Impact of ideal vs actual body weight on analgesic and sedative requirements in critically ill patients with obesity

PURPOSE: Analgosedation is the standard of care for managing mechanically ventilated critically ill patients. Most sedative medications are lipophilic, with increased volume of distribution in patients with obesity; however, data about dosing these drugs in critically ill patients with obesity are limited. In 2022, our institution changed to an ideal body weight (IBW) dosing strategy for all weight-based continuous infusions of analgesia and sedation agents, including fentanyl, ketamine, propofol, and dexmedetomidine. This study evaluated whether utilizing IBW dosing for critically ill patients with obesity results in decreased analgesic requirements. METHODS: This was a single-center, retrospective, observational cohort study that included critically ill adult patients with a body mass index (BMI) of greater than 30 kg/m2 receiving analgosedation with continuous fentanyl from January 1 to March 31, 2020 (actual body weight ABW group) and from January 1 to March 31, 2024 (IBW group). Patients were excluded if they required deep sedation or mechanical circulatory support, had a history of chronic opioid use or opioid use disorder, or had a positive COVID-19 result. The primary outcome was cumulative morphine milligram equivalent (MME) requirements during the fentanyl continuous infusion. Secondary outcomes included the cumulative doses of sedation and duration of mechanical ventilation, as well as intensive care unit (ICU) and hospital length of stay (LOS). Efficacy was evaluated via RASS and CPOT score and by as-needed opioid and benzodiazepine requirements in MME and midazolam equivalents. RESULTS: Forty-six patients in the ABW group and 31 patients in the IBW group were included. The median BMI was similar (ABW group, 35.3 kg/m2; IBW group, 34.9 kg/m2; P = 0.83). The IBW group had significantly lower median cumulative intravenous MME requirements (ABW group, 931.2 mg; IBW group, 537.9 mg; P = 0.04). For the secondary outcomes, the cumulative MME requirements for fentanyl differed between the dosing strategies (ABW group, 914.1; IBW group, 485.8; P = 0.03), but no differences were found for other sedatives, as-needed opioids or benzodiazepines, duration of mechanical ventilation, ICU LOS, or hospital LOS. CONCLUSION: Utilizing IBW dosing decreased cumulative opioid requirements in critically ill patients with obesity without resulting in increased doses of other sedatives or as-needed medications.