Physics Exam 3

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Questions and Answers

What is the result of the Joule-Thompson Effect on a gas?

Volume increase of the gas

Pressure increase of the gas

Temperature increase of the gas

Expansion of gas causes cooling (correct)

What is the primary reason why tubing becomes extremely hot during compression?

Work done to compress the gas

Friction generated during compression

Adiabatic compression of the gas (correct)

Heat exchange with the surroundings

When is an anesthesia machine typically in a semi-open circuit mode?

During maintenance of anesthesia

During delivery of precise inspired gas concentrations

During controlled ventilation

During induction and emergence (correct)

What is the purpose of inspiratory and expiratory valves in an anesthetic breathing circuit?

To prevent rebreathing from mechanical deadspace Signup and view all the answers

What is the primary purpose of the Diameter Index Safety System (DISS) in anesthesia machines?

To ensure the correct gas is connected to the correct outlet via the specific threaded connections for each type of gas Signup and view all the answers

What is the purpose of the Pin Index Safety System?

To prevent mounting of the wrong cylinder by using specific holes in the tank Signup and view all the answers

What is the primary advantage of using a low flow system?

It saves volatile and retains heat and moisture Signup and view all the answers

What is the purpose of the sidestream sampler in a circle system?

Last chance to prevent administration of hypoxic gas mixture Signup and view all the answers

What is the effect of inhaling dry gases without heat and humidity?

It increases mucus viscosity and promotes ciliary dysfunction Signup and view all the answers

What is the effect of a stuck closed inspiratory or expiratory valve?

It increases the risk of airway obstruction Signup and view all the answers

What is the primary purpose of the Mapleson breathing systems?

To provide a semi-open system for pediatrics and transport Signup and view all the answers

What is the effect of a desiccated CO2 absorber on sevoflurane?

It breaks down sevoflurane into Compound A Signup and view all the answers

Match each system to its classification

Open = No rebreathing and no reservoir Semi-open = No rebreathing with a reservoir Semi-closed = Partial rebreathing with a reservoir Closed = Complete rebreathing with a reservoir Signup and view all the answers

In closed breathing systems, the amount of gas consumed by the patient should match what metric?

Amount of gas added to the circuit Signup and view all the answers

What are examples of open breathing systems?

Insufflation Signup and view all the answers

What type of breathing system is a non-rebreather?

Semi-open circuit - no rebreathing with a reservoir Signup and view all the answers

What allows rebreathing of exhaled gas in semi-closed and closed breathing systems?

Carbon dioxide absorbent Signup and view all the answers

What are two ways to address rebreathing of CO2?

Replace the CO2 absorbent Signup and view all the answers

In a semi-open circle system, what is the relationship between FGF (Fresh Gas Flow) and minute ventilation?

FGF > Minute ventilation Signup and view all the answers

In a semi-closed circle system, what is the relationship between FGF (fresh gas flow) and minute ventilation?

FGF < Minute ventilation Signup and view all the answers

A circle system with a very low FGF and APL closed is what type of breathing system?

Closed - FGF only replaces gas consumed by the pt (APL is closed) Signup and view all the answers

What is the result of a malfunction of either unidirectional valve in a circle system? (select 2)

Hypercarbia Signup and view all the answers

What is the role of the APL in a circle system? (select 2)

To direct gas into the scavenger when circuit pressure reaches a certain limit Signup and view all the answers

How do you convert a closed or semi-closed circuit into a semi-open one?

By increasing the FGF Signup and view all the answers

Which Mapelson circuit is best for spontaneous ventilation?

Mapelson A Signup and view all the answers

Which Mapelson circuit is best and worst for controlled ventilation?

Mapelson A - worst Signup and view all the answers

What is unique about Mapelson breathing systems?

They lack CO2 absorbers because CO2 is lowered by the addition of fresh gas and elimination through the APL Signup and view all the answers

Which Mapelson circuit is best and worst for spontaneous ventilation?

Mapelson A is best, Mapelson B is worst Signup and view all the answers

What is the Bain system and how does it deliver fresh gas?

The Bain system is a type of anesthetic breathing circuit that delivers fresh gas through a concentric tube inside the corrugated tubing, allowing for a humidification, but it makes it easier to be kinked Signup and view all the answers

When is an anesthesia machine in semi-closed mode?

During maintenance of anesthesia Signup and view all the answers

What is a benefit of rebreathing?

Increase heat and humidity while decreasing costs Signup and view all the answers

Where is mechanical dead space located in circle systems?

Y-piece and endotracheal tube Signup and view all the answers

What are the effects of lower FGF?

Increased humidity in the system and slower reduction in body temperature Signup and view all the answers

Full E cylinder of O2 volume of 4.8 L at 14.7psi

True Signup and view all the answers

What is the main difference between the pressure of oxygen cylinders and nitrous oxide cylinders?

Pressure of oxygen accurate reflects gas remaining while the pressure of nitrous oxide will fall only once all the liquid N2O has evaporated Signup and view all the answers

What action can you take if the inspiratory or expiratory valves are stuck open?

Convert the system to a semi-open one by increasing FGF > MV to wash out CO2 Signup and view all the answers

What actions can you take if the inspiratory/expiratory valves are stuck closed?

Take patient off the ventilator and bag ventilate them Signup and view all the answers

In the bag/vent selector switch in a circle system, when are the reservoir bag and APL valve used?

During manual/spontaneous ventilation Signup and view all the answers

In the bag/vent selector switch in a circle system, when are the vent and pressure relief valve used?

During mechanical ventilation Signup and view all the answers

What is the function of the APL (Adjustable Pressure Limiting) valve in an anesthesia circuit?

To determine how much gas remains in the circuit and how much is directed towards the scavenger Signup and view all the answers

What is a byproduct of desflurane, enflurane, and isoflurane as a result of prolonged high gas flows, high temperatures, high concentrations of agents, and use of barium hydroxide lime?

CO Signup and view all the answers

What is the function of a scavenger in an anesthetic system?

To remove excess gas from the breathing circuit and minimize environmental exposure to waste anesthetic gases Signup and view all the answers

What plays a role in the scavenger system during spontaneous ventilation?

APL Signup and view all the answers

What plays a role in the scavenger system during mechanical ventilation?

Ventilator spill valve Signup and view all the answers

What are the key negative consequences of uneven gas removal from the scavenger system?

Too much gas removal results in negative pressure in the circuit Signup and view all the answers

What is the main difference between active and passive scavenging systems?

Active systems use suction to remove gas while passive systems rely on positive pressure from FGF to remove gas Signup and view all the answers

What is true about open scavenging interface?

It can only be used with active systems and works by releasing waste gas to the environment or pulling room air into the system Signup and view all the answers

What is the primary purpose of pressure relief valves in closed scavenging interfaces?

To communicate with the atmosphere Signup and view all the answers

What is the purpose of sodium hydroxide in sodium lime?

To neutralize carbonic acid Signup and view all the answers

What is the purpose of using 4-8 mesh granules with soda lime?

To balance surface area and airflow resistance Signup and view all the answers

What are the reactions that work to remove CO2 from a breathing circuit?

All of the above Signup and view all the answers

Match the correct dye with its color on exhaustion

Ethyl violet white when fresh = purple on exhaustion Phenolphthalein white when fresh = pink on exhaustion Clayton yellow red when fresh = yellow on exhaustion Ethyl orange orange when fresh = yellow on exhaustion Signup and view all the answers

Mimosa Z red when fresh and white on exhaustion

True Signup and view all the answers

What are the ideal width and lengths for blood pressure cuffs?

40% of the arm circumference, 2/3 or 80% the length of the arm Signup and view all the answers

In doppler BP, only the ____ can be measured

SBP Signup and view all the answers

What is the difference in light absorption between oxygenated and deoxygenated hemoglobin?

Oxygenated hemoglobin absorbs more infrared light, and deoxygenated hemoglobin absorbs more red light. Signup and view all the answers

Which of the following relationships describe how pulse oximetry works?

Lambert's relationship: light absorption to the thickness of the absorbing layer, Beer's relationship: light absorbed and amount of solute Signup and view all the answers

What Spo2 measurements does methyhemoglobin result in?

Overestimation with a plateau Signup and view all the answers

Bilirubin causes falsely high SPO2

False Signup and view all the answers

Methylene blue and indocyanine green, nail polish underestimates SPO2 (i.e. falsely low)

True Signup and view all the answers

When does SPO2 tend to be falsely overestimated?

At low SPO2 <80% Signup and view all the answers

What is the primary cause of the penumbra effect when using a pulse oximeter?

Different path lengths of red and infrared light causing light to be shunted Signup and view all the answers

What is the result of the penumbra effect on SpO2?

Falsely high if SPO2 <85% Signup and view all the answers

What curve shifts may change the patient's PaO2 without changes in SPO2?

Oxyhemoglobin dissociation Signup and view all the answers

What is the implication of severe anemia with Hct<25% on SPO2 readings?

It results in decreased reliability when SPO2 is low. Signup and view all the answers

What happens to the reliability of SPO2 readings when Hct is less than 10%?

Reliability decreases at all levels Signup and view all the answers

• ETCO2 (expired) < alveolar CO2 (at alveoli)

True Signup and view all the answers

The mass spectroscopy and Raman spectroscopy are able to measure O2, CO2, N2O, and volatile agents

True Signup and view all the answers

What does it indicate when ETCO2 doesn't come down and stays persistently elevated?

An incompetent expiratory valve Signup and view all the answers

What is indicated by the loss of leveling at the bottom of the waveform during the inspiration phase?

Incompetent inspiratory valve Signup and view all the answers

What is the purpose of using EEG and EMG in anesthesia?

To calculate the level of consciousness and sedation Signup and view all the answers

What is the bispectral index (BIS) goal for sedation and general anesthesia?

40-60 for GA Signup and view all the answers

What is Zone 3 in an MRI environment?

A strictly restricted area immediately outside of the MRI room where interaction between ferromagnetic objects and MRI can result in serious injury or death Signup and view all the answers

What is Zone 4 in an MRI facility?

MRI scanner magnet room Signup and view all the answers

What does pulse pressure variation during inspiration and expiration rely on?

Frank-Starling curve to determine fluid responsiveness Signup and view all the answers

In atrial fibrillation, what would you expect to observe on CVP?

Absence of a wave and prominent c wave Signup and view all the answers

What occurs when the right atrium (RA) contracts against a closed tricuspid valve during right ventricle (RV) systole?

Cannon waves in CVP Signup and view all the answers

What are the three components of the fire triad?

Oxidizer, ignition source, and fuel Signup and view all the answers

What is macro shock?

A type of electrocution where electricity enters through the skin and flows through a substantial portion of the body, only a fraction actually going through the heart Signup and view all the answers

What is a key difference between electricity conducted directly to the heart via microshock and other forms of electric shock?

It is more concentrated and can cause fibrillation at smaller levels of current Signup and view all the answers

What is the main difference between AC and DC?

AC uses less amperage to move electricity long distances and DC moves electricity short distances Signup and view all the answers

If electricity is like water, what is the voltage equivalent to?

Pressure Signup and view all the answers

If electricity is like water, what is the current equivalent to?

Flow rate Signup and view all the answers

What is the definition of inductance?

The tendency of a AC circuits to resist changes in the current flowing through it by generating a magnetic field. Signup and view all the answers

What is a capacitor and what type of medical device uses this technology?

A capacitor is a device that stores electrical energy, and a defibrillator uses this technology Signup and view all the answers

What is the relationship between impedance and conductivity?

Impedance is inversely proportional to conductivity Signup and view all the answers

Impedance = resistance

True Signup and view all the answers

What is reactance a measure of in an AC circuit?

The opposition to a change in current due to the inductor or capacitor Signup and view all the answers

In inductive reactance, changes in ____ are resisted by generating a magnetic field

Current Signup and view all the answers

What happens in capacitive reactance?

Capacitors resist changes by storing energy Signup and view all the answers

What is the purpose of the isolation transformer in the OR?

To convert grounded power to ungrounded power Signup and view all the answers

What is the purpose of ensuring the OR is ungrounded?

All of the above Signup and view all the answers

What is the function of a Line Isolation Monitor (LIM)?

To continuously test the impedance of the two isolated power wires to determine impedance to the ground Signup and view all the answers

What is the relationship between impedance and isolation in a circuit?

The lower the impedance, the poorer the isolation, resulting in an alarm Signup and view all the answers

What is a consequence of capacitance in AC operated equipment?

Small leakage currents that degrade the isolated power system Signup and view all the answers

What happens when a ground fault is detected in a GFCI?

It trips and cuts off power Signup and view all the answers

Match each characteristic to the proper Mapelson circuit

A = APL close to pt B = Both APL and FGF close to pt C = No corrugated tubing D = FGF close to pt Signup and view all the answers

What are the characteristics of Mapelson E and F circuits?

Mapelson E has no APL or reservoir Signup and view all the answers

660 nanometers (nm) in the red part of the visible spectrum and 940 nm in the infrared part

True Signup and view all the answers

Study Notes

Physics of Gases

Work done to compress a gas requires energy, which is manifested as heat.
Adiabatic process: no exchange of heat with surroundings, but temperature of the gas rises.
Gay-Lussac's gas law: as pressure increases, temperature increases with a constant volume.
Tubing can become extremely hot during compression, and any particles or dirt can combust.
"Crack" cylinder before use to remove any particles that may be in the connector.

Joule-Thompson Effect (Joule-Kelvin Effect)

Expansion of gas causes cooling.
Examples of compressed gases expanding in anesthesia:
- Nitrous oxide tanks have gas and liquid; as gas is pulled off the top, the liquid continuously expands to gas.
- Will fall rapidly as residual gas flows from the cylinder.

Medical Compressed Gases

Common medical compressed gases:
- Oxygen (O2)
- Nitrous oxide (N2O)
- Medical air
- Entonox (50/50 nitrous and oxygen)
- Heliox
- Xenon
Importance of checking labels to verify what gas is inside a tank, as colors differ and tanks are reusable.

Cylinder Information

Cylinder markings:
- Material of the tank
- Maximum filling pressure (psig)
- Serial number and inspection date
Checked for leaks and structural integrity with overpressure test every 10 years.
Types of cylinders:
- E cylinder: nominal value of 4.8L at 14.7psi, max fill 1900psig holds 660L
- H cylinder: nominal value of 43.6L at 14.7psi, max fill 2200psig holds 6900L

Pin Index Safety System

Prevents mounting of the wrong cylinder using pins placed complementary to specific holes in the tank.
Each gas has a unique pin configuration.

Quick Couplers

Each has a specific pin configuration for individual gases.
Attached hose should be color-coded for specific gas.

Diameter Index Safety System (DISS)

Threaded connections with specific diameters for each gas.
Required on all anesthesia machine gas inlets.
Prevents cross-connection of gases.
Standardized.

Safety Precautions

Gas cylinders should never be left standing upright and unsecured.
Risk of breaking at the neck if they fall over and release intense pressure.

Liquid Oxygen

Stored in liquid form at large facilities with "unlimited" volume.
Requires specific technology and equipment.
Liquid O2 stored at -160°C, pressure inside storage vessel ~85 psig.
Insulated with vacuum to maintain temperature.
Oxygen gas pulled from top of container, heated, then passed through pressure regulator to bring to pipeline pressure (50 psi).

Medical Vacuum and Nitrogen

Medical vacuum used for Bovie smoke and exhaled air and volatiles.
Nitrogen in OR used for air tools.

Breathing Circuits

Types of breathing circuits:
- Open: no reservoir, no rebreathing
- Semi-open: reservoir, no rebreathing
- Semi-closed: reservoir, partial rebreathing
- Closed: reservoir, complete rebreathing
Rebreathing prevented by inspiratory and expiratory valves in the circuit.
CO2 removed from breathing circuit using Y-piece.

Mapleson Breathing Systems

Semi-open circuits used for pediatrics and transport.
Inhaled and exhaled gases travel through the same tubing.
Requires high FGF to wash out CO2, no scrubber, and risks rebreathing and hypercarbia if gas flows are too low.
Typical fresh gas flows: 20-25Lpm or 2.5x MV.
Circle system only takes 1-2Lpm.

CO2 Removal Methods

Chemical absorption
Washout by fresh gas
Separation of exhaled gas from fresh gas
Use of T-piece without reservoir

Soda Lime

Most common CO2 absorbent
Composition: 80% calcium hydroxide, 15% water, 4% sodium hydroxide, 1% potassium hydroxide (activator), silica
Irregular shape to increase surface area
Optimal size: 4-8 mesh
Should be shaken before use to prevent air channeling, and turned off when not in use to prevent desiccation.

HMEF (Heat and Moisture Exchange Filter)

Hydrophobic filter that precipitates water vapor on the filter.
May also offer some bacterial and viral filtration, but not adequate for infectious patients.

Scavenger System

Removes waste gases from the system via APL valve or vent pressure relief valve.
Has adjustment knob to control vacuum pressure.
Points of exit for waste gas in circle system:
- APL valve
- Reservoir bag
- Ventilator relief valve
If suction is too high, pulls air from patient breath, causing low TV and hypoxia.
If suction is too low, gas backs up, causing increased pressure to the patient and barotrauma.

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Description

Review of thermodynamic concepts including work done to compress a gas, adiabatic processes, and pressure changes in anesthesia machines.