For obese patients, is the 40% adjustment for Sugammadex (Bridion, cyclohexanol) dosing calculated from the ideal body weight or the actual body weight?

Sugammadex Dosing in Obese Patients: The 40% is Added to Ideal Body Weight

The 40% adjustment is calculated FROM and ADDED TO the ideal body weight (IBW), not from actual body weight—this gives you "corrected body weight" (CBW) = IBW + (0.40 × IBW). 1, 2

How to Calculate the Dose

The dosing formula works as follows:

1. Calculate ideal body weight (IBW):

   • Men: height in cm minus 100
   • Women: height in cm minus 110 1

2. Calculate corrected body weight (CBW):

   • CBW = IBW + (40% of IBW)
   • This equals IBW × 1.4 1, 2

3. Apply the appropriate mg/kg dose based on depth of blockade:

   • Moderate blockade (2 TOF responses): 2 mg/kg × CBW 1, 2
   • Deep blockade (1-2 PTC responses): 4 mg/kg × CBW 1, 3
   • Immediate reversal after high-dose rocuronium: 8 mg/kg × actual body weight (exception to the rule) 1

Why This Dosing Strategy

Sugammadex is water-soluble and distributes in lean mass and extracellular volumes, not adipose tissue, making actual body weight dosing inappropriate and wasteful. 4, 1 The IBW + 40% formula accounts for the increased extracellular fluid volume in obese patients without overdosing based on fat mass. 4

Evidence Supporting This Approach

The European Society of Anaesthesiology and American Society of Anesthesiologists both recommend using IBW + 40% for sugammadex dosing in obese patients with BMI ≥35-40 kg/m². 4, 1

Multiple randomized trials confirm this approach is safe and effective:

• A 2011 study in 100 morbidly obese patients demonstrated that 2 mg/kg based on IBW + 40% successfully reversed moderate blockade without any residual paralysis (p < 0.0001). 2
• A 2021 study showed that 4 mg/kg based on corrected body weight (IBW + 40%) reversed deep blockade to TOF ≥0.9 in 2.2 ± 0.7 minutes, with no difference in safety compared to actual body weight dosing. 3

Critical Monitoring Requirements

Quantitative neuromuscular monitoring using acceleromyography or electromyography at the adductor pollicis is mandatory before and after sugammadex administration. 1 This ensures you're giving the correct dose for the actual depth of blockade and can detect potential recurarization. 1

Common Pitfall to Avoid

Do not confuse this with suxamethonium dosing, which is the only muscle relaxant that should be dosed on actual body weight (1.0 mg/kg) in obese patients. 4, 5 All other non-depolarizing agents and their reversal agents use lean body weight or corrected body weight formulas. 4

Advantage Over Neostigmine

Sugammadex is strongly preferred over neostigmine in obese patients because neostigmine dosed on actual body weight causes prolonged recovery time. 4, 1 This makes sugammadex the safer choice for this population.