase Alveolar dead space is increased in cases of lung emphysema, lung overdistension, pulmonary embolism, pulmonary hypertension, and cardiac output compromise. Decrease If the above mentioned conditions improve due to successful therapy, the alveolar dead space decreases.  Area Z - Anatomical Dead Space Anatomical dead space measurement using a volumetric capnogram gives an effective, in- vivo measure of volume lost in the conducting airway. This area represents a volume without CO2. It does not take part in the gas exchange and consists of the airway, endotracheal tube, and artificial accessories, such as a flex-tube positioned between the CO2 sensor and the patient. An expansion of Area Z can indicate an increase in anatomical dead space ventilation (VDaw). Consider a reduction of your artificial dead space volume. A reduction of Area Z is seen when artificial dead space volume is decreased and when excessive PEEP is decreased  Alveolar Minute Ventilation – V‘alv Phase III of the waveform represents the quantity of gas that comes from the alveoli and actively participates in gas exchange. V‘alv is calculated by subtracting the anatomical dead space (VDaw) from the Tidal Volume (VTE) multiplied by the respiratory rate from the minute volume. Increase. An increase in V‘alv is seen after an efficient recruitment maneuver and induces a transient increase in V‘CO2. Decrease. A decrease in V‘alv can indicate that fewer alveoli are participating in the gas exchange, for example, due to pulmonary edema. Improve Ventilation Quality & Efficiency You can use the insights from the CO2 curve to improve ventilation quality and efficiency for your patients. On the following pages, you will find examples for the use of the CO2 curve in the clinical scenarios listed below: Signs of ARDS PEEP management Recruitment maneuver Expiratory resistance Obstructive lung disease Pulmonary embolism Hemorrhagic shock Optimize management of the weaning process Monitor perfusion during patient transport Detection of rebreathing Signs of ARDS In ARDS, the ventilation/perfusion ratio is disturbed and changes in the slope of the volumetric capnogram curve can be observed. Phase I is larger due to increased anatomical dead space caused by PEEP. The slope of Phase II is decreased due to lung perfusion abnormalities. The slope of Phase III is increased due to lung heterogeneity  PEEP Management If PEEP is too high, the intrathoracic pressure rises, the venous return decreases, and pulmonal vascular resistance (PVR) increases. These changes can be easily observed on the volumetric capnogram. An increase in Phase I shows an increase in anatomical dead space. A decrease in the Phase II slope indicates a decrease in perfusion. An increase in the Phase III slope depicts a maldistribution of gas, which can be caused by an inappropriately low PEEP setting or an inappropriately high PEEP setting causing lung overdistension  Recruitment Maneuver The volumetric capnogram can be used to assess the effectiveness of recruitment maneuvers and might give you an insight into the recruited lung volume. After a sucessful recruitment maneuver, you should see a transient increase in V‘CO2. Phase I may decrease a little. The slope of Phase II becomes steeper with improved lung perfusion. The slope of Phase III improves as a result of more homogeneous lung emptying.  Expiratory Resistance Concave Phase-III volumetric capnograms have been seen with obese patients and patients with increased expiratory resistance. Obese patients can have biphasic emptying and higher PetCO2 than PaCO2. That difference suggests varying mechanical and ventilation/perfusion properties. The increase in expiratory resistance may reflect a slow expiratory phase with a slow accumulation of alveolar CO2. The alveoli that empty last may have more time for CO2 diffusion.  Obstructive Lung Disease When spirometry cannot be reliably performed, volumetric capnography can be used as an alternative test to evaluate the degree of functional involvement in obstructive lung disease patients (COPD, asthma, cystic fibrosis, etc.). Obstructive lung disease is characterized by asynchronous emptying of compartments with different ventilation/perfusion ratios. The volumetric capnogram in COPD patients shows a prolonged Phase II, an increase in PetCO2 , and a continuously ascending slope without plateau in Phase III.  Obstructive Lung Disease Patients with high airway resistance demonstrate a decrease in the Phase II slope and a steep slope in Phase III. The volumetric capnogram can give you insights into therapy efficiency. A Phase II shift to the left indicates reduced resistance. Phase III slope shows a decrease in steepness indicating better gas distribution and reduced alveolar dead space  Signs of Pulmonary Embolism PE leads to an abnormal alveolar dead space that is expired in synchrony with gas from normally perfused alveoli. This feature of PE separates it from pulmonary diseases affecting the airway, which are characterized by nonsynchronous emptying of compartments with an uneven ventilation/ perfusion relationship. In case of sudden pulmonary embolism, volumetric capnography has a typical unique shape. In patients with sudden pulmonary vascular occlusion due to pulmonary embolism, Phase I is increased due to increased anatomical dead space. The slope of Phase II is decreased due to poor lung perfusion. Phase III has a normal plateau with low PetCO2 because the number of functional alveoli is reduced. In this case, V‘CO2 drops suddenly.  Hemorrhagic Shock Hemorrhagic shock is a condition of reduced tissue perfusion, resulting in the inadequate delivery of oxygen and nutrients that are necessary for cellular function. The expired CO2 drops drastically. Phase I is unchanged and the slopes of Phase II and III are unchanged, but PetCO2 is decreased due to the increase in alveolar dead space.  Optimize Management of the Weaning Process The volumetric capnogram and trends show the patient‘s response to the weaning trial and allow for better management of the weaning process. Indications for a successful weaning trial are: Stable V‘alv and constant tidal volumes - As ventilatory support is being weaned, the patient assumes the additional work of breathing while V‘alv remains stable and spontaneous tidal volumes remain constant. V‘CO2 remains stable and then slightly increases - The slight increase in V‘CO2 represents an increase in CO2 production as patient work of breathing increases in association with the decrease in ventilatory support. This suggests an increase in metabolic activity due to the additional task of breathing by the patient.  Optimize Management of the Weaning Process Indications for an unsuccessful weaning trial are: Dramatic increase in V‘CO2 A more dramatic increase in V‘CO2 would suggest excessive work of breathing and the potential for impending respiratory decompensation. This scenario would be consistent with a visual assessment of increasing respiratory distress (for example, retraction, tachypnea, and agitation). The V‘CO2 will eventually decrease if the patient gets exhausted. Decrease in V‘CO2 As the ventilator settings are decreased, the patient is no longer able to maintain an adequate degree of spontaneous ventilation, and total minute ventilation falls with a decrease in CO2 elimination. Increased VD aw /VTE ratio If reducing ventilatory support is followed by a decrease in tidal volume, the VDaw /VTE ratio increases. This reduces ventilatory efficiency and the patient’s ability to remove CO2.  Monitor Perfusion During Patient Transport If arterial access is not something you routinely perform when you transport a ventilated patient, PetCO2 can be used for monitoring perfusion and ventilation during transport. A decrease in PetCO2 accompanied by a decrease of VCO2 can signify: ET tube displacement Decreased cardiac output Pulmonary embolism Atelectasis Overdistension of alveoli (for example, excessive PEEP)  Detection of Rebreathing An elevation of the baseline during Phase I indicates rebreathing of CO2 , which may be due to mechanical problems or therapeutic use of mechanical dead space. Consider recalibration of the CO2 sensor or reduction of the airway accessories.  PetCO2 versus V‘CO2 - Opposing, Asynchronous Trends If the PetCO2 trend moves up while the V‘CO2 trend decreases for a while and then returns to baseline, this indicates a worsening of ventilation. If the PetCO2 trend moves down while the V‘CO2 trend increases for a while and then returns to baseline, this indicates an improvement of ventilation.  PetCO2 versus V‘CO2 - Opposing, Synchronous Trends Rising PetCO2 and V‘CO2 trends indicate increasing CO2 production (agitation, pain, fever). Falling PetCO2 and V‘CO2 trends indicate a decrease in CO2 production.  Optimizing PEEP by Trends When PEEP change is associated with an improving ventilation/perfusion ratio, V‘CO2 shows a transient increase for a couple of minutes and then returns back to baseline, that is, in equilibrium with CO2 production. When PEEP change is associated with a worsening of the ventilation/perfusion ratio, V‘CO2 transiently decreases for a few minutes and then returns to baseline.  Detecting Alveolar De-recruitment Volumetric CO2 provides continuous monitoring to detect derecruitment and recruitment of alveoli. Alveolar ventilation and V‘CO2 will first decrease if the lung derecruits, and will then stabilize again at equilibrium. Recruitment, during, for example, a PEEP increase, can be detected by short V‘CO2 peaks before V‘CO2 returns to equilibrium. Summary