Abstract
Acute noninvasive ventilation (NIV) is a well-established therapy for acute respiratory failure but the dose-response characteristics of this therapy have not been defined. The aim of this study was to define this dose-response relationship. This study was a retrospective review of patients receiving NIV for acute respiratory failure in a tertiary hospital respiratory high-dependency unit between July 2012 and June 2017. Mask-on time (rather than the period that NIV was in use) as the "dose" was compared with hospital survival as the "response". 654 patients were included, 594 (91%) with hypercapnic respiratory failure (HCRF). NIV was used for a median (interquartile range (IQR)) duration of 2.74 (1.51-4.73) days and median (IQR) mask-on time was 34 (18-60) h (56.1% (41.2-69.5%) of treatment time). There was evidence of a dose-response relationship in the HCRF group up to a ceiling of 24 h mask-on time, but not in the hypoxaemic respiratory failure (HRF) group. There was a difference in survival with as little as 2 h mask-on time (92% compared with 73%; p<0.001). Patients requiring NIV for 80-100% of therapy time had lower survival. We conclude that there is evidence of a dose-response relationship between cumulative NIV usage (mask-on time) and survival from as little as 2 h to a ceiling of ∼24 h in HCRF, but not in HRF.