Pre-Use Check
On this page
Direct answer
Two bags, one oxygen analyser and a printed sequence stand between a normal list and a hypoxic disaster. A pre-use check walks the machine from gas supply to patient end: verify back-up equipment first, then pipeline and cylinder pressures, then flowmeters and vapourisers, then prove the low-pressure system holds pressure with a leak test — repeated with each vapouriser open — then confirm the breathing system, the ventilator, the alarms and finally the two-bag test. Automated self-tests never cover the breathing system beyond the machine, nor the identity of the gas flowing; the oxygen analyser, calibrated to 21% on room air, is the only check that detects a hypoxic mixture from a crossed pipeline or misfilled supply.
What you must remember
- Check order follows the gas: emergency back-up (self-inflating bag, oxygen cylinder, laryngoscope, suction, airway drawer), then the high-pressure system (cylinders at least half full, pipeline gauges near 400 kPa), then the low-pressure leak test, breathing system, ventilator, monitors and alarms, and a final scan.
- Calibrate the oxygen analyser to 21% on room air, then place it in the breathing system — the only check that detects crossed pipelines or wrong gas content.
- Low-pressure leak test: occlude the patient end, close the APL valve, inflate the system with the oxygen flush and confirm the pressure holds; some machines require the suction-bulb negative-pressure test instead — know which your machine needs.
- Repeat the leak test with each vapouriser turned on: leaks hide at vapouriser seals and caps and appear only in the open position.
- The two-bag test: attach a second reservoir bag at the mask end; squeeze the machine's bag and watch the test bag fill and empty — manual and then ventilator-powered — catching leaks between machine and breathing system that automated checks miss.
- Confirm flowmeter bobbins move freely across the full range, vapourisers are filled, seated and dialled off, sodalime colour and fill are adequate, and circle valves move freely.
- Check the emergency oxygen flush works, but never discharge it against a closed system (barotrauma risk).
- Suction, positioned at the anaesthetist's right hand and reaching the floor, is the first item needed in any airway emergency — test it audibly.
- Repeat an abbreviated check (levels, leaks, analyser, breathing system) between cases and after any change: vapouriser swap, machine move or maintenance.
At 2 am, before an emergency laparotomy
Build the routine as a narrative so stress cannot dismantle it. Back-up first, checked personally: an Ambu bag with oxygen, a working laryngoscope with a spare blade, two suction sets (Yankauer and soft), the difficult-airway drawer. Then the machine: pipeline gauges at 400 kPa, the machine's oxygen cylinder opened — 110 bar, adequate — and closed again. The oxygen analyser is calibrated to 21% in room air and seated in the circle. Flowmeters sweep smoothly; the sevoflurane vapouriser is filled and locked off. The circle valves flutter, the sodalime is fresh, and the leak test holds 30 cm H2O — repeated with the vapouriser open, where a leak at the filling cap makes itself visible.
The ventilator cycles its bellows, alarms are set (low oxygen, low pressure, apnoea, high pressure), scavenging is connected, and the two-bag test shows gas moving both ways. A final scan: all dials zero, APL open, switches off, machine level — ninety seconds of habits, each of which has caught a documented anaesthetic disaster.
Where the routine fails
Automated checks seduce their users: a machine that passed its self-test can still be fitted to a cracked breathing system, and the self-test does not know which gas is in the pipeline. The second is the vapouriser-blind leak test — testing only in the off position misses the cracked cap that leaks only when the dial is open. The third is tick-box fatigue: the checklist performed silently while talking, then signed. The discipline that survives night duty is the readback — speaking each step aloud as it is completed, which is why aviation adopted it and why FDA-style anaesthesia checklists are written to be said, not skimmed.
Frequently asked questions
Which single check detects a crossed gas pipeline?
The oxygen analyser, calibrated to 21% in room air before use — no other check measures the identity of the delivered gas.
What is the two-bag test?
A second bag attached at the mask end: ventilating the machine's bag should fill and empty the test bag, proving patency both ways and exposing leaks the machine self-test cannot reach.
Why must the leak test be repeated with each vapouriser on?
Leaks at vapouriser seals, fillers and caps appear only in the open position, when gas can escape through them.
How often should the machine be checked?
A full check before the first case of the day and after any maintenance or vapouriser change, with an abbreviated check (levels, leak, analyser, breathing system) between cases.
To what value is the oxygen analyser calibrated?
Twenty-one per cent on room air, before it is placed in the breathing system.
What is checked before the machine itself?
The back-up: a self-inflating bag with oxygen, a working laryngoscope, suction and airway equipment — the plan for total machine failure.