PRESSURE-TIME PRODUCT DURING CONTINUOUS POSITIVE AIRWAY PRESSURE, PRESSURE SUPPORT VENTILATION, AND T-PIECE DURING WEANING FROM MECHANICAL VENTILATION

The objective of this study was to compare the effects of continuous positive airway pressure (CPAP), pressure support ventilation (PS), and T-piece on the pressure-time product (PTP) during weaning from mechanical ventilation. The PTP is an estimate of the metabolic work or oxygen consumption of the respiratory muscles. We studied 10 intubated patients recovering from acute respiratory failure of various etiologies. A modified continous flow (flow-by) CPAP of 0 and 5 cm H2O (CPAP-0 and CPAP-5, respectively), PS of 5 cm H2O (PS-5), and T-piece were applied in random order for 30 min each. In the last 5 min of the 30-min periods, we measured the esophageal pressure and transdiaphragmatic pressure-time products-PTP(es) and PTP(di), cm H2O.s/min, respectively-multiplied by respiratory frequency. Breathing pattern, total lung resistance (RL), quasi-static lung compliance (CL), intrinsic positive end-expiratory pressure (PEEPi), end-expiratory transpulmonary pressure (Ptpexp), arterial blood gases, blood pressure, and heart rate were also measured. In comparison to T-piece, CPAP-5 decreased PTP(es) 40% (p < 0.01) and PTP(di) 43% (p < 0.02), whereas PS-5 decreased PTP(es) 34% (p < 0.01) and PTP(di) 38% 38% (p < 0.05). The decrease in PTP(es) with CPAP-5 was associated with a significant reduction in RL, and to a less extent in PEEPi relative to airway pressure. The contribution of the decrease in PEEPi to the reduction in PTP(es) amounted to 36%. With PS-5, respiratory system mechanics and PEEPi were not significantly different compared with T-piece. With CPAP-0, PTP tended to be lower than with T-piece. This was likely due to the inherent small end-inspiratory positive pressure related to the CPAP system. Breathing pattern, arterial blood gas measurements, and hemodynamics were similar in all the ventilatory modes. In conclusion, during weaning from mechanical ventilation of patients recovering from acute respiratory failure, low levels of CPAP and PS significantly decrease the pressure-time product by 40 and 34%, respectively, compared with T-piece.