The Morbidly Obese Patient

Yasuko Nagasaka

Jean Kwo

I. INTRODUCTION

Excess body weight is associated with an increased risk of death, because an elevated body mass index (BMI) increases the risk for type 2 diabetes mellitus (T2DM), cardiovascular disease, pulmonary disease, metabolic syndrome, and obstructive sleep apnea (OSA). Patients with high BMIs challenge clinicians during the postoperative period secondary to acute complications or exacerbations of chronic comorbidities and often present with complex clinical pictures. In this chapter, we will summarize the pathophysiology of obesity, postoperative management and monitoring, and pharmacologic approaches of the morbidly obese patients. Our goal is to provide a better understanding of why obese patients may deteriorate postoperatively, with a hope to further improve patient care.

II. DEFINITION

Obesity is a medical condition in which excess body weight causes increased health risks and reduced longevity. The diagnosis of obesity is based on BMI because it correlates with the amount of body fat.

The World Health Organization classifies BMI as:

Normal: 18.5 to 24.9

Overweight: 25 to 29.9

Obese: >30

Obesity is further categorized into Class I (BMI 30 to 34.9), Class II (BMI 35 to 39.9), and Class III (BMI >40). The distribution of fat is also important in the risk of developing comorbid diseases. Central or abdominal obesity, as reflected by the ratio of the circumference of the waist to that of the hips (waist-hip ratio), is associated with increased insulin resistance, dyslipidemia, and risk of atherosclerotic heart disease. Relative to healthy weight women, overweight women have been shown to be 3 to 6 times more likely to have mobility disability.

III. PATHOPHYSIOLOGY

Obesity causes systemic oxidative stress and inflammatory changes resulting in increased levels of inflammatory markers, such as tumor necrosis factor alpha and interleukin 6, which result in changes that affect multiple body systems.

A. Cardiac

1. Coronary artery disease (CAD): Obese individuals have a higher prevalence of CAD than nonobese individuals. The prevalence of high total cholesterol (defined as ≥240 mg/dL) is higher with increased BMI. In a meta-analysis of 19,388 bariatric surgery patients, 7% had a history of CAD.

2. Cardiomyopathy can develop due to increased total blood volume, resulting in left ventricular chamber dilation. Fatty infiltration of the myocardium can develop resulting in a pattern of restrictive cardiomyopathy. Approximately 31% of individuals with extreme obesity develop obesity-related cardiomyopathy.

3. Heart failure: An increase in blood volume leads to an increase in stroke volume, resulting in left ventricular overload, dilation and left ventricular hypertrophy, and finally culminating in heart failure.

4. Pulmonary hypertension and biventricular dysfunction: Prolonged exposure to cardiotoxic factors such as insulin resistance, steatosis, neurohumoral overactivation, and nocturnal hypoxia and hypercarbia associated with OSA can eventually conclude in the development of pulmonary hypertension and biventricular dysfunction.

5. Arrhythmias: There is an association between obesity and atrial fibrillation (AF). Patients with a BMI >40 have a 2.3-fold increased risk of postoperative AF compared to a 1.2-fold increased risk in those with a BMI between 25 and 30.

6. Hypertension: A recent cohort study with a median follow-up period of 46 years disclosed that those who were overweight or obese in early adulthood or middle age were at higher risk of developing hypertension later in life.

7. Metabolic syndrome is a group of conditions that increase the risk of cardiovascular disease and T2DM. A recent definition includes elevated waist circumference (value determined by individual populations) plus any two of the following: elevated triglycerides (≥150 mg/dL), reduced high-density lipoprotein C (≤40 mg/dL in males, ≤50 mg/dL in females), hypertension (systolic ≥130 and/or diastolic ≥85 mm Hg), and elevated fasting glucose (≥100 mg/dL).

B. Respiratory

Increased BMI adversely impacts respiratory function with significant impairment observed once BMI exceeds 45. Coexisting polycythemia may suggest long-standing hypoxemia.

1. Obstructive sleep apnea (OSA): OSA affects approximately 94% of patients presenting for weight loss surgery and is often undiagnosed. OSA increases perioperative morbidity and mortality and is significantly associated with a composite endpoint of death, venous thromboembolism, reintervention, or failure to be discharged by 30 days after surgery. Treating patients with continuous positive airway pressure (CPAP) or bilevel positive airway pressure for several weeks to months preoperatively combined with postoperative pulse oximetry monitoring has been shown to reduce postoperative complications. The American Society of Anesthesiologists recommends perioperative initiation of CPAP if OSA is severe, and continuation of CPAP or noninvasive positive pressure ventilation in the perioperative period unless contraindicated.

2. Anatomic airway changes: Ever-increasing weight is associated with the deposition of adipose tissue around pharyngeal structures and a reduction in airway caliber. This results in impaired of pharyngeal dilator activity and an increased risk of airway collapse. These changes can lead to difficulty with laryngoscopy and intubation.

3. Obesity hypoventilation syndrome (defined as BMI >30 kg/m², chronic alveolar hypoventilation, and sleep-disordered breathing) and overlap syndrome (coexisting OSA and chronic obstructive pulmonary disease without pathologic link) are often seen in the morbidly obese. These patients are at higher risk of developing pulmonary hypertension.

4. Asthma: Obese individuals (BMI >30) are nearly twice as likely to develop asthma as individuals with a BMI <25. Weight loss is associated with improved asthma control.

C. Hepatobiliary/Gastrointestinal

1. Liver disease: In bariatric patients, the prevalence of nonalcoholic fatty liver disease (NAFLD) and nonalcoholic steatohepatitis (NASH) has been estimated to be as high as 91% and 37%, respectively. Risk factors for metabolic syndrome are concurrent risk factors for NAFLD and NASH.

2. Gastroesophageal reflux disease (GERD): Obese individuals are at higher risk of GERD due to mechanical and hormonal changes. However, in otherwise healthy obese patients, gastric emptying appears normal.

3. Gallstones: Obesity is a risk factor for the formation of cholesterol gallstones and exposes patients to an increased risk of gallstone-related complications and need for cholecystectomy. Female gender and rapid weight loss are major risk factors for postoperative cholelithiasis.

D. Renal

Obesity is associated with an increased risk of developing Stage 3 chronic kidney disease when studied in a cohort with over 20 years of follow-up.

E. Central Nervous System

1. Stroke: Obesity is associated with stroke and has a significantly higher prevalence in patients with younger age as compared to nonobese patients.

2. Psychosocial aspects and depression: Individuals with obesity have elevated psychologic risk factors for developing psychologic strains and thus, this patient population exhibits a higher prevalence of depression.

F. Hematology

1. The blood volume of obese patients is increased and can be estimated by the following equation:

2. Hypercoagulability: Obesity is associated with an overproduction of procoagulant agents and increased thrombin generation resulting in hypercoagulability.

3. Venous thromboembolism (VTE): The obesity-related state of chronic inflammation and impaired fibrinolysis place patients with elevated BMIs at an increased risk for postoperative thromboembolic events. The rate of VTE in patients undergoing bariatric surgery is 2%. Risk factors for postoperative VTE include increased age, high BMI, male gender, and history of prior VTE. Patients undergoing surgery should receive chemoprophylaxis with either low-dose unfractionated heparin or low-molecular weight heparin in addition to mechanical prophylaxis with elastic stockings or intermittent pneumatic compression. Because most VTE occurs after discharge, continuing chemoprophylaxis after hospital discharge should be considered in high-risk patients (e.g., those with history of deep venous thrombosis).

G. Endocrine

1. Type 2 diabetes mellitus: Obesity promotes insulin resistance and the development of T2DM. Adults with a BMI ≥40 are 7 times more
likely to have diabetes compared to normal weight individuals. Patients with poorly controlled diabetes are more prone to developing wound infections, acute renal failure, and postoperative wound dehiscence.

2. Thyroid: Obesity has been strongly associated with thyroid cancer, perhaps via the increase of insulin or insulin-like growth factor 1 that results from insulin resistance.

H. Cancer

Obesity has been linked to 20% of all cancer deaths in women and 14% in men. Increased BMI is associated with a higher risk of both common and less common cancers. In men, significant positive associations with obesity were noted with rectal and prostate cancers. In women, positive associations were found with endometrial, gastrointestinal, and postmenopausal breast cancers. Underlying pathophysiologic mechanisms of cancer susceptibility in patients with elevated BMIs are related to genetic factors, insulin/IGF-I signaling axis, chronic low-grade inflammation, adipokine secretion, and gut microbiota.

I. Other Conditions

1. Polycystic ovarian syndrome is characterized by obesity, insulin resistance, cardiometabolic features, ovarian cysts, hirsutism, and infertility. Weight gain exacerbates reproductive and metabolic risks.

2. Pediatric obesity syndromes: The most recent data from the National Health and Nutrition Examination Survey report a 5.5% decrease in the prevalence of obesity among 2- to 5-year-olds between 2003 to 2004 and 2011 to 2012. Children with obesity are at risk for adult conditions such as T2DM, hypertension, and dyslipidemia. Certain congenital conditions are associated with morbid obesity. These include Prader-Willi syndrome, Alstrom syndrome, Cohen syndrome, Albright hereditary osteodystrophy (pseudohypoparathyroidism), Carpenter syndrome, MOMO syndrome, and Rubinstein-Taybi syndrome.

IV. PERIOPERATIVE RISK ASSESSMENT

A. Cardiac Risk Assessment

Cardiac risk assessment requires an analysis of the patient’s personal risk factors and functional status in conjunction with the planned procedure. The American College of Cardiologist and the American Heart Association guidelines do not recommend cardiac testing if the risk of a major adverse cardiac event (MACE) is <1%. If the MACE risk is ≥1%, functional status should guide whether further cardiac testing is necessary.

Surgical risk scoring indices: There are several validated tools to help assess perioperative cardiac risk, including the following:

1. American College of Surgeons National Surgical Quality Improvement Program Risk Calculator can be accessed at http://www.surgicalriskcalculator.com

2. The Revised Cardiac Risk Index (Table 31.1) uses six categories to risk-stratify patients for adverse cardiac events after noncardiac surgery.

B. Diabetes Risk

Poorly controlled diabetes is associated with increased perioperative complications such as wound infections, surgical anastomotic breakdown, and acute renal failure. In patients undergoing bariatric surgery, a glycohemoglobin (Hgb A1c) value of <6.5% was associated with a 10% less complication rate when compared to Hgb A1c value of >8%.

TABLE 31.1 Revised Cardiac Risk Index

One point for each factor:
1. High-risk surgery (intraperitoneal, intrathoracic, and suprainguinal vascular procedures)
2. Ischemic heart disease
3. History of congestive heart failure
4. History of cerebrovascular disease
5. Insulin therapy for diabetes mellitus
6. Preoperative serum creatinine >2.0 mg/dL
Number of Factors	Rates of Major Cardiac Complications (%)
0	0.5
1	0.9-1.3
2	3.6-6.6
≥3	9.1-11
Adapted from Lee TH, Marcantonio ER, Mangione CM, et al. Derivation and prospective validation of a simple index for prediction of cardiac risk of major noncardiac surgery. Circulation 1999;100: 1043-1049.

TABLE 31.2 STOP-Bang Questionnaire

Snoring: Do you snore loudly (loud enough to be heard through closed doors)?
Tired: Do you often feel tired, fatigued, or sleepy during daytime?
Observed: Has anyone observed you stop breathing during your sleep?
Blood Pressure: Do you have or are you being treated for high blood pressure?
BMI: BMI more than 35 kg/m²?
Age: Age over 50 years old?
Neck circumference: Neck circumference greater than 40 cm?
Gender: Male?
High risk of OSA	Yes to three or more questions
Low risk of OSA	Yes to less than three questions
BMI, body mass index; OSA, obstructive sleep apnea.
Adapted from Chung F, Yegneswaran B, Liao P, et al. STOP questionnaire: a tool to screen patients for obstructive sleep apnea. Anesthesiology 2008;108:812-821.