Apneic Oxygenation Techniques

Apneic oxygenation (ApOx) can be defined as passive flow of oxygen into the patient’s alveoli in the absence of spontaneous respiration or mechanical ventilation. During apnea, alveolar oxygen gets absorbed into the blood but carbon dioxide gets buffered. Hence, oxygen and carbon dioxide differ in the flow rates associated with their absorption and excretion between the alveoli and bloodstream (O2: 250 mL/min and CO2: 8–20 mL/min). This creates a differential pressure gradient facilitating oxygen insufflation into patient’s airways provided patency is maintained. Therefore, apneic oxygenation is also called mass flow ventilation. However, apnoeic oxygenation does not occur if oxygen insufflation is started after alveolar hypoxia set in; hence early intervention is the key to successful mass flow ventilation. Using this technique, sustainable oxygen levels can be maintained in critically ill patients in presence of adequate circulation and optimum gas flows.