Anesthesia considerations in the patient with obesity Flashcards
Overweight is defined as
increased body weight above a standard related to height
Obesity is defined as
excessive body weight for the patient’s age, gender, & height” (body weight of 20% or more above ideal body weight)
In the US population,
68% are overweight
33% are obese
Describe the BMI calculations
weight (kg)/height ^2 (m)
Ideal body weight is the
weight associated with maximum life expectancy for a given height & gender
IBW is useful in calculating some drug doses to avoid toxicity or hemodynamic instability
Adjusted body weight takes into account
metabolically active tissue
ABW= 0.4 (ABW-IBW)+ IBW
Lean body mass is useful for
drug dosing in obese patients because it takes into account the muscle that are used to carry weight
it is 120% of IBW
Overweight is defined as BMI of
25-29 kg/m^2
approx. body weight 20% more than IBW
Obesity is defined as BMI of
> 30
Describe the classes of obesity
Class I: 30-34.9 BMI
Class II: 35-39.9 BMI
Class III: 40-49.9 BMI
Extreme obesity is defined as
BMI >50
BMI >30 (obese) is associated with increased
morbidity related to stroke, ischemic heart disease, HTN, and diabetes
Android obesity is
abdominal (central) obesity
- more common in men, higher incidence of metabolic disturbances, increased risk of ischemic heart disease, stroke, diabetes, death
Gynecoid obesity is
fat around hips & buttocks
more common in females
Associated disturbances with obesity include
OSA/hypoventilation syndrome, restrictive lung disease, HTN, CAD, HLD, GERD, DMII, gall bladder disease (cholelithiasis), cirrhosis/fatty liver disease, venous stasis/ thromboembolic disease, degenerative joint/disc disease, increased breast, prostrate, cervical, uterine, and colorectal cancer, psychological and socioeconomic impairment
Respiratory alterations in obesity include
chest wall and lung compliance reduced due to fat accumulation in thorax and abdomen
lung volume changes- reduced FRC, VC, TLC, & ERV
RV & CC are not changed but the relationship between FRC & CC is adversely affected leading to
increased metabolic demand, work of breathing, closure of small airways with VQ mismatch & resulting hypoxemia
Patients who are obese may have these spinal conditions that affect respiration.
thoracic kyphosis/lumbar lordosis
Patients who are obese have (pulm. blood volume, O2 consumption, & CO2 production)
increased pulmonary blood volume, increased O2 consumption and carbon dioxide production
PFTs in the obesity may remain normal until
the obesity worsens and you see lung disease & pulmonary HTN
Describe minute ventilation and work of breathing in the obese patient.
increased minute ventilation
increased work of breathing
Frequent episodes of apnea during sleep leads to
chronic hypoxia, hypercapnia, pulmonary & systemic vasoconstriction (HTN) snoring sleep fragmentation/daytime somnolence impaired concentration/memory problems morning headache
Repeated episodes of apnea/hypoventilation lead to
oxygen desaturation, sympathetic arousal, awakening leading to fragmented sleep
Obstructive apnea is caused by
mechanical obstruction of upper airway, loss of respiratory drive or both
Risk factors for OSA include
middle age, male, obesity (BMI >30), ETOH use, drug induce sleep aids, abdominal fat distribution, neck girth (41 cm)
For the obese patient, respiratory changes are exaggerated with
operative positions- supine, trendelenburg, lateral, & prone
Rapid desaturation may be seen when anesthesia is induced in the
recumbent/supine position
Types of OSA include
OSA< central sleep apnea, & pickwickian Syndrome (most severe)
Describe Pickwickian syndrome
severe chronic OSA leading to cor pulmonale
related to morbid obesity
Describe central sleep apnea
cessation of both airflow & respiratory efforts
problem in ventilatory center of medulla–> d/t exposure to chronic hypercarbia
Describe obstructive sleep apnea.
cessation of airflow but maintain respiratory effort
abnormal relaxation of genioglossus & pharyngeal muscles will pull tongue forward
AHI index is
> 30 severe
16-30 moderate
15 or < mild
This test is needed for the diagnosis of obstructive sleep apnea
polysomnography
Hypoapnea is a
50% reduction in size or number of breaths that lasts at least 10 seconds compared to normal; or a reduction sufficient enough to cause a 4% or >decrease in arterial SaO2
Apnea is considered to be
> 10 seconds total cessation of airflow despite respiratory effort against a closed glottis
Corrective procedures for OSA include
uvulopalatopharyngoplasty (UPPP)- enlarges airway through removal tonsils, part of soft palate, uvula
diathermy palatoplasty- heat tissue producing scar which tightens in 6-8 weeks
OSA treatment includes
CPAP
-attenuates hemodynamic responses induced by apnea including BP surges and increased sympathetic nerve activity
CPAP may also include O2 therapy for those with
severe arterial oxygen desaturation
OSA results in
hypoxemia, RHF, hypercapnia, pulmonary & systemic vasoconstriction, polycythemia, respiratory acidosis during sleep, arterial hypoxemia, systemic hypertension, and pulmonary hypertension
Pickwickian syndrome or obesity hypoventilation syndrome is due to
extreme obesity with hypercapnia, hypoxia, cyanosis induced polycythemia, somnolence, and eventual RHF and pHTN
Pickwickian syndrome is clinically distinct from OSA because
OSA–> nocturnal sleep disruption
OHS–> nocturnal central apneic events (apnea without respiratory effort)
Pickwickian syndrome CO2 is
PCO2 >45 mmHg in an obese patient without significant COPD is diagnostic
Pickwickian syndrome is characterized by:
obesity, hypercapnia, chronic daytime hypoxemia, hypersomnolence, pHTN, respiratory acidosis, RHF, & airway difficulty
Airway changes in obesity include
TMJ & atlanto-axial joint & cervical spine movement limited by upper thoracic and low cervical fat pads
Patients who are obese have redundant tissue folds in the
mouth & pharynx leading to a narrowed upper airway
As neck circumference increases, the incidence of
difficult intubation increases
OSA increases the risk of
excess pharyngeal tissue on lateral walls
Obesity creates difficulty maintaining
mask airway, laryngoscopy, and intubation
CV alterations in obesity include
increased total blood volume
increased CO- expanded blood volume puts strain on myocardium
increased RAAS & SNS activity (increased risk for HTN)
risk of CAD is double and presents with angina, CHF, acute MI and sudden death
increased left sided heart pressures and left ventricular hypertrophy
Patients who are obese must undergo (CV related)
ECG to identify left or right ventricular hypertrophy, ischemia, and conduction defects
Eventually LV wall thickening fails to keep pace with ventricular dilation and systolic function
or obesity cardiomyopathy
results with eventual biventricular failure
Hematologic alterations in obesity include
polycythemia & hypercoagulation leading to thromboembolic risk
Thromboembolic risk in the obese patients casues
risk of DVT to double
polycythemia leads to increased blood viscosity
increased intra-abdominal pressure
immobility leads to venostasis
There is an increased incidence of these GI alterations in obesity:
hiatal hernia, GERD, gallbladder disease, & high risk for aspiration pneumonitis
Obesity in itself does not increase the risk of
aspiration; it is by virtue of being prone to other diseases
Hepatic alterations in the obese patient include
fatty infiltration of the liver- inflammation, cirrhosis, focal necrosis, high prevalence of NAFLD
abnormal LFTS
Renal alterations in the obese patient include
increased renal plasma flow & increased GFR
increased renal tubular resporption & impaired naturesis secondary to SNS & RAAS activation
eventually nephron function can be lost
Obese patients secrete more
insulin but resistant to the effects of insulin
-develop type 2 diabetes
Metabolic syndrome is the presence of at least three of the following signs
large waist circumference (central obesity), high triglyceride levels, low HDL levels, glucose intolerance, and hypertension
Musculoskeletal changes in obesity include
OA & degenerative joint disease- mechanical loading of weight bearing joints, inflammatory response, back pain, stress fractures (bone demineralization)
CNS changes in obesity include
ANS dysfunction, peripheral neuropathies, stroke, idiopathic intracranial HTN
Increased LDL and decreased HDL cholesterol is linked to
atherosclerosis
Hyperlipidemia can lead to
premature coronary artery disease, premature vascular disease, pancreatitis
Pharmacokinetics in the obese patient include
increased blood volume & CO, decreased total body water, adipose and lean tissue increase, variable alterations in protein binding, organomegaly
Clearance changes in the obese patient due to
-hepatic clearance unchanged despite histological and LFT alterations
renal clearance of drugs increased (GFR, RBF, & tubular secretion)
liphophilic drugs have an increased elimination half-life because of increased Vd but have normal clearance
Dosing for weak or moderate liphophilic drugs should be dose on
IBW or LBM
Describe the dosing of propofol for obese patients.
induction- LBW
maintenance- TBW
Describe the dosing of benzodiazepines for obese patients.
highly liphophilic
initial dose LBW- may titrate to TBW
infusions LBW
Describe NMBD dosages in obese patients.
pseudocholinesterase activity increases as weight and ECF increase- dose succinylcholine on TBW
-Vec, roc, atricurium, & ciastricurium based on LBW
exhibit prolonged DOA & recovery
Describe opioid dosages in obese patients.
fentanyl & sufentanil are highly lipid soluble so increased Vd & elimination half life- dose fentanyl on LBW (Miller says TBW) may need to dose sufentanil on TBW but then decrease maintenance to LBM
Describe remifentanil dosages in obese patients.
dosing based on LBW
Describe dexmedetomidine dosages in obese patients.
nice adjunct to consider when respiratory depression avoidance is priority
dose on TBW 0.2-0.7 mcg/kg/hr
Describe volatile anesthetics in obese patients.
metabolism is greater in obese patients= greater increase in inorganic fluoride
greater incidence of halothane hepatitis
N2O often avoided to maximize PaO2
Describe medications that can be used to treat obesity.
lipase inhibitors & SSRIs/sympathomimetics
Describe the MOA of lipase inhibitors (arlistat)
acts by blocking absorption and digestion of dietary fat & binding lipases in GI tract
Describe the use of SSRIs/sympathomimetics.
appetite suppressants- unacceptable side effects (primary pHTN & valvular heart disease)
phentermine is currently approved but can only be used for <3 months d/t side effects
Describe the obesity preop evaluation.
be non-judgmental
emphasis should be on the difficulties obesity presents to the anesthesia provider
discuss the likely post-operative course
Morbid obesity is an independent risk factor for sudden death from
acute PE
Thromboprophylaxis for the obese patient includes
LMWH, heparin, & pneumatic compression stockings
Pulmonary HTN signs include
dyspnea, fatigue, syncope, tricuspid regurgitation on echo, ECG (RVH, tall precordial R waves, right axis deviation), prominent pulmonary artery on CXR
Preop considerations of the obese patient include high incidence of
HTN, pHTN, right/left ventricular failure, & CAD
Excess adipose tissue may hide signs of
cardiac failure
Airway preop for the obese patient includes
does patient have a history of previous difficult airway obstructive sleep apnea assess ROM of cervical spine mouth opening TM distance interior of the mouth mallampati classification Neck size is the single best predictor of problematic intubation
Symptoms of severe respiratory disease include
orthopnea, sleep apnea, obesity hypoventilation syndrome, & previous history of upper airway obstruction especially regarding a past anesthetic
What does STOPBANG stand for?
snoring, tired, observed, high BP, BMI, age, neck size, gender
Respiratory pre-op labs that may be indicated include
chest XR, room air SaO2, ABGs, optimize pulmonary status pre-op, PFTs
Signs of HTN, RV/LV hypertrophy and pHTN should be assessed by
assess venous access, EKG, chest XR, ECHO, LV ejection fraction, cardiac clearance if needed, previous diet aids
Describe the endocrine, metabolic and GI preop concerns for the obese patient.
fasting blood sugar, diabetes, does the patient have a history of reflux
Additional pre-op labs for the obese patient include
LFTs, albumin level, glucose, consider clotting studies (if risk factors present)
Aspiration prophylaxis includes
great risk to morbidly obese patients, pre-operative anxiety
treatment includes: H2 receptor antagonists, bicitra, metoclopramide, omeprazole
For laryngoscopy of the obese patients, it is important to
have head elevation, ramping, and ear to sternal notch
General anesthesia for the obese patient recommendations include:
higher doses of Sux
des, sevo, iso are useful
avoid nitrous due to O2 demands
short-acting opioids to minimize respiratory depression
dexmedetomidine- no adverse effects on respiration
profound muscle relaxation needed for laparoscopy
The number one problem for emergence of the obese patient is
respiratory failure
Emergence of the obese patient includes
extubation after fully awake & reversed
semi-upright position (>30 degrees head up)
wean on pressure-support ventilation w/ PEEP
oxygen 100%
placement of nasopharyngeal airway
Ventilatory support postop may include
CPAP, BiPAP, mechanical ventilation, & respiratory monitoring
Fluid management for the obese patient should be calculated on
lean body weight or IBW
there is greater blood loss compared to non-obese r/t technical difficulties /extensive surgical dissection
Describe the mechanical ventilation for the obese patient
PEEP can improve FRC and arterial oxygenation- watch BP
recruitment maneuvers to improve oxygenation
pressure-controlled ventilation may help
changing I:E ratio
Postop analgesia includes
opioids based on IBW
local infiltration of wound
peripheral nerve blocks
multimodal approach is recommended because opioid-induced ventilatory depression is a concern
