Predictors of extubation outcome in patients who have successfully completed a spontaneous breathing trial.

Background: After patients recovering from respiratory failure have successfully completed a spontaneous breathing trial (SBT), clinicians must determine whether an artificial airway is still required. We hypothesized that cough strength and the magnitude of endotracheal secretions affect extubation outcomes.

Methods: We conducted a prospective study of 91 adult patients treated in medical-cardiac ICUs who were recovering from respiratory failure, had successfully completed an SBT, and were about to be extubated. A number of demographic and physiologic parameters were recorded with the patient receiving full ventilatory support and during the SBT, just prior to extubation. Cough strength on command was measured with a semiobjective scale of 0 to 5, and the magnitude of endotracheal secretions was measured as none, mild, moderate, or abundant by a single observer. In addition, patients were asked to cough onto a white card held 1 to 2 cm from the endotracheal tube; if secretions were propelled onto the card, it was termed a positive white card test (WCT) result. All patients were then extubated from T-piece or continuous positive airway pressure breathing trials. If 72 h elapsed and patients did not require reintubation, they were defined as successfully extubated.

Results: Ninety-one patients with a mean (+/- SE) age of 65.2 +/- 1.6 years, ICU admission APACHE (acute physiology and chronic health evaluation) II score of 17.7 +/- 0.7, and duration of mechanical ventilation of 5.0 +/- 0.5 days were studied over 100 extubations. Sixteen patients could not be extubated, and 2 patients underwent two unsuccessful extubation attempts, for a total of 18 unsuccessful extubations. Age, severity of illness, duration of mechanical ventilation, oxygenation, rapid shallow breathing index, and vital signs during SBTs did not differ between patients with successful extubations vs patients with unsuccessful extubations. The WCT result was highly correlated with cough strength. Patients with weak (grade 0 to 2) coughs were four times as likely to have unsuccessful extubations, compared to those with moderate-to-strong (grade 3 to 5) coughs (risk ratio [RR], 4.0; 95% confidence interval [CI],1.8 to 8.9). Patients with moderate-to-abundant secretions were more than eight times as times as likely to have unsuccessful extubations as those with no or mild secretions (RR, 8.7; 95% CI, 2.1 to 35.7). Patients with negative WCT results were three times as likely to have unsuccessful extubations as those with positive WCT results (RR, 3.0; 95% CI, 1.3 to 6.7). Poor cough strength and endotracheal secretions were synergistic in predicting extubation failure (Rothman synergy index, 3.7; RR, 31.9; 95% CI, 4.5 to 225.3). Patients with PaO(2)/fraction of inspired oxygen (P:F) ratios of 120 to 200 (receiving mechanical ventilation) were not less likely to be successfully extubated than those with P:F ratios of > 200, but those with hemoglobin levels < or = 10 g/dL were more than five times as likely to have unsuccessful extubations as those with hemoglobin levels > 10 g/dL.

Conclusions: After patients recovering from respiratory failure have successfully completed an SBT, factors affecting airway competence, such as cough strength and amount of endotracheal secretions, may be important predictors of extubation outcomes. Also, a majority (89%) of medically ill patients with P:F ratios of 120 to 200 (four of five patients with P:F ratios from 120 to 150), values sometimes used to preclude weaning, were extubated successfully.