01Etiology of O₂ Failure
Loss of pipeline O₂: - Exhaustion of central O₂ supply - Obstruction of central O₂ supply line - OR O₂ shutoff valve closed - Disconnection of hose - Failure of O₂ regulator in machine
Faulty O₂ supply: - Crossed pipelines during construction - Incorrect gas hose connection - Non-O₂ cylinder at the O₂ yoke - Wrong gas in the O₂ cylinder - Broken flowmeter
02Daily Pre-Anesthesia Machine Check
- Auxiliary O₂ cylinder + AMBU available and functioning
- Pipeline gas pressure ≥ 50 psi
- Spare O₂ cylinder mounted on machine > 50%
- FiO₂ analyzer calibrated (should read 21% sampling room air); low-O₂ alarm audible
- Vaporizers filled, capped
- Circuit leak test, ventilator, scavenging system
03Cylinder Reference
| Gas | E-Cylinder Capacity | Pressure (psi) | Color (USA) | Form |
|---|---|---|---|---|
| O₂ | 660 L | 1900 | Green | Gas |
| Air | 625 L | 1900 | Yellow | Gas |
| N₂O | 1590 L | 745 | Blue | Liquid + gas |
| N₂ | 650 L | 1900 | Black | Gas |
N₂O is stored as a liquid — pressure stays at 745 until ~1/4 full; weigh the tank to assess.
Tank time: Time (min) = PSI ÷ 3 ÷ flow (L/min). E.g., O₂ at 430 psi running 5 L/min → 430 ÷ 3 ÷ 5 = 29 min.
04Safety Systems
Supply side: - Color-coded gas tanks (green = O₂ in US) - DISS (Diameter Index Safety System): non-interchangeable threaded connectors at the wall outlet - PISS (Pin Index Safety System): unique pin pattern on cylinder yoke - Quick connects for portable hoses
Anesthesia machine: - Flowmeter arrangement with O₂ closest to FGF outlet (Datex-Ohmeda, Draeger) → leak in O₂ flowmeter is hypoxic risk; leak in air/N₂O flowmeter is NOT (the mixture won't be hypoxic) - O₂:N₂O proportioning ("hypoxic guard") — prevents FiO₂ < 25% with N₂O via mechanical, pneumatic, or electronic linkage - Oxygen Supply Failure Protection Device ("fail-safe valve"): if O₂ pressure falls < 30 psi, N₂O cannot flow AND alarm sounds
Caveats: Proportioning can still deliver hypoxic mixtures with incorrect supply gas connections, defective components, downstream leaks, or addition of helium.
05Detection
- Pressure gauges fall (pipeline, tank)
- Low O₂ alarms (supply failure, FiO₂ analyzer)
- Flowmeters fall (O₂ and other gases)
- O₂ flush inoperative
- Bellows fail
- Apnea alarms (spirometer, capnograph)
- Increasing O₂ flow makes the problem worse (drains the supply)
- Hypoxemia, hypercarbia, arrhythmias, bradycardia, arrest
06Management
- Notify the surgeon, call for help, use the emergency manual.
- Verify the problem.
- Disconnect from the machine and ventilate with an AMBU bag and either room air or a backup tank.
- - Do NOT use the machine auxiliary O₂ — same source!
- Switch to TIVA if anesthesia must be maintained.
- Open the E-cylinder O₂ on the machine if pipeline is the problem (and pipeline is disconnected from supply).
- Calculate remaining tank time to plan.
- Get patient to an OR with working O₂ as soon as feasible.
Commonly missed steps: - Identifying empty O₂ E-cylinder before case start - Identifying easily accessible AMBU and backup cylinder