The obese patient: Difference between revisions
Mceledon83 (talk | contribs) |
ClaireLewis (talk | contribs) |
||
(23 intermediate revisions by 7 users not shown) | |||
Line 1: | Line 1: | ||
= Definitions | ==Definitions== | ||
*BMI 25-29 = Overweight | |||
*BMI 30-39 = Obese | |||
*BMI 40-49 = Morbidly obese | |||
*BMI >50 = Super obese | |||
==Dosing Scalars== | |||
*Total body weight '''(TBW)'''= Actual weight | |||
**May result in over dosing | |||
*[[ideal body weight estimation|Ideal body weight]] '''(IBW)'''= Calc. based on height & weight | |||
**May result in under dosing | |||
*Lean body weight '''(LBW)'''= Difference between TBW and fat mass<br> | |||
**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=== | ||
''There are multiple formulas to estimate weight - these are the 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 | |||
*'''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 | |||
*'''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'' | |||
{| class="wikitable" | |||
|+ Medication Adjustment in Obesity<ref>Venkat A, Ingrande J, and Lemmens HJM. Challenging & Emerging Conditions in EM. Dose adjustment of anaesthetics in the morbidly obese. British journal of anaesthesia. 2010; 105(suppl 1):i16-i23.</ref> | |||
Obesity alters hepatic/renal clearance and volume of distribution (Vd) of many drugs | |||
{| | |||
|+ Medication Adjustment in Obesity | |||
|- | |- | ||
| '''Medication''' | | '''Medication''' | ||
| '''Dose Adjustment ''' | | '''Dose Adjustment ''' | ||
|- | |- | ||
| Morphine | | [[Morphine]] | ||
| Dose by IBW | | Dose by IBW | ||
|- | |- | ||
| Fentanyl | | [[Fentanyl]] | ||
| Dose by LBW; Alternative | | Dose by LBW; Alternative: Initial dose TBW, subsequent dose by IBW (risk over dose when use TBW) | ||
|- | |- | ||
| Midazolam | | [[Midazolam]] | ||
| Initial dose TBW, subsequent dose by IBW | | Initial dose TBW, subsequent dose by IBW | ||
|- | |- | ||
| Propofol | | [[Propofol]] | ||
| Dose by LBW | | Dose by LBW | ||
|- | |- | ||
| Etomidate | | [[Etomidate]] | ||
| Dose by LBW | | Dose by LBW | ||
|- | |- | ||
| Succinylcholine | | [[Succinylcholine]] | ||
| Dose by TBW @ 1mg/kg | | Dose by TBW @ 1mg/kg | ||
|- | |- | ||
| Rocuronium | | [[Rocuronium]] | ||
| Dose by IBW | | Dose by IBW | ||
|- | |- | ||
| | | [[Heparin]] | ||
| | | Same as non-obese patient (80U/kg followed by 18U/kg/h using TBW) | ||
|- | |- | ||
| | | [[Vancomycin]] | ||
| | | 30mg/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 | ||
|} | |} | ||
< | ==Airway Management== | ||
Obesity associated with difficult bag-mask ventilation ([[BVM]]) and intubation | |||
*Consider prolonged pre-oxygenation period and two provider BMV | |||
*May improve lung function through use of pre-intubation period of [[NIPPV]] | |||
**Obesity hypoventilation syndrome may cause chronic hypercapnia | |||
*Place patient in "ramp" position | |||
**Stack blankets behind patient's back to horizontally align external auditory meatus with sternal notch | |||
*Consider Airtraq laryngoscope (shortened mean intubation time & desat episodes vs Mac DL in obese patients) OR other hyperangulated video laryngoscope such as glidescope | |||
*Increased BMI associated with higher rate of developing ARDS | |||
**Methods to improve oxygenation/ventilation: | |||
***Use PEEP 10 to improve oxygenation if needed | |||
***Place in reverse Trendelenburg ("beach chair" position) to improve ventilation | |||
***Both may decrease CO so use cautiously in unstable patients | |||
==[[Lumbar Puncture]]== | |||
*Obese patients have increased distance from skin to subarachnoid space | |||
*Upright patient positioning improves LP success | |||
*Estimated lumbar puncture depth (cm) = 1 + 17[weight(kg)/height(cm)] | |||
*Ultrasound may improve identification of landmarks | |||
*If failure, consider fluoroscopy-guided procedure by IR | |||
==References== | |||
<references/> | |||
[[Category:Misc/General]] |
Latest revision as of 14:12, 13 October 2019
Definitions
- BMI 25-29 = Overweight
- BMI 30-39 = Obese
- BMI 40-49 = Morbidly obese
- BMI >50 = Super obese
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
There are multiple formulas to estimate weight - these are the 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 patient (80U/kg followed by 18U/kg/h using TBW) |
Vancomycin | 30mg/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 |
Airway Management
Obesity associated with difficult bag-mask ventilation (BVM) and intubation
- Consider prolonged pre-oxygenation period and two provider BMV
- May improve lung function through use of pre-intubation period of NIPPV
- Obesity hypoventilation syndrome may cause chronic hypercapnia
- Place patient in "ramp" position
- Stack blankets behind patient's back to horizontally align external auditory meatus with sternal notch
- Consider Airtraq laryngoscope (shortened mean intubation time & desat episodes vs Mac DL in obese patients) OR other hyperangulated video laryngoscope such as glidescope
- Increased BMI associated with higher rate of developing ARDS
- Methods to improve oxygenation/ventilation:
- Use PEEP 10 to improve oxygenation if needed
- Place in reverse Trendelenburg ("beach chair" position) to improve ventilation
- Both may decrease CO so use cautiously in unstable patients
- Methods to improve oxygenation/ventilation:
Lumbar Puncture
- Obese patients have increased distance from skin to subarachnoid space
- Upright patient positioning improves LP success
- Estimated lumbar puncture depth (cm) = 1 + 17[weight(kg)/height(cm)]
- Ultrasound may improve identification of landmarks
- If failure, consider fluoroscopy-guided procedure by IR
References
- ↑ Venkat A, Ingrande J, and Lemmens HJM. Challenging & Emerging Conditions in EM. Dose adjustment of anaesthetics in the morbidly obese. British journal of anaesthesia. 2010; 105(suppl 1):i16-i23.