Hemodynamic, mechanical and renal effects during 'apneic oxygenation' with extracorporeal carbon dioxide removal, at different levels of intrapulmonary pressure in lambs

It has been shown that apneic oxygenation can be safely performed for many days when metabolic carbon dioxide is removed by an extracorporeal membrane lung, and 100% oxygen is supplied directly into the trachea to keep the intrapulmonary pressure at 5 cm. H₂O. The study was designed to find 'best intrapulmonary pressure (IP)', analogous to 'best PEEP' during continuous positive pressure ventilation. In the present study we have shown that when IP was progressively raised from 5 cm H₂O to 20 cm H₂O the PaO₂ rose significantly due to progressive decrease in ̇Q(VA)/̇Q. A linear positive correlation was found between CO and ̇Q(VA)/̇Q. There was a negative correlation between ̇Q(VA)/̇Q and FRC. Total static lung compliance and FRC increased significantly at 15-20 cm H₂O IP. There was no significant change in urinary flow, urea and creatinine clearances. We conclude that in apneic oxygenation a more 'optimal IP' is attained at an IP pressure of 20 cm H₂O than at 5 cm H₂O.