Obesity

Learning objectives

Understand the impact of obesity and related health conditions upon the provision of anesthesia
Identify the high-risk obese patient
Plan safe and individualized perioperative care determined by comorbidities and the extent of surgery

Definition and mechanisms

Obesity is an excessive fat accumulation that presents a risk to health, defined by the WHO as having a body mass index (BMI) over 30 kg/m2
Obesity is a leading preventable cause of death worldwide
The prevalence of obesity has tripled over the past 40 years, and there are more than 650 million obese adults worldwide

Risk factors

Family inheritance and influences
Lifestyle choices: Unhealthy diet, liquid calories, inactivity, sedentary lifestyle
Certain diseases: Prader-Willi syndrome, Cushing syndrome, hypothyroidism, growth hormone deficiency, eating disorders (i.e., binge eating disorder, night eating syndrome)
Certain medications: Antidepressants, insulin, sulfonylureas, thiazolidinediones, atypical antipsychotics, steroids, β-blockers, anticonvulsants (i.e., phenytoin and valproate), pizotifen, some forms of hormonal contraception
Socioeconomic issues
Aging
Other factors: Pregnancy, quitting smoking, lack of sleep, stress, microbiome

Complications

Hypertension
Cardiovascular diseases and stroke
Type 2 diabetes mellitus
Metabolic syndrome
Increased risk of cancer of the uterus, cervix, endometrium, ovary, breast, colon, rectum, esophagus, liver, gallbladder, pancreas, kidney, and prostate
Digestive problems
Obstructive sleep apnea (OSA)
Obesity hypoventilation syndrome (OHS)
Osteoarthritis
Depression

Treatment

Goal: Reach and stay at a healthy weight → improve overall health and lower the risk of developing complications related to obesity
Initial treatment: Modest weight loss (5-10% of total weight)
Changes in eating habits and increased physical activity

Dietary changes

Reduce calories
Eat healthier
Restrict certain foods (e.g., high carbohydrates, full-fat foods)
Feel full on less
Meal replacements (e.g., low-calorie shakes or meal bars)

Exercise and activity

Exercise: 150 minutes/week of moderate-intensity physical activity
Keep moving

Behavior changes

Counseling
Support groups

Weight-loss medication

Used along with diet, exercise, and behavior changes
Bupropion-naltrexone
Liraglutide
Orlistat
Phentermine-topiramate

Endoscopic procedures for weight loss

Endoscopic sleeve gastroplasty
Intragastric balloon for weight loss

Bariatric surgery

Limits the amount of food the patient can comfortably eat or decreases the absorption of food and calories
May result in nutritional and vitamin deficiencies
Adjustable gastric banding
Gastric bypass surgery
Sleeve gastrectomy

Management

Preoperative assessment and risk prediction

Most important to identify
- Central or peripheral distribution of fat
- Presence of metabolic syndrome
- Peripheral oxygen saturation <95% breathing air
Optimize associated health conditions before scheduling surgery (see table)

Conditions	Suggestive features	Perioperative actions
Respiratory
Sleep-disordered breathing (OSA, OHS)	Shortness of breath SpO2 <95% breathing air Stop-BANG ≥5 OHS-BMI >30, hypercapnia when awake, raised HCO3, hypoxia, exclusion other causes of hypoventilation	ABG initially Spirometry CPET if abnormalities found in above tests Airway planning, 4x ↑ risk of difficult intubation and difficult mask ventilation Refer for further investigation and treatment Commence CPAP before surgery and continue after surgery BiPAP sometimes necessary for improvement in symptoms (especially OHS) Plan for postoperative HDU/ICU admission if symptoms not improved by time of surgery
Asthma	Dyspnea Wheezing	Asthmatic symptoms common but reversibility with β2-agonists not always found - cause is partly chronic pro-inflammatory state from excess adipose tissue and fat within/around chest/abdomen causing small airway collapse Weight loss: Symptoms from asthma and fat-related wheeze will improve
Cardiovascular
Hypertension Left ventricular hypertrophy Left ventricular failure Conduction abnormalities Cardiomyopathy	Clinical signs of heart failure History of cardiac syncope Increased SBP Reduced exercise capacity	Preoperative ECG ECHO if structural or functional disease suspected Referral to cardiologist Medical management and optimization before surgery
Right heart failure	Pulmonary hypertension resulting from sleep-disordered breathing Polycythemia
Reduced functional capacity	Difficult to assess in obese patients Ability to achieve 4 metabolic equivalents indicates fitness and low risk patient	Assess ability to walk on a flat level surface Assess climbing stairs CPET
Metabolic
Diabetes mellitus	Deranged serum glucose, HbA1C, or associated complications	Optimize glucose control with referral to endocrinologist Avoid delaying surgery based on HbA1C concentrations only
Liver involvement (NASH/NAFLD)	Evidence of cirrhosis, deranged liver function tests	Liver-shrinking diet (<1000 calories/day) can reverse the disease processes somewhat
Metabolic syndrome	Central obesity, hypertension, impaired glucose handing or diabetes, increased triglycerides, decreased HDL cholesterol	Actively seek components of metabolic syndrome (≥3 required for diagnosis)

Organization and equipment

Preparation and positioning

Ensure availability of theatre gowns of appropriate size
Assess deep vein thrombosis risk and use prophylaxis measures
Maintain patient’s dignity and safety
Use gel pads to protect pressure points

Monitoring and ventilation

Use non-invasive blood pressure cuffs of the correct size
Anesthetic ventilators should be able to deliver high driving pressures and PEEP
Potential for incomplete neuromuscular block antagonism requires routine neuromuscular monitoring

Ultrasound

Facilitate successful regional blocks and aid with difficult venous access

Induction of anesthesia

Patient position

Head up ramped position with elevation of the upper body until the ear tragus and sternal notch are aligned horizontally
Position offers advantages
- Increased comfort for the patient
- Maintain functional residual capacity
- Reduce dyspnea
- Facilitate bag-mask ventilation
- Improve laryngoscopy

Airway

Tracheal intubation is the recommended technique for airway management
Obesity is associated with a higher risk of developing airway problems under anesthesia
Routine airway assessment to determine potential difficult laryngoscopy or ventilation
- Mallampati score 3 (predicts difficult facemask ventilation and intubation)
- Neck circumference >42 cm (predicts difficult intubation)
- BMI >50 kg/m2 (independent predictor of difficult intubation and facemask ventilation)
- Symptoms of gastroesophageal reflux disease
Obese patients have increased oxygen consumption and CO2 production due to increased total body tissue mass and increased work of breathing → can lead to hypercapnia and hypoxemia when ventilation is impaired
Delay onset of hypoxemia by
- Preoxygenation of the lungs
- Induction of anesthesia in the semi-upright position with application of CPAP or high-flow nasal oxygen
- Avoid prolonged apnea
Excess adipose tissue reduces chest wall compliance, which reduces functional residual capacity (FRC) to closing capacity, leading to atelectasis

Routine rapid sequence intubation (RSI)

Obesity is associated with an increased incidence of known risk factors for aspiration (e.g., hiatus hernia, diabetes with autonomic neuropathy causing delayed gastric emptying)
RSI is not routinely required in the absence of risk factors for aspiration
Failed intubation after induction of anesthesia requires antagonism of neuromuscular block

Awareness

Reduce awareness shortly after induction of anesthesia by
- Ensuring adequate dosing of i.v. anesthetic agents
- Prompt delivery of maintenance anesthetic agent
- Further i.v. bolus(es) of the anesthetic agent before airway manipulation or protracted airway maneuvers

Maintenance of anesthesia

TIVA with propofol offers advantages over volatile anesthetics
- Reduced incidence of laryngospasm
- Reliable clearance of hypnotic agents
- Reduced postoperative nausea and vomiting
- Maintained anesthesia during protracted airway manipulation
To minimize the risk of accidental awareness, the use of processed EEG-based depth of anesthesia monitoring, continuous clinical observation, and interpretation of vital signs should guide titration of drug infusion targets and rates
Volatile anesthetics with a rapid offset of action (i.e., desflurane and sevoflurane) limit absorption into adipose tissue, reduce the risk of resedation, deteriorate respiration function, and may obstruct the airway at emergence

Ventilation

Obesity is an independent risk factor for developing postoperative pulmonary complications
Use lung protective volumes (6-8 mL/kg), plateau pressures <30 cm H2O, and titration of PEEP guided by the patient’s respiratory and cardiovascular state
Position the patient in the 20° reverse Trendelenburg position with 45° hip flexion for laparoscopy for upper abdominal surgery to reduce airway pressures
Position the patient in the flat Trendelenburg position for lower abdominal surgery to reduce airway pressures

Postoperative care

Place the patient in a 30-45° head up position in the recovery room
CPAP may enhance recovery of normal respiratory function if started in the early postoperative period
Avoid opioids; if required monitor SpO2 continuously and consider a higher level of care
Early mobilization with regular reviews
Discharge criteria
- Unsupported stable vital signs with minimal inspired oxygen requirement
- No evidence of hypoventilation
- Free from apneas without stimulation
- Patient must be able to use a CPAP device if required
Consider critical care admission for all patients with significant comorbidities (e.g., diabetes mellitus, chronic respiratory disease)

Day-case surgery

	Patient-specific factors	Anesthetic factors	Surgical factors
Appropriate for day-case surgery	Any BMI Good functional capacity OSA/OHS effectively treated with CPAP/NIV Able to continue venous thromboembolism (VTE) prophylaxis at home if required	Adequate time on list to anesthetize Regional anesthesia possible Experienced anesthesiologist, OR, and day-case ward team	Adequate time on operating list to perform surgery, taking into account expected time to discharge Appropriate equipment for surgery and postoperative care available
Inappropriate for day-case surgery	Poor functional capacity Unstable hypertension, ischemic heart disease, congestive heart failure Unstable respiratory disease (low SpO2, OSA/OHS untreated or no symptomatic improvement after treatment) Previous VTE Metabolic syndrome	Likely to require long-acting potent opioids

Implications of previous bariatric surgery

Sleeve gastrectomy: Routinely intubate these patients as there is a risk of reflux of gastric contents, regardless of presence of symptoms
Roux-en-Y gastric bypass; one anastomosis gastric bypass: May affect bioavailability of oral medications due to shortening of the small bowel and loss of surface area (e.g., postoperative analgesia absorption)
Adjustable gastric banding
- High risk of aspiration despite prolonged fasting times
- RSI with antacid premedication should be routine
- Avoid nasogastric tubes unless acute abdomen or bowel obstruction (risk of displacing band or perforation of proximal stomach)
- The band should not be deflated (risk infection to system, band erosion in stomach or damage to the band)

Keep in mind

Obesity only increases perioperative risk significantly when BMI is ≥40 kg/m2, or when associated with significant comorbidities
Day-case surgery is usually appropriate if BMI is <50 kg/m2 and comorbidities are optimized
OSA and OHS are common high-risk conditions that influence the management of anesthesia
RSI should not be routine in the absence of specific indications
Previous bariatric surgery has important implications for subsequent anesthesia

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