Evaluation of Response to Weight-based Dosing Strategies of Continuous, Fixed-Rate Atracurium Infusions in Critically Ill, Obese Adults With Acute Respiratory Distress Syndrome.

Background: Fixed-rate infusions of weight-based neuromuscular blocking agents (NMBAs) were adopted during the COVID pandemic to limit caregiver exposure during titrations. Although fixed-rate infusions are supported in studies of acute respiratory distress syndrome (ARDS), the optimal scalar for weight-based NMBAs in patients with obesity remains controversial.

Objective: This study sought to compare change in oxygenation using two weight-based dosing strategies for atracurium in obese patients with ARDS. Secondary outcomes included total atracurium dose, mortality, and intensive care unit (ICU) and ventilator-free days.

Methods: Following an institutional practice update to use ideal body weight (IBW) for patients with obesity, we retrospectively compared adults (≥18 years) with ARDS and a body mass index (BMI) ≥ 30 kg/m² who received atracurium (15 µg/kg/min) based on actual body weight (ABW) with those using IBW. The primary outcome was change in PaO₂/FiO₂ ratio (P/F) 48 hours after atracurium initiation. Analysis-of-covariance compared change in P/F between groups after adjustment for confounders.

Results: The IBW group (n = 123), compared with the ABW group (n = 133), had lower baseline P/F (85.0 [71.0, 118.3] vs 93.3 [76.0, 128.3], P = 0.025) and sequential organ failure assessment (SOFA) score (9.7 ± 2.6 vs 10.5 ± 2.6, P = 0.015), with greater use of steroids (96% vs 89%, P = 0.032) and prone positioning (72% vs 58%, P = 0.015). No difference was detected in change in P/F at 48 hours (adjusted least squares mean [95% confidence interval, CI]: 55.8 [37.0, 74.5] vs 56.9 [39.6, 74.1], P = 0.90). Atracurium doses were higher in the ABW group (97.4 mg/h [84.4, 110.3] vs 55.4 [47.2, 65.7], P < 0.001). There was no difference in hospital mortality, ICU mortality, and ICU-free days or ventilator-free days.

Conclusion and relevance: In patients with obesity with ARDS receiving fixed-rate atracurium infusions, the change in P/F at 48 hours did not differ based on weight. Atracurium dosed on IBW may use less total drug without compromising ability to improve oxygenation. This is the first study comparing the dosing weight used for continuous infusion atracurium in hospitalized, critically ill ARDS patients with obesity. Additional studies are warranted to optimize dosing in obese patients.