Is weaning failure caused by low-frequency fatigue of the diaphragm?
Because patients who fail a trial of weaning from mechanical ventilation experience a marked increase in respiratory load, we hypothesized that these patients develop diaphragmatic fatigue. Accordingly, we measured twitch transdiaphragmatic pressure using phrenic nerve stimulation in 11 weaning failure and 8 weaning success patients. Measurements were made before and 30 minutes after spontaneous breathing trials that lasted up to 60 minutes. Twitch transdiaphragmatic pressure was 8.9 +/- 2.2 cm H2O before the trials and 9.4 +/- 2.4 cm H2O after their completion in the weaning failure patients (p = 0.17); the corresponding values in the weaning success patients were 10.3 +/- 1.5 and 11.2 +/- 1.8 cm H2O (p = 0.18). Despite greater load (p = 0.04) and diaphragmatic effort (p = 0.01), the weaning failure patients did not develop low-frequency fatigue probably because of greater recruitment of rib cage and expiratory muscles (p = 0.004) and because clinical signs of distress mandating the r
