Background:While numerous investigations have described worse outcomes for patients undergoing emergent procedures at night, few studies have investigated the impact of nighttime on the outcomes of emergent endotracheal intubation (EEI). We hypothesized that for patients requiring EEI at night, the outcome of first pass success would be lower as compared to during the day.Methods:We performed a retrospective cohort study of all patients admitted to our institution between January 1st, 2016 and July 17st, 2019 who underwent EEI outside of an emergency department or operating room. Nighttime was defined as between 7:00 pm and 6:59 am. The primary outcome was the rate of first pass success. Logistic regression was utilized with adjustment for demographic, morbidity and procedure related covariables.Results:The final examined cohort included 1,674 EEI during the day and 1,229 EEI at night. The unadjusted rate of first pass success was not different between the day and night (77.5% vs. 74.6%, unadjusted odds ratio (OR): 0.85; 95% confidence interval (CI): 0.72, 1.0; P = 0.073 though following adjustment for prespecified covariables the odds of first pass success was lower at night (adjusted OR: 0.83, 95% CI: 0.69, 0.99; P = 0.042. Obesity was found to be an effect modifier on first pass success rate for day vs. night intubations. In obese patients, nighttime intubations had significantly lower odds of first pass success (adjusted OR: 0.71, 95% CI: 0.52, 0.98; P = 0.037).Discussion:After adjustment for patient and procedure related factors, we have found that the odds of first pass success is lower at night as compared to the day. This finding was, to some degree, driven by obesity which was found to be a significant effect modifier in this relationship.