Chris Thompson   USyd Lectures Listing

Checking Anaesthesia Machines

Checks to be performed when starting at a new hospital


  • Locate the line gas supply monitoring panel/s
  • Know who to contact in the event of a gas supply problem
  • Identify the gas isolation valves for each anaesthetising location and know how to operate them
  • Locate the gas line pressure indicators in the operating room
  • Know where reserve oxygen cylinders are stored
  • Plan how to manage an extended total gas supply failure


  • Check which electrical safety system is in use - either Isolating Transformers or Residual Current Devices (RCD's or 'safety switches')
    • For Line Isolation Transformers, know where each Isolation Monitor panel is located and which sockets it monitors
    • For RCD's know how to reset them and which outlets are covered by which RCD
  • Know which mains power outlets are 'always on' (i.e. powered from a UPS)
    Know how long the UPS will provide power for in the event of total power loss
    Know who to call should the primary mains power fail
    Know how long the battery backup lasts for in critical devices e.g. machine, ventilator, monitors
    Plan how to manage an extended total mains power failure



"An anaesthesia delivery system includes any machine, equipment or apparatus which supplies gases, vapours, local anaesthesia and/or intravenous anaesthesia agents."

Checking the Anaesthesia Delivery System

ANZCA detail their requirements for checking the anaesthetic machine and related equipment in:

This document first outlines the infrastructure required to safely maintain anaesthetic equipment safely, stating that

  • The service requirements for each device must be identified, i.e. what needs checked and how frequently the checks should be performed
  • Every service must be recorded.
  • All devices must be labeled with date of last service and when the next service is due
  • Equipment must include appropriate alarms
  • A secondary means of providing ventilation and oxygenation must be available if required
  • The Department must attach a protocol for an appropriate Level 2 check to the machine

It also notes that there are three different levels of checks to be performed, and identifies the intent of each check but not the details of how to best perform that check, because this varies greatly from machine to machine.


Very detailed; on new systems or after servicing; includes electrical safety testing, comprehensive leak testing, calibration, checking of alarms and defaults; usually performed by Biomedical staff.

The Department should define what must be done at the Level 1 check in association with the Biomedical staff. All test results should be documented and retained on file.


Before each session, either by the Anaesthetist or a suitably trained person, the following must be checked:

  • Service label is present, not out of date
  • Pipeline and cylinder pressures are adequate (turn cylinders off after check)
    Oxygen failure alarm is operational (not required on electronic machines)
    Oxygen supply isn't crossed - turn oxygen on at rotameters / mixer and note increase in oxygen level in circuit
    Each gas can be delivered - turn each on and check bag fills
    Check mechanical anti-hypoxia device if present
    • i.e., run high flow nitrous / air at lowest possible oxygen concentration, confirm anti-hypoxia device is operational while watching bag fill; switch to 100% oxygen on and note the increase in measured oxygen.
  • Vapourisers are adequately full, filler cap closed, seating OK, can be turned on, power 'on' for Des
    confirm the absence of 'backbar' leaks with vapourisers on or off (see below).
  • Circuit is assembled properly, doesn't leak, valves & APL valve are OK, manual ventilation is possible.
    • manual ventilation test is easy with a second bag
  • Ventilator including alarms, bellows; confirm presence of emergency ventilating system
  • Scavenging, suction, airway / intubation equipment, monitoring etc
  • Drugs, IV infusions, syringe pumps (esp. that mains power is on)


Performed by the Anaesthetist before commencing every anaesthetic:

  • full check of anything that has been changed
    (e.g. new circuits, vapourisers filled / changed = full leak/functional tests must be done)
  • check drugs, airway/intubation equipment, suction, IV's, pumps, monitoring, software settings etc


My personal approach

Check that manual ventilation is possible before EVERY case by routinely doing the two following tests:


1. The Quick Squeeze the Bag Test

At ZERO Fresh Gas Flow:

  • set the APL to 30
  • occlude the Y-piece,
  • hit the oxygen flush,
  • squeeze the bag,
  • then check that the valves go up and down with intermittent squeezing

2. Check that the patient can breathe easily through the circuit BEFORE induction

At ZERO fresh gas flow, with the APL OPEN, attach a suitable mask, then...

  • Put the mask on the patient (after explaining that you want to see if it is a nice fit),
  • gently get a reasonable seal,
  • confirm that the bag goes up and down with minimal patient effort


If the quick squeeze the bag test (with no fresh gas flow) fails, you've got a big leak! Inspect, listen and feel for leaks, eliminate common problems one by one.

If the small leak test repeatedly fails and nothing is obviously wrong with the circuit, formally test the backbar with a pressure manometer (ETT cuff pressure tester, non-mercury sphygmo, etc). Confirm that pressure in the backbar rapidly increases from zero to above 30 cmH2O with less than 150 ml/min FGF.

Once the backbar has been confirmed to be airtight, repeatedly test each circuit component until the leak is eliminated.

Leak testing with a vapouriser in the 'ON' position detects all the leaks that would be present if it was OFF (but not vice versa).

When testing multiple vapourisers, always depressurise the circuit between each test.

Newer machines do not have a backbar non-return valve; they can be adequately leak tested by pressuring the system with the oxygen flush, and checking, in the absence of incoming fresh gas flow, that the bag stays tight for at least 15s per vapouriser.


My Level 2 check for non-electronic machines:

  • Check cylinder levels, line pressures, mains power
  • Do the 'quick squeeze the bag test' as above
  • Test for crossed supplies:
    - turn on the nitrous (or air) rotameter
    - check that the bag starts to fill
    - note a falling oxygen concentration at the Y-piece
    - turn off the nitrous or air and hit the oxygen flush until bag is nearly full
    - note increasing measured O2 at the Y-piece
  • Test for small leaks (requires an in-circuit pressure gauge; on new machines set APL to 30):
    - start FGF at 300 ml/min
    - occlude Y-piece; flush circuit until bag has some pressure in it i.e. say 10cmH2O
    - turn on vapouriser #1 and check its backbar attachment, contents & filler cap
    ..... wait for 30s
    .... during this time check ancillary equipment, suction, monitors, airway stuff etc...
    - confirm that the circuit pressure has increased to 30cmH2O or more
    - turn the vapouriser off!
  • repeat for vapouriser #2 if you're going to use it



Last updated Monday, February 25, 2013
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