Sodium Thiopental Dosing Strategies in Overweight Patients: A Randomized Clinical Trial

Abstract

Background: Sodium thiopental is commonly used for the induction of general anesthesia; however, selecting an appropriate weight descriptor for dosing in patients with BMI > 25 kg/m2 remains challenging because excess body weight and associated physiologic changes may affect anesthetic depth and dosing requirements. Objectives: To compare the effectiveness and safety of using total body weight, ideal body weight, and adjusted body weight to calculate sodium thiopental induction doses in adults with BMI > 25 kg/m2, using the bispectral index (BIS) as the primary measure of anesthetic depth and using hemodynamic responses and supplemental thiopental requirements as secondary outcomes. Methods: In this single-center randomized clinical trial, 91 adults with a body mass index greater than 25 kg/m2 were allocated to receive sodium thiopental at 5 mg/kg, calculated using total body weight, ideal body weight, or adjusted body weight. The bispectral index, heart rate, and mean arterial pressure were recorded at baseline, 1 minute after completion of the initial sodium thiopental injection, and 3 minutes after tracheal intubation. The primary outcome was the bispectral index 1 minute after completion of the initial thiopental dose. Secondary outcomes included heart rate, mean arterial pressure, total thiopental dose, and the need for supplemental thiopental boluses. Results: After the initial dose, the bispectral index differed significantly among groups (P < 0.001), with higher values in the ideal body weight group (59.81 ± 14.2) than in the total body weight group (38.75 ± 12.66) and the adjusted body weight group (44.21 ± 12.53). The mean total thiopental dose was 427.25 ± 44.17 mg in the total body weight group, 433.75 ± 125.25 mg in the ideal body weight group, and 371.93 ± 69.96 mg in the adjusted body weight group. Supplemental thiopental boluses were required in 3.3% of patients in the total body weight group, 24.1% in the adjusted body weight group, and 78.1% in the ideal body weight group; 15.6% of patients in the ideal body weight group did not achieve a BIS < 50 despite receiving a total thiopental dose of 500 mg. After intubation, the mean arterial pressure was highest in the adjusted body weight group (117.76 ± 16.98 mm Hg; P = 0.035), whereas the heart rate did not differ significantly among groups. Conclusions: Overall, adjusted body weight dosing appeared to provide a more dose-efficient induction profile, achieving clinically acceptable anesthetic depth with a lower total thiopental requirement than total body weight dosing while maintaining broadly comparable hemodynamic responses. In contrast, ideal body weight dosing at 5 mg/kg appeared less reliable in this population, as reflected by the markedly higher need for supplemental thiopental boluses and occasional failure to achieve the target bispectral index threshold. These findings support the concept that an intermediate weight descriptor may better balance the competing risks of excessive hypnotic depth with total body weight dosing and insufficient hypnotic depth with ideal body weight dosing in patients with BMI > 25 kg/m2. Adjusted body weight dosing appeared to provide a more dose-efficient induction strategy than total body weight dosing while avoiding the frequent requirement for supplemental thiopental boluses observed with ideal body weight dosing. Ideal body weight dosing at 5 mg/kg appeared less reliable in adults with BMI > 25 kg/m2 under the conditions of this study.