Adjusted Body Weight Calculation
For a patient with IBW 52 kg and actual weight 146 kg, the Adjusted Body Weight (ABW) is 89.6 kg using the standard formula: ABW = 52 + 0.4 × (146 - 52) = 89.6 kg. 1, 2
Formula and Calculation
The universally accepted formula for ABW is: 1, 2
ABW (kg) = IBW (kg) + 0.4 × (Total Body Weight - IBW)
Applying this to your patient:
- ABW = 52 + 0.4 × (146 - 52)
- ABW = 52 + 0.4 × 94
- ABW = 52 + 37.6
- ABW = 89.6 kg
Clinical Rationale
The 0.4 adjustment factor (40% of excess weight) accounts for the fact that obese individuals have increased lean body mass and volume of distribution for drugs, but the metabolic needs and dietary requirements of adipose tissue are less than that of lean body mass. 1, 2
This formula is recommended by the Association of Anaesthetists of Great Britain and Ireland and is widely used across multiple clinical contexts including anesthesia, critical care nutrition, and renal disease management. 1, 2
Important Clinical Caveats
Dosing to total body weight (146 kg) is rarely appropriate and significantly increases the risk of relative overdose, particularly for anesthetic agents and many medications. 1, 3
Alternative adjustment factors exist depending on clinical context: 1, 2
- 0.25 factor: Used by ESPEN for critical care nutrition calculations (would yield ABW = 75.5 kg) 1
- 0.33 factor: Alternative ESPEN recommendation for nutritional assessment (would yield ABW = 83 kg) 2
- 0.4 factor: Standard for anesthesia and most medication dosing (yields ABW = 89.6 kg) 1, 2, 4
For medication dosing and anesthesia, use the 0.4 factor (89.6 kg) as this is the most widely validated approach. 1, 2, 4
For nutritional calculations in critical care, consider using the 0.25 factor (75.5 kg) if following ESPEN guidelines. 1