The pattern of breathing during successful and unsuccessful trials of weaning from mechanical ventilation.

We prospectively examined the pattern of breathing in patients being weaned from mechanical ventilation: one group (n = 10) underwent a successful weaning trial and were extubated, whereas another group (n = 7) developed respiratory failure and required the reinstitution of mechanical ventilation. During the period of ventilator support, minute ventilation (), tidal volume (Vt), and respiratory frequency (f) were similar in the 2 groups. After discontinuation of the ventilator, remained similar in the 2 groups, but Vt was lower and f was higher in the patients who failed the trial compared with those who were successful, 194 ± 23 and 398 ± 56 ml (p < 0.001), respectively, and 32.3 ± 2.3 and 20.9 ± 2.8 breaths/min (p < 0.001), respectively. The failure group displayed a significant increase in PaCO2 (p < 0.005) during spontaneous breathing, without a concomitant increase in the alveolar-arterial PO2 difference. Eighty-one percent of the variance in PaCO2 was accounted for by the pattern of rapid, shallow b...