The obese patient: Difference between revisions
Mceledon83 (talk | contribs) |
Mceledon83 (talk | contribs) No edit summary |
||
| Line 14: | Line 14: | ||
#Lean body weight '''(LBW)'''= Difference between TBW and fat mass<br> | #Lean body weight '''(LBW)'''= Difference between TBW and fat mass<br> | ||
##Technically best weight scalar for drug administration but difficult to accurately measure | ##Technically best weight scalar for drug administration but difficult to accurately measure | ||
#Adjusted body weight (ABW) = Scalar derived from aminoglycoside pharmacokinetics (PK) in obesity | |||
== Estimating Patient Weight == | == Estimating Patient Weight == | ||
| Line 28: | Line 29: | ||
###IBW (female) in kg = 45kg + 2.3kg for each in. over 5ft | ###IBW (female) in kg = 45kg + 2.3kg for each in. over 5ft | ||
#'''Estimated LBW''' = 1.3 x IBW | #'''Estimated LBW''' = 1.3 x IBW | ||
# | #'''Estimated ABW''' = IBW + [C x(TBW-IBW)] | ||
##C = correction factor ususally 0.2 to 0.4 | |||
#Apps/Online resources: | |||
##Epocrates has IBW calculator | ##Epocrates has IBW calculator | ||
##Http://www.medcalc.com/body.html | ##Http://www.medcalc.com/body.html | ||
| Line 63: | Line 66: | ||
| Dose by IBW | | Dose by IBW | ||
|- | |- | ||
| | | Heparin | ||
| | | Same as non-obese pt (80U/kg followed by 18U/kg/h using TBW) | ||
|- | |- | ||
| | | Vancomycin | ||
| | | 30 mg/kg TBW (then follow serum levels) | ||
|- | |- | ||
| | | Aminoglycosides | ||
| | | Dose by ABW (C= 0.4; then follow serum levels) | ||
|- | |- | ||
| | | Beta-lactams | ||
| | | No good data, may consider doubling dose | ||
|- | |- | ||
| | | Carbapenems | ||
| | | No empiric change recommended | ||
|- | |- | ||
| | | Antifungals | ||
| | | No empiric change recommended; use LBW when dosing weight-based agents | ||
|} | |} | ||
<br> | <br> | ||
Revision as of 06:43, 19 August 2013
Definitions
- Overweight = BMI 25-29
- Obesity = BMI 30-39
- Morbid obesity = BMI 40-49
- Super obesity = BMI >50
Dosing Scalars
- Total body weight (TBW)= Actual weight
- May result in over dosing
- Ideal body weight (IBW)= Calc. based on height & weight
- May result in under dosing
- Lean body weight (LBW)= Difference between TBW and fat mass
- Technically best weight scalar for drug administration but difficult to accurately measure
- Adjusted body weight (ABW) = Scalar derived from aminoglycoside pharmacokinetics (PK) in obesity
Estimating Patient Weight
Multiple formulas to estimate weight, below are most common:
- Estimated male TBW = 93.2 + 3.29[arm circumference (cm)] + 0.43[height (cm)]
- Estimated female TBW = 64.6 + 2.15[arm circumference (cm)] + 0.54[height (cm)]
- Estimated male IBW in kg = height in cm - 100
- More accurate IBW estimate:
- IBW (male) in kg = 50kg + 2.3kg for each in. over 5ft
- More accurate IBW estimate:
- Estimated female IBW in kg = height in cm - 105
- More accurate IBW estimate:
- IBW (female) in kg = 45kg + 2.3kg for each in. over 5ft
- More accurate IBW estimate:
- Estimated LBW = 1.3 x IBW
- Estimated ABW = IBW + [C x(TBW-IBW)]
- C = correction factor ususally 0.2 to 0.4
- Apps/Online resources:
- Epocrates has IBW calculator
- Http://www.medcalc.com/body.html
Medication Adjustments in Obesity
Obesity alters hepatic/renal clearance and volume of distribution (Vd) of many drugs.
| Medication | Dose Adjustment |
| Morphine | Dose by IBW |
| Fentanyl | Dose by LBW; Alternative initial dose TBW, subsequent dose by IBW (risk over dose when use TBW) |
| Midazolam | Initial dose TBW, subsequent dose by IBW |
| Propofol | Dose by LBW |
| Etomidate | Dose by LBW |
| Succinylcholine | Dose by TBW @ 1mg/kg |
| Rocuronium | Dose by IBW |
| Heparin | Same as non-obese pt (80U/kg followed by 18U/kg/h using TBW) |
| Vancomycin | 30 mg/kg TBW (then follow serum levels) |
| Aminoglycosides | Dose by ABW (C= 0.4; then follow serum levels) |
| Beta-lactams | No good data, may consider doubling dose |
| Carbapenems | No empiric change recommended |
| Antifungals | No empiric change recommended; use LBW when dosing weight-based agents |