The obese patient

Definitions

1. Overweight = BMI 25-29
2. Obesity = BMI 30-39
3. Morbid obesity = BMI 40-49
4. Super obesity = BMI >50

Dosing Scalars

1. Total body weight (TBW)= Actual weight
   1. May result in over dosing
2. Ideal body weight (IBW)= Calc. based on height & weight
   1. May result in under dosing
3. Lean body weight (LBW)= Difference between TBW and fat mass
   
   1. Technically best weight scalar for drug administration but difficult to accurately measure

Estimating Patient Weight

Multiple formulas to estimate weight, below are most common:

1. Estimated male TBW = 93.2 + 3.29[arm circumference (cm)] + 0.43[height (cm)]
2. Estimated female TBW = 64.6 + 2.15[arm circumference (cm)] + 0.54[height (cm)]
3. Estimated male IBW in kg = height in cm - 100
   1. More accurate IBW estimate:
      1. IBW (male) in kg = 50kg + 2.3kg for each in. over 5ft
4. Estimated female IBW in kg = height in cm - 105
   1. More accurate IBW estimate:
      1. IBW (female) in kg = 45kg + 2.3kg for each in. over 5ft
5. Estimated LBW = 1.3 x IBW
6. Others:
   1. Epocrates has IBW calculator
   2. Http://www.medcalc.com/body.html

Medication Adjustments in Obesity

Obesity alters hepatic/renal clearance and volume of distribution (Vd) of many drugs

Medication Adjustment in Obesity

Medication	Dose Adjustment
Morphine	Dose by IBW
Fentanyl	Initial dose TBW, subsequent dose by IBW (prolonged half-life)
Midazolam	Initial dose TBW, subsequent dose by IBW
Propofol	LBW
Etomidate	LBW