Perioperative Care of the Morbidly Obese Patient

Chapter 93


Perioperative Care of the Morbidly Obese Patient



Obesity has become a major health epidemic. Not only is it associated with significant comorbidities, but it also serves as an independent risk factor for early mortality. In a 2009-2010 survey, more than 50% of U.S. adults were overweight (body mass index [BMI] 25 to 29.9 kg/m2), as many as one third were obese (BMI ≥ 30 kg/m2), and up to 5% were morbidly (or severely) obese (BMI ≥ 40 kg/m2).


As a result of the increasing prevalence of obesity in the United States, health care providers are caring for a greater number of morbidly obese patients undergoing both bariatric and nonbariatric surgical procedures. Optimal perioperative management requires the ability to accurately assess and treat multiple organ systems in order to reduce the likelihood of complications.




Preoperative Evaluation


Morbidly obese patients are at increased risk for perioperative complications. Risk stratification remains difficult, however, as progressive organ dysfunction often goes undetected until the patient is faced with a surgical stress response. The Obesity Surgery Mortality Risk Score (OS-MRS) was developed as a tool to risk-stratify obese patients undergoing bariatric surgery. This system utilizes five patient characteristics that have been identified as independent risk factors for perioperative mortality, including (1) BMI ≥ 50 kg/m2, (2) hypertension, (3) male gender, (4) significant risk factors for pulmonary embolism (such as pulmonary hypertension or previous venous thromboembolism), and (5) age ≥ 45. Predicted postoperative mortality risks are as follows: 0.2% to 0.3% for patients with zero or one risk factor, 1.1% to 1.3% for those with two or three risk factors, and 2.4% to 4.3% for those with four or five risk factors. Although this system was designed to risk-stratify patients specifically undergoing bariatric surgery, it is likely that similar attributes play a contributing role in many major abdominal procedures.


The American Heart Association (AHA) has developed specific guidelines for the preoperative cardiovascular evaluation of the morbidly obese patient for noncardiac surgery. In addition to a thorough history and physical examination, additional preoperative testing should be targeted according to symptoms and risk factors with the purpose of identifying undiagnosed comorbidities. Supplementary laboratory investigations should be tailored to the specific operation. General recommendations for preoperative screening include a complete blood cell count, comprehensive metabolic panel with liver function tests, coagulation panel, hemoglobin A1C, urinalysis, spirometry, standard posterior-anterior (PA) and lateral chest radiograph (CXR), and an electrocardiograph (ECG). Given the magnitude of organ systems affected by obesity, each patient much be assessed on an individual basis with appropriate system-specific screening as indicated.



Pulmonary


Pulmonary dysfunction is highly prevalent among morbidly obese patients. Conditions such as obstructive sleep apnea, obesity hypoventilation syndrome, and pulmonary hypertension all result in severe alterations of respiratory physiology and significantly increase perioperative risk. Furthermore, morbidly obese patients are more likely to experience perioperative respiratory complications such as hypoxemia, pneumonia, and respiratory failure.



Obstructive Sleep Apnea (see Chapter 80)


Obstructive sleep apnea (OSA) is common among obese individuals and is a potentially fatal condition in the perioperative period if not identified and treated appropriately. The diagnosis should be suspected when patients (or their partners) report symptoms including snoring, frequent awakening from sleep with dyspnea, or daytime somnolence. Patients frequently experience apneic episodes resulting from upper airway obstruction secondary to excessive fat and redundant pharyngeal tissue. Large neck circumference is strongly predictive of clinically significant obstructive symptoms.


OSA significantly increases the risk for perioperative complications and postoperative respiratory failure. Apneic episodes are associated with an increased risk for aspiration, cardiac dysrhythmias, pulmonary hypertension, hypoxia, and hypercapnia. Several studies have suggested that OSA may be a positive predictor for an increased incidence of anastomotic leaks, prolonged hospitalization, and intensive care unit (ICU) admission.


Patients suspected of having OSA should undergo preoperative polysomnography testing. The degree and severity of OSA can be quantified during such testing by counting the number of times a patient develops apnea or hypopnea over a period of time—the so-called apnea-hypopnea index (AHI). By combining the AHI with more subtle sleep interruptions (respiratory event–related arousals [RERAs]), one can calculate the respiratory disturbance index (RDI). The RDI equals the number of RERAs, hypopneas, and apneas, all divided by the number of hours taken for the test. Continuous positive airway pressure (CPAP) or non-invasive assisted respiration (e.g., using bilevel positive airway pressure [BIPAP]) is recommended when patients demonstrate a significant respiratory disturbance index (RDI) > 25 (Chapter 3). Non-invasive ventilatory support is also indicated for patients who have apnea-induced comorbidities including pulmonary hypertension or cardiac dysrhythmias. Once the need for positive airway pressure support is established, it is recommended that patients have several weeks of use prior to their elective procedure. Patients with severe obstructive sleep apnea or an inability to tolerate CPAP/BIPAP may be considered for elective tracheostomy.



Obesity Hypoventilation Syndrome (see Chapter 80)


Obesity hypoventilation syndrome (OHS) is characterized by chronic hypoxemia and hypercapnia that worsens when asleep. The syndrome results from a restrictive lung pattern created by the excess weight of the chest wall with a predisposition to CO2 retention. Obese patients demonstrate reduced spirometric measures including functional residual capacity and expiratory reserve volume as a result of poor chest compliance (Figure 29.1 in Chapter 29).


Chronic hypoxemia may eventually lead to compensatory polycythemia and increase the risk for venous stasis. Phlebotomy is recommended for patients with hemoglobin concentrations ≥ 16 g/dL. The state of chronic hypoxemia and secondary vasoconstriction often results in pulmonary hypertension. Patients with concomitant pulmonary hypertension and right-sided heart failure should be considered for prophylactic inferior vena cava (IVC) filter placement, as pulmonary embolism would be tolerated poorly.


Preoperative arterial blood gas evaluation is recommended for morbidly obese patients with a history of cardiopulmonary disease. Severe hypoxemia or hypercapnia may indicate a need for right heart catheterization. Preoperative medical optimization under the care of a cardiologist or pulmonologist is indicated in the setting of pulmonary hypertension with cor pulmonale.



Cardiac


Obesity has been cited as an independent risk factor for cardiac disease. This is likely, at least in part, an epiphenomenon, as obese patients frequently suffer from other comorbidities including hypertension, hypercholesterolemia, diabetes, and altered respiratory physiology.


Assessment of cardiac risk in the morbidly obese patient should initially be based on history and physical examination. Historical information used to evaluate functional capacity and baseline cardiac function, however, may be difficult to interpret because of the deconditioning and respiratory problems that often accompany morbid obesity. The American College of Cardiology/American Heart Association has published guidelines that specify what further testing is warranted.


There is general consensus that morbidly obese patients should, at the very least, be screened with a preoperative ECG. Patients with more than one cardiac risk factor and decreased functional capacity may benefit from further non-invasive stress testing. Echocardiography or cardiac catheterization may be indicated in the obese patient with significant respiratory comorbidities or signs of heart failure. If abnormalities are identified, patients should undergo evaluation by a cardiologist with preoperative optimization as indicated.



Endocrine


Diabetes is associated with increased perioperative morbidity and mortality. Morbidly obese patients often suffer from dysregulated glycemic control secondary to insulin resistance or frank diabetes mellitus. Furthermore, the stress response and elevated catecholamines induced by surgery typically exacerbate hyperglycemia.


Preoperative assessment should include a basic metabolic panel with blood glucose and hemoglobin A1C. Patients with diabetes should establish appropriate glycemic control with the assistance of their primary care physician or endocrinologist prior to operative intervention. Although there are no strict guidelines, blood glucose should generally be maintained between 80 and 150 mg/dL preoperatively and HbA1C < 7. The overnight fast or nil per os (NPO) status required prior to surgery mandates adjustment of hypoglycemic medications or insulin dosing to avoid perioperative hypoglycemia. Thiazolidinediones and insulin secretagogues should be held on the morning of surgery. Metformin has been associated with lactic acidosis and should be held 1 day prior to surgery. Long-acting oral hypoglycemics should be held 2 to 3 days prior to surgery. Patients who require insulin should continue their typical basal dosage to avoid ketoacidosis.

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Jul 7, 2016 | Posted by in CRITICAL CARE | Comments Off on Perioperative Care of the Morbidly Obese Patient

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