Patient weight as a predictor of pain response to morphine in the emergency department

Study Objectives: There is little evidence that patient weight is associated with pain response to morphine in the emergency department (ED). The primary outcome of this study is to identify demographic variables including patient weight that are associated with an adequate pain reduction after the first dose of morphine. Methods: A retrospective chart review of all patients with severe nontraumatic abdominal pain receiving intravenous morphine was conducted in our ED over a 3-month time period. Pain score, using an 11-point verbal numerical pain scale (0-10), was measured before and after each dose of morphine. Adequate response was defined as a ≥ 4-point reduction from baseline pain score. Results: A total of 105 patients were included in the analysis. Univariate logistic regression analyses stratified by dose (2 or 4 mg) showed that patient weight was not predictive of adequate pain response after the first dose of morphine (2 mg: odds ratio = 1; 95% confidence interval 0.97-1.03; P = .88; 4 mg: odds ratio = 1; 95% confidence interval 0.97-1.03; P = .86). Conclusions: Patient weight may not predict pain response to morphine in the ED. Dosing strategies based on patient weight may not be necessary in this patient population.