The obese patient: Difference between revisions
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==Definitions== | ==Definitions== | ||
* | *BMI 25-29 = Overweight | ||
* | *BMI 30-39 = Obese | ||
* | *BMI 40-49 = Morbidly obese | ||
* | *BMI >50 = Super obese | ||
==Dosing Scalars== | ==Dosing Scalars== | ||
*Total body weight '''(TBW)'''= Actual weight | *Total body weight '''(TBW)'''= Actual weight | ||
**May result in over dosing | **May result in over dosing | ||
*Ideal body weight '''(IBW)'''= Calc. based on height & weight | *[[ideal body weight estimation|Ideal body weight]] '''(IBW)'''= Calc. based on height & weight | ||
**May result in under dosing | **May result in under dosing | ||
*Lean body weight '''(LBW)'''= Difference between TBW and fat mass<br> | *Lean body weight '''(LBW)'''= Difference between TBW and fat mass<br> | ||
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===Estimating Patient Weight=== | ===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 male TBW''' = 93.2 + 3.29[arm circumference (cm)] + 0.43[height (cm)] | ||
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''Obesity alters hepatic/renal clearance and volume of distribution (Vd) of many drugs'' | ''Obesity alters hepatic/renal clearance and volume of distribution (Vd) of many drugs'' | ||
{| class="wikitable" | {| class="wikitable" | ||
|+ Medication Adjustment in Obesity | |+ 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> | ||
|- | |- | ||
| '''Medication''' | | '''Medication''' | ||
| '''Dose Adjustment ''' | | '''Dose Adjustment ''' | ||
|- | |- | ||
| Morphine | | [[Morphine]] | ||
| Dose by IBW | | Dose by IBW | ||
|- | |- | ||
| Fentanyl | | [[Fentanyl]] | ||
| Dose by LBW; Alternative: Initial dose TBW, subsequent dose by IBW (risk over dose when use TBW) | | 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 | | [[Heparin]] | ||
| Same as non-obese | | Same as non-obese patient (80U/kg followed by 18U/kg/h using TBW) | ||
|- | |- | ||
| Vancomycin | | [[Vancomycin]] | ||
| | | 30mg/kg TBW (then follow serum levels) | ||
|- | |- | ||
| Aminoglycosides | | [[Aminoglycosides]] | ||
| Dose by ABW (C= 0.4; then follow serum levels) | | Dose by ABW (C= 0.4; then follow serum levels) | ||
|- | |- | ||
| Beta-lactams | | [[Beta-lactams]] | ||
| No good data, may consider doubling dose | | No good data, may consider doubling dose | ||
|- | |- | ||
| Carbapenems | | [[Carbapenems]] | ||
| No empiric change recommended | | No empiric change recommended | ||
|- | |- | ||
| Antifungals | | [[Antifungals]] | ||
| No empiric change recommended; use LBW when dosing weight-based agents | | No empiric change recommended; use LBW when dosing weight-based agents | ||
|} | |} | ||
==Airway Management== | ==Airway Management== | ||
Obesity associated with difficult bag-mask ventilation ( | Obesity associated with difficult bag-mask ventilation ([[BVM]]) and intubation | ||
* Consider prolonged pre-oxygenation period and two provider BMV | *Consider prolonged pre-oxygenation period and two provider BMV | ||
* May improve lung function through use of pre-intubation period of NIPPV | *May improve lung function through use of pre-intubation period of [[NIPPV]] | ||
** Obesity hypoventilation syndrome may cause chronic hypercapnia | **Obesity hypoventilation syndrome may cause chronic hypercapnia | ||
* Place | *Place patient in "ramp" position | ||
** Stack blankets behind patient's back to horizontally align external auditory meatus with sternal notch | **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) | *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 | *Increased BMI associated with higher rate of developing ARDS | ||
** Methods to improve oxygenation/ventilation: | **Methods to improve oxygenation/ventilation: | ||
*** Use PEEP 10 to improve oxygenation if needed | ***Use PEEP 10 to improve oxygenation if needed | ||
*** Place in reverse Trendelenburg ("beach chair" position) to improve ventilation | ***Place in reverse Trendelenburg ("beach chair" position) to improve ventilation | ||
*** Both may decrease CO so use cautiously in unstable patients | ***Both may decrease CO so use cautiously in unstable patients | ||
==[[Lumbar Puncture]]== | ==[[Lumbar Puncture]]== | ||
Obese patients have increased distance from skin to subarachnoid space | *Obese patients have increased distance from skin to subarachnoid space | ||
* Upright | *Upright patient positioning improves LP success | ||
* Estimated lumbar puncture depth (cm) = 1 + 17[weight(kg)/height(cm)] | *Estimated lumbar puncture depth (cm) = 1 + 17[weight(kg)/height(cm)] | ||
* Ultrasound may improve | *Ultrasound may improve identification of landmarks | ||
*If failure, consider fluoroscopy-guided procedure by IR | |||
==References== | ==References== | ||
<references/> | |||
[[Category:Misc/General]] | [[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.