P153 The effect of body mass index on outcomes of acute non-invasive ventilation (NIV) in a district general hospital

Introduction The increasing prevalence of obesity is likely to affect the caseload of Non-invasive Ventilation (NIV) units. We hypothesised that outcomes in the obese and morbidly obese population would differ from patients with a normal Body Mass Index (BMI) on the NIV unit. Method We audited all patients admitted to the NIV unit from January 2007 to December 2009. Patient demographics, admitting diagnosis, baseline arterial blood gases (ABG), duration on NIV, length of stay and outcome were recorded on BTS NIV audit proformas. BMI was obtained from GP records. Data were analysed using Prism 5. Results A total of 176 patients (46% male, median age 74), were managed on the NIV unit. The admitting diagnosis was COPD (59%), Obesity hypoventilation syndrome (OHS) (13%), Cardiac failure (13%), Neuromuscular disorders (2%) or “other” diagnoses (13%). The median BMI was 27 (IQR 22.7–35.0); 6% of patients were underweight, 33% normal weight, 18% overweight, 26% obese and 17% morbidly obese. An increasing proportion of females were found in the obese and morbidly obese population (χ 2 p=0.003). No statistical differences were found in baseline ABG and NIV duration between different BMI categories. Compared to patients with a normal weight, obese and morbidly obese individuals had significantly longer lengths of hospital stay (Mann–Whitney U test p=0.004 and p=0.001, respectively). Outcomes did not differ between normal weight, underweight, or overweight patients. However, obese and morbidly obese patients were significantly more likely to survive admission compared to patients with a normal BMI (Abstract P153 Figure 1; χ 2 p=0.035 and p=0.0008, respectively). Similarly, there was no significant difference in age, gender, ABG parameters, NIV duration or length of stay between COPD and OHS patients. However, OHS patients were significantly more likely to survive admission (χ 2 p=0.0042). Conclusion The outcomes for obese and morbidly obese patients were significantly better than patients with a normal BMI, although the length of stay was higher. Despite similar demographic features and metabolic disturbance of COPD and OHS patients, OHS patients were more likely to survive admission.