Section 1(1).pdf

Section 1 Medical Gas Supply Equipment  Physics of the Principles Kinetic Theory of Gases – Gases are composed of discrete molecules – Molecules are in random motion – Molecular collisions are elastic – Molecular activity depends on temp. – No physical attraction b/t molecu...

Section 1 Medical Gas Supply Equipment  Physics of the Principles Kinetic Theory of Gases – Gases are composed of discrete molecules – Molecules are in random motion – Molecular collisions are elastic – Molecular activity depends on temp. – No physical attraction b/t molecules 2  Gas Pressure – Force per unit area – Caused by molecules colliding w/ other molecules & walls of container – Temp. influences velocity by level of kinetic energy 3  Pascal’s Law – Fluid in a container transmits pressure equally in all directions – Pressure against wall of container is transmitted to said wall 4  Measurement of Gas Pressure (usually in cmH2o) Mercury Barometer – Uses column of Hg as opposing force of atm to measure atm P 5  Aneroid Barometer – Uses evacuated metal container, spring, & pointer 6  Mechanical Manometer – Similar to anaeroid barometer – Uses diaphragm or evacuated container 7  Bourdon Gauge – Hollow coiled metal tube w/ elliptical cross section – Commonly found on medical gas cylinders 8  Physics of the Principles (continued) Gas Flow – Occurs due to P difference b/t 2 points – Flow from area of P to P – Rate (velocity) depends on: Difference in P Size of opening 9  Bernoulli’s Principle – Gas flow through a tube – As velocity of gas , lateral P (since total energy is constant) 10  Viscous Shearing, Vorticity, and Ejectors – Viscous shearing: a high-velocity jet injected into a quiescent (stationary) gas – Vorticity: tendency of velocity of jet gas to due to “swirling” mixture of 2 gases – Ejectors (Ducted): use nozzle, viscous shearing, & vorticity to total flow 11 Viscous Shearing 12  Venturi’s Principle – Expanded on Bernoulli Tube w/ radius (angle must be K Conversion: C° + 273 = K – Pressure = 1 atm or 760 mmHg 19  Physics of the Principles (continued) Boyle’s Law – w/ constant T0, volume varies inversely w/ P – Formula: P1V1=P2V2 20  Charles’ Law – w/ constant P, volume varies directly w/ T0(K) – Formula: V1 = V2 T1 T2 21  Gay-Lussac’s Law w/ volume constant, pressure will w/ T0 Formula: P1 = P2 T1 T2 22  Combined Gas Law (a.k.a. general gas law) – Combines Boyle’s, Charles’, & Gay-Lussac’s – Formula: P1 V1 = P2 V2 T1 T2 23  Dalton’s Law – The Law of Partial Pressures – The P of a gas mixture = the sum of the partial P of the component gases – The partial P of each is proportional to its volumetric percentage 24  Gas Diffusion Fick’s Law – Rate of diffusion of a gas into another is proportional to its concentration – As gradient , rate of diffusion 25  Gas Diffusion Henry’s Law – Rate of gas diffusion into liquid is proportional to partial P of gas @ given T0 – Example: opening a Coke (or beer.) CO2 diffuses out of liquid into atm, where partial P of CO2 is less 26  Gas Diffusion Graham’s Law – Rate of gas diffusion through liquid is proportional to gas solubility & inversely to gm. mol. wt. CO2 is 19x more diffusable in blood than O2 But…Graham assumes = partial P In reality, alveolar PO2 > PCO2 27  Water Content in Gas @ 370C gas may hold 44 mg of H2O per L @ 760mmHg (1 atm), 47 mmHg is due to water vapor pressure 28 Medical Gas Supply Equipment 29 REMINDER: Flow and FiO2 are different! Flow Fraction of inspired oxygen (FiO2) Velocity of the gas Percentage of the gas that is comprised of oxygen 3 Lpm 3 Lpm 40% Oxyegn Gas 60% Room Air 100% 30  Compressors Provide compressed air to power equipment & mix w/ O2 Air must be oil-free (oil + O2 = FIRE!) – No vaseline in a O2 rich environment! P must be reduced to 50psi for use! 3 types: – Piston – Diaphragm – Centrifugal 31  Piston Compressor Uses a piston driven by an electric motor 32  Diaphragm Compressor Uses flexible diaphragm driven by electric motor Typically used in small nebulizers 33  Centrifugal Compressor Uses electrically powered impeller May produce large volumes of air (power an entire hospital) 34  Production of O2 Fractional Distillation – Air is liquefied & cooled – Slowly heated – N & trace gases have lower boiling point – Result is 99.5% pure O2 Physical Separation (Concentrators) – Molecular sieves – Semi-permeable plastic membrane 35  Concentrators Molecular sieve – Most effective – Uses Zeolite to adsorb the N – 50-90% FiO2 Membrane enricher – Uses semipermeable polymer to allow O2 through (N molecules > O2 molecules) – 40% FiO2 @ 1-10 LPM 36  Liquid Reservoir Systems Bulk supply systems – large amounts of gas – -1830 C – 1 ft3 liquid O2 = 861 ft3 gas Portable reservoirs – Portable reservoir duration based on liquid weight (342.8 L gas/lb of liquid) – Stationary home models = 20-43 L – Ambulatory versions = 0.6-1.23 L 37  Piping Systems Construction of piping systems – Supply Manifold, bulk liquid, or both 24hr reserve supply required Copper pipes tested to 1.5x working P – Safety features Alarms- alert to drop in system P Zone valves- emergency shutoffs (fire) Pressure sensors- ensure 50psi – Station outlets DISS: gas-specific threading & diameter ( working P) – Serial # – Owner’s stamp 41 Cylinder Markings 42 Cylinder Markings 43 Cylinder Markings (cont’d.) 44  Hydrostatic testing – Q 5 or 10yrs – Filled to 5/3 working P – Difficult w/ carbon fiber tanks 45  Cylinder sizes – H, G, M, E, D, B – H & E most common in hospital H = 244 ft3 of O2 E = 22 ft3 of O2 – D most common on ambulance 46 47  Color coding – O2 green (or white) – CO2 gray – N2O light blue – C3H6 orange (extremely reactive) – He brown – CO2 + O2 gray & green – He + O2 brown & green – Air yellow 48  Although label is most reliable indicatory of contents, if label & color code do not match… DO NOT USE THE CYLINDER!!! 49  Safety rules for cylinder use – Mostly common sense – Review Box 3.3 (page 54) What happens when safety rules aren’t followed? 50  E-cylinder tank went through the drywall… Bounced off the outside wall brick… 51  Went through the glass wall in the patient’s room… 52 And finally lodged itself in a 45m fire door across the hall. Tank safety matters! 53  Duration of gas flow – 4 key factors Full H contains 244 ft3 O2 Full E contains 22 ft3 O2 Full cylinder = 2200 psi 1 ft3 = 28.3L O2 54  Tank Factor Calculation Tank Factor = Size (ft3) x 28.3L/ft3 Pressure when full H = 3.14L/psi E = 0.28L/psi 55  Let’s Try One… You are asked to transport an intubated patient to CT scan for a procedure. Travel time to radiology is approximately 20 minutes. Your E cylinder currently reads 2100 psi, and your patient is utilizing 15 LPM for manual ventilation. Do you have enough O2? (Hint: Don’t forget about the return trip!) 56  Safety Factor Most hospitals consider a tank empty at 500psi Why??? Ensures that you always have a buffer You never want to come back from a transport with an EMPTY tank! Actual tank PSI – 500 PSI Subtract out before calculating tank duration when asked to consider safety factor! 57  Oxygen Regulation Devices Cylinder valves – Direct acting cylinder valve Opens & closes valve directly D & E cylinders – Diaphragm cylinder valve a.k.a. “indirect acting” Diaphragm opens & closes valve H cylinder 58 59 60  Cylinder Valve Safety Features American Standard Safety System (ASSS) – Uses variants in threading to prevent attachment of wrong equipment (Fig 3.8 p60) – Found on larger cylinders, like H Pin Index Safety System (PISS) – Uses variants in pin placement to prevent attachment of wrong equipment (Fig 3.9 p 61) – Found on smaller cylinders, like D & E 61 62 63  Cylinder Valve Safety Features (cont’d.) Pressure release devices – Frangible disk Thin metal disk that ruptures if P is too – Fusible plug Melts @ T0 > 208-220 0F 64 Oxygen Regulation Devices (continued) Reducing valves – Single-stage reducing valve – Modified single-stage reducing valve – Multistage reducing valves 65  Single-stage reducing valve – Reduces P to 50 psi in single step – Uses 2 opposing forces Spring tension Gas pressure 66  Modified single-stage reducing valve – Has an additional spring – Allows > flow rates 67  Multistage reducing valves – Allows > flow & more precise P – 2 or more single-stage combined 1st drops to 200 psi 2nd drops to 50 psi 68  Reducing valve safety features – Pressure relief valves Safety, or pop-off valves 1 per stage – Indexing of inlet & outlet Inlet utilizes ASSS or PISS Outlet utilizes DISS 69  Regulators – A reducing valve & a flowmeter combined – 2 types of flowmeters Bourdon-type Thorpe tube 70  Oxygen Flowmeters Fixed orifice flowmeter Bourdon gauge flowmeter Uncompensated thorpe tube flowmeter Compensated thorpe tube flowmeter 71  Fixed orifice flowmeters Sets flow by adjusting size of outlet orifice Very common E cylinder flowmeter: 72  Bourdon gauge flowmeter Bourdon gauge + adjustable reducing valve Reads P, but indicates flow Accurate only @ ambient P Back pressure causes flow to appear > actual Can’t tell if O2 is flowing by looking @ gauge!!! Lightweight & not gravity-dependent 73 Bourdon Flowmeter 74  Bourdon Gauge Flowmeter FIGURE 4-8 A, Bourdon gauge operating under normal conditions. The actual flow delivered equals the flow registered on the flowmeter. B, The effect when resistance is added downstream of the flowmeter at the outlet. Notice that the flow registered on the flowmeter is higher than the actual flow. C, Complete occlusion of the outlet has a similar 75 effect; that is, the flow registered on the flowmeter is erroneously high.  Uncompensated thorpe tube flowmeter Needle valve is proximal to tube Not compensated for back P – P downstream may cause flow to appear < delivered 76  Compensated thorpe tube flowmeter Needle valve is distal to Thorpe tube Back P has no effect Ball “jumps” when attached to gas source 77 Uncompensated VS compensated Fig 4.5 p80 78  Flowmeter Range Typically 0-15 LPM Low-range = 0-3 LPM – Peds/neonates – COPD High-range = 0-75 LPM – CPAP – Vapotherm® 79  Other Medical Gas Supply Equipment Proportioners (Air-Oxygen Blenders) – Mix air & O2 to precise concentrations – Provide 50 psi – Proportioning valve controls concentration – Built-in alarm Senses gas P 80  Demand Pulse Flow O2 Delivery Devices – Deliver O2 only during inspiration Reduces oxygenation of anatomical dead space Sense inspiration via P transducer No need for humidity (???) – a.k.a. O2 conserving device (OCD) – Requires exercise oximetry study 81