And how many litres of o2 is flushed when we press o2 flush button in anaesthesia workstation
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oxygen flush valve anaesthesia machine flow rate litres per minute
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Here is the complete answer with textbook-backed details:
O2 Flush Valve - Flow Rate
When you press the oxygen flush button on an anaesthesia workstation, it delivers 35-75 litres per minute (L/min) of 100% oxygen directly into the breathing circuit.
- Miller's Anesthesia, 10e - "Flow from the oxygen flush valve enters the low-pressure circuit downstream from the vaporizers at a rate between 35 and 75 L/min, depending on the machine and operating pressure."
- Barash's Clinical Anesthesia, 9e and multiple other sources confirm the same range.
Practical implication of this flow rate
At a typical flow of ~60 L/min, approximately 1 litre of O2 enters the breathing circuit for every 1 second the button is held down (University of Florida Virtual Anesthesia Machine data).
Key features of the O2 flush valve
| Feature | Detail |
|---|---|
| Flow rate | 35-75 L/min (100% O2) |
| Pressure source | Intermediate-pressure circuit (40-50 psi pipeline pressure), bypasses flowmeters and vaporizer |
| Entry point | Downstream of vaporizers, into the low-pressure/breathing circuit |
| Works when | Machine is OFF - it is active as long as O2 supply is connected |
| Color coding | Green, labeled "O2", recessed to prevent accidental activation |
| Self-closing | Stops flow the moment you release the button |
Hazards to remember
- Barotrauma - If pressed during the inspiratory phase of mechanical ventilation (especially on machines without fresh gas decoupling), the high flow can cause dangerously elevated airway pressures.
- Awareness under anaesthesia - Prolonged or inadvertent flushing dilutes the volatile agent concentration downstream of the vaporizer, potentially reducing anaesthetic depth.
- Valve sticking - A stuck-open valve continuously dilutes the inhaled agent; a stuck-partially-open valve is a subtle but dangerous cause of awareness.
The 35-75 L/min range is the standard cited in all major anaesthesia textbooks (Miller's, Barash's, Morgan & Mikhail's) and is also the requirement per ASTM/ISO anaesthesia machine standards.
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