Anesthesia for Obese Population Flashcards
overweight
increased body weight above a standard related to height
obesity
- excessive body weight for the patient’s age, gender, and height
- body weight of 20% or more above ideal weight
US population and obesity
-2 of 3 are overweight or obese
-33% obese
ages 2-19 1 of 6 are obese
factors that influence obesity
- behavioral
- genetic
- cultural
- SES what can people afford
- food deserts
ideal body weight
weight associated with max life expectancy for given height and gender
broca’s index
IBW = height cm - x x = 100 males x = 105 females
adjusted body weight
- used by dieticians to predict basal energy expenditure
- obese individuals have some metabolically active adipose tissue
- AdBW = 0.4 (ABW - IBW) + IBW
lean body mass
- drug calc for obese individuals
- takes into account lean muscle mass developed from carrying extra adipose tissue
- 120% of IBW
BMI
accepted measure of body habitus that normalizes adiposity for height
BMI = weight in kg/(height in meters)^2
overweight BMI
25-29.9
approximate body weight 20% more that IBW
class 1 obesity BMI
30-34.9
class 2 obesity BMI
35-39.9
class 3 obesity BMI
40-49.9
superobese BMI
> 50
obesity BMI
> 30
associated with increased morbidity r/t stroke, ischemic heart disease, HTN, and DM
android obesity
- abdominal central obesity
- fat more metabolically active
- more common in men, higher incidence of metabolic disturbances, increased risk of ischemic heart disease, stroke, DM, death
- “apple”
gynecoid obesity
- fat around hips/buttocks
- more common in females
waist circumferene and risk of pathophysiology
- 102 cm or 40 in men
- 89 cm or 35 in women
disturbances associated with obesity
- OSA
- hypoventilation syndrome
- restrictive lung disease
- HTN
- CAD
- hyperlipidemia
- delayed gastric emptying/GERD
- T II DM
- gall bladder disease (cholelithiasis)
- cirrhosis/fatty liver disease
- venous stasis/thromboembolic disease
- degenerative joint/disc disease
- increased breast/prostate, cervical, uterine, and colorectal cancer
- psychological and SES effects
RLD in obesity
- chest wall and lung compliance reduced due to fat accumulation in thorax and abdomen –> breath at LOW lung vol
- thoracic kyphosis/lumbar lordosis = further restrict
- reduced lung volumes
- cc is close to or within normal tidal breathing –> increased demand –> increased WOB –> closure of small airways –> V/Q mismatch –> hypoxemia
other resp alterations in obesity
- increased pulmonary blood volume
- increased O2 consumption and CO2 production
- high Ve, increased WOB
- with progression –> lung disease and pulm HTN
OSA risk factors
- middle age
- male
- obesity
- ETOH use
- drug induced sleep
- abdominal fat distribution
- neck circumference > 40 cm
OSA
- changes in airway dynamics during sleep but physiologic changes that endure beyond
- repeated episodes of apnea/hypoventilation - oxygen desat, sympathetic arousal, awakening leading to fragmented sleep
OSA causes
- mechanical obstruction of upper airway
- loss of resp drive
- BOTH
OSA pathophysiology
- chronic hypoxia, hypercapnia, pulmonary and systemic vasoconstriction (HTN)
- snoring
- sleep fragmentation/daytime somnolence
- impaired concentration/memory problems
- morning HA
three types of OSA
- OSA
- central sleep apnea
- obesity hypoventilation syndrome/pickwickian syndrome
reg OSA
- cessation of airflow but maintain resp effort
- abnormal relaxation of genioglossus and pharyngeal muscles pull tongue forward causing obstruction
central sleep apnea
- cessation of both airflow and resp effort
- problem in ventilatory center of medulla
- occurs as resp center exposed to chronic hypercarbia/hypoxia so it doesn’t respond as well
obesity hypoventilation syndrome/pickwickian syndrome
- most severe chronic/long-term OSA leading to cor pulmonale
- related to morbid obesity
- extreme obesity with hypercapnia, hypoxia, cyanosis, induced polycythemia, somnolence and eventual RHF, + pulm HTN
- PCO2 > 45 mmHg in an obese patient without significant COPD is diagnostic
- clinically distinct from OSA –> has nocturnal central apneic events
polysomnography
- used for OSA diagnosis
- EEG, REM, EKG, SpO2, airflow, thoraco-abdominal excursion
- apnea hypopnea index (# per hour measured)
apnea
> 10 seconds total cessation of airflow despite resp effort against closed glottis
hypopnea
- 50% reduction in size or number of breaths that lasts at least 10 seconds compared to normal
- reduction sufficient enough to cause a 4% or > decrease in arterial SaO2
severe OSA
apnea-hypopnea index >30
moderate OSA
apnea-hypopnea index 16-30
mild OSA
apnea-hypopnea index <15
OSA treatment
- Nasal CPAP
- attenuates hemodynamic responses induced by apnea including BP surge and increased SNS activity
- level of + pressure determined in sleep lap
- improves neuropsychiatric functioning
- less daytime somnolence
- drugs not reliably effective in severe cases
- noctural oxygen for those with severe arterial oxygen desaturation
corrective procedures for OSA
- uvulopalatopharyngoplasty (UPPP) - enlarges airway by removing tonsils, part of soft palate and uvula
- diatherpy palatoplasty - heat tissue producing scar which tightens in 6-8 weeks
pathophysiologic effects of OSA
- hypoxemia
- R heart failure
- hypercapnia
- pulmonary + systemic vasoconstriction
- polycythemia
- resp acidosis during sleep
- arterial hypoxemia
- systemic HTN
- pulm HTN
- cor pulmonale
characteristics of OHS or pickwickian syndrome
- obesity BMI > 30
- hypercapnia PaCO2 > 45 mmHg in obese patient without significant COPD is diagnostic
- chronic daytime hypoxemia
- daytime hyper-somnolence
- pulmonary HTN
- resp acidosis
- RHF
- airway difficulty (actual structural changes)
airway changes in obese individual
- TMJ + alanto-axial joint and cervial spine movement limited by upper thoracic and low cervical fat pads
- redundant tissue folds in mouth + pharynx = narrowed airway
- short, thick neck
- fat in suprasternal, presternal, posterior cervical and submental regions
- shortened distance between mandible and sternal fat pads
- OSA = increased risk excess pharyngeal tissue on lateral walls
- difficulty maintaining mask airway
- difficult laryngoscopy + intubation
CV alterations in obesity
- increased total blood volume
- increased CO
- increased RAAS + SNS activity –> HTN (RAAS activated by fat in flank area –> increased pressure on renal artery)
- risk CAD doubled presents with angina, CHF, acute MI, and sudden death
- increased L sided pressure and LV hypertrophy
- ECG changes (d/t LV hypertrophy); can also have ischemia and conduction defects
- increased LV wall stress = hypertrophy, decreased compliance, impaired filling (i.e., diastolic dysfunction), pulmonary edema
- eventually systolic dysfunction (or obesity cardiomyopathy)
- eventual biventricular failure
heme alterations in obesity
- polycythemia + hypercoagulation
- increased risk of thrombotic events
- DVT risk doubles
- polycythemia leads to increased blood viscosity, so increased fibrinogen, factor VII, factor VIII, vWf, plasminogen
- increased intra-abdominal pressure
- immobility –> venous stasis
GI alterations in obesity
- increased incidence –> hiatal hernia, GERD, gallbladder disease
- risk for asp pneumonitis –> obesity itself does not increase it but they have a higher chance of having more risk factors for aspiration
hepatic alterations in obesity
- fatty infiltration of liver - NAFLD, inflammation, cirrhosis
- abnormal LFTs (weight loss of 5 lbs can reverse this)
renal alterations in obesity
- increased renal plasma flow and GFR
- increased renal tubular resorption and impaired naturesis secondary to SNS + RAAS activation
- eventually nephron fxn lost
endocrine alterations in obesity
- secrete more insulin, but resistant to effects of insulin –> develop T2DM
- metabolic syndrome (at least 3 symptoms)
what are the symptoms of metabolic syndrome?
- large waist circumference (central obesity)
- high triglycerides
- low HDLs
- glucose intolerance
- HTN
MSK alterations in obesity
- osteoarthritis and degenerative joint disease
- mechanical loading of weight-bearing joints
- inflammatory response
- back pain
- stress fractures (bone dimineralization)
CNS alterations in obesity
- ANS dysfunction (resp centers impacted + SNS activation)
- peripheral neuropathies
- stroke
- idiopathic intracranial hypertension
hyperlipidemia
- associated with obesity
- increased LDL and decreased HDL cholesterol linked to atherosclerosis
what can hyperlipidemia lead to?
- premature CAD
- premature vascular disease
- pancreatitis
pharmacokinetic alterations in obese patient
- increased blood volume and CO
- decreased total body water
- adipose and lean tissue increase
- variable alterations in protein binding
- organomegaly
clearance alterations in obese patient
- hepatic clearance unchanged despite histological and LFT alterations
- renal clearance of drugs increased due to increased GFR, RBF, and tubular secretion
- lipophilic drugs have an increased elimination half-life because of increased Vd but have normal clearance
dosing drugs for obese
weak or moderate lipophilicity dose on IBW or LBM
propofol for obese
induction on LBW; maintenance on TBW
benzos for obese
- highly lipophilic
- initial doses on LBW, may titrate to TBW to reach adequate serum concentration
- infusion on LBW
NMBDs for obese
- increased pseudocholinesterase activity (linear relationship with weight + ECF); succ dose on TBW
- vec + roc on IBW
- Cis on TBW
- general trend = prolonged DOA and recovery
fentanyl + sufentanil for obese
- both highly lipid soluble
- increased Vd and e1/2 life
- dose on TBW but then decrease maintenance to IBW + response
remifentanil for obese
IBW because PK similar in obese and non-obese individuals
dexmedetomidine for obese
- nice adjunct to avoid resp depression
- 0.2-0.5 mcg/kg/min to reduce analgesic and anesthetic requirements
- dose on TBW
sugammadex for obese
-miller = IBW
-nagel = TBW
UNKNOWN LOL
volatile anesthetics for obese
-N2O avoided to maximize PaO2
appetite suppressant
- used to treat obesity
- adrenergic reuptake inhibitors
- decrease appetite and increase metabolic rate
- SE = HTN, tachycardia, abuse, N/V/D
- 5-HT2C receptor agonist Lorcaserin is selective
- reduces food intake through activation of pro-opiomelanocortin
lipase inhibitor orlistat
- acts by blocking absorption and digestion of dietary fat and binding lipases in GI tract
- significant GI effects and interferes with fat soluble vitamins
obesity pre-op eval
- assess pt in non-judgmental fashion
- emphasis on difficulties obesity presents to anesthesia
- discuss likely post-op course
S/S pulm HTN
- dyspnea
- fatigue
- syncope
- triscupid regurg
- ECG = RVH, tall precordial R waves, R axis deviation
- prominent pulm artery on CXR
preop considerations for obese patient
- morbid obesity = independent risk factor for sudden death from acute PE
- thromboprophylaxis = IMPORTANT; heparin, pneumatic compression stockings, LMWH
airway pre-op for obese
- history of difficult airway
- OSA
- assess ROM
- mouth opening
- thyromental distance
- interior of mouht
- mallampati
- neck size
what is the single best predictor of problematic intubation?
- neck circumference
- 5% with neck circ of 40 cm
- 35% with neck circ of 60 cm
resp pre-op assessment obese
- identify symptoms of severe resp disease
- orthopnea
- OSA
- OHS
- previous hx of upper airway obstruction (esp if had a past anesthetic)
STOP BANG
- S = snoring
- T = tired (daytime sleepiness)
- O = observed apneic
- P = pressure (HTN)
- B = BMI (greater than 30)
- A = age older than 55
- N = neck circumference greater than 40 cm
- G = gender (male)
potential resp pre-op tests for obese
- CXR
- room air SpO2
- ABGs
- optimize pulm status
- PFTs
CV assessment/tests pre-op for obese
- identify signs of HTN, RV/LV hypertrophy, pulm HTN
- assess venous access
- EKG
- CXR
- ECHO
- LV EF
- Cardiac clearance
- previous diet aids
endo, metabolic, + GI pre-op for obese
- fasting BG
- diabetics non-insulin or insulin dependent
- does patient have GERD?
aspiration prophylaxis for obese
- high risk
- treatment options = H2 antagonists, sodium citrate, metoclopramide, omeprazole
induction
- optimize the patient position
- use neck roll
- elevate HOB
- ramp up!! (gravity baby!!)
general anesthesia tips for obese
- higher dose of succ
- des, sevo, iso useful
- avoid nitrous due to oxygen demands
- short acting opioids to minimize resp depression
- dex use bc no adverse resp effects
- profound muscle relaxation needed for laparoscopic so use vec, roc, or cis
mechanical vent of obese
- PEEP to improve FRC and oxygenation
- recruitment maneuvers
- pressure controlled ventilation may help
- changing I:E ratio
fluid management of obese
- calc of fluid requirement in obese based on LBW or IBW
- greater blood loss compared to non-obese r/t technical difficulties/extensive surgical dissection
emergence of obese
- resp failure = #1 problem
- awake extubation (NMB fully reversed)
- semi upright position (>30 degrees HOB)
- wean on PS ventilation with PEEP
- 100% O2 (controversial)
- place NPA or OPA
vent support post-op for obese
- CPAP or BiPAP
- mechanical ventilation
- resp monitoring
post-op analgesia for obese
- multimodal approach because worried about opioid induced vent depression
- nerve blocks with continuous infusion of LA
- local infiltration of wound
- opioids based on IBW if used
