Complete Extracorporeal Removal of Metabolic Carbon Dioxide by Alkali Administration and Dialysis in Apnea

Abstract

The high mortality rate of patients afflicted with adult respiratory distress syndrome (ARDS) may be due, in part, to the hemodynamic changes and the barotrauma accompanying mechanical ventilation, especially when high positive pressure and oxygen tension are used. Recent experimental evidence suggests that prognosis may be improved by suspending ventilation: in the apneic condition, oxygenation can be maintained by trans-alveolar oxygen diffusion, while extracorporeal carbon dioxide removal (ECCO₂R), achieved with membrane lungs, assures CO₂ homeostasis. This technology, however, requires high blood flow rates, and is available only to very few specially equipped centers. We report results of experiments in dogs using an alternative approach to ECCO₂R during apnea. Dissolved CO₂ was converted to bicarbonate by the systemic infusion of NaOH at the rate of 0.15 mM/kg/min; the generated bicarbonate was then removed by hemodialysis against a bicarbonate-free dialysate, at a blood flow rate of 200 ml/min. Sodium and fluid balance were maintained by ultrafiltration. Observations in five dogs confirm that systemic pCO₂, TCO₂, and pH can be maintained well within physiologic ranges, and that prolonged apnea followed by full recovery can be achieved with this methodology. Mecause of the wide availability of dialysis equipment and expertise, and of lowerr extracorporeal blood flow requirements, ECCO₂R by alkali administration and hemodialysis offers a potentially attractive alternative approach to the use of membrane lungs in the apneic therapy of ARDS.