Breathing pattern during acute respiratory failure and recovery.

The objective of this study was to compare the breathing pattern of patients who failed to wean from mechanical ventilation to the pattern during acute respiratory failure. We hypothesized that a similar breathing pattern occurs under both conditions. Breathing pattern, mouth occlusion pressure (P[0.1]) and maximum inspiratory pressure (P[I,max]) were measured in 15 patients during acute respiratory failure, within 24 h of the institution of mechanical ventilation, and in 49 patients during recovery, when they were ready for discontinuation from mechanical ventilation. The following indices were calculated: rapid shallow breathing index (respiratory frequency/tidal volume (fR/VT)); rapid shallow breathing-occlusion pressure index (ROP = P[0.1 x fR/VT]); P(0.1)/P(I,max); and effective inspiratory impedance (P[0.1]/VT/(inspiratory time (tI)). Patients who failed to wean (n=11) had a similar ROP,fR/VT and P(0.1)/P(I,max) to those with acute respiratory failure despite a significantly reduced P(0.1)/VT/tI, the value of which was comparable to that of patients who weaned successfully (n=38). The P(I,max) of patients who failed to wean was similar to that of patients who weaned successfully. We conclude that patients who failed to wean had a breathing pattern similar to that during acute respiratory failure, despite a reduced mechanical load on the respiratory muscles and a relatively adequate inspiratory muscle strength. This suggests that strategies that enhance respiratory muscle endurance may facilitate weaning.