Metabolic and respiratory changes during weaning from mechanical ventilation.

Weaning from mechanical ventilation is a procedure performed daily in intensive care units. This study sought to determine whether among postoperative patients there were any differences in the changes in oxygen consumption (VO2) and carbon dioxide production (VCO2) between those patients in whom mechanical ventilation was successfully discontinued and those in whom it was continued or reinstituted. A stepwise reduction in mandatory breaths (from 10 to 12 to 4 to 6), followed by a period of continuous positive airway pressure (CPAP), was the weaning method. In the group of patients (N = 18) who were successfully weaned, VO2 and VCO2 increased 10 +/- 8 (SD) percent and 10 +/- 9 percent, respectively, while VE decreased 9 +/- 8 percent and PaCO2 was unchanged when values at an IMV of 10 to 12 were compared with those on CPAP. In the group (N = 17) who were not successfully weaned, VO2 and VCO2 increased 8 +/- 10 percent and 6 +/- 9 percent, respectively, while PaCO2 rose (37.9 +/- 4 to 42.5 +/- 2.9) significantly (p less than 0.02). There was a significantly greater decrease (15 +/- 3 percent) in VE than in the other group. Changes in VO2 or VCO2 did not aid in predicting which patients would be successfully weaned.