Non-invasive ventilation in acute exacerbations of chronic obstructive pulmonary disease: long term survival and predictors of in-hospital outcome

Background-Non-invasive ventilation (NIV) reduces the need for intubation and the mortality associated with an exacerbation of chronic obstructive pulmonary disease (COPD). This study aimed to identify factors that could be used to stratify patients according to their risk of requiring invasive mechanical ventilation. The second aim was to determine the long term survival of patients treated with and without NIV. Methods-In this prospective multicentre randomised controlled trial 118 patients were allocated to standard treatment and 118 to NIV between November 1996 and September 1998. Arterial blood gas tensions and respiratory rate were recorded at enrolment and after 1 and 4 hours. Prognostic factors were identified using logistic regression analysis. All patients were followed until death or 1 January 1999. Results-At enrolment the H+ concentration (OR 1.22 per nmol/l, 95% CI 1.09 to 1.37, p <0.01) and Paco(2) (OR 1.14 per kPa, 95% CI 1.14 to 1.81, p <0.01) were associated with treatment failure. Allocation to NIV was protective (OR 0.39, 95% CI 0.19 to 0.80). After 4 hours of treatment improvement in acidosis (OR 0.89 per nmol/l, 95% CI 0.82 to 0.97, p <0.01) and fall in respiratory rate (OR 0.92 per breaths/min, 95% CI 0.84 to 0.99, p=0.04) were associated with success. Median length of survival was 16.8 months in those treated with NIV and 13.4 months in those receiving standard treatment (p=0.12). The trend in improved survival was attributable to prevention of death during the index admission. Conclusion-Initial pH and hypercapnia. can be used to stratify groups of patients according to their risk of needing intubation. NIV reduces this risk and progress should be monitored using change in respiratory rate and pH. The long term survival after NIV is sufficiently good to render treatment appropriate.