ALTERNATIVE TO BREATHING

Abstract

If CO2 is removed by an extracorporeal membrane lung ventilated with room air, the natural lung can be used for O2 transport alone; this was demonstrated in lambs by maintaining lungs inflated with 100% O2 at constant pressure and removing all CO2 through the membrane lung. This process is a variant of apneic oxygenation without its advantages, because the arterial pH, PCO2 [CO2 partial pressure] and PO2 [O2 partial pressure] all remain normal. No N washout is needed. These studies were performed in 5 lambs anesthetized and paralyzed for 24 h. For CO2 removal, blood from the subclavian artery was pumped through an extracorporeal membrane lung and was returned into the external jugular vein. For O2 delivery, the lungs were inflated through a tracheostomy tube with 100% O2 to a pressure of 5 cm H2O. There was no significant change in arterial blood PO2 after perfusion had begun or at the end of the perfusion 24 h later. The arterial PCO2 remained steady, and there was no change in acid-base balance. The functional residual capacity (FRC) and static lung compliance remained unchanged. The total dead space was 10-15 ml. All animals recovered and survived in good health. At equilibrium, alveolar N partial pressure was always equal to the partial pressure of N in the ventilating gas of the membrane lung and was the sole determining factor in controlling alveolar O2 concentration. Direct measurement of pulmonary gas showed alveolar gas at the level of the carina.