Practical Bedside Estimation of Lean Body Weights using Body Mass Index for Regional Anesthesia

Jeremy Tsui1, Weiran Liu2, Jonathan Jenkin Tsui2, Ban Tsui 2

 

1 Anesthesiology and Pain Medicine, University of Washington

2 The Chinese University of Hong Kong - Shenzhen

Introdution:

Increasing clinical obesity has changed local anesthetic dose determination.
•Pharmacokinetic differences justify lean body weight (LBW)-based maximum local anesthetic dosing modifications.
•Retrospective research showed significant differences in LBW- and TBW-based ropivacaine doses.
•The study hypothesizes that male lean body weight is directly related to (100-BMI) % x TBW.
•We also hypothesize that female lean body weight is directly related to (90 - BMI) % x TBW because females have a 10% higher percentage fat than males

Methods:
•Study on Lean Body Weight Estimation
•Testing consistency uses Bland-Altman plots.
•Compares estimated LBWs from Boer's equation vs simplified equations (BMI-M and BMI-F).
•(Male: LBM = 0.407weight(kg) + 0.267height(cm) - 19.2
•Female: LBM = 0.252weight(kg) + 0.473height(cm) - 48.3)

Results:
•A demographic retrospective study of 500 single-shot peripheral nerve block patients
•Figure 1 & 2 shows that the simplified equations (BMI-M and BMI-F) estimate LBM similarly to the Boer equation.
•Bland- Altman plots show that most LBM simplified using BMI-M and BMI-F values are within 10% of the Boer equation LBM.

DISCUSSION & CONCLUSION

A simplified BMI equation can offer a more practical method of estimating LBW using a single, easier-to-remember, gender-specific equation that yields the same results.