[A study of cough peak expiratory flow in predicting extubation outcome]

To study the value of cough peak expiratory flow (CPEF) in predicting extubation outcome of patients.

A prospective study of 200 adult patients was conducted and treated in the Third Central Hospital intensive care unit (ICU), receiving mechanical ventilation (MV) via an endotracheal tube during November 2006 through December 2007. All the patients received MV longer than 24 hours. They were conscious and cooperative at the time of extubation. Extubation was successful after 30 minutes of spontaneous breathing trial (SBT). They were asked to cough for three times, during which CPEF was measured with an in-line spirometer, and the average value was recorded. They were classified as strong, moderate, and weak according to the ability to cough. If the patients did not require reintubation within 72 hours, extubation was noted as successful.

In 200 patients, in 172 patients extubation was successful and failed in 28 patients. Sex, age, severity of illness and vital signs during SBT showed no difference between patients with successful extubation and patients with unsuccessful extubation. CPEF was the independent predictor for the extubation outcome [odds ratio (OR) < 1]. The cut-point was 58.5 L/min. CPEF< or =58.5 L/min had a specificity of 68.0% and sensitivity of 71.4% in predicting extubation failure. The positive predicted value was 0.16, and the negative predicted value was 0.94. The cough strength in patients with successful extubation was almost always "strong", and in very few it was "medium". In those extubation failed, there were only 3 patients showed strong cough strength, and for the rest it was "moderate" or "weak".

After patients have recovered from respiratory failure and SBT is successful, factors affecting airway competence, such as cough strength, may be important predictors of extubation outcome. The study confirms that CPEF is a strong and independent predictor of extubation outcome when the patient is mentally clear and has a successful SBT. When the CPEF>58.5 L/min, the successful rate is high. On the contrary, when the CPEF< or =58.5 L/min, the unsuccessful rate is high. Failure is often due to poor cough. The extubation outcome is highly correlated with cough strength. The prognosis in patients with failure is poor.