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25. Bariatric Surgery: Clinical Presentation and Evaluation
Keywords
Metabolic syndromeMorbid obesityObesityDiabetes mellitusDyslipidemiaHypertensionWeight loss surgeryPreoperative workupIntroduction
Obesity is defined by the World Health Organization (WHO) as an excessive fat accumulation that may impair health [1]. It is frequently classified using the body mass index (BMI) , defined as weight in kilograms divided by the height in meters, squared, which provides a value in units of kg/m2. According to the NIH, overweight encompasses BMIs between 25.0 and 29.9, while obesity I is defined as BMI between 30.0 and 34.9 and obesity II as 35–39.9. Patients with a BMI ≥40 are referred to as having extreme or morbid obesity III [2] and ≥50 kg/m2 as the super obese [1].
The global prevalence of obesity has risen dramatically in recent decades [3]. This rising has been described as “globesity” by the interdisciplinary European guidelines on metabolic and bariatric surgery [4] and is currently affecting both developed and developing countries. Worldwide, the number of people who are overweight or obese climbed from 857 million in 1980 to 2.1 billion in 2013 [5]. A recent study from the WHO showed that for overweight, rates increased from 55.9% of the population in 2010 to 58.7% in 2016 and for obesity, from 20.8% to 23.3% [6].
Obesity, in addition to causing various physical disabilities and psychological problems, has severe deleterious health effects, such as diabetes, high blood pressure, dyslipidemia, and obstructive sleep apnea (OSA), among other disorders [7, 8]. Because of these multiple health risks accompanying excess weight and the absence of an effective nonsurgical weight loss treatments, bariatric surgery has become increasingly common, especially in patients with morbid obesity [9]. This also was proven by the Swedish Obese Subjects (SOS) study , were they confirmed that bariatric surgery is associated with reduced long-term morbidity and mortality, considerably contributing to the evidence base for the increased use of surgery for morbidly obese patients [10, 11].
For many years, bariatric surgery has been synonymous only with weight loss, but these procedures have demonstrated to be effective on the resolution of the comorbid conditions, therefore assuming the role of “metabolic surgery” [12]. In this chapter, we will discuss the metabolic disorders associated with obesity and the proper preoperative workup, a cornerstone for the success of bariatric surgery.
Clinical Presentation, Sequelae of Obesity
Obesity is associated with increased mortality. Each 5 kg/m2 increase in BMI above 25 kg/m2 increases overall mortality by approximately 30%. At 30–35 kg/m2, median survival is reduced by 2–4 years and at 40–45 kg/m2 by 8–10 years [13]. The main causes of death include ischemic heart disease [14], stroke [15], and diabetes-related complications [13]. The vicious cycle resulting in increased mortality in obesity involves insulin resistance, as well as all the components of metabolic syndrome (i.e., hyperglycemia, dyslipidemia, and hypertension).
Metabolic Syndrome
Fasting plasma glucose ≥100 mg/dL or undergoing drug treatment for elevated glucose.
HDL-C <40 mg/dL in males or <50 mg/dL in females or undergoing drug treatment for reduced HDL-C.
Triglycerides ≥150 mg/dL or undergoing drug treatment for elevated triglycerides.
Waist circumference >102 cm in males or >88 cm in females for people of most ancestries living in the United States. Ethnicity and country-specific thresholds can be used for diagnosis in other groups, particularly Asians and individuals of non-European ancestry who have predominantly resided outside the United States.
Blood pressure ≥130 mm Hg systolic or ≥85 mm Hg diastolic or undergoing drug treatment for hypertension or antihypertensive drug treatment in a patient with a history of hypertension.
The risk of metabolic syndrome probably begins before birth [17]. The Prediction of Metabolic Syndrome in Adolescence Study showed that the coexistence of low birth weight, small head circumference, and parental history of overweight or obesity places children at the highest risk for metabolic syndrome in adolescence [18]. According to the National Cholesterol Education Program (NCEP) criteria , the prevalence of metabolic syndrome in bariatric surgical patients is 80% [19], and there is evidence that surgical patients with metabolic syndrome are likely to develop hyperglycemia which increases the risk for postoperative complications including surgical site infection [20–22].
Based on the data presented above, patient optimization before surgery is vital to ensure favorable outcomes after surgery. The importance of perioperative management of obese patients cannot be overemphasized.
Type 2 Diabetes Mellitus (T2DM)
Although T2DM is a heterogeneous disease with causes that are yet not fully explained, obesity is considered the primary risk factor [23]. It has been estimated that the risk of developing T2DM is increased 93-fold in women and 42-fold in men who are severely obese when compared to healthy-weight individuals [24, 25]. Currently, only a small proportion of patients with T2DM are not overweight [26].
In the United States, only 52% of patients with T2DM maintain hemoglobin A1c (HbA1c) <7% [27]. Implementing more effective strategies to prevent and treat diabetes has become a top priority in twenty-first-century medicine. Preoperative glycemic control should be optimized using a diabetes comprehensive care plan, including healthy dietary patterns, medical nutrition therapy, physical activity, and as-needed pharmacotherapy. Reasonable targets for preoperative glycemic control , which may be associated with improved bariatric surgery outcomes, include a HbA1c value of 6.5–7.0% or less, a fasting blood glucose level of <110 mg/dL, and a 2-hour postprandial blood glucose concentration of <140 mg/dL [28].
There is substantial evidence demonstrating that metabolic surgery achieves superior glycemic control and reduction of cardiovascular risk factors in obese patients with type 2 diabetes compared with various lifestyle/medical interventions [29, 30]. Schauer et al. [31] conducted the STAMPEDE (Surgical Therapy and Medications Potentially Eradicate Diabetes Efficiently) trial , a randomized controlled trial involving 150 patients comparing medical therapy (MT) versus Roux-en-Y gastric bypass (RYGB) and sleeve gastrectomy (SG) for the treatment of T2DM. The primary outcome was HbA1 <6% with or without the use of medications. At 5 years follow-up, results were available in 139 patients. The primary end point was met by 5% of patients who received MT, compared with 29% of patients who underwent RYGB and 23% of those who underwent SG (P value, RYGB versus MT = 0.01; SG versus MT = 0.03; and RYGB versus SG = 0.53). They concluded that bariatric surgery was clearly superior to MT in terms of glycemic control.
Recently, the American Diabetes Association proposed that “metabolic surgery” (involving procedures initially developed to treat obesity) should be considered as a standard diabetes treatment option for appropriate candidates with inadequately controlled type 2 diabetes and a BMI >30 kg/m2 or >27.5 kg/m2 for Asian individuals [32].
Comparison Between RYGB and SG
Some other studies compared T2DM remission rates between SG and RYGB . Pournaras et al. [33] analyzed a cohort of 1006 patients, of whom 209 (20.7%) had T2DM, with a mean follow-up of 23 months. Remission was defined as a return to HbA1c <6%, fasting glucose <5.6 mmol/L at least 1 year after bariatric surgery without the use of hypoglycemic medications. These authors found that remission rates were 26% after SG and 40.6% after RYGB. On the other hand, a recent systematic review, including seven randomized controlled trials with 732 patients, showed that measures of glycemic control (HbA1c and fasting blood glucose levels) improved with both procedures, with similar improvement after laparoscopic RYGB and laparoscopic SG at 12 months postoperatively [34]. In the STAMPEDE trial [31], although no statistically significant difference between the two surgical groups was found for the primary end point, other end points such as the number of antidiabetic medications showed superiority of the RYGB over the SG .
These results have been recently substantiated by two randomized and multicenter trials performed in Finland and in Switzerland, with large number of patients and 5-year follow-up. Both studies confirmed similar results between the RYGB and the SG in terms of metabolic control, which was improved by both procedures [35, 36].
Overall, both RYGB and SG seem to be equally effective in improving or resolving T2DM; however, long-term data are still lacking.
Hypertension
Hypertension is one of the most common comorbidities associated with obesity and a major risk factor for stroke and coronary artery disease. It is estimated that hypertension is present in up to 40–70% of obese patients. Despite the well-known correlation between obesity and hypertension, the underlying mechanisms are not fully understood. Insulin resistance and hyperinsulinemia are frequent in obese patients, and both play a role in elevating the blood pressure. There is evidence showing that hyperinsulinemia stimulates the sympathetic nervous system (SNS) [37]. This is further supported by studies showing a decrease in blood pressure and SNS activity when insulin levels are lowered by low-energy diets. Renin–angiotensin–aldosterone system is also activated and stimulated in obese patients [38]. This stimulation is a result of an increase in angiotensin production by adipocytes, SNS overstimulation by hyperinsulinemia, and high levels of aldosterone production by free fatty acids [39]. Another potential mechanism implicated in the pathophysiology of obesity-related hypertension is a decrease in natriuretic peptides [40].
Schiavon et al. [41] hypothesized that hypertension improvement after bariatric surgery could be attributable to hemodynamic changes and decreased intra-abdominal pressure associated with weight loss. The reduction of the hyperinsulinemia decreases the renal sodium reabsorption and sympathetic tone. In addition, the reduction in perivascular adipocyte inflammation may help in reducing blood pressure by decreasing arterial stiffness. Interestingly, Ahmed et al. [42] found reduction in systolic (9 mmHg) and diastolic (7 mmHg) blood pressure as early as week 1 after RYGB. This early drop in blood pressure before any significant weight loss suggests a possible weight-independent hormonal mechanism behind this effect of bariatric surgery .
Dyslipidemia
Dyslipidemia can be present in more than 50% of bariatric patients [36]. Dyslipidemia creates a pro-inflammatory state with an increased production of reactive oxygen species, tumor necrosis factor alpha, interleukin-6, and C-reactive protein. This process contributes to atherosclerosis by direct endothelial damage or indirectly by promoting other diseases such as T2DM or hypertension [43].
Bariatric surgery has shown to lower total cholesterol, low-density lipoprotein (LDL) cholesterol , and triglycerides, and increase high-density lipoprotein (HDL) cholesterol , allowing a significant number of patients to discontinue statins and other lipid-lowering medications.
Nguyen et al. [44] showed that 1 year after RYGB, mean total cholesterol levels decreased by 16%, triglyceride levels decreased by 63%, LDL cholesterol levels decreased by 31%, and HDL cholesterol levels increased by 39%. In addition, within 1 year, 82% of patients requiring lipid-lowering medications preoperatively were able to discontinue their medications.
These results have been recently confirmed by the two European trials previously discussed [35, 36]. The SLEEVEPASS study showed that after 5 years, medications for dyslipidemia were discontinued in 47% of patients (n = 14/30) after SG and in 60% of patients (n = 24/40) after RYGB (P = 0.15). Of the 38 patients in the whole study group who discontinued dyslipidemia medication, 22 had true dyslipidemia remission (LDL-C level <115.8 mg/dL [3.0 mmol/L] and no dyslipidemia medications); the remission rate was 20% (6/30) in the SG group and 40% (n = 16/40) in the RYGB group [35]. Similarly, the SM-BOSS study (36) showed that a complete remission was seen in 29 (42.6%) of 68 in the SG group versus 33 (62.3%) of 53 in the RYGB group, 5 years after surgery (absolute difference, −0.19%; 95% CI, −0.38% to −0.003%) [36].
Despite both SG and RYGB having metabolic effects in obese patients, the lipid-lowering effect seems to be more pronounced after RYGB. In fact, recent studies have shown that dyslipidemia resolved significantly more often after RYGB compared with SG [45]. This can be attributed to the endocrine changes that occur after RYGB such as an increase in adrenocorticotrophic hormone, GLP, and peptide YY and a decrease in insulin, insulin-like growth factor-1, leptin, and ghrelin [43].
Obstructive Sleep Apnea (OSA)
Obesity is a well-known risk factor for this disorder that has implications beyond disrupted sleep [46]. OSA is characterized by repetitive partial or complete airway collapse causing hypoxemia and/or hypercarbia. It is defined by overnight polysomnography as cessation of airflow of greater than 10 seconds with continued ventilatory effort, five or more times per hour of sleep, with a decrease in arterial oxygen saturation [47]. Signs and symptoms of OSA may include a family report of disruptive snoring, daytime sleepiness, obesity, large neck circumference, systemic and pulmonary hypertension, cardiac arrhythmias, myocardial ischemia, ventricular hypertrophy, and failure [48, 49]. In addition to BMI, age, male sex, and smoking are well-known risk factors for OSA [50–53].
The prevalence of OSA can be as high as 78% in morbidly obese patients who present for bariatric surgery [54]. Up to 80% of individuals with less severe forms of OSA are undiagnosed [51], while severe OSA is undiagnosed in approximately 10–20% of patients with BMI >35 [55]. Undiagnosed OSA may lead to perioperative complications including difficult mask ventilation and/or intubation, postoperative reintubation, cardiac dysrhythmias, and increased hospital length of stay [20]. The Sleep Heart Health Study found a strong correlation between weight change and progression/regression of OSA (stronger relationship for men than women) [56]. Bariatric surgery is a reasonable option for weight reduction for patients with clinically severe obesity [57, 58].
Obesity is a complex interaction between multiple genetic, socioeconomic, and cultural factors that also are associated with existing or resulting comorbidities and their treatment. The prevalence of obesity continues to be high, as are associated comorbidities and healthcare costs. Early intervention and effective treatment of obesity are needed to reduce costs and improve outcomes for these patients. Metabolic surgery has proven to offer health benefits that extend beyond weight loss, and most patients suffering from these disorders will obtain significant improvements after surgery.
Preoperative Evaluation
Preoperative care of the bariatric patient remains a challenging proposition because of the metabolic, pharmacologic, and system-wide disorders that are the foundational basis for the complications that can ensue. Hence, patients should undergo a routine preoperative assessment with a comprehensive multidisciplinary group. The core team providing such workup should optimally consist of obesity-experienced specialists .
Best preoperative care will yield a comprehensive understanding of a patient’s medical status as it pertains to predicted outcomes and psychological ability to comply with required postoperative recommendations for health maintenance and to achieve success following weight loss surgery.
Patient Selection
Perhaps the most important step of the preoperative process is patient selection. Many patients approach bariatric surgeons to help them with their weight without an appreciation of the need for preoperative physical and psychological evaluation, knowledge of surgical options, potential perioperative complications, the need for lifelong follow-up after bariatric surgery, and with unrealistic weight loss expectations. During an initial evaluation, a surgeon should consider if a patient has any hard contraindications for surgery based on history or physical exam. If a patient is acceptable at that point, that only means they are acceptable to continue the workup for bariatric surgery. A multidisciplinary preoperative assessment by a team of endocrinologists, dieticians, psychologists, and the surgeon, to evaluate and educate the patient, helps in appropriate patient selection and ensure that the patient is physically and psychologically fit to undergo weight loss surgery (WLS) .
Patient Education
The lack of patient education leads to patient’s frustration with the process of preparation for bariatric surgery and the preoperative requirements proposed by the multidisciplinary team. In addition, patients may have unrealistic expectations regarding the potential perioperative complications and weight loss after surgery. Many patients seeking bariatric surgery hold unrealistic expectations, without a complete understanding of the procedures and the subsequent long-term implications [59–61].
Patient’s understanding of long-term consequences of bariatric surgery, such as postoperative lifestyle modifications, need for long-term follow-up, and consistent implementation of recommended postoperative regimens, facilitates a more informed decision-making, leading to better outcomes .
Medical Evaluation
A comprehensive medical evaluation entails a meticulous history, a thorough physical examination, and a review of the cardiovascular, pulmonary, and gastrointestinal systems, as well as a metabolic and nutritional status assessment.
Cardiac Evaluation
One of the essential elements of promoting safety in any surgical patient, but especially morbidly obese patients, is adequate evaluation of their cardiac status and cardiac risk preoperatively. Obesity is a well-established risk factor for cardiovascular comorbidities including coronary heart disease (CHD), arrhythmias, left ventricular hypertrophy, and heart failure [62].
Calle et al. [63] ran a prospective study of over a million people followed for 14 years, where they showed that obesity was strongly associated with an increased risk of cardiovascular mortality. This study directly correlated CHD mortality risk with increasing BMI, reporting a twofold to threefold greater risk in individuals who had a BMI of 35 kg/m2 or higher compared with leaner persons (BMI 18.5–24.9 kg/m2).
Bariatric patients need a focused cardiac history, which should include history of coronary artery disease (CAD), coronary symptoms, and coronary risk factors (hypertension, diabetes, hyperlipidemia, smoking, stress, sedentary lifestyle, etc.). Cardiac evaluation includes a 12-lead electrocardiogram, followed by assessment of cardiac function with stress testing. The traditional stress testing methods (e.g., treadmill exercise, scintigraphic imaging) may not be feasible in morbidly obese patients given the weight limitations of the testing equipment and the difficulty to accurately interpret the images owing to the patient’s body habitus [64, 65]. Pharmacological stress echocardiography, with or without ultrasound contrast agents, is an effective alternative for this patient population that can provide an accurate assessment of cardiac function [66, 67].
Airway and Pulmonary Evaluation
Given that obesity is a risk factor for airway disease secondary to mechanical restriction, routine preoperative pulmonary function tests help assess the pulmonary reserve and identify those at risk for postoperative pulmonary complications [68]. OSA is common among morbidly obese patients, especially males, as discussed above. Recently, a meta-analysis including more than 1000 patients showed that the impact of gaining weight on pulmonary function was greater in men than in women, as each kilogram gained results in a 26 mL FVC (forced vital capacity) and 23 mL FEV1 (forced expiratory volume in the first second) decrease in men versus 14- and 9-mL decrease, respectively, in women [69]. Knowing that these patients are at a higher risk for morbidity and mortality, it is important to screen all patients for OSA before embarking on bariatric surgery. The most appropriate test to evaluate OSA is nocturnal polysomnography (PSG). Albeit most patients diagnosed with OSA benefit from continuous positive airway pressure (CPAP) or bilevel positive pressure preoperatively [70, 71], it is recommended a period of preoperative adjustment prior to surgery, as many patients have trouble tolerating the face mask.
Venous Thromboembolism (VTE) Evaluation
VTE , including pulmonary embolism (PE) and deep vein thrombosis (DVT), remains a significant cause of mortality and morbidity after bariatric surgery (72). Common factors thought to predispose patients to higher risk of VTE are previous history of VTE, male gender, operative time more than 3 hours, higher BMI, and advanced age [72]. The most common methods of prophylaxis range from mechanical compression devices with early ambulation alone to the addition of chemoprophylaxis and the use of inferior vena cava filters [73].
A comprehensive assessment and stratification of the risk of adverse events can inform clinical decision-making and help in identifying ideal candidates for bariatric surgery and those that may require closer postsurgical monitoring.
Psychological Support
Weight history
History of eating behaviors/disorders (including binge eating, anorexia nervosa, night eating syndrome, and compensatory behaviors)
Current or lifetime history of mood and anxiety disorders
Cognitive functioning
Current and past mental health treatment
Patient knowledge and motivation for weight loss
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