WORK OF BREATHING AFTER EXTUBATION

Recently we showed that work of breathing was higher in the immediate period after extubation as compared with spontaneous breathing through an endotracheal tube. In this study, we evaluated the glottis and tra chea as potential sites of increased airway resistance after extubatio n. We measured breathing pattern, work of breathing, and pressure time product in eight patients during weaning from mechanical ventilation. We acquired data during pressure support ventilation and spontaneous breathing via the ventilator, with the endotracheal tube in place, and after extubation. During bronchoscopy at the time of extubation, we e xamined the trachea and measured the cross-sectional area of the glott is. Work of breathing and pressure time product were significantly low er during pressure support ventilation as compared with spontaneous br eathing after extubation (0.43 +/- 0.10 vs 1.49 +/- 0.10 J/L and 101 /- 22 vs 299 +/- 30 cm H2O.s/min, respectively; p<0.05). However, both indexes were significantly higher after extubation as compared with b reathing through the endotracheal tube (1.49 +/- 0.10 vs 0.95 +/- 0.12 J/L, 299 +/- 31 vs 196 +/- 26 cm H2O.s/min respectively; p<0.05). Dur ing bronchoscopy, no tracheal or glottic narrowing was detected. The g lottic cross-sectional area was successfully measured in four patients at the onset of inspiration and found to be 140 +/- 15 mm(2). This va lue was larger than the mean cross-sectional area of the endotracheal tubes used in these patients (50 mm(2)). We conclude that neither trac heal nor laryngeal disease caused the increase in work of breathing af ter extubation. Our data suggest that upper airway narrowing at a more proximal site, such as the oropharynx or velopharynx may be the cause of the increase in respiratory work.