Unit 12 - Obesity Flashcards
how many calories are required to produce one gram of body fat
9
top 2 leading causes of preventable death
- smoking
- adult obesity
diseases that contribute to obesity
- Cushing’s
- hypothyroidism
- depression
- eating disorders
- PCOS
genetic conditions that contribute to obesity
- Prader-Willi syndrome
- Bardet-Biedl syndrome
what percent of american adults are obese
33
android obesity is often equated to what body shape
diseases assoc. with this type of fat accumulation
apple
increased risk ischemic heart disease, HTN, DM, dyslipidemia, death
gynecoid obesity is often equated with what body shape
diseases associated with this fat distribution
pear
joint disease, varicose veins
at what point does adipose become pathologic
when it releases significant quantities of free fatty acids and cytokines
terminal consequence of excess adipose tissue
insulin resistance and systemic inflammation
what fat storage site releases the highest quantities of free fatty acids and cytokines
visceral fat
is android obesity more common in men or women
men
waist sizes assoc. with increased health risks with android obesity
men > 40 inches
women > 35 inches
type of obesity more common in women
what is it characterized by?
gynecoid
gluteal and femoral fat accumulation
how is gynecoid fat different from abdominal fat
gynecoid fat is metabolically inactive, primarily used for energy storage
type of fat associated with reduced incidence of non-insulin dependent diabetes
gynecoid
what is metabolic syndrome?
several disease states that coincide with obesity
diagnosis requires 3 or more:
- fasting glucose > 110 mg/dL
- abdominal obesity (waist > 40” men, 35” women)
- serum triglyceride level > 150 mg/dL
- serum HDL < 40 mg/dL in men
- serum HDL < 50 mg/dL in women
- BP > 135/85 mmHg
CV risk in pts with metabolic syndrome vs. general population
50-60% greater
BMI calculation
- convert weight in lbs to kgs
- convert height from inches to cm ( in x 2.54 )
- convert cm to meters ( cm/100 )
- BMI = kg/m squared
why is BMI not a perfect measure of fat mass
- doesn’t take fat distribution into account
- can be skewed with a large percentage of muscle mass
BMI for:
- underweight
- normal
- overweight
- class 1 obesity
- class 2 obesity
- morbid obesity (class 3)
- underweight: < 18.5
- normal: 18.5 - 24.9
- overweight: 25-29.9
- class 1 obesity: 30-34.9
- class 2 obesity: 35-39.9
- morbid obesity (class 3): > 40
child body weight class (2-18 yrs old):
- overweight
- obese
- severely obese
- overweight: 85th-94th percentile
- obese: 95th-98th
- severely obese: 99th
what is ideal body weight?
how is it calculated?
BMI assoc. with lowest risk of body weight-related comorbidities
men: height (cm) - 100
women: height (cm) - 105
how does obesity affect:
- FRC
- ERV
- RV
- closing volume
- vital capacity
- FRC decreases
- ERV decreases
- RV remains constant
- closing volume increases
- vital capacity decreases
why is pulmonary blood flow increased in obesity?
increased CO
factors assoc. with obesity that inhibit lung inflation
- chest fat (compresses rib cage, hinders expansion)
- abdominal fat (shifts diaphragm cephalad and compresses lungs)
- kyphosis and lordosis develop over time and alter geometry of ribcage
relationship between FRC and BMI
inversely proportional
what causes distal airway collapse during tidal breathing in obese patients
what are the consequences of this
FRC decreased below closing capacity
leads to V/Q mismatch, shunt, hypoxemia, increased dead space
how does general anesthesia affect FRC in obese vs. non-obese pts
decreases by 50% in obese
decreases by 20% in non-obese
why is PaCO2 usually normal in obese pts
high diffusing capacity of CO2 and favorable characteristics of CO2 dissociation curve
why do obese pts have an increased O2 consumption and CO2 production?
what vent changes should be made in these pts
fat is a metabolically active organ
increase minute ventilation to maintain normal blood gas tensions
optimal tidal volume for an obese patient
6 - 8 mL/kg ideal body weight
why is the obese patient predisposed to oxygen desaturation during apneic periods
smaller FRC + increased O2 consumption
optimal positioning for airway management of an obese patient
head-elevated laryngoscopy position (HELP)
elevate head, shoulders, and upper body above the chest - should be able to envision a horizontal line from sternal notch to external auditory meatus
optimal preoxygenation for an obese patient
100% FiO2 + CPAP 10 cm H2O until end-tidal O2 exceeds 90%
prolongs desat time by 50%
optimal position to extubate an obese patient
reverse Trendelenburg - relieves pressure on thorax, improves FRC
best way to control PaCO2 in obese patient
adjust RR, not Vt
does obesity alone mandate RSI?
no - make decision on case by case basis
strategies to maximize postoperative oxygenation in the obese pt
- CPAP or BiPAP after extubation
- HOB 30 degrees
- early ambulation
- control surgical pain
- incentive spirometry
when is postop hypoxemia most likely to occur in the obese pt
immediately after extubation and up to 2-5 days postop
why is cardiac output increased in the obese patient
increased stroke volume (HR usually unchanged)
CO in obese patients
increased by 100 mL/min for every extra kg of fat
why do obese patients need an increased blood volume and CO
proliferation of adipocytes requires that vasculature grows to support growth
factors that lead to increased workload on myocardium in obese patient
how does the heart compensate
- larger vascular network
- larger blood volume
- increased O2 consumption
heart dilates and becomes thicker, eventually causes diastolic dysfunction
why are obese pts less tolerant of excessive fluid amin
reduced ventricular compliance and diastolic dysfunction increase the risk of fluid overload
what weight should be used to calculate periop fluid requirements in obese pts
lean body weight
what leads to systolic dysfunction in obese pts
eventually the heart dilates beyond its ability to increase wall thickness
what contributes to HTN in obese pt
- hyperinsulinemia
- SNS and RAAS activation
- atherosclerosis
- elevated cytokine in plasma
common EKG changes in obese pts
- low voltage
- LAD
- RAD
- prolonged QT
- ischemia
- dysrhythmias
what causes low voltage EKG in obese pts
increased distance between heart and leads
what causes left axis deviation in obese pts
stomach pushes the heart up and to the left
also LVH secondary to volume overload and HTN
what causes right axis deviation in obese pts
RVH from OSA and volume overload
what causes ischemia in obese pts
O2 supply and demand mismatch
what causes dysrhythmias in obese pts
- fatty infiltration of conduction system
- myocardial hypertrophy
- hypoxemia
- hypercarbia
- obesity hypoventilation syndrome
- ischemic heart disease
what leads to biventricular failure in obese patients
- increased blood volume results in increased pulmonary blood volume, pHTN, increased RV workload, and right heart failure
- increased blood volume results in increased CO, increased LV workload, and LV failure
which is calculated based on IBW: water or lipid soluble drugs?
water soluble
which is calculated based on TBW: water or lipid soluble drugs?
lipid soluble
4 factors that alter volume of distribution in obese pts
- increased blood volume
- increased CO
- altered plasma protein binding
- large fat mass
which increases in obese patients: Vd of water souble or lipid soluble drugs?
both increase - fat mass and muscle mass both increase
(Vd for lipid soluble increases more)
what weight should be used to dose the obese patient
LBW
what is LBW?
how is it estimated?
lean body weight is the IBW + extra muscle mass that occurs with weight gain
estimated by IBW x 1.3
what volatiles are best for obese patients?
those with lower blood:gas coefficients (volatiles are lipophilic) - ex. sevo or des
why is N2O generally avoided in obese patients?
restricts max FiO2 that can be delivered
should midazolam be dosed based on TBW or LBW?
TBW
dosing rocuronium and vecuronium - TBW or LBW?
LBW
dosing propofol - LBW or TBW?
induction - LBW
maintenance - TBW
fentanyl and sufentanil dosing - LBW or TBW? why?
initial doses are based on TBW because of fat solubility and large Vd
maintenance dosing is based on LBW (increased Vd = prolonged elminination half-life)
why is the loading dose of propofol based on LBW?
its offset is caused by redistribution, not clearance
why is TBW used to calculate succinylcholine dosing
combination of increased blood volume and increased pseudocholinesterase deficiency
why is remifentanil dosed based on LBW
since it’s rapidly cleared by plasma esterases, it doesn’t behave like a high Vd drug
why is midazolam administered by TBW
increased central volume of distribution - may cause oversedation in the obese patient
dosing epidural LA in obese patients
reduce to 75% of the normal dose due to engorgement of epidural veins and increased epidural fat content = greater LA spread in epidural space
what is responsible for airway patency
balance between pharyngeal muscles that dilate airway and negative pressure of inspiration that collapses it
why do obese patients have an increased tendency for airway collapse?
fat tends to accumulate in the lateral walls of pharynx, causing the internal diameter to narrow
how is OSA defined
cessation of airflow for at least 10 seconds (apnea) with 5 or more unsuccessful efforts to breathe (obstruction) and a greater than 4% reduction in SaO2
what is hypopnea?
50% reduction in airflow for 10 seconds, 15 or more times per hour, and is linked to snoring and decreased O2 sat
things that increase the likelihood that a patient has OSA
- BMI > 30
- abdominal fat distribution
- neck girth > 17” for men, 16” for women
OSA is an independent risk factor for what 3 complications
- HTN
- cardiovascular morbidity
- death
what results in snoring in OSA
sleep = decreased upper airway tone = increased upper airway resistance = obstruction
apnea hypopnea index
helps quantify the severity of OSA - derived by the number of apnea episodes and hypopnea divided by total hours of sleep
mild = 5-15 episodes/hr
moderate = 15-30 episodes/hr
severe = > 30 episodes/hr
classic triad of dysfunctional sleep
- apnea or snoring with hypopnea during sleep
- arousal from sleep
- daytime somnolence
definitive test for OSA
polysomnography
STOP-BANG questions for OSA screening
Snoring
Tiredness
Observed apnea
Pressure (HTN)
BMI (>35)
Age (>50)
Neck circumference (>40 cm)
Gender (male)
high risk for OSA = 3 or more questions yes
low risk for OSA = less than 3 yes
what is obesity hypoventilation syndrome?
aka Pickwickian syndrome
long-term consequence of untreated OSA
over time, resp. center in medulla fails to respond to hypercarbia appropriately
classic syndrome of obesity hypoventilation syndrome
apnea during sleep without any respiratory effort
diagnostic criteria for obesity hypoventilation syndrome
- BMI > 30
- awake PaCo2 > 45 mmHg
- dysfunctional breathing during sleep
s/s obesity hypoventilation syndrome
- obesity
- hypersomnolence during the day
- hypoxemia
- hypercarbia
- respiratory acidosis
- compensatory metabolic alkalosis
- polycythemia
- pulmonary HTN
- right heart failure
most sensitive sign of an anastomotic leak following gastric bypass
what are other symptoms?
unexplained tachycardia
abdominal pain, shoulder pain, fever, pelvic pain, substernal pressure, dyspnea, hypotension, oliguria, increased thirst, restlessness, hiccups
3 different types of procedures used for surgical weight loss
which is the least invasive?
- malabsorption
- restriction - least invasive
- combination
vitamin deficiencies patient is at risk for after a jejunoileal bypass surgery?
- vitamin K
- vitamin B12
- iron
- folate
what type of surgical weight loss surgery yields the best weight loss and improvement of comorbidities?
combination malabsorption/restriction (Roux-en-Y gastric bypass)
most significant risk factor for development of nonalchoholic liver disease and nonalchoholic steatohepatitis
obesity
what is Mu Huang?
complications of use?
a natural source of ephedrine, an indirect-acting adrenergic agonist and thermogenic agent used as ingredient in appetite suppresants
complications of adrenergic overstimulation - HTN, CVA, sz, death
what is phentermine?
a norepi reuptake inhibitor that acts as an appetite suppressant and increases BMR
what is sibutramine?
associated risks?
a norepinephrine and serotonin reuptake inhibitor that acts as an appetite suppressant and increasess BMR
risk of adrenergic overstimulation and serotonin syndrome
what is orlistat?
associated risks?
a lipase inhibitor that reversibly binds to lipase and hinders absorption and digestion of consumed fats
vitamins A, E, D, and K must be supplemented. insufficient vitamin K will impair certain clotting factors
vitamin K synthesized clotting factors
2, 7, 9, and 10
