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Emerg Med J doi:10.1136/emermed-2012-202168
  • Original article

Analgesic response to morphine in obese and morbidly obese patients in the emergency department

  1. Brian L Erstad1
  1. 1Department of Pharmacy Practice & Science, College of Pharmacy, University of Arizona, Tucson, Arizona, USA
  2. 2Department of Pharmacy Services, Maricopa Integrated Health System, Phoenix, Arizona, USA
  1. Correspondence to Dr Asad E Patanwala, Department of Pharmacy Practice & Science, College of Pharmacy, University of Arizona, 1295 N. Martin, PO Box 210202, Tucson, AZ 85721, USA; patanwala{at}pharmacy.arizona.edu
  • Received 13 November 2012
  • Revised 17 December 2012
  • Accepted 19 December 2012
  • Published Online First 12 January 2013

Abstract

Objective The primary objective of this study was to compare the analgesic response to morphine in non-obese, obese and morbidly obese patients for acute pain.

Methods This was a retrospective cohort study conducted in a tertiary care emergency department in the USA. Consecutive adults who received intravenous morphine 4 mg for pain were included. Patients were categorised into three groups based on body mass index (BMI): non-obese (18.5–29.9 kg/m2); obese (30.0–39.9 kg/m2); and morbidly obese (≥40 kg/m2). Baseline and post-dose pain scores were recorded. Pain was measured on a 0–10 numerical rating scale (0=no pain; 10=worst possible pain). Analgesic response was defined as the difference between the initial pain score and post-dose pain score.

Results 300 patients were included in the study (100 in each group). The median baseline pain scores were 8.5, 8 and 8.5 in the non-obese, obese and morbidly obese groups, respectively (p=0.464). The median analgesic response after morphine administration was 2, 3 and 2 in the non-obese, obese and morbidly obese groups, respectively (p=0.160). In the linear regression analysis (R2=0.006), BMI was not predictive of analgesic response (coefficient −0.020; p=0.199).

Conclusions Obesity status did not influence analgesic response to a fixed dose of morphine. This suggests that obese and morbidly obese patients do not require a higher dose of morphine for acute pain reduction compared to non-obese patients.