45 Care of the obese patient undergoing bariatric surgery
Laparoscopic Adjustable Gastric Banding (LAGB): One of the most common weight loss surgical procedures, it involves placing an adjustable silicone band around the upper portion of the stomach to restrict the size of the stomach. The band is tightened by adding saline through a port that is placed under the skin in the abdomen.
Morbid Obesity: Generally involves a state of being 50% to 100% over normal weight, being more than 100 pounds (45.5 kg) over normal weight, having a BMI of 40 or higher, or being sufficiently overweight to severely interfere with health or normal function.
Roux-En-Y (RNY): Common gastric bypass surgery that divides the stomach into a small upper pouch leaving a much larger, lower remnant pouch and then rearranges the small intestine into a Y configuration to enable outflow of food from the small upper stomach pouch, via a Roux limb.
Sleeve Gastric Resection (SGR): A newer weight loss surgery that creates a thin, vertical sleeve of stomach using a stapling device, removing the rest of the stomach, thus limiting the amount of food eaten without causing any malabsorption.
Obesity is the most common nutritional disorder in the world today. Current estimates suggest that more than one third of the adult population in the United States is affected by excess weight. Approximately 33.3% of adult males, 35.3% of adult females, and 10% to 16.5% of teenagers and children are clinically obese.1 Weight loss surgery is one treatment option for patients who are overweight. Bariatric surgeries increased during 1993 to 2005 from 9189 to more than 140,000 per year.2 Caring for the patient with bariatric concerns presents a number of challenges for the perianesthesia nurse.
The most useful anthropometric index for determination of obesity is the body mass index (BMI). This measurement describes the relationship between height and weight using one of the following calculations:
The higher the BMI, the greater the weight associated with a given height (Table 45-1). 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.3 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 surgery.
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. The reason for the decrease in expiratory reserve volume 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 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. Reportedly more than 70% of patients undergoing weight loss surgery have been clinically diagnosed with sleep apnea.4 OSA can occur in patients with redundant pharyngeal tissue. Obstructive sleep apnea 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.4
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.
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.
There are a number of contributing factors associated with obesity such as environment, genetics, highly processed and energy-dense foods, lack of exercise, 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 sooth 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. 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.