Adjustable Pressure Limiting Valve (APL)
Bailey Freeman, DNP, CRNA and Angela Mordecai
Quick Facts
- The Adjustable Pressure-Limiting (APL) valve controls the pressure in the breathing circuit during manual ventilation.
- It is used to vent excess gas and prevent barotrauma when the anesthesia machine is in manual/spontaneous mode.
- Turning the APL valve clockwise increases pressure; turning it counterclockwise decreases it.
- The APL valve is bypassed when the ventilator is in use (mechanical ventilation mode).
Procedure
Function and Use
- Located near the reservoir bag on the anesthesia machine breathing circuit.
- During manual ventilation, the provider controls airway pressure by adjusting the APL valve.
- Fully open: gases vent freely from the circuit, minimal pressure builds up.
- Partially closed: builds pressure to assist with positive-pressure ventilation.
- Fully closed: maximum pressure is allowed to build; dangerous if held too long without observing chest rise or manometer.
Steps for Use
- Set the anesthesia machine to manual/spontaneous mode.
- Connect circuit to patient and begin ventilating via reservoir bag.
- Adjust the APL valve based on desired airway pressure. Monitor the pressure gauge and chest rise carefully—keep inspiratory pressure below 18–20 cm H₂O to avoid opening the lower esophageal sphincter and causing gastric insufflation.
- Use the valve cautiously: avoid excessive closure (>18–20 cm H₂O) that could cause barotrauma or gastric insufflation.
Confirmation Steps
- Observe patient’s chest rise with each manual breath.
- Verify adequate ETCO₂ waveform and oxygenation.
- Check anesthesia machine pressure gauge for appropriate peak inspiratory pressures.
- Listen for gas escaping from the scavenging system when valve is opened.
Documentation Requirements
- Ventilation mode used during induction or emergence (manual vs. mechanical).
- Any issues with circuit pressure or need for APL valve adjustments.
- Peak airway pressures if recorded during manual ventilation.
Scope Guide
Strategies
- Understand that the APL valve is active only during manual/spontaneous mode. When in ventilator mode, keep the APL valve open so that if you need to switch to manual ventilation urgently, you avoid sudden pressure buildup that could cause coughing, patient “bucking,” barotrauma, or decreased venous return.
- Always start with the valve partially open to avoid accidental over-pressurization.
- Train learners to pair APL valve use with tactile feel of reservoir bag compliance.
Clinical Optimization
- Monitor the pressure manometer during manual ventilation to stay within safe limits (typically <20 cmH₂O).
- Adjust the valve slowly and deliberately while observing patient response.
- Use positive pressure only as needed to assist spontaneous effort or overcome resistance.
Pearls
- The APL valve has no effect when in ventilator mode—do not rely on it for pressure control then.
- Inadequate chest rise during manual ventilation may indicate the valve is too open or there’s a leak.
- High airway pressures with little chest movement may mean the valve is too closed or the airway is obstructed.
References
- StatPearls. Anesthesia Machine. National Center for Biotechnology Information. https://www.ncbi.nlm.nih.gov/books/NBK572060/
- How Equipment Works. Circle Breathing Systems. https://www.howequipmentworks.com/circle_breathing_system/
- Royal College of Anaesthetists. Basic Anaesthetic Machine. https://www.rcoa.ac.uk/documents/basic-anaesthetic-machine
