Predicting survival following non-invasive ventilation for hypercapnic exacerbations of chronic obstructive pulmonary disease

Introduction: Non-invasive ventilation (NIV) has revolutionised the management of hypercapnic exacerbations of chronic obstructive pulmonary disease (COPD). We wished to evaluate factors related to its overall success in the real-life setting. Methods: A retrospective analysis of patients receiving NIV for a hypercapnic exacerbation of COPD was performed. Demographics, laboratory data, blood gases and outcomes (hospital discharge or in- patient death) were extracted and subsequently analysed to identify factors relating to its overall success or failure. Results: Over 6 years, 240 patients (mean age 70 years), received NIV with mean pH and pCO2 prior to NIV 7.24 and 10.4kPa respectively; of these, 167 survived to hospital discharge with a median age (70 vs. 74; p = 0.02) lower than non- survivors. Absolute values of pH and pCO2 (higher and lower respectively) prior to NIV and at 1 h were both associated with successful hospital discharge. An improvement (p = 0.02) in pH within an hour of receiving NIV - but not pCO2 was associated with surviving to hospital discharge. Of all laboratory data assessed, only baseline urea was significantly (p = 0.021) associated with a successful outcome. Conclusion: Younger patients with a lower urea, higher pH and lower pCO2 at baseline and who demonstrate an improvement in pH within 1 h, are more likely to have a successful outcome when given NIV for a hypercapnic exacerbation of COPD on an unselected basis. Prospective studies evaluating many other parameters are now required to help identify patients in whom NIV is likely to be successful.