3 Lecture Outline The Machine Gas Supply Systems: Hospital pipeline CylinderHigh Pressure System (exposed to cylinder pressure)Intermediate Pressure System (exposed to pipeline press)Low Pressure System (distal to flowmeter needle valve)Circle System CO2 Absorber System Unidirectional ValvesVentilatorScavenger System
4 Anesthesia Machine Checkout General:Anesthesia Apparatus Checkout Recommendations, 1993 (Taken from the FDA)This checkout, or a reasonable equivalent, should be conducted before administration of anesthesia. These recommendations are only valid for an anesthesia system that conforms to current and relevant standards and includes an ascending bellows ventilator and at least the following monitors: capnograph, pulse oximeter, oxygen analyzer, respiratory volume monitor (spirometer) and breathing system pressure monitor with high and low pressure alarms. This is a guideline which users are encouraged to modify to accommodate differences in equipment design and variations in local clinical practice. Such local modifications should have appropriate peer review. Users should refer to the operator's manual for the manufacturer's specific procedures and precautions, especially the manufacturer's low pressure leak test (step #5).* If an anesthesia provider uses the same machine in successive cases, these steps need not be repeated or may be abbreviated after the initial checkout.
5 Anesthesia Machine Checkout Steps 1-3:Emergency Ventilation Equipment *1. Verify Backup Ventilation Equipment is Available & FunctioningHigh Pressure System *2. Check Oxygen Cylinder Supply a. Open 02 cylinder and verify at least half full (about 1000 psi). b. Close cylinder. *3. Check Central Pipeline Supplies a. Check that hoses are connected and pipeline gauges read about 50 psi.
6 Anesthesia Machine Checkout Steps 4-7:Low Pressure Systems *4. Check Initial Status of Low Pressure System a. Close flow control valves and turn vaporizers off. b. Check fill level and tighten vaporizers' filler caps. *5. Perform Leak Check of Machine Low Pressure System a. Verify that the machine master switch and flow control valves are OFF. b. Attach "Suction Bulb" to common Fresh gas outlet. c. Squeeze bulb repeatedly until fully collapsed. d. Verify bulb stays fully collapsed for at least 10 seconds. e. Open one vaporizer at a time and repeat 'c' and 'd' as above. f. Remove suction bulb, and reconnect fresh gas hose. *6. Turn On Machine Master Switch and all other necessary electrical equipment. *7. Test Flowmeters a. Adjust flow of all gases through their full range, checking for smooth operation of floats and undamaged flowtubes. b. Attempt to create a hypoxic 02/N20 mixture and verify correct changes in flow and/or alarm.
7 Anesthesia Machine Checkout Scavenging System *8. Adjust and Check Scavenging System a. Ensure proper connections between the scavenging system and both APL (pop-off) valve and ventilator relief valve. b. Adjust waste gas vacuum (if possible). c. Fully open APL valve and occlude Y-piece. d. With minimum 02 flow, allow scavenger reservoir bag to collapse completely and verify that absorber pressure gauge reads about zero. e. With the 02 flush activated allow the scavenger reservoir bag to distend fully, and then verify that absorber pressure gauge reads <10 cm H20.
8 Anesthesia Machine Checkout Breathing System *9. Calibrate 02 Monitor a. Ensure monitor reads 21% in room air. b. Verify low 02 alarm is enabled and functioning. c. Reinstall sensor in circuit and flush breathing system with 02. d. Verify that monitor now reads greater than 90%. 10. Check Initial Status of Breathing System a. Set selector switch to "Bag" mode. b. Check that breathing circuit is complete, undamaged and unobstructed. c. Verify that C02 absorbent is adequate. d. Install breathing circuit accessory equipment (e.g. humidifier, PEEP valve) to be used during the case. 11. Perform Leak Check of the Breathing System a. Set all gas flows to zero (or minimum). b. Close APL (pop-off) valve and occlude Y-piece. c. Pressurize breathing system to about 30 cm H20 with 02 flush. d. Ensure that pressure remains fixed for at least 10 seconds. e. Open APL (Pop-off) valve and ensure that pressure decreases.
9 Anesthesia Machine Checkout Manual and Automatic Ventilation Systems 12. Test Ventilation Systems and Unidirectional Valves a. Place a second breathing bag on Y-piece. b. Set appropriate ventilator parameters for next patient. c. Switch to automatic ventilation (Ventilator) mode. d. Fill bellows and breathing bag with 02 flush and then turn ventilator ON. e. Set 02 flow to minimum, other gas flows to zero. f. Verify that during inspiration bellows delivers appropriate tidal volume and that during expiration bellows fills completely. g. Set fresh gas flow to about 5 L/min. h. Verify that the ventilator bellows and simulated lungs fill and empty appropriately without sustained pressure at end expiration. i. Check for proper action of unidirectional valves. j. Exercise breathing circuit accessories to ensure proper function. k. Turn ventilator OFF and switch to manual ventilation (Bag/APL) mode. l. Ventilate manually and assure inflation and deflation of artificial lungs and appropriate feel of system resistance and compliance. m. Remove second breathing bag from Y-piece.
10 Anesthesia Machine Checkout Monitors 13. Check, Calibrate and/or Set Alarm Limits of all Monitors Capnometer, Pulse Oximeter, Oxygen Analyzer, Respiratory Volume Monitor (Spirometer), Pressure Monitor with High and Low Airway AlarmsFinal Position 14. Check Final Status of Machine a. Vaporizers off b. AFL valve open c. Selector switch to "Bag" d. All flowmeters to zero e. Patient suction level adequate f. Breathing system ready to use
11 The Anesthesia Machine The anesthesia gas machine is a device which delivers a precisely-known but variable gas mixture, including anesthetizing and life-sustaining gases.
14 Manufacturers & NamesNorth American Dräger (Telford, PA) is the manufacturer of the Narkomed 2C, Narkomed 4, Narkomed GS, Narkomed 6000, Narkomed Julian, Narkomed MRI and Narkomed Mobile models.Datex-Ohmeda (Madison WI) manufactures the AS/3 ADU, Aestiva, Modulus SE, Excel 210, and Excel 110
15 Some Numbers to Remember The hospital pipeline is the primary gas source at 50 psi (normal working pressure of most machines).Cylinders – O2 is supplied at around 2000 psi (regulated to approximately 45 psi after it enters the machine).Oxygen flush is a "straight shot" from supply to delivery point, L/min.OSHA Fact Sheet (1991) on Waste Anesthetic Gases (WAGs) occupational exposure should be limited to an eight hour time-weighted average of not more than 2 ppm halogenated agents (Halothane, Enflurane, Isoflurane, Sevoflurane, Desflurane)If Halogenated agent is used in combination with nitrous oxide, then ONLY 0.5 ppm OF THE HALOGENATED AGENT IS ALLOWEDNo more than 25 ppm nitrous oxide can be used at all times (with or without Halogenated Agent)
17 Straight-line model SPDD (Supply/Processing/Delivery/Disposal)
18 Oxygen has five "tasks” It powers the ventilator driving gas O2 flush Activation of low pressure alarmsActivation of fail-safe mechanisms (O2 pressure sensor shut-off )Proceeding through the flowmeter
19 “Other gases: One task Only” Transported via flowmeter & breathing circuit to:Anesthetize pt (N2O)Sustain Life (Air)
23 DISSPipeline inlets are connected with DISS (diameter index safety system) non-interchangeable connections.The check valve, located down stream from the pipeline inlet, prevents reverse flow of gases (from machine to pipeline, or to atmosphere), which allows use of the gas machine when pipeline gas sources are unavailable.
24 PISSPISS (pin-index safety system) prevents misconnection of a cylinder to the wrong yoke. Keep cylinders closed except when checking machine, or while in use (if O2 from pipeline is unavailable)
26 Gas Supply Systems Cylinder Pin Index Safety System:O2 2,5N2O 3,5
27 High Pressure System (parts which receive gas at cylinder pressure) hanger yoke (including filter and unidirectional valve)yoke block (with check valves)cylinder pressure gaugecylinder pressure regulators
29 Hanger Yoke & Check Valve orients cylindersprovides unidirectional flowensures gas-tight seal.Check Valveminimize trans-fillingallows change of cylinders during useminimize leaks to atmosphere if a yoke is empty.
32 More on CylindersThe cylinder pressure regulator converts high, variable cylinder pressure to a constant pressure of approximately 45 psi downstream of the regulator.This is intentionally slightly less than pipeline pressure, to prevent silent depletion of cylinder contents if a cylinder is inadvertently left open after checking its pressure.Cylinder pressure gauge indicates pressure in the higher-pressure cylinder only (if two are opened simultaneously).
33 E cylinder Characteristics Gas US (International) PSI Capacity (L) PISSO Green (white)N2O Blue (blue)Air Yellow (B & W)**** We’ll use 2000psi for O2 instead of 1900psi****
35 Intermediate Pressure System (receives gases at low, relatively constant pressures (37-55 psi, = pipeline pressure)(*For consistency we’ll use 50 psi)pipeline inlets and pressure gaugesventilator power inletOxygen pressure-failure device (fail-safe) and alarmflowmeter valvesoxygen second-stage regulatoroxygen flush valve
36 Oxygen pressure-failure device (fail-safe) and alarm What happens if you lose oxygen pipeline pressure?The fail safe device ensures that "Whenever oxygen pressure is reduced and until flow ceases, the set oxygen concentration shall not decrease at the common gas outlet" (from ASTM F1161).The loss of oxygen pressure results in alarms, audible and visible, at 30 psi pipeline pressure.Fail-safe systems don't prevent hypoxic mixtures.
37 Fail-safe systems don't prevent hypoxic mixtures as long as there is pressure in the O2 line, nothing in the fail safe system prevents you from turning on a gas mixture of 100% nitrous oxide (however, this should be prevented by the hypoxic guard system)or 100% helium (which wouldn’t be prevented by the hypoxic guard).Datex-Ohmeda terms their fail safe a "pressure sensor shut off valve"- at 20 psi oxygen, the flow of all other gases are shut off. Dräger's, "oxygen failure protection device" (OFPD) threshold is proportional, unlike Ohmeda's which is off-or-on.
38 Fail-safe systems don't prevent hypoxic mixtures (Cont…) Ohmeda uses a second-stage O2 pressure regulator (ensures constant oxygen flowmeter input until supply pressure is less than psi). The oxygen ratio monitor controller (ORM [newer] or ORMC, both by Dräger) shuts off nitrous oxide when oxygen pressure is less than 10 psi
39 Pipeline TroublePipeline sources are not trouble free: contamination (particles, bacteria, viral, moisture), inadequate pressure, excessive pressures, and accidental crossover (switch between oxygen and some other gas such as nitrous oxide or nitrogen) are all reported.
40 What if you lose oxygen pipeline pressure? Open the emergency oxygen cylinder fully (not just the three or four turns used for checking)Disconnect the pipeline connection at the wallWhy? Something is wrong with the oxygen pipeline.What if the supply problem evolves into a non-oxygen gas in the oxygen pipeline? If so, it will flow to the patient (pipeline pressure 50 psi) rather than your oxygen cylinder source (down-regulated to 45 psi).If you are lucky, the oxygen alarm will sound to warn you of the change (you do set your alarms, don't you?).If for some reason the oxygen analyzer does not warn of the crossover, the pulse oximeter will- but only after the oxygen has been washed out by ventilation from the patient's functional residual capacity and vessel-rich group.
41 Reinforcement!!!!Disconnect the pipeline connection at the wall if oxygen pipeline pressure is lost. It's also easier to remember one strategy which works for any problem with the pipeline, rather than to remember that sometimes you must, and sometimes it is optional, to disconnect. And use that oxygen analyzer always!Ventilate by hand rather than with the mechanical ventilator (which uses cylinder oxygen for the driving gas if the pipeline is unavailable)
42 HOW LONG BEFORE O2 TANK IS EXHAUSTED??? -The time to exhaustion is calculated by dividing the remaining O2 volume in the cylinder by the rate of consumption of O2.-Remaining volume in liters (L) in an E-cylinder is calculated by dividing the cylinder pressure in psig by 2000 psig and multiplying by 660 L.
43 EXAMPLEIf cylinder gauge reads 1,000 psig, this represents (1000/2000) X 660 = 330 L left in that tank. The rate of consumption of O2 during mechanical ventilation is the sum of the O2 flow meter setting and the patient’s minute ventilation (VT in L x RR in breaths/min).If FGF is 0.5 L/min O2 and 1.0 L/min N2O and VT is 0.7 L and RR is 10 bpm, then the minute ventilation is7 L/min (0.7L x 10 bpm)* The total O2 consumption is 7.5 L/min. The expected time to exhaustion is thus approximately 330 L divided by 7.5 L/min = 44 min (ignoring the gas sampled by the gas analyzer and leaks)
44 The Low-pressure system (distal to flowmeter needle valve) flowmeter tubesvaporizerscheck valves (if present)common gas outlet
45 Flowmeters -Thorpe tube is an older term for flowmeters. -Components: needle valve, indicator float, knobs, valve stops.-Flow increases when the knob is turned counterclockwise (same as vaporizers).-At low flows, the annular-shaped orifice around the float is (relatively) tubular so (according to Poiseuille's Law) flow is governed by viscosity. (laminar flow)-At high flows (indicated on the wider top part of the float tube), the annular opening is more like an orifice, and density governs flows. (turbulent flow)
46 Low Pressure System Distal to Flowmeter Needdle Valve Flow Meters- measures and indicates the rate of gas flowing through it. Variable orifice/Thorpe tube-constant press. flow meters Rate of flow r/t: 1) pressure drop across the constriction ) size of annular opening ) Physical properties of the gas (viscosity and density) Indicator, float or bobbin ) rotometers ) non-rotating floats ) ball floats Sequence of flowmeters tubes is very important to decrease chance of hypoxic mixture., Gas flow is from left to right, O2 on right side Any leak in flowmeters will vent other gas out orentrain air before O2 is added to gas mixture decreasing chance that O2 will be lost or diluted.FLOW
47 More on FlowmetersNeedle valve can be damaged if it is closed with forceFlowtube (Thorpe tube) is tapered (narrower at bottom) and gas-specificIf gas has 2 tubes, they are connected in series with a single control valve
48 Did anyone say Flowmeters?? Care of flowmeters includes ensuring that:floats spin freelyqualified service personnel regularly maintain gas machinesan O2 analyzer used always (of course, the readings are erroneous during use of nasal cannula)one never adjusts a flowmeter without looking at itone includes flowmeters in visual monitoring sweepsone turns flowmeters off before opening cylinders, connecting pipelines, or turning machine "on".
49 Low Pressure SystemSafety Devices-Purpose is to decrease risk of hypoxic mixture * Mandatory Minimum O2 Flow- factory preset minimum O2 flow that always flows when machine is on * Minimum O2/N2O Ratio– 1:3 Device or proportioning system: Flow valves linked mechanically or pneumatically so O2 cannot be set below 25%. Alarm will signal if O2/NO2 ratio falls below preset value* O2/NO2 Proportioning Device-Automatically mixes O2 and NO2 to setting selected on dial
53 Hypoxic breathing is POSSIBLE hypoxic guard systems CAN permit hypoxic breathing mixtures IF:wrong supply gas in oxygen pipeline or cylinder,defective pneumatic or mechanical components,leaks exist downstream of flow control valves, orif third inert gas (such as helium) is used.
54 Low Pressure SystemVaporizers- Classification: A. Method of regulating output concentration Concentration calibrated Measured flow B. Method of vaporization Flow over Bubble Through Injection C. Temperature compensation Thermocompensation Supplied heat D. Specificity Agent specific Multiple agent E. Resistance Plenum Low resistance
55 VAPORIZERSVapor Pressure (VP) Molecules escape from a volatile liquid to the vapor phase, creating a “saturated vapor pressure” at equilibriumVP is independent of Atmospheric PressVP increases with TemperatureVP depends ONLY on the Physical Characteristics of the Liquid & on its Temperature
56 CLASSIFICATION Variable bypass Fresh gas flow from the flowmeters enters the inlet of any vaporizer which is on. The concentration control dial setting splits this stream into bypass gas (which does not enter the vaporizing chamber), and carrier gas (also called chamber flow, which flows over the liquid agent)
57 CLASSIFICATION Flow over Carrier gas flows over the surface of the liquid volatile agent in the vaporizing chamber (as opposed to bubbling up through it (as in the copper kettle and Vernitrol)
58 CLASSIFICATION Temperature compensated Equipped with automatic devices that ensure steady vaporizer output over a wide range of ambient temperaturesAgent-specificOnly calibrated for a single gas, usually with keyed fillers that decrease the likelihood of filling the vaporizer with the wrong agentOut of circuitAs opposed to (much) older models such as the Ohio #8 (Boyle's bottle) which were inserted within the circle system.
59 Vaporizer Interlock Mechanism Safety mechanism that allows ONLY one vaporizer at a time to be opened
60 Circle SystemCircle System- CO2 absorber housing and absorber, unidirectional valves, inspiratory and expiratory ports, fresh gas inlet, APL valve, pressure gauge, breathing tubes, Y-piece, reservoir bag, bag/vent switch selector, respiratory gas monitor sensor.
61 Circle SystemCO2 Absorber System: Housing (canister support), Absorbent, baffles, side tubeUnidirectional Valves-aka Flutter valves, one way valves, check valves, directional valves, dome valvesCanister-Air space 50%, void space 42%, pore space 8%Soda Lime: 4% Sodium Hydroxide, 1% potassium hydroxide, 14-19% H2O, and calcium hydroxide to make 100%, Silica and kielselguhr for hardness Indicator for color change with exhaustion of CO2 absorption capabilities CO2+H2OH2CO NaOH+2H2CO3+Ca(OH)2 CaCO3+NaCO3+4H2O heat released 13,700 cal./mole CO2 absorbedBarium Hydroxide Lime: 20% Barium hydroxide, 80% calcium hydroxide, and +/- potassium hydroxide, Indicator for color change with exhaustion of CO2 absorption capabilities Ba(OH)2 . 8H2O+CO2BaCO3+9H2O 9H2O+9CO2 9H2CO H2CO3+9Ca(OH) 2 9CaCO3+18H2O 2KOH+H2CO3 K2CO3+2H2O Ca(OH)2+K2CO3 CaCO3+2KOH Regeneration (color change loss) with rest can occur. Appears new but is exhausted Granule size 4-8 mesh- 4 mesh equals strainer with 4 openings/inch
62 Circle system CO2 Absorber System Removing canister & soda limecanister locking levercanisters unlockedRemoving both canisters & soda limeReplacing fresh soda limeExhausted soda lime
63 Circle system Unidirectional Valves Unidirectional valves-aka flutter valves, one way valves, check valves, directional valves, dome valves. Found on Inspiratory and Expiratory flow portsOhmeda MachineNarkomed Machine
65 VentilatorDriving gas supply or power gas supply-O2 pneumatically drives (compresses) ventilator bellowsInjector or Venturi mechanism-Increases the flow of driving gas by using the BERNOULLI Principle- As a gas flow meets a restriction, its lateral pressure drops. Any opening in the tube at this constriction will entrain air (suck air in)Controls-Adjusts Flow, Volume, Timing, and Pressure of the driving gas that compresses the bellows Pneumatic-Uses pressure changes to initiate changes in respiratory cycle Fluidic or fluid logic-Uses gas streams through channels in solid material. Allow for compact ventilator Electronic-Electronic control of many addition ventilation parameters powered by a driving gas on newer machines. Must have both power and pnuematics.Alarms-ASTM standards group alarms into three levels: High, Medium, Low Priority correlates to;operator immediate action, prompt action,or awareness. Loss of main power is the only required alarm with a required duration of at least 2 minutesSafety relief valve-aka pressure limiting valve, drving gas pressure relief valve. Vents driving gas if factory pre-set pressure is reached (65-80 cm H2O) or adjustable set pressure is reached.
66 Bernoulli’s Principle At constriction:Flow is higherPressure is lower
67 VentilatorBellows Assembly: Housing- Usually made of hard rigid clear plastic Bellows; ASCENDING-standing, upright. Compressed downward during inspiration. ASCEND DURING EXPIRATIONPressure is always positive. PEEP 2-4 cm H2O. DESCENDING-hanging, inverted. Compressed upward during inspiration. DESCEND DURING EXPIRATION. Weight of bellows results in negative airway pressure during exhalation until bellow refilled.IMPORTANT difference between ascending and descending is that when there is a major leak or disconnect, the ascending bellows will collapse (unless prevented by scavenging system). When a disconnection occurs with a descending bellows system, the ventilator will continue it’s upward movement and downward movements, drawing in room air and driving gas during it’s descent and discharging it during the upward movement. Gas flow during upward movement may generate enough pressure such that the low pressure alarm is not activated.What type is shown?Remember that the type is described by how the bellows moveduring EXPIRATION
68 Scavenger SystemScavenger System consists of: 1) gas collecting assembly, 2) a transfer means, 3) the interface, 4) gas disposal tubing, 5) gas disposal assembly. (some or all components may be combined) ASTM standard fitting size for scavenger hoses 19 mm ( international standard 30mm) to prevent incorrect connection to breathing hoses (22mm).3214&54&51