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Flashcards in Obesity Deck (50)
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Definition of overweight and obesity?

  • Overweight Defined: “increased body weight above a standard related to height”
  • Obesity Defined: “excessive body weight for the patient’s age, gender and height” (body weight of 20% or more above ideal weight)
  • US population:
    • 68%  overweight
    • 33%  obese
    • 25% of children are obese


What is ideal body weight? How do you calculate it?

  • Ideal Body Weight:  weight associated with maximum life expectancy for a given height and gender
    • IBW (male) = 105 lb + 6 lb for each inch > 5 ft.
    • IBW (female) = 100 lb + 5 lb for each inch > 5 ft
    • Broca’s Index:  IBW (kg) = height (cm)-x
      • x = 100 males, x = 105 females<remember this one
    • Miller 8th:
      • Male: 50 kg + 2.3 kg for each 2.54 cm (1 in) >152 cm (5 ft) 
      • Female: 45.5 kg + 2.3 kg for each 2.54 cm (1 in) >  152 cm (5 ft)
  • IBW useful in calculating some drug doses to avoid toxicity or hemodynamic instability 
  • In morbidly obese patients, increasing the IBW by 20%  gives an estimate of LBW. In nonobese and nonmuscular individuals, TBW approximates IBW.


What is BMI? How do you calculate it?

  • BMI is an accepted measure of body habitus that normalizes adiposity for height
  • Calculation (memorize):
    • BMI= weight (kg)/ height2 (m)
  • cannot distinguish overweight and overfat as heavily muscular people can easily be classiied as overweight using BMI
    • other factors such as age and fat distribution should be taken into consideration, amonth other health predictors that utilize concept of BMI


Various BMI stratifications?

  • Overweight defined as BMI of 25-29 kg/m²
    • Approximate body weight 20% more than ideal body weight
  • Obesity is defined as BMI > 30 kg/m²  
  • Clinically Severe Obese: (formally Morbid Obesity): BMI > 40 kg/m2 
  • Super-Obese: BMI > 50 kg/m2
  • Super-Super Obesity: >60 kg/m2
  • BMI > 30 (obese) is associated with increased morbidity related to stroke, ischemic heart disease, HTN, and diabetes


Various distributions of body fat?

  • Android obesity (android fat distribution)
    • Abdominal (central) obesity
    • More common in men, higher incidence of metabolic disturbances, increased risk of ischemic heart disease, stroke, diabetes, death
  • Gynecoid obesity (gynecoid fat distribution)
    • Fat around hips and buttocks
    • More common in females
  • Waist circumference & risk of pathophysiology (>102 cm (40") men or >88 cm (35") women)


What disturbances are associated with obesity

  • Obstructive sleep apnea/ hypoventilation syndrome
  • Restrictive lung disease
  • Hypertension
  • CAD
  • Hyperlipidemia
  • Delayed gastric emptying/ GERD
  • Type II Diabetes Mellitus
  • Gall bladder disease (cholelithiasis)
  • Cirrhosis/ Fatty liver disease
  • Venous stasis/ Thromboembolic disease
  • Degenerative joint/disc disease
  • Increased breast, prostate, cervical, uterine, and colorectal cancer


Lung volume alterations in obesity?

  • Chest wall and lung compliance reduced
  • Lung volume changes
    • Reduced Functional Residual Capacity (FRC)
    • Reduced Expiratory reserve volume  (ERV)
    • RV and CC are not changed
    • However….the relationship between FRC and CC is adversely affected
    • FEV1 and FVC usually within normal limits
    • Reduced Tidal Volume
      • TV may fall into the range of the Closing Capacity (CC)
  • from added weight of thoracic cage, chest wall and abdomen, which impedes the diaphragm


Pulm physio changes in obesity?

  • Increased pulmonary blood volume
  • Increased oxygen consumption and carbon dioxide production
    • because of obese pt's increased body mass, o2 consumption and CO2 production. obese pt must increase MV to compensate
    • rapid, shoow breathing to use less energy and prevent fatigue
  • High minute ventilation; increased work of breathing
  • As obesity worsens you will see lung disease and pulmonary hypertension-- > RHF
    • (PFTs may remain normal until this occurs)


Respiratory alterations in obese patient r/t positioning?

  • For the obese patient respiratory changes are exaggerated with operative positions
    • Supine
    • Trendelenberg
    • Lateral
    • Prone
  • Rapid de-saturation may be seen when anesthesia is induced in recumbent/supine position
    • sit up as much as possible


  • Deviations in lung volumes lead to:
    • V/Q mismatch
    • hypoxemia
    • Increased right to left intrapulmonary shunt
  • PIC:
    • ​upright- obese and nonobese have similar lung volumes but still restrictive in obese
    • obese supine - significant decrease in lung volume
    • obese trendelenberg- restrictive physio even wrose
      • ​can cause V/q mismatch, hypoxemia and right ot left intrapulmonary shunt


Airway changes in obesity?

  • TMJ & atlanto-axial joint and cervical spine movement limited by upper thoracic and low cervical fat pads
  • Redundant tissue folds in the mouth and pharynx = narrowed upper airway
  • Short, thick neck: measure neck circumferenceSTRONG predictor of difficult intubation
    • 40cm = 5% incidence difficult intubation
    • 60cm= 35% incidence difficult intubation 
  • Fat in suprasternal, presternal, posterior cervical and submental regions- difficult laryngoscopy
  • Shortened distance between mandible & sternal fat pads
  • OSA = increase risk of excess pharyngeal tissue on lateral walls
    • inverse relationship b/w obesity nf pharyngeal area size
    • changes shape of oropharynx into an ellipse with short transverse and long anteroposterior axis
    • contribute to airway obstruction
    • almost always need OPA to help with mask ventilation
  • Creates difficulty maintaining mask airway
  • Creates difficult laryngoscopy and intubation


Obstructive sleep apnea?

  • Obesity is an independent risk factor for OSA
  • Characterized by
    • Apnea >10 seconds  total cessation of airflow despite respiratory effort against a closed glottis- rocking horse"
    • Hypopnea  is 50% reduction in size or number of breaths that lasts at least 10 seconds compared to normal; partial or intermittent collapse of pharyngeal airway during sleep
  • Obese pt have airway narrowing d/t excess tissue. decrease in upper airway muscle tone during REM sleep.
  • cannot predict OSA on BMI, Neck circumference, PFT or daytime ABG or questionaiires
  • 80-90% pt with sleep apnea are undiagnosed
  • Need polysomnography
    • ​apneic-hypopneic index is total number of apneic or hypopneic events (or both) per hour of sleep
    • severity of OSA directly related to magnitude of index



  • Daytime somnolence
  • SNS activation in response to hypoxemia-- may aloshave HTN
  • Habitual snoring
  • interrupted breathing during sleep (apneic spells followed by short gasps, grunts, reuscitative snorting)
  • impaired daytime performance
  • morning headache
  • irritability
  • increased neck circumference (>40-42 cm at cricoid cartilage)


OSA Risk factors?

  • Middle age
  • Male
  • Obesity  (BMI>30)
  • ETOH use
  • Drug induce sleep aids
  • Abdominal fat distribution
  • Neck girth (41cm)
    • >17 inches for men
    • >16 inches for women


What do apenic episodes of OSA lead to? Severity of OSA?

  • Frequent episodes of apnea during sleep leads to
    • Chronic hypoxia, hypercapnia, pulmonay and systemic vasoconstriction (HTN) 
      • get lots of SNS activation d/t chronic hypoxemia
      • pro-inflammatory state
      • get historical info from family member
    • Snoring
    • Sleep fragmentation/daytime somnolence
    • Impaired concentration
    • Morning headache
  • Severity of OSA is graded by # of apnea or hypopneic episodes during 1 hour observation
    • Mild  >5 but ≤15 /hour
    • Moderate 15 to 30 /hour
    • Severe >30 events/hour


What is Pickwickian syndrome (obesity hypoventilation syndrome)

  • Complication of extreme obesity/ long term OSA
  • Extreme obesity (>40 BMI) with:
    •  hypercapnia
    • cyanosis induced polycythemia
    • somnolence
    •  eventual right sided heart failure 
    •  pulmonary HTN
  • PCO2 >45 mm Hg in an obese patient without significant COPD is diagnostic
  • Clinically distinct from OSA-- progression from OSA
  • OSA you have nocturnal sleep disruption
    • respiratory effort without ventilation
  • OHS you have nocturnal central apneic events (apnea without respiratory effort)


Characterization of pickwickian syndrome (obesity hypoventilation syndrome)

Characterized by

  • Obesity
  • Hypercapnia (>45 at RA, daytime-- increase monitoring in PACU necessary)
  • Daytime hyper-somnolence
  • Arterial haypoxemia
  • Pulmonary hypertension
  • Respiratory acidosis
  • Right sided heart failure
  • Airway Difficulty


CV Alterations in Obesity?

  • Increased total blood volume
  • Increased Cardiac Output
    • Expanded blood volume puts strain  on myocardium
  • Increased renin-angiotensin system & SNS activity: HTN (Arterial hypertension risk is twice as high as for lean men and women)
    • releated to insulin effects on SNS
    • Insulin activated adipocytes to release angiotensinogen, which activates the RAAS pathway, leading to sodium retention and development of HTN
    • circulating cytokines may cause damage to and fibrosis of arterial wall, causing arterial stiffness
  • Risk of CAD is double and presents with angina, CHF, acute MI and sudden death
  • Increased left-sided heart pressures and left ventricular hypertrophy
    • leads to concentric hypertrophy--> first diastolic and then systolic dysfunction


Factors to consider preop r/t CV alteration in obesity?

  • Assessment pre-operatively is essential to determine their cardiac tolerance
  • Obese patients have limited reserve for 
    • hypotension
    • hypertension
    • tachycardia 
    • fluid overload


Hematologic alterations in obesity?

  • Polycythemia & Hypercoagulation
  • Thromboembolic Risk
    • Risk of DVT is doubles
    • Polycythemia leads to increased blood viscosity; increased fibrinogen levels
    • Increased intra-abdominal pressure
    • Immobility leads to venostasis


GI alterations in obesity?

  • Increased incidence
    • Hiatal hernia
    • GERD
    • Gallbladder disease
  • High risk for aspiration pneumonitis
    • Greater gastric volumes >25ml related to delayed gastric emptying
    • Increased gastric acidity pH<2.5 (increased parietal cell secretion)
    • Gastric emptying delays promoted by increased abdominal mass


Hepatic alterations in obesity?

  • Fatty infiltration of liver
    • High prevalence of nonalcoholic fatty liver disease
      • fatty infiltration reflects the duraiton more than the degree of obesity
      • 1/3 obese pt LFT are disrupted
    • Inflammation
    • Cirrhosis
  • Abnormal LFTs
    • Weight loss (even 5 lbs) can reverse the elevated liver enzymes
      • Obesity causes excess
        • intrahepatic triglycerides,
        • impaired insulin activity,
        • inflammatory cytokines
      • lead to destruction in hepatocytes and disruption of hepatic phsyiology and architecture
      • fat is proinflammatory
      • no clear correlation with routine LFT and cpaacity of liver to metabolize drugs
    • Caution with Fluorinated volatile anesthetics
      • theoretical risk, increased risk for halothane hepatitis


Renal alterations in obese pt?

  • Increased renal plasma flow and increased GFR
  • Increased renal tubular resorption and impaired naturesis secondary to SNS and renin-angiotensin system activation (also physical compression of the kidney)
  • Eventually nephron function can be lost


Endocrine alterations in obesity?

Metabolic syndrome occurence?

  • Obese patients secrete more insulin, BUT resistant to the effects of insulin
    • Develop Non-insulin-dependent (type 2) diabetes
  • Metabolic Syndrome
    • Presence of at least three of the following signs: 
      • large waist circumference (central obesity)
      • high triglyceride levels
      •  low levels of high-density lipoprotein (HDL) cholesterol
      • glucose intolerance
      •  hypertension. 
    • pt with metabolic syndrome are at much higher risk of morbidity/mortality r/t obesity
      • ​doubles CV risk


There is a high prevalence of hyperglycemia, insulin resistance, and diabetes in obesity.

Disturbances in insulin regulation.  At the cellular level, fatty infiltration of the pancreas leads to decreased secretion of insulin while at the same time, engorgement of adipocytes promotes insulin resistance.  In addition, the engorged adipocytes are capable of secreting various cytokines and tumor necrosis factor.  These cytokines worsen glucose intolerance by decreasing the secretion of adiponectin, a powerful insulin sensitizer.  Leptin, another hormone secreted by adipose tissue, accelerates inflammatory changes.  All these substances stimulate the liver to produce increased levels of low-density lipoproteins and apolipoprotein B.  As a result, the pancreas is stimulated to secrete more insulin and pancreatic polypeptides, leading to inflammatory changes. (Stoelting, 7th ed. 2017, p. 387)


Musculoskeletal changes in obesity?


  • Osteoarthritis and degenerative joint disease
    • Mechanical loading of weight-bearing joints
    • Inflammatory response


CNS changes in obesity?

ANS dysfunction

Peripheral neuropathies


Hyperlipiedmia and obesity?

  • Hyperlipidemia is associated with obesity
    • Increased LDL and decreased HDL cholesterol linked to atherosclerosis
  • Can lead to :
    • Premature coronary artery disease
    • Premature vascular disease
    • Pancreatitis


Pharmacology alteration in obese patient?

  • Increased blood volume and CO
  • Decreased total body water
  • Adipose and lean tissue increase
  • Variable alterations in protein binding
  • VOD- central compartment unchanged
  • dosing on LBW/TBW varies source to source
    • ​most clinical useful approach is to calculate drug dosing based on LBW rather than TBW
      • ​LBW more highly correlated with CO and drug clearance


  • Metabolism
    • Phase I (oxidation, reduction, hydrolysis) unaffected
    • Phase II (glucuronidation, sulfation) enhanced
  • Clearance
    • Hepatic clearance unchanged despite histological and LFT alterations
    • Renal clearance of drugs increased (increased GFR, RBF, and tubular secretion)
    • Lipophilic drugs have an increased elimination half-life because of increased Vd but have normal clearance


Summary of drug dosing for obese patient?



Roc, vec?

Cis, Atracurium





  • Propofol
    • induction= LBW
    • maintenance- TBW
  • Succinylcholine
    • Intubation- TBW
  • ROC/VEC- LBW both induction and maintenance
  • Cisatracurium- TBW
  • Atracurium- tbw or lbw
  • Fentanyl/Sufentanil
    • loading= TBW
    • Maintenance- LBW
  • Remifentanil
    • Maintenance- LBW
  • Midaz- TBW both loading and maintenance
  • Epidural- 75% of normal dose


in genearl, NMB exhibit prolonged DOA and recovery in obese patient. use PNS monitor frequently!!


Use of precedex in obses patients?

  • Nice adjunct to consider when respiratory depression avoidance is priority
  • 0.2-0.7 mcg/kg/hr to reduce analgesic and anesthetic requirements
  • Dose on TBW


VA use in obses patients?

  • Metabolism is greater in obese patients = greater increase in inorganic fluoride
  • Greater incidence of halothane hepatitis
  • N20 often avoided to maximize PaO2
    • only because obsese patient usually needs high FIo2, use of N2O not contraindicated