Objectives The primary objective of this study was to determine the association between patient weight and first pass success (FPS) during rapid sequence intubation (RSI) in the ED. The secondary objective was to evaluate the association between patient weight and neuromuscular blocking agent (NMBA) dosing.

Methods This was a retrospective cohort study conducted in a tertiary care academic ED. Consecutive adult patients who underwent RSI in the ED between January 2014 and June 2016 were included. Data were collected on patient, operator and procedural characteristics. The cohort was categorised into the following weight strata: <80 kg, 80 to <100 kg, 100 to <120 kg and ≥120 kg. The primary outcome of interest was FPS. A multivariable logistic regression analysis was conducted to evaluate the relationship between patient weight category and FPS. NMBA dosing was reported descriptively.

Results The sample included 891 patients. FPS for each weight category was as follows: <80 kg (91%), 80 to <100 kg (90%), 100 to <120 kg (91%) and ≥120 kg (76%). After adjusting for potential confounders, the heaviest weight category was associated with decreased odds of FPS (OR 0.2, 95% CI 0.1 to 0.5, p<0.001). Median doses for succinylcholine (based on total body weight) decreased as weight increased: <80 kg (1.5 mg/kg), 80 to <100 kg (1.3 mg/kg), 100 to <120 kg (1.2 mg/kg) and ≥120 kg (1.0 mg/kg). Median doses for rocuronium (based on ideal body weight) were similar across weight categories: <80 kg (1.3 mg/kg), 80 to <100 kg (1.4 mg/kg), 100 to <120 kg (1.3 mg/kg) and ≥120 kg (1.4 mg/kg).

Conclusions Very heavy patients (>120 kg) undergoing RSI in the ED had a reduced FPS, and succinylcholine was more commonly underdosed than rocuronium in the heavier weight group.