Impact of endotracheal tube size on preextubation respiratory variables

Many parameters have been evaluated to predict successful extubation. These are all affected by extrapulmonary variables. The purpose of this study was to evaluate the effect of endotracheal tube (ETT) size on preextubation predictors of successful extubation.

Twenty-two intubated and mechanically ventilated subjects were recruited when ready for extubation. Subjects were ventilated with T-piece, continuous positive airway pressure (CPAP) of 5 cm H(2)O, and pressure support ventilation (PSV) of 5 cm H(2)O in randomized order for 15 minutes each. Pulmonary mechanics-including respiratory frequency (f), tidal volume (V(T)), f/V(T) ratio, negative change in esophageal pressure, pressure time product (PTP), work of breathing, and the airway occlusion pressure 100 milliseconds after the onset of inspiratory flow-were measured using a microprocessor-based monitor at the end of each interval. After extubation, measurement of pulmonary mechanics was repeated at 15 and 60 minutes.

In patients with 7.0- or 7.5-mm ETT compared with patients with 8.0-mm ETT, (1) f was significantly higher during all ventilatory modes and 15 minutes after extubation; (2) V(T) during PSV and CPAP was significantly lower; (3) mean f/V(T) was significantly higher (122 ± 57 vs 69 ± 35, P = .026); and (4) PTP was significantly higher during CPAP, PSV, and 15 minutes after extubation. There was a nonsignificant trend toward increased negative change in esophageal pressure, work of breathing, and airway occlusion pressure 100 milliseconds after the onset of inspiratory flow in the smaller-ETT group.

The ETT size has a significant impact on f, V(T), f/V(T) ratio, and PTP.