Estimation of Total Body Weight in Obese Patients

Abstract 

Objective

Knowledge of accurate patient weight is vital to safe air medical transport and critical care. Patient weight is often unknown in emergency settings, and visual estimations have been shown to be inaccurate, especially in obese patients. We hypothesized that a simple formula based on anthropometric measurements could accurately predict patient weight for obese adult men and women.

Methods

Data from cross-sectional anthropometric measurements from the National Health and Nutrition Examination Survey (NHANES) III (1988–1994)—height, leg length, thigh circumference, and mid-arm circumference—were used to estimate patient weight among adult (18 years and older) men and nonpregnant women who weighed at least 100 kg (N = 1,471). Linear modeling was used to develop simple sex-specific linear models to estimate patient weight. Models were derived on a random 67% subset of the original sample and then validated against the remaining 33% to assess the model's predictive capacity.

Results

The combination of arm circumference and height yielded the best model: Women: weight (WT) = −64.6 + 2.15 × arm circumference (ARM) + 0.54 × height (HT) (adjusted R²: 0.55); men: WT = −93.2 + 3.29 × ARM + 0.43 × HT (adjusted R²: 0.59). Approximately 90% of patient weights were accurately estimated within a 15% error tolerance.

Conclusion

We have derived and validated simple equations with easy-to-use tables to accurately predict total body weight of obese men and women using only height and arm circumference. These tables may assist air medical transport pilots and medical crews make decisions about which patients may be safely transported, how far they may be transported, how much fuel is required, and how many crewmembers and family members may accompany them.