CAN APNEIC OXYGENATION EXTEND THE DURATION OF SAFE APNEA?

Scott D. Weingart, MD, Richard M. Levitan, MD

Alveoli will continue to take up oxygen even without diaphragmatic movements or lung expansion. In an apneic patient, approximately 250 mL/minute of oxygen will move from the alveoli into the bloodstream. Conversely, only 8 to 20 mL/minute of carbon dioxide moves into the alveoli during apnea, with the remainder being buffered in the bloodstream.53 The difference in oxygen and carbon dioxide movement across the alveolar membrane is due to the significant differences in gas solubility in the blood, as well as the affinity of hemoglobin for oxygen. This causes the net pressure in the alveoli to become slightly subatmospheric, generating a mass flow of gas from pharynx to alveoli. This phenomenon, called apneic oxygenation, permits maintenance of oxygenation without spontaneous or administered ventilations. Under optimal circumstances, a PaO2 can be maintained at greater than 100 mm Hg for up to 100 minutes without a single breath, although the lack of ventilation will eventually cause marked hypercapnia and significant acidosis.

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