Oxygen cost of breathing and diaphragmatic pressure-time index. Measurement in patients with COPD during weaning with pressure support ventilation

The oxygen cost of breathing and the time integral of the transdiaphragmatic pressure were measured at the onset of the weaning period in eight patients with chronic obstructive pulmonary disease requiring mechanical ventilation. Measurements were achieved during continuous positive airway pressure ventilation and during 15 cmH2O pressure support ventilation. For both periods, the O2COB was estimated as the difference between oxygen uptake of the period and that during controlled ventilation. During CPAP ventilation, the O2COB was 16.9 +/- 1.5 percent. During PSV, it was only 6.3 +/- 1.3 percent, and PTdi decreased by 73 percent compared to the CPAP period. Both effects illustrate the ability of PSV to facilitate spontaneous breathing during weaning from mechanical ventilation. However, we found these measurements to be of no help in predicting the duration of the weaning process.