Anaesthesia Machine Check Protocol

(For MD Anaesthesia Examinations)

Why Check the Machine?

• The anaesthesia machine has evolved from a simple pneumatic device to a complex anaesthesia workstation with mechanical, electrical, and electronic components.
• Despite technological advances, a remote but life-threatening possibility of intraoperative machine malfunction always exists.
• Human factors contribute more to complications than machine faults alone.
• A single checklist cannot satisfactorily test all machines due to variations in design among manufacturers.
• An in-depth check is mandatory after servicing; a daily check is required before first use; and a minor check must be done between anaesthetic conducts.

Timing of Machine Checks

The Concise Machine Checklist (Figure 1 from article)

Items in bold = Minor check procedure to be followed between anaesthetic conducts.

1. Self-inflating bag appropriate for patient's age + alternate O2 source available
2. Machine and wiring secured safely
3. Power source plugged on, battery backup sufficient and charging
4. Pipelines - Quick coupling, tug test, sufficient pressures present
5. Cylinders - Pin indices, fitted correctly, sufficient gas present
6. Oxygen fail-safe mechanism intact - Single hose test, hypoxic guard functioning, high-pitch alarm on O2 discontinuation
7. Oxygen flush works appropriately
8. Machine leak check - first with vaporiser off, then with individual vaporiser turned on
9. Flow meters working appropriately through full range
10. Vaporisers in upright position, filled adequately
11. Oxygen analyser calibrated
12. Breathing system checked for leak, unidirectional valve function, appropriate circuit chosen, sufficient CO2 absorbent present
13. Ventilator - functioning appropriately, appropriate alarm settings for patient's age
14. Suction apparatus - functioning well
15. Monitors - SpO2, ETCO2, NIBP checked on self; alarm settings adjusted to patient; unwanted monitors turned off; tubing leak-free and kink-free
16. Scavenging system appropriately connected and functioning well

Systematic Breakdown

A. Checking the High Pressure System (Cylinders)

1. Preparation: Master switch off, pipelines disconnected, cylinders completely closed, residual gas exhausted (pressure gauges reading zero). Confirm each cylinder by colour coding and label. Confirm proper attachment through the hanger yoke assembly.
2. O2 Cylinder: Open with cylinder key by full 3.5 rotations anticlockwise. Confirm at least half full (>7000 kPa or >1000 psi). Open O2 flow control valve (anticlockwise) - confirm flow meter registers. Open N2O flow control valve - confirm N2O flow meter shows no flow. Close O2 cylinder, wait until flow reaches zero and O2 pressure gauge reads zero.
3. N2O Slave Mechanism / O2 Fail-Safe Check: With O2 supply off, open N2O cylinder fully. Confirm N2O pressure gauge reads >5000 kPa or >750 psi (lesser = liquid N2O exhausted). Open N2O flow control valve - confirm absence of flow (presence of flow = defect). Now open both O2 cylinder and O2 flow control valve - both O2 and N2O flow meters should register flows. Close O2 cylinder and flush O2 - flows in both O2 and N2O flow meters should return to zero.
4. O2 Flush: Should function even with master switch and O2 flow meter turned off, as long as O2 supply is intact. Flush must stop immediately when pressure on the knob is released.
5. Close both O2 and N2O cylinders and turn off flow control valves.

B. Checking the Intermediate Pressure System (Pipelines)

1. Tug Test: Connect O2 pipeline to oxygen wall outlet via Schrader quick coupler. Correct coupling - pipeline cannot be detached when a tug is given. Repeat for N2O pipeline.
2. Single Hose Test: Disconnect N2O pipeline (keep O2 intact). Open O2 flow control valve - confirm O2 is flowing. Open N2O flow control valve - shows initial flow (residual N2O) that then falls to zero. Now reconnect N2O pipeline - confirm N2O flow meter registers flow again.
   • This test detects accidental mix-up of O2 and N2O pipeline connections.
   • Disconnecting O2 pipeline should cause both flow meters to register zero and activate the oxygen fail-safe mechanism.
3. Pressure Confirmation: Connect both pipelines; confirm pressure gauges read >400 kPa or 55-60 psi (correct manifold supply pressure).

C. Checking the Low Pressure System

1. Close flow control valves. Place vaporisers on the machine with dial turned off. Confirm sufficient liquid volatile agent and filler cap tightly shut. Ensure vaporisers are upright and not tilted (tilting causes unsafe delivery of vapours).
2. Universal Negative Pressure Leak Test:
   • Turn master switch off. Close all flow control valves.
   • Attach suction bulb to the common gas outlet and repeatedly squeeze until bulb is well collapsed.
   • Bulb should remain collapsed for at least 10 seconds - indicates no leak.
   • To test individual vaporisers: turn one vaporiser on and repeat - re-inflation within 10 seconds = leak in that vaporiser.
   • At end of test: master switch on, remove bulb, connect breathing apparatus.
3. Flow Meters: Open individual flow meters to maximum range to confirm Thorpe tube and float functioning. Confirm anti-hypoxic (gas proportionating) mechanisms work across various O2 and N2O flow ranges.

D. Checking Electrical/Electronic Components

1. Turn master switch on. Confirm all associated electrical/electronic equipment functions. If machine has minimum mandatory O2 flow, confirm O2 flow meter registers ~50-200 mL with O2 flow control valve turned off.
2. Machine connected to AC mains; battery has at least 30 min backup and is charging during use.
3. Monitors:
   • SpO2 on your own finger should read >96%.
   • Exhaling into capnograph port should register a CO2 waveform.
   • Adjust alarm settings according to patient profile.
   • Gas sampling line must be proximal to the airway filter (to avoid moisture obstruction).
   • Turn off monitoring parameters not required for that patient.
4. O2 Analyser Calibration (21% to >95%):
   • Calibrate to read 21% in atmosphere.
   • With O2 from cylinder (pipeline disconnected), open O2 flow control valve, connect analyser to common gas outlet - should register at least 95%.

E. Checking Other Components

1. Confirm the correct breathing circuit is chosen (circle vs. Mapleson - check knob position).
2. Circle System Leak Test:
   • Verify adequate fresh CO2 absorbent and proper attachment.
   • Occlude patient end of breathing circuit.
   • Increase O2 flows or use O2 flush to pressurise to >30 cm H2O.
   • Turn off O2 flow control valve and stop flush.
   • Pressure drop to <30 cm H2O within 10 seconds = leak.
   • Quantify leak: increase O2 flows in small increments until pressure is sustained >30 cm H2O.
   • Release system pressure via APL valve - also confirms APL valve functions and prevents absorbent dust entry into breathing system.
   • Simultaneously evaluate unidirectional (one-way) valve response.
3. Ventilator:
   • With breathing system in situ and patient end occluded, turn on ventilator.
   • For ascending bellows: bellows should reach the top of the bottle. Turn off fresh gas flows - bellows should still reach the top at end of each breath. Failure to reach the top = leak.
   • (For descending bellows, this cannot be verified.)
   • Set appropriate ventilator settings for patient weight; adjust alarm settings.
4. Scavenging: Confirm appropriate connection to the machine and correct functioning.
5. Suction: Confirm working and that sufficient negative pressure is rapidly developed.
6. Workstation notes: Check last servicing date, last time CO2 absorbent was changed.
7. Patient end of breathing circuit - when not in use, cover with a sterile layer (e.g., sterile glove).

Between Anaesthetic Conducts (Minor Check)

• Test new suction tubing, breathing circuitry intended for next patient.
• Verify sufficient CO2 absorbent and volatile anaesthetic liquid.
• If O2 cylinder was used, confirm it is at least half full, or replace with a new full cylinder.
• During handover of anaesthesiologist in long procedures: proper handover regarding machine check and component functioning is mandatory.

Important Exam Points to Remember

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