Preoperative Evaluation: Priorities and Pointers, Part 2
ABSTRACT: In patients with diabetes, tight glucose control during the perioperative period may improve outcomes. Insulin therapy is usually needed, often as a continuous infusion. Smoking is associated with an increased likelihood of postoperative complications even in patients without lung disease; recommend that patients quit smoking at least 8 weeks before surgery. Preoperative bronchodilator therapy is indicated for patients with chronic obstructive pulmonary disease whose disease is not well controlled; if symptoms continue, prescribe a 2-week course of systemic corticosteroids before surgery. The need for and type of thromboprophylaxis is determined by patient age, presence of risk factors, and type of surgery. Risk factors for postoperative delirium include advanced age, low educational level, polypharmacy, alcohol and sedative withdrawal, impaired vision and hearing, sleep deficiency, anxiety, depression, and dementia. Key words: perioperative care, diabetes mellitus, chronic obstructive pulmonary disease, delirium ___________________________________________________________________________________________ In patients with underlying disease, a preoperative evaluation and targeted perioperative management strategies can minimize surgical complications and maximize healing. In my article "Preoperative Evaluation: Priorities and Pointers Part 1, Cardiac Assessment", I discussed interventions that can reduce the risk of perioperative cardiac mortality and morbidity. Here I focus on how to identify surgery patients at risk for complications caused by diabetes, chronic obstructive pulmonary disease (COPD), and other medical conditions; I also describe strategies to minimize such risk. Note that preoperative testing in apparently healthy persons is likely to produce little, if any, benefit. A systematic review found that results of routine chest radiographs, ECGs, complete blood cell counts, tests of hemostasis and biochemistry, and urinalysis led to a management change in fewer than 3% of patients.1 GENERAL RECOMMENDATIONS Maintenance of normothermia may reduce the risk of postoperative infection. A randomized trial of maintaining normothermia was stopped halfway through the protocol because of the dramatic decrease in wound infections and the concomitant decrease in hospital days, days to solid food, and days to suture removal in those patients in whom normothermia was maintained.2 The practice of requiring an 8- to 12-hour preoperative NPO fast may be coming to an end. A recent study now recommends free intake of clear fluids up to 2 hours before anesthesia and suggests that a preoperative carbohydrate- rich beverage may reduce postoperative insulin resistance and improve recovery.3 DIABETES MELLITUS Diabetes is a risk factor for vascular, infectious, and wound-related postoperative complications.4,5 In addition, patients with diabetes are at higher risk for perioperative metabolic decompensation because of alterations in their glycemic control regimen and because of the stress of surgery itself. Advantages of tight glucose control. Hyperglycemia has a detrimental effect on white blood cell and immunoglobulin function. Recent studies of tight glucose control in hospitalized patients have shown improved outcomes for those who have sustained an acute myocardial infarction, those who are critically ill, and those undergoing cardiac surgery.6-13 Despite the lack of direct evidence, it seems reasonable to extrapolate these findings to patients with diabetes who are undergoing any surgical procedure. Guidelines for perioperative glycemic control were recently published by the American Association of Clinical Endocrinologists. These recommend a target blood glucose level of 110 mg/dL for patients in the ICU, and a preprandial target of 110 mg/dL and a postprandial target of 180 mg/dL for patients in non–critical care units.14 How to achieve good control. To attain tight glycemic control in the perioperative period, insulin therapy is frequently needed, often as a continuous infusion. Guidelines from the American College of Endocrinology recommend insulin infusions for patients who must fast for a prolonged period (more than 12 hours), critically ill patients, and patients undergoing major surgical procedures.14 Insulin infusions are safe and effective as long as the patient’s glucose level is sufficiently high to prevent starvation ketosis and hypoglycemia. Between 5 and 10 g/h of a 5% dextrose infusion is usually adequate. Check glucose levels hourly until they stabilize. Standard orders for insulin infusion can be helpful for both the physician and the nursing staff. Insulin infusion protocols need to be easy to follow, safe, and conducive to the quick achievement of target goals. One example of an insulin infusion protocol is shown in the Box. Maintaining control postoperatively. When helping a patient make the transition to subcutaneous insulin therapy, keep the glucose level at goal. To do this, give a dose of shortacting or rapid-acting insulin 1 to 2 hours before you stop the insulin infusion. Basal and prandial insulin doses are titrated to the patient’s needs. To determine a patient’s 24-hour insulin requirement, calculate the average hourly insulin dose required over the previous 6 to 8 hours (provided the blood glucose was at target and the insulin dose was stable). Multiply this average hourly dose by 24 to determine the daily insulin requirement. Give half this amount as intermediate-acting or long-acting insulin for basal coverage and half as short-acting or rapid-acting insulin in divided doses before meals.15 Further adjustments to the insulin dose may be needed to compensate for changes in stress level, oral intake, intravenous or enteral alimentation, weight, insulin sensitivity, medications, and other factors. PULMONARY DISEASE Strategies that can help reduce postoperative pulmonary complications are summarized in Table 1. Patient-related risk factors. The best way to determine a patient’s risk of postoperative pulmonary complications is to perform a careful history taking and physical examination.16 Be alert for a history of exercise intolerance, chronic cough, or unexplained dyspnea. During the examination, look for decreased breath sounds, dullness to percussion, wheezes, coarse crackles, and a prolonged expiratory phase. All these are associated with an increased risk of pulmonary complications.17 Reserve preoperative pulmonary function testing for patients undergoing lung resection; such testing has not been shown to be predictive of pulmonary complications in studies of other procedures.17-19 Arterial blood gas analysis is not indicated as part of the routine preoperative evaluation of patients with a preexisting lung condition. Smoking. This risk factor is associated with an increased likelihood of postoperative complications even in persons without lung disease. The relative risk of pulmonary complications for smokers ranges from 1.4 to 4.3. To lessen the risk, the patient must stop smoking at least 8 weeks before surgery.20 COPD. This disorder also increases the risk of pulmonary complications; the relative risk ranges from 2.7 to 4.7. Patients with COPD whose symptoms are not well controlled preoperatively, who have signs of airflow obstruction, or whose exercise capacity is suboptimal require aggressive preoperative treatment. Combination therapy is best. Baseline treatment consists of regular use of inhaled ipratropium, with inhaled beta2-agonists added up to 4 times a day as needed to control symptoms. For patients who continue to have symptoms despite bronchodilator therapy or who are not at their personal baseline level of symptoms, a 2-week preoperative course of systemic corticosteroids is reasonable.21 Reserve preoperative antibiotics for patients in whom a change in the character or amount of sputum suggests infection. Asthma. The results of studies of asthma’s association with postoperative complications have been mixed. Nonetheless, before surgery it is reasonable to strive to have patients free of wheezing, with a peak expiratory flow of greater than 80% of their personal best value.22 Procedure-related risk. Certain attributes of a planned procedure can also predict increased risk of pulmonary complications. Risk increases as the incision approaches the diaphragm; upper abdominal and thoracic surgery poses the highest risk of postoperative complications. Postoperative pulmonary complications in patients undergoing abdominal surgery can increase the hospital stay by 1 to 2 weeks.17 However, pulmonary complications from surgery outside the thorax or abdomen are rare, and the risk associated with laparoscopic abdominal surgery is much less than that associated with open procedures. Procedures that last longer than 3 hours also have a higher risk of complications.16 In patients who are at high risk for pulmonary complications, consider using shorter procedures. Epidural, spinal, and regional forms of anesthesia are associated with fewer pulmonary complications than is general anesthesia.16,23,24 Consider using the former whenever this is possible. ADRENAL INSUFFICIENCY Suppression of the hypothalamic-pituitary-adrenal (HPA) axis is a common consequence of glucocorticoid therapy. Overt secondary adrenal insufficiency, which can be precipitated by surgery in a patient with HPA suppression, is a rare but lifethreatening condition. The ability to diagnose HPA suppression depends on the detection of plasma cortisol levels that are inappropriately low for the clinical situation. Any patient who has received a glucocorticoid in a dosage equivalent to 20 mg/d (or more) of prednisone for more than 5 days is at risk for HPA suppression. Recovery from short courses (5 days) occurs rapidly—within 5 days. However, patients who have been exposed to high doses of glucocorticoids for prolonged periods may take up to 1 year to recover their adrenal function. The standard short adrenocorticotropic hormone stimulation test can be used to assess adrenocortical function before surgery.25 Increased perioperative “stress” dosing is recommended for patients at risk for adrenal insufficiency. Appropriate dosages for various types of procedures and baseline glucocorticoid requirements are shown in Table 2.26 THROMBOTIC DISEASE The rationale for interventions to prevent thrombotic disease in perioperative patients has 3 aspects. First, there is a high prevalence of venous thromboembolism in perioperative patients because of the increased risk of venous stasis in this setting. The prevalence of deep venous thrombosis is between 15% and 40% in patients undergoing most types of surgery, and it increases to 40% to 60% in patients undergoing hip or knee arthroplasty or hip fracture surgery. Often, these occurrences are clinically silent. Second, the adverse consequences of venous thromboembolism are significant; they include pulmonary embolism, deep venous thrombosis, and post-thrombotic syndromes. Third, thromboprophylaxis is effective at preventing deep venous thrombosis and pulmonary embolism. Studies have shown it to be cost-effective as well.27 Patients can be assigned to 1 of 4 risk categories based on their age, the presence of risk factors, and the type of surgery planned. Recommendations for thromboprophylaxis for patients in each of these risk categories are listed in Table 3. POSTOPERATIVE DELIRIUM IN ELDERLY PATIENTS Postoperative delirium, characterized by incoherent speech and thought, disorientation, and impaired memory and attention, has been reported in 5.1% to 61.3% of older patients after surgery.28 The condition is considered reversible, since only 1% of patients have persistent cognitive dysfunction 1 to 2 years after surgery. Preoperative risk factors that can contribute to postoperative delirium include advanced age, low educational level, polypharmacy, alcohol and sedative withdrawal, impaired vision and hearing, sleep deficiency, anxiety, depression, and dementia.29 Other important risk factors include the use of physical restraints, malnutrition, more than 3 new medications, and the use of a bladder catheter.30 Correct risk factors preoperatively whenever possible, and be alert for early signs of delirium during the postoperative period. Ambulatory surgery is preferable because the duration of the procedure is shorter and the patient can recover in a familiar home environment. Avoid medications such as meperidine, benzodiazepines, and anticholinergic agents; these agents have been associated with an increased risk of postoperative delirium.31 Patients at high risk may also be assessed before and after surgery with the Mini-Mental State Examination (MMSE) to measure changes in baseline cognitive function. If delirium occurs, search for common postoperative complications, such as pneumonia, urinary tract infection, fluid imbalance, or electrolyte disorders; these are frequent causes of postoperative delirium. After the cause has been identified and treated, the preferred approach for treating delirium is oral haloperidol, 0.25 to 2 mg 1 to 2 hours before bedtime.28 REFERENCES: 1. Munro J, Booth A, Nicholl J. Routine preoperative testing: a systematic review of the evidence. Health Technol Assess. 1997;1:1-63. 2. 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