Impact of Ideal Versus Actual Body Weight on Analgesic Requirements in Patients With Obesity

Introduction: Analgosedation is the standard of care for management of mechanically ventilated, critically ill patients. During the COVID-19 pandemic, there was a trend in over sedation of ICU patients, despite studies showing that light sedation improves outcomes. There is limited data about the appropriate dosing of analgesia and sedative medications in patients with obesity in the ICU setting. In 2022, our institution changed from using actual body weight (ABW) to ideal body weight (IBW) for all weight-based, continuous infusion analgesics and sedatives. This study aims to determine whether IBW dosing for critically ill patients with obesity results in decreased analgesic requirements.


Methods: This is a single center, retrospective, observational chart review of adult patients with a BMI > 30 kg/m² who received analgosedation with a continuous infusion of fentanyl between January 1, 2020 – March 31, 2020 and January 1, 2024 – March 31, 2024. Patients were excluded if they had an indication for deep sedation, a history of opioid use disorder, or a positive COVID-19 test. The primary outcome was cumulative morphine milligram equivalent (MME) requirements during the duration of fentanyl continuous infusion. Secondary outcomes included cumulative rates of other sedatives, duration of mechanical ventilation, ICU length of stay (LOS), and hospital LOS.


Results: Out of 904 patients screened, 46 patients in the ABW group and 31 patients in the IBW group were included. Baseline characteristics were similar, with a median BMI of 35.3 in the ABW group and 34.9 in the IBW group. Most of the patients were admitted to the medical ICU (62%). For the primary outcome of median cumulative MME requirements during the total duration of the fentanyl infusion, there was a significant difference between the groups, with the IBW group having lower MME requirements (931.2 mg vs. 537.9 mg, p=0.037). There was no difference in cumulative requirements of sedative drips, except for fentanyl, as well as no difference in duration of mechanical ventilation, ICU LOS, or hospital LOS.


Conclusions: Utilizing an IBW dosing strategy led to decreased cumulative opioid requirements in patients with obesity. However, there were no differences in the requirements of other sedative infusion medications.