Anesthesia for Bariatric Surgery
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What BMI is considered superobese
> = 50 kg / m2
Obese lean body weight equals
120% of lean body weight for their ht
Lean body wt calculation for men
50+ 2.3 x (ht (in) - 60)
Lean body wt calculation for women
45.5 + 2.3 x (ht (in) - 60)
As obesity how does fat mass compare to TBW?
Adipose tissue accounts for an increasing amount of TBW
Dosing based on TBW in an obese pt will result in over or underdosing?
Dosing based on IBW in an obese pt will result in over or underdosing?
How does the central volume compartment change in an obese pt?
How are the pharmacokinetics of most anesthetic drugs altered in an obese pt
Prolonged effects and less predictable
How does the Vd and elimination half life of lipophilic drugs change in an obese pt?
- Vd increased
- Elim half life increased despite increased clearance
How does the Vd of less lipophilic drugs (roc and vec) change in an obese pt?
Min or no change
What factors affecting Vd and Pd occur in the obese pt?
- decreased fx TBW
- increased adipose tissue
- increased lean body mass
- altered tissue protein binding
- increased blood volume and CO
- increased concentration free fatty acids, cholesterol, and alpha 1 acid glycoprotein
How is drug clearance affected in the obese pt? What factors contribute to this?
- Increased drug clearance due to:
- increased renal blood flow, GFR, tubular secretion
T or F, waist circ correlates with abd fat and is an ind predictor of disease?
Is android (central) or gynecoid (peripheral) obesity associated with increased incidence of CV disease?
- increased O2 consumption vs. gynecoid fat is less metabolically active
Describe android vs. gynecoid body fat dist
- Android- fat is central, truncal fat
- Gynecoid- fat is on hips, but, and thighs
What resp issues are obese pts prone to?
- obesity hypoventilation syndrome
What GI issues are obese pts prone to?
- Gallbladder disease
- Colon cancer
- Non-alc fatty liver disease
What heme issues are obese pts prone to?
What GU / Reproductive issues are obese pts prone to?
- Macrosomia- large BW infant
- Pre-eclampsia / eclampsia
- prostate ca
- urinary inc
Respiratory effects of obesity
-FRC and ERV
- increased WOB
- inefficient resp muscles
- decreased FRC and ERV
Results of resp issues associated with obesity
V/Q mismatch esp. in supine position
Why is pulmonary compliance decreased in the obese pt? How does it affect VC, FRC, and TLC
- Excess thoracic and abd fat leads to decreased chest wall and lung compliance
- All are decreased
What is the primary cause of reduced FRC in the obese pt?
What is ERV?
- Expiratory reserve volume
- FRC minus RV
Effects of reduced FRC
- small airway closure
- V/Q mismatch
- R to L shunting
- arterial hypoxemia
How does anesthesia affect FRC in an obese pt vs. a non obese pt?
FRC reduced up to 50% in an obese pt vs. only 20% in non obese pt
What BMI is considered obese?
> = to 30 kg / m2
What BMI is considered normal weight
18.5 - 24.9 kg / m2
What is the most sensitive indicator of the effect of obesity on pulmonary function?
T or F, OSA/ OSH has no effect on chronic inflammation?
F, cycles of hypoxia and reoxygenation activate the SNS causes elevated levels of pro inflammatory cytokines and oxidative stress of endothelium which increases systemic inflammation
SE r/t OSA
- Secondary polycythemia (due to hypoxemia)
- Increased risk cerebral vascular disease
What is Pickwickian syndrome?
- AKA obesity hypoventilation syndrome
- May result from LT OSA
- leptin rx may play a role
- most common in older pts and the super obese
regulates food intake and body weight
SE r/t Obesity hypoventilation syndrome
- Hypoxia and hypercarbia
- RV enlargement and failure
How are OSA and OHS differentiated?
OSA complete obstruction, lasts 10 secs or longer, occurs 5x or more / hr
OHS partial obstruction, lasts 10 secs or longer, occurs 15x or more / hr
both have a decrease in O2 sat of at least 4%
How are CO and total blood volume affected by obesity?
- Both increased
- up to 20-30 ml / kg of excess body fat
What type of ventricular hypertrophy is typically seen in obese pts?
Eccentric (increased volume)
T or F, an obese pt with a normal BP also has normal CO?
F, CO is still increased
How are pre-load, after load, PA pressures, and stroke work affected in obesity?
Why do obese pts have hypertrophy, decreased compliance, diastolic dysfunction, and pulmonary edema?
Increased SV and ventricular dilation causes increased LV wall stress
Why do obese pts have increased total blood volume?
- Perfusion of excess fat
- Polycythemia of chronic hypoxia
Is diastolic or systolic HF more common in obese pts?
Are the cardiac changes and associated affect on function that occur with obesity reversible with weight loss?
Yes many are
How are gastric volume and acidity affected in obesity? Why?
- Increased gastric volume, >25 ml
- increased acidity, <2.5
- Due to delayed gastric emptying 2/2 increased abd mass which causes astral distention, gastrin release, and decreased pH
How are the clearance of hepatically cleared drugs affected by obesity?
No change even though liver function is altered
S/sx of non-alcoholic steatohepatitis (fatty liver disease)
- Elevated LFTs
- Abn liver histology
Glucose tolerance in the obese pt
- Impaired, leads to DM2
- Hyperinsulinemia activates SNS leading to Na retention, ins rx, and dyslipidemia
T or F, subclinical hypothyroidism seen in up to 25% of obese pts?
Does metabolic syndrome affect more men or women?
Metabolic syndrome puts pts at risk for?
- DM2 and atherosclerotic disease
- all around mortality
Features of metabolic syndrome
- Abd obesity
- Insulin rx
- Decreased HDL
- Proinflammatory state
- Procoag state
- Endothelial dysfunction
- Polycystic ovary syndrome
- Non -alc fatty liver disease
What are the clinical criteria for diagnosis of metabolic syndrome?
- At least 3 of the following:
- abd obesity (> 102 cm for men and > 80 cm in women)
- elevated fasting glucose (> 110)
- HTN (>= 130-85)
- Low HDL (< 40 for men and <50 in women)
- High triglycerides (>= 150)
What change in the renal system may lead to increased drug clearance?
Increased GFR and renal blood flow
What effect does activation of SNS and RAAS and compression of the kidneys have?
- Increased tubular reabsorption
- Impaired natriuresis
- developed in early 90's
- combined gastric restriction to limit food intake and some malabsorption of the small intestines
- minimal complications compared to prior methods
- reduces stomach size only, by about 2/3's
- restrictive procedure
- restriction and malabsorption
- intestine is bypassed to a greater extent than in RNY
- greater weight loss but also higher complications
Cons of RNY
- Malabsorption leading to vit deficiencies (B12)
- Decreased Calcium abs may lead to osteoporosis
- Risk anastomotic leaks
- Dumping syndrome
What is ghrelin?
- Appetite stimulant
- Reduced with both RNY and sleeve gastrectomy
Pros of RNY
- sustained wt loss
- decreased ghrelin secretion
- potential reversal of DM, HTN, non-alc fatty liver, OSA, cardiac dysfunction, GERD, arthritis, infertility, stress inc
Early complications of bariatric surgeries
- bowel obstruction
- DVT / PE
Late complications of bariatric surgeries
- cholecystitis or cholelithiasis
- pouch dilation
- GERD / dysphagia
- incisional hernia
- vitamin deficiencies
Contraind to bariatric surgery
- Chronic alcohol or drug dependence
- Uncontrolled severe psych illness
- cardiopulm disease that would prohibit the surgery
T or F, BMI >= 50 and cig smoking are associated with greater rate of complications?
Super obese pts have an associated increased LOS and mortality from bariatric surgery, T or F?
- F, no increase in mortality
- There IS an increased LOS and increased risk RF and assisted ventilation
Is OSA assessment by polysomnography required for pts undergoing bariatric surgery?
What criteria are evaluated with the stop bang score?
- Observed apnea
- Pressure (HTN)
- BMI > 35
- Age > 50
- Neck circ > 15.75 "
- Gender- male
What stop bang score = high risk for OSA?
>= 3 yes answers
T or F, wt and BMI correlate with difficult intubation?
What pre-op meds are given for pts undergoing bariatric surgery?
- 5000 U SQ heparin
- scop patch (if not contraind), want to avoid PONV
- if anxiolytic is given ensure supplemental O2 and pulse ox are used!!
Prop and succ are dosed on ____?
Induction dose prop, etomidate, fent, and remi are dosed on _____?
Vec, roc, benzos, and barbs are dosed on _____?
IBW- but not really done in practice...
- alpha 2 agonist
- sedative, analgesic, sympatholytic, and anxiolytic effects
benefits of using dexmedetominine
reduces requirement for volatiles, sedatives, and analgesics
SE of dexmedetominine
bradycardia, hypotension, sinus arrest, transient hypotension
- 120% of IBW
- loading dose 1 mcg/ kg over 10-20 mins then 0.2-0.7 mcg/ kg / hr
T or F, pts can wake up low dose dexmedetominine?
T, can wake up on 0.2 mcg/ kg/ hr
- alpha 2 agonist
- reduces anesthetic and analgesia requirements
Optimal position for induction
- pre-oxygenate with ramp and reverse T-burg
- Sniff position with a ramp
T or F, the forearm BP is less accurate than the upper arm BP in an obese pt
F, both accurate
Best volatile to use for bariatric surgery?
des- faster recovery and higher O2 sat
PEEP of ___ cmH20 has been shown to maintain FRC and improve oxygenation
Position for RNY
OGT and RNY
- Insert to decompress stomach
- Remove BEFORE stomach stapling!!
Is incidence of anastomotic leak increased with the use of Bipap / Cpap post-op?
What monitoring is required post-op on floor?
pulse ox, ETCO2 sometimes as well
Major issues of post-op care for bariatric surgery pts?
Underlying OSA complicated by anesthetic agents and need for post-op pain management
NSAIDs and bariatric surgery
Avoided if intestinal anastomosis
Is it ok to blindly place an OGT in a pt s/p RNY or gastric sleeve?
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