Predicting the result of noninvasive ventilation in severe acute exacerbations of patients with chronic airflow limitation

Objective: To analyze prospectively the factors related to the success of noninvasive ventilation (NIV) in the treatment of acute exacerbations of chronic airflow limitation (CAFL) and to generate a multiple regression model in order to detect which patients can be successfully treated by this method. Setting: A respiratory medicine ward of a referral hospital. Methods and principal results: Initially, we examined 44 episodes of acute respiratory failure in 36 patients with CAFL in whom mechanical ventilation was advisable. In 34 of 44 episodes (77%), NIV was used successfully. Patients in whom NIV succeeded had a lower FEV1 prior to admission, a higher level of consciousness (LC), and significant improvements in PaCO2, pH, and LC after 1 h of NIV. A logistic regression model consisting of baseline FEV1 and PaCO2 values, initial PaCO2, pH, and LC values on admission, and Paco2 values after 1 h of NIV allowed us to correctly classify > 95% of the 44 episodes in which the outcome was successful. In the second part of the study, we prospectively validated the equation in another 15 consecutive CAFL patients with acute hypercapnic respiratory failure. NIV successfully treated 12 patients (80%), and the model correctly classified 14 patients (93%). Conclusion: Good LC at the beginning of NIV and improvements in pH, PaCO2, and LC values after 1 h of NIV are associated with successful responses to NIV in COPD patients with acute hypercapnic respiratory failure. Our validated multiple regression model confirms that these variables predict the result of NIV in acute hypercapnic failure in CAFL patients.