Care of the Patient Undergoing Bariatric Surgery

BMI=weightinlb×703/heightinin2

The higher the BMI, the greater the weight associated with a given height. Recent studies have demonstrated that the patient who is considered overweight and one who is considered moderately obese usually experience minimal risks in the perioperative period.^7,8 Underweight patients, as well as patients with a BMI greater than 30, are found to have increased perioperative mortality rates. Although obesity is not equally distributed across gender or race, the incidence of obesity in a given community is relevant and clinically important. Patients in the obese and morbidly obese categories are seen in perianesthesia services for a wide variety of conditions for a wide variety of services including bariatric and nonbariatric surgery.⁹

Physiologic Considerations in Obesity

Pulmonary

Preoperative evaluation of obese patients reveals that 85% have exertional dyspnea and some degree of orthopnea.⁸ Periodic breathing, especially when sleeping, may also be present.

Obese patients tend to develop some degree of thoracic kyphosis and lumbar lordosis because of a protuberant abdomen. In addition, the layers of fat on the chest and abdomen reduce the bellows action of the thoracic cage. The overall lung-thorax compliance is reduced and thus leads to increased elastic resistance of the system. Usually, the diaphragm is elevated, and the total work of breathing is increased as a result of the deposition of abdominal fat. Because of these factors, the oxygen cost of breathing is threefold or greater than normal even at rest.

The primary respiratory defect of obese patients is a marked reduction in the expiratory reserve volume (ERV). The reason for the decrease in ERV and other lung volumes is that the obese patient is unable to expand the chest in a normal fashion. As a result, diaphragmatic movement must account for the changes in lung volume to a much greater extent than thoracic expansion does. As discussed previously, the diaphragmatic movement is moderately limited by the anatomic changes of obesity, which account for the decreased lung volumes.

In the obese patient, the functional residual capacity (FRC) may be less than the closing capacity in the sitting and supine positions; therefore, the dependent lung zones may be effectively closed throughout the respiratory cycle. Consequently, inspired gas is distributed mainly to the upper or nondependent lung zones. The resulting mismatch of ventilation to perfusion produces systemic arterial hypoxemia. The hypoventilation and ventilation-perfusion abnormalities that contribute to systemic arterial hypoxemia also contribute to retention of carbon dioxide and thus lead to hypercarbia.

In the general population, undiagnosed obstructive sleep apnea (OSA) is common in obese patients despite awareness that increased abdominal girth is a significant risk factor.¹⁰ Reportedly more than 70% of patients undergoing weight loss surgery have been clinically diagnosed with sleep apnea. OSA can occur in patients with redundant pharyngeal tissue. OSA is characterized by excessive episodes of apnea (approximately 10 seconds), apneic episodes occurring more than five times per hour, and a 50% reduction in airflow or a reduction sufficient to lead to a 4% decrease in oxygen saturation during sleep as a result of a partial or complete upper airway obstruction. Clinically significant apnea episodes of more than five episodes in 1 hour or 30 per night result in hypoxia, hypercapnia, systemic and pulmonary hypertension, and cardiac arrhythmias. In obese patients with OSA, there is an increased risk of difficult intubations as well as postextubation complications.

Cardiovascular

Thirty pounds of fat are estimated to contain 25 miles of blood vessels, and the increased body mass in obesity leads to increased oxygen consumption and carbon dioxide production. It is not surprising that the cardiac output and the total blood volume are increased in the obese state. This increase in cardiac output is a result of an increase in stroke volume rather than an increase in heart rate; the latter usually remains normal. The transverse cardiac diameter has been shown to be greater than normal in approximately two thirds of obese patients. A linear relationship seems to exist between cardiac diameter and body weight.

Obesity has been suggested to predispose one to electrocardiographic changes. The Q-T interval is often prolonged, and the QRS voltage is reduced because of the increased distance between the heart and the electrodes. Finally, the likelihood of ventricular arrhythmias is increased in the obese patient. These arrhythmias are believed to be a result of myocardial hypertrophy, hypoxemia, coronary artery disease, and fatty infiltration of the conducting and pacing systems.

A positive correlation exists between an increase in body weight and increased arterial pressure. Hypertension is a known risk factor for the development of coronary artery disease. A weight gain of 28 lb (12.75 kg) can increase the systolic and diastolic blood pressure by 10 and 7 torr, respectively. Systemic hypertension is tenfold more likely in the obese patient. The increase in blood pressure is probably caused by the increased cardiac output.

Chronic heart failure, although uncommon, can occur in persons with long-standing morbid obesity with or without hypertension. It is usually characterized by high output and biventricular dysfunction with the left ventricle predominating. Clinically, heart failure can be difficult to diagnose because pedal edema may be chronically present.

Cerebral blood flow in obese persons does not differ significantly from that in persons of normal weight. Oxygen uptake of the brain remains normal in the obese person; however, the fraction of the total body oxygen represented in the cerebral metabolism is less than normal because the total body oxygen requirement is increased. Although the kidneys of obese subjects weigh more than those of nonobese counterparts, renal blood flow is the same as or slightly lower than that of patients of normal weight.

Psychological

There are a number of contributing factors associated with obesity such as environment, genetics, highly processed and energy-dense foods, lack of exercise, and ethnic culture in addition to numerous psychological and social issues. Often, eating has nothing to do with hunger. Many people eat in response to emotions such as boredom, sadness, or anger. Disordered eating may also be a symptom of depression and low self-esteem. Some individuals use food to fill emptiness, provide good feelings, and soothe job pressures and personal conflicts. Socially, obese people are perceived as lazy and lacking self-discipline and willpower, which can lead to a cycle of self-blame, guilt, shame, depression, and social withdrawal.¹¹ Body image, along with the ability to interact with others, may be a problem for obese patients. Many bariatric patients have avoided routine medical care for fear of being judged and disrespected.

Integumentary

The presence of multiple skinfolds can lead to impaired hygiene in the patient who may have difficulty seeing or reaching areas that need cleaning. Retained moisture on this redundant skin can lead to excoriations or rashes if not kept clean and dry. Problem areas tend to be found in the groin, perineum, or axilla; beneath the breasts; and in large skinfolds. Wound infections can develop and commonly include yeast and fungi. Adipose tissue is poorly vascularized and can cause delayed wound healing.

Endocrine

Metabolic syndrome, also known as insulin resistance, is related to the effect of chronically high-normal serum blood glucose. The body has consistently high levels of glucose, requiring the pancreas to secrete greater and greater amounts of insulin to keep blood sugar regulated. Eventually, the cells no longer respond to insulin, and glucose begins to accumulate in the blood, leading to diabetes. Diabetes mellitus has been associated with obesity and metabolic resistance. It is the third most prevalent preoperative pathologic condition found in obese patients. Hypertension and dyslipidemia frequently occur concurrently and in association with resistance to insulin-stimulated glucose metabolism. When these risk factors cluster, the risks for coronary heart disease (CHD), stroke, diabetes, and cardiovascular disease mortality are further increased. This clustering of risk factors is frequent but not invariably associated with obesity, particularly abdominal obesity. Insulin resistance is also associated with an unfavorable imbalance in the endothelial production of mediators that regulate platelet aggregation, coagulation, fibrinolysis, and vessel tone.

Other Disorders

Other problems associated with clinical obesity include abnormal liver function tests, fatty infiltration of the liver (nonalcoholic steatohepatitis), gallstones, hiatal hernia, stress incontinence, and varicose veins. Gastroesophageal reflux is prevalent among the obese. Overweight patients are at higher risk for deep vein thrombosis and pulmonary emboli because of the limited or lack of mobility, stasis, and polycythemia related to chronic respiratory insufficiency. Obese individuals will also have some degree of degenerative joint disease affecting mobility. Higher body weights are also associated with a higher risk for certain cancers including endometrial, breast, prostate, and colon.

Bariatric Procedures

For centuries, standard diet and exercise was the usual prescription for weight loss. These approaches may be ineffective for many individuals with obesity. Considering the increase in incidence of obesity and obesity-related health concerns, weight-related issues have become a priority in health care. Multiple venues for managing weight have been established, and newer safer techniques in weight loss surgery are among the many treatment options for reducing excess body fat.

Evidence-Based Practice

Eligibility criteria for bariatric procedures include a BMI of 40 kg/m² or higher without comorbidities or a BMI between 35 and 39.9 kg/m² with at least one serious illness such as type 2 diabetes mellitus or hypertension. Individuals with a BMI between 30 and 34.9 kg/m² are potential candidates if they have comorbidities that are difficult to optimize such as type 2 diabetes mellitus or metabolic syndrome. If comorbidities are severe, the very young (under 18) or older patient (over 65), surgery may be a consideration.

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