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

Background: After patients recovering from respiratory failure have success fully completed a spontaneous breathing trial (SBT), clinicians must determ ine whether an artificial airway is still required. We hypothesized that co ugh strength and the magnitude of endotracheal secretions affect extubation outcomes. Methods: We conducted a prospective study of 91 adult patients treated in m edical-cardiac ICUs who were recovering from respiratory failure, had succe ssfully completed an SBT, and were about to be extubated. A number of demog raphic and physiologic parameters were recorded with the patient receiving full ventilatory support and during the SBT, just prior to extubation. Coug h strength on command was measured with a semiobjective scale of 0 to 5, an d the magnitude of endotracheal secretions was measured as none, mild, mode rate, 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 secr etions were propelled onto the card, it was termed a positive white card te st (WCT) result. All patients were then extubated from T-piece or continuou s positive airway pressure breathing trials. If 72 h elapsed and patients d id 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 ext ubated, 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 ext ubations vs patients with unsuccessful extubations. The WCT result was high ly correlated with cough strength. Patients with weak (grade 0 to 2) coughs were four times as likely to have unsuccessful extubations, compared to th ose 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 unsuccessf ul 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 tunes as likely to ha ve 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 syn ergistic 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 oxyg en (P:F) ratios of 120 to 200 (receiving mechanical ventilation) were not l ess likely to be successfully extubated than those with P:F ratios of > 200 , but those with hemoglobin levels less than or equal to 10 g/dL were snore than hive times as likely to have unsuccessful extubations as those with h emoglobin levels > 10 g/dL. Conclusions: After patients recovering from respiratory failure have succes sfully completed an SBT, factors affecting airway competence, such as cough strength and amount of endotracheal secretions, may be important predictor s 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 1 20 to 150), values sometimes used to preclude weaning, were extubated succe ssfully.