Flashcards in anesthesia for obese pt./bariatric surgery Deck (52)
what is obesity?
-abnormally high percentage of body fat
-BMI > 30 accepted by clinicians
-waist circumference (WC), waist: height ratio (WHR), and waist: stature ratio (WSR) correlate better with mortality and obesity related diseases
what groups are obesity seen more with?
-women (33%), men (27%)
-minorities: Hispanics/blacks > whites
how does obesity affect health risk?
-decreased life expectancy
-50-100% greater risk for death
-increased depression, OSA, gall bladder disease, reflux, cancer
-independent risk factor for: ischemic heart disease, HF
-obesity related: HTN, Type II DM, CAD, stroke, malignant tumors
*1 kg wt. gain per year x 10 years increases risk to health
describe anatomic distribution of body fat
-indicator of increased health risks
-associated with certain pathophysiological characteristics
*central android (apple)
*peripheral gynecoid or gluteal (pear)
describe central android fat distribution
-truncal, visceral (abdominal) fat
-encouraged with increased ETOH
-increased O2 consumption, CV disease, ventricular dysfunction
-metabolically active adipose tissue: increased free fatty acids (FFA), LDL, insulin resistance
describe peripheral gynecoid or gluteal fat distribution
-hips, butt, thigh fat
-less CV risks since metabolically static adipose
describe waist circumference measurement
-new standard for determining abdominal obesity
-represents abdominal fat
-independent predictor of disease
*greater than 102 cm (40 in.) for men and 88 cm (35 in.) for women increases risk of IHD, HTN, DM, and death
describe waist : height ratio
if > 0.9 in women and > 1.0 in men increased mortality and morbidity
*ex: man height of 5' 6'' and WC 66 in. has WHR of 1.0
describe waist : stature ratio
recommended that WC no exceed 1/2 the stature (or height)
what are obesity effects on the respiratory system?
-increased fat intra-abdominally, chest wall, and diaphragm
*decreased chest wall compliance (esp. lying supine)
*impaired respiratory muscle strength
*decreased lung volumes/capacities, functional residual capacity (FRC), expiratory reserve volume (ERV), vital capacity (VC), total lung capacity (TLC)
-decreased FRC d/t markedly reduced ERV; residual volume (RV) is UNCHANGED (anesthesia can further reduce FRC up to 50%)
-diaphragm moves cephalad when supine
**obese pt. will desat quickly even after preoxygenation
what is the most sensitive indicator of effects of obesity on pulmonary function testing?
-expiratory reserve volume (ERV)
*when it drops, FRC is reduced
how does obesity affect O2 demand and supply?
-increased demand: increased O2 consumption, increased CO2 production, increased alveolar ventilation
-decreased supply: decreased chest wall compliance, decreased lung volume, decreased FRC, premature air closure, V/Q mismatch, arterial hypoxemia
both: increased work of breathing, decreased respiratory muscle efficiency
describe obesity effects on FRC
-decreased FRC causes closing capacity (CC) to exceed normal tidal volume
-supine decreases FRC even more d/t cephalad diaphragm
-airway closure, atelectasis
-VQ mismatch, intrapulmonary shunt
*rapid desaturation during apnea time on induction regardless of preoxygenation
*must preoxygenate longer and intubate quick
describe obesity effects on VO2 and CO2
-increased VO2 (O2 consumption) and increased CO2 production
-increased metabolic activity of excess fat increases demand
-stress on supporting respiratory muscles also increases demand
how does the respiratory system attempt to compensate for respiratory issues of obesity?
-extra work of breathing to maintain augmented ventilation
**VO2 used for respiratory muscle work instead of vital functions so instead increases demand further
what effects occur d/t increased pulmonary blood volume?
-further decreases compliance
-chronic hypoxia causes polycythemia (dusty/ashy skin)
-increased pulmonary blood volume causes pulm. HTN, cor pulmonale
what promotes airway closure in obesity?
increased tissue within bony enclosures can only grow towards inside the airway, creating a more narrow airway
describe obesity hypoventilation syndrome
-10% of morbidly obese have OHS
-clinically similar to OSA, hypoxemia
*hypercapnia while awake is cardinal sign (more CO2 is produced than can be eliminated)
-respiratory center is desensitized and ventilation becomes dependent on hypoxic drive
-ventilation inefficient r/t decreased TV and inspiratory strength
*polycythemia, cyanosis, hypoxemia
*right CHF, cor pulmonale
*greater sensitivity to respiratory depressant effects of GA (don't pre-op with versed!)
what are effects of obesity on the CV system?
-IHD, HTN (2x >), CHF
-extra blood vessels (25 mi/ 13 kg fat) and volume (CHF)
-increased CO (100ml/min for every 1 kg of fat; 2x IBW pts.)
-increased renin-angiotensin leads to increased intravascular fluid volume
-increased blood viscosity and catecholamines lead to arrhythmias
-decreased activity accelerates CAD
what causes increased CO and what happens as a result of it?
increased SV, NOT HR
-increased preload: cardiomegaly, atrial and biventricular dilation
-LVH, CHF, HTN develops
-decreased ventricle compliance leads to increased LVEDP which leads to pulmonary edema
what are CV implications?
-may display angina w/o evidence of CAD
-less cardiac reserve d/t increased workload (assess functional capacity: can you walk up 2 flights of stairs w/o difficulty? this is about equal to stimulation of laryngoscopy)
-asymptomatic/undetected CAD d/t decreased activity (increased risk of MI with increased BMI)
-greater degree of EKG changes
-arrhythmias by multiple causes
-H/O MI, HTN, angina, PVD common
-assess exercise tolerance, orthopnea may indicate LV dysfunction
-drug list will point to co morbidities
-EKG can show ventricular hypertrophy, CAD, ischemia, old infarct, etc.
-echo can show cardiomyopathy, tricuspid regurg, abnormal wall motion
-chemical stress test may be indicated
-CXR may identify cardiomegaly and cephalad diaphragm
what are some EKG changes seen in obesity?
-low QRS voltage (has to travel through more fat)
-left axis shift consistent with LVH
-left shift of the P wave, lengthened QT interval
-flattened T waves
how does obesity affect the GI system?
-after 8 hrs. of fasting, gastric volume > 25 ml in 80-90%
-gastric volume up to 75% larger
-gastric acidity (ph
how does obesity affect the liver?
-liver function abnormalities
what are endocrine effects of obesity?
increased possibility of type 2 DM
-risk increases linearly with BMI
-80% are obese
* rarely thyroid or pituitary problem
what effects does obesity have on metabolic state?
metabolic insulin resistance syndrome
-impaired glucose tolerance
how does obesity affect lipid soluble drugs?
-increased volume of distribution d/t increased fat stores
-propofol, benzos, opioids
*clearance may be delayed
*base on total body weight BUT give less frequent maintenance doses
how does obesity affect water soluble drugs?
-limited volume of distribution
*based on lean mass or ideal body weight (if based on TBW can lead to OD)
how does obesity affect inhalation agents?
-longer to reach equilibrium
*Desflurane faster on and off than Sevo or Iso
*low blood solubility volatile inhalation agents have faster uptake and distribution and elimination