© Springer International Publishing Switzerland 2017Andrew Loveitt, Margaret M. Martin and Marc A. Neff (eds.)Passing the Certified Bariatric Nurses Exam10.1007/978-3-319-41703-5_9
9. Preoperative Evaluation of the Bariatric Surgery Patient
Department of General Surgery, Rowan University, Stratford, NJ, USA
As with any operative undertaking, a careful analysis of the risks and benefits of the planned bariatric surgical procedure must be made. The initial encounter between the patient and bariatric surgeon typically occurs as a result of referral, whether from another physician involved in the patient’s care, a satisfied past patient, or research and self-referral. From this time, a careful bond is formed between the surgeon and patient to facilitate the safest and most efficient realization of the patient’s weight loss goals. By its nature, bariatric surgery is performed only on an elective basis; as such a thorough preoperative evaluation is necessary to minimize the risk of undue complications. The goal of this evaluation and workup is not necessarily to uncover any and all underlying medical diseases but to identify, analyze, and account for any comorbidities which could affect the patient in the perioperative (surgery and 48 h after) and postoperative (30 days) periods. Well-proven indicators for increased risk of peri- and postoperative complication include American Society of Anesthesiologist classification, American Heart Association/American College of Cardiologist guidelines, age, and multiple other indications of underlying medical diseases such as diabetes mellitus, cardiovascular disease, and renal impairment. When deciding the extent of necessary preoperative workup, the patient’s history and physical exam, the intended procedure, anesthesia plan (all laparoscopic bariatric surgeries are performed under general anesthesia), and the expected postoperative disposition are analyzed .
When a thorough history and physical exam reveal signs of underlying comorbid disease, which are increasingly common in the morbidly obese patient population, further workup is warranted. In the setting of uncontrolled or poorly controlled medical diseases, consultation to a medical internist and/or medical subspecialist can be exceedingly helpful. Common comorbid diseases and a general understanding of their workup and management will be discussed by organ system.
Approximately 30 % of patients undergoing surgery in the United States have significant coronary artery disease or a severe cardiac comorbidity. One in eight of these will suffer a perioperative complication . If a patient has a known history of cardiac disease, he or she should receive a full evaluation and workup by his/her existing cardiologist. Evaluation of the patient’s functional status, presence of symptoms, and the use of one of many accepted cardiac risk assessment guidelines should be performed. Essential hypertension, pulmonary hypertension, left ventricular hypertrophy, congestive heart failure, and ischemic heart disease are all found at a higher frequency in morbidly obese patients. Patients with any of these factors are eligible for beta-blocker therapy, and patients with two or more should undergo further noninvasive cardiovascular testing prior to any elective operation . Tests that may be ordered include exercise or chemical stress test, echocardiogram, or even direct coronary angiography in patients with a substantial cardiac history or previous revascularization (catheterization with balloon angioplasty or bypass graft). If warranted, elective bariatric surgery may be postponed in favor of having coronary revascularization. In the setting of a recent myocardial infarction and subsequent revascularization, the risks of surgery and anesthesia are substantially elevated in the first six weeks, and elective operations are contraindicated during that time. Patients with a history of coronary stenting require antiplatelet therapy and will often be continued on aspirin and other medications such as clopidogrel or ticagrelor .
Obesity, obstructive sleep apnea (OSA), and obesity hypoventilation syndrome (OHVS) are all substantial risks for perioperative complication. Most morbidly obese patients suffer from OSA and OHVS. Many already follow with pulmonologists and are being treated. While weight reduction offers the greatest likelihood of curing these diseases, the patients should still remain under the care of their pulmonary specialists during the pre-, peri-, and postoperative periods . Careful history taking and examination of patients who may not carry these diagnoses are critical as they may have OSA and OHVS but not be diagnosed or properly treated. These patients should also be sent to a pulmonologist for consultation and sleep study evaluation. Treatments such as continuous positive pressure ventilation and bronchodilators will likely need to be continued before and after the surgery.
Evaluation for signs of renal dysfunction is of utmost importance in the patient undergoing bariatric surgery. Patients with known renal impairment should be followed by their primary nephrologists. Occasionally, patients on renal replacement therapy will undergo bariatric surgery and will therefore need hemodialysis treatments and close monitoring of their serum chemistry while in the hospital. Kidney disease raises the risks for cardiac events in the perioperative setting as well as many other complications . Patients with renal disease will need electrocardiogram monitoring, and signs of heart failure or volume overload should be monitored. Dialysis and other medical interventions for electrolyte abnormalities such as hyperkalemia, hyperphosphatemia, hypocalcemia, and others may need to occur. Anemia of chronic kidney disease is also commonly present in such patients. The pharmacodynamics of many medication classes including opiate pain medications is typically prolonged in patients with renal impairment.
Even in the patient without existing renal impairment, preventing any insult to the kidneys is a concern in the bariatric patient. In the post- and perioperative periods, maintaining adequate intravascular volume can be challenging. Obese postoperative patients who have a difficult time taking adequate liquids by mouth pose a unique risk for hypovolemia and may require substantial intravenous fluid administrations. Further, nephrotoxic medications such as NSAIDs and several diuretic antihypertensive medications should generally be avoided. To avoid the need for invasive monitoring of volume status, strict vital signs and intake/output measurements are very important and will be closely followed by the bariatric surgeon.
A number of endocrine diseases and deficiencies play a role in the perioperative care of bariatric patients: most commonly diabetes mellitus, thyroid disorders, and adrenal disorders. With an increasing incidence in the general population, especially in the obese, as well as representing an indication for bariatric surgery, diabetes mellitus is a common and potentially complicated illness in the bariatric population. Patients should be carefully screened in the preoperative evaluation for signs and symptoms of DM to include neuropathy and retinopathy plus laboratory testing for signs of complications of DM such as nephropathy, cardiac disease, and peripheral vascular disease . Adequate control of blood sugars, typically with the assistance of an internist or endocrinologist, is paramount. A serum hemoglobin A1c value can be drawn to assess the adequacy of blood sugar control over recent weeks. The patient will continue on his/her prescribed glucose control regimen in the preoperative period, which often requires subcutaneous injections of insulin. This regimen will be seen to change in the perioperative period as insulin resistance in type 2 diabetics begins to resolve almost immediately after bariatric surgery. Most patients will be able to omit oral antihyperglycemic medications by the time of discharge and will see substantial reductions in their insulin needs as well. Typically, surgeons will instruct patients to use one half to one third of their regularly prescribed insulin doses the evening and morning of surgery to account for prolonged NPO status. Oral medications are held the day of surgery and often discontinued. The medication metformin should be noted to increase the risk of acute kidney injury, especially in the setting of hypovolemia or IV contrast administration. While in the hospital, frequent finger stick blood glucose values (every six hours) with an insulin sliding scale are prudent for following glucose values in the perioperative period. Any circumstances of overt hypoglycemia should beckon a call to the physician and prompt treatment with oral supplementation (juice, glucose) or intravenous dextrose for a symptomatic patient.