What is apnea ventilation?

Apnea Ventilation: Definition and Clinical Context

Apnea ventilation refers to the provision of mechanical respiratory support during periods when a patient has ceased spontaneous breathing efforts, either as a diagnostic test (apnea testing) or as a therapeutic intervention to maintain oxygenation while allowing CO2 accumulation or preventing respiratory muscle fatigue.

Primary Clinical Applications

Apnea Testing for Brain Death Determination

In the context of brain death evaluation, apnea testing involves discontinuing mechanical ventilation while providing passive oxygenation to determine if spontaneous respiratory drive exists when PaCO2 rises to sufficient levels. 1

The technique requires:

• Preoxygenation with 100% oxygen for 5-10 minutes before disconnecting mechanical ventilation 1
• Maintenance of core temperature >35°C and age-appropriate blood pressure 1
• Allowing PaCO2 to rise to ≥60 mm Hg AND ≥20 mm Hg above baseline while observing for any spontaneous respiratory effort 1

During this procedure, oxygen delivery continues through:

• T-piece attached to the endotracheal tube 1
• Self-inflating bag valve system (Mapleson circuit) 1
• Tracheal insufflation of oxygen via catheter inserted through the ETT (though caution is needed as high flow rates may wash out CO2 and prevent adequate rise) 1

Critical pitfall: CPAP ventilation during apnea testing can falsely trigger automatic mandatory ventilation on many modern ventilators, creating the appearance of spontaneous breathing when none exists. 1

Therapeutic Mechanical Ventilation During Apnea

In emergency and critical care settings, apnea ventilation describes complete mechanical support when patients cannot initiate breaths:

Pressure Control Ventilation (PCV) delivers mandatory breaths at preset intervals with set inspiratory pressure, regardless of patient effort, providing complete ventilatory support for apneic or heavily sedated patients. 2

This differs fundamentally from pressure support ventilation (PSV), which requires patient-initiated breaths and will provide no ventilation if the patient becomes apneic—though many manufacturers now incorporate backup rates of 6-8 breaths per minute to prevent this dangerous scenario. 1

Emergency Airway Management in Apneic Patients

Patients presenting with apnea or gasping breathing patterns (respiratory rate <6/min) require immediate endotracheal intubation and mechanical ventilation. 3

For apneic patients without preoxygenation, bag-valve-mask ventilation with 100% oxygen using small tidal volumes (via pediatric self-inflating bag, maximum 700 mL) proved most successful in achieving adequate oxygenation compared to supraglottic airways. 4

Pharmacologic Considerations

Doxapram may be used to stimulate respiration in patients with drug-induced postanesthesia respiratory depression or apnea, but should not be used in conjunction with mechanical ventilation. 5

Ventilator-Induced Apnea: A Critical Complication

High tidal volume normocapnic mechanical ventilation during NREM sleep can completely inhibit inspiratory motor output, causing apnea lasting over 20 seconds immediately after cessation of passive ventilation. 6

This neuromechanical inhibition represents a significant risk when:

• High levels of pressure support ventilation are used, particularly in heart failure patients, causing central apneas and major sleep fragmentation 2
• Fixed pressure support is applied without backup rate protection 7, 8

To prevent ventilator-induced central apneas, volume-assured pressure support (VAPS) with spontaneous-timed (ST) mode should be used, incorporating a backup rate that equals or slightly exceeds the patient's spontaneous sleeping respiratory rate (minimum 10 breaths/minute). 7

Monitoring Requirements

During any form of apnea ventilation:

• Capnography is absolutely mandatory to confirm correct endotracheal tube placement and monitor for tube dislocation 3
• Continuous monitoring of heart rate, blood pressure, and oxygen saturation is essential 1
• If oxygen saturation falls below 85% during apnea testing, the test should be terminated and mechanical ventilation resumed 1