The Assessment of Muscle Relaxation and Anesthesia Depth in Morbidly Obese Patients: Should We Determine Drug doses According to Lean Body Weight (LBW)?

Background: To give a good planned anesthesia to a morbidly obese patient, it is better to have knowledge about morbid obesity’s interaction and impact on drug dosages. For safe drug dosing, not only increased body weight and changed body composition but also physiological changes and comorbid conditions have to be considered.

In this study, we aimed to examine the adequacy of the associated drug with the BIS and TOF monitoring for patients who are scheduled the surgical intervention due to morbid obesity in anesthesia induction.The induction of drug doses were calculated based on LBW; were compared with the calculated dose based on IBW and TBW and were evaluated statistically.

Methods: Study was carried out at 35 patients who undergone bariatric surgery. Induction was done with thiopental, rocuronium and fentanyl according to the estimation of lean body weight (LBW). Later, whether enough muscle relaxation and anesthesia depth occurred or not at expected normal period of time, was observed with bispectral index (BIS) and train of four (TOF) monitorization.

Results: According to estimated lean body weight at morbidly obese patients, 5 mg/kg thiopental, 0.6 mg/kg rocuronium and 2 mcg/kg fentanyl found to be not enough for BIS, TOF and entubation quality at any of patients. According to LBW with 8 mg/kg thiopental, 1 mg/kg rocuronium and 2 mcg/kg fentanyl, enough depth of anesthesia and muscle relaxation and good quality of intubation were shown by evaluation of BIS and TOF.

Conclusion: At morbidly obese patients LBW can be estimated by Janmahasatian formula. After administration of 8 mg/kg thiopental, 1 mg/kg rocuronium and 2 mcg/kg fentanyl according to patients’ lean body weights that estimated with this formula; evaluation with BIS and TOF have shown that enough depth of anesthesia and muscle relaxation. When intubation quality was evaluated, it was revealed that good and perfect intubation quality.