# Pre-Use Check > Anaesthesia machine pre-use check for Anaesthesia Technology: FDA-style checklist steps, leak tests, oxygen analyser calibration, two-bag test and back-up kit. - Canonical URL: https://prepelephant.com/topics/allied/anaesthesia-technology/pre-use-check-at - Exam / course: Allied Health · Subject: Anaesthesia Technology - Publisher: PrepElephant (https://prepelephant.com) — Prepared and reviewed by the PrepElephant Academic Review Team - First published: 2026-10-02 - Last updated: 2026-10-02 - How to cite: "Pre-Use Check", PrepElephant, https://prepelephant.com/topics/allied/anaesthesia-technology/pre-use-check-at ## 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.