What is the pressure (PSI) delivered to the patient when the oxygen flush button is pressed on an anesthesia machine?

Oxygen Flush Button Pressure on Anesthesia Machines

The oxygen flush button on an anesthesia machine delivers oxygen at 400-500 kPa (58-72.5 PSI) to the patient. 1

Understanding the Oxygen Flush System

The oxygen flush system is a safety feature on anesthesia machines that provides a high-flow, high-pressure supply of 100% oxygen directly to the patient breathing circuit, bypassing the vaporizers and flowmeters. According to the Association of Anaesthetists of Great Britain and Ireland guidelines, this system should be regularly checked as part of the pre-use machine check.

Key Characteristics:

• Pressure: 400-500 kPa (58-72.5 PSI) 1
• Flow rate: Typically 35-75 L/min depending on the machine model
• Delivery: Direct to the common gas outlet, bypassing vaporizers
• Activation: Spring-loaded button that ceases operation when released 1

Clinical Implications and Safety Considerations

The high pressure delivered by the oxygen flush button has important clinical implications:

• Barotrauma risk: The high pressure can potentially cause barotrauma, especially in patients with compromised lung compliance or when used with certain airway devices
• Vaporizer dilution: Using the oxygen flush during anesthesia maintenance will dilute anesthetic gases and may cause awareness
• Proper testing: Guidelines recommend testing the oxygen flush system before each use by ensuring "flow occurs from the gas outlet without significant decrease in the pipeline supply pressure" 1

Important Limitations for Emergency Ventilation

Despite delivering high pressure, the oxygen flush system has limitations for emergency ventilation:

• Not suitable for transtracheal jet ventilation: Research shows that the oxygen flush systems of most modern anesthesia machines do not provide sufficient pressure for effective transtracheal jet ventilation 1, 2
• Variable performance: Different anesthesia machine models provide different working pressures through their oxygen flush valves:
  • Draeger machines: 96-117 kPa (14-17 PSI) - may be adequate for some jet ventilation 2
  • Datex-Ohmeda machines: 50-62 kPa (7-9 PSI) - insufficient for jet ventilation 2

Proper Use in Clinical Practice

When using the oxygen flush button:

• Brief activation: Use briefly to prevent barotrauma
• Monitoring: Always monitor airway pressure when using the flush button
• Avoid during inspiration: Do not use during mechanical ventilation's inspiratory phase
• Pre-use check: Verify proper function before each case as part of the anesthesia machine check 1

Conclusion

The oxygen flush button delivers 400-500 kPa (58-72.5 PSI) of pressure to the patient breathing circuit. While this high-pressure oxygen source is valuable for rapidly filling the breathing circuit or clearing anesthetic gases, it must be used with caution to prevent barotrauma, especially in patients with compromised lung compliance.