Diabetes is increasingly more common as the population ages and becomes more sedentary and obese. The American Diabetes Association reports that 20.8 million Americans have diabetes and over 54 million have "prediabetes."1 Many of our surgical patients will have diabetes with various levels of glucose control (see Diagnostic criteria and target values).2,3
Even patients with well-controlled diabetes or no prior diagnosis of diabetes can become hyperglyce-mic with severe illness. The stress of illness or surgery increases the levels of catecholamines, glucocorticoids, glucagons, and growth hormone, which leads to increased gluconeogenesis and lipolysis and de-creased peripheral glucose uptake. Changes in activity level, mealtime, food intake, dextrose infusions, and medication regimens all contribute to hyperglycemia. Finally, insulin absorption is unreliable in those with edema or hypotension, so subcutaneous insulin corrections can be less effective. In type 1 diabetes, control of hyperglycemia is essential as the stress response to illness can rapidly cause diabetic ketoacidosis if insufficient insulin is administered. In both type 1 and type 2 diabetes, hyperglycemia can cause osmotic diuresis and electrolyte imbalances. (See Pathogenesis of type 2 diabetes.) Hyperglycemia delays gastric motility and can exacerbate nausea and vomiting. Hyperglycemia may also contribute to an increased risk of surgical site infections (SSIs). Preven-tion of SSIs is one of the target areas of the Surgical Care Improvement Project.4 The evidence-based recommendations to prevent SSIs include appropriate use of antibiotics, glucose control in patients under-going cardiac surgery, appropriate preoperative sur-gical hair removal, and normothermia in colorectal surgical patients.4
One study found that in the perioperative period, a blood glucose measurement of 300 mg/dL or greater increased the risk of wound infection to more than three times that of patients with blood glucose less than 200 mg/dL.4
Preoperative preparation
Hemoglobin A1C (A1C) levels may help identify patients who are at greatest risk for perioperative hyperglycemia and a poor surgical outcome. Fasting preoperative diagnostic testing for the patient with diabetes will help identify the patient at risk for hyperglycemia and potential postoperative complications. Serum electrolytes may be done to identify electrolyte imbalance, especially hyperkalemia or hypokalemia, and a creatinine level to help assess renal function.5 Myocardial ischemia may be evident on an ECG despite a negative history for heart problems. Diabetic patients with hypertension also have an increased likelihood of diabetic autonomic neuropathy, which may limit the heart's ability to compensate for intravascular volume changes and predispose the patient to cardiovascular instability (postinduction hypotension) and even sudden death.6 Some surgeons request advanced cardiac testing before certain procedures to identify at-risk patients.
When speaking with a patient in the preoperative setting, obtain a complete list of all medications currently used, including herbal supplements. Also include the usual timing of insulin in relationship to meals and correction doses of rapid-acting insulin if home glucose level is elevated. Determine how often the patient checks his glucose levels and if he has had readings under 80 mg/dL or over 180 mg/dL in the past 2 weeks to identify uncontrolled or brittle diabetes. The A1C level can be within the normal range, but this is only part of the picture. The preoperative interview will give you some understanding of the individual's diabetes management before admission as well as insulin sensitivity. The list of medications and lab work indicates specific areas to direct your patient education. If the patient is on medication, suggest he or she discuss modifications with the healthcare provider managing his or her diabetes. It's helpful for the healthcare provider to know the change in diet before surgery, anticipated length of time the patient will be N.P.O. before admission, and expected length of hospital stay. Patients using mixed dosage insulin will likely need a reduced dosage the morning of the procedure. If there's a prep with diet change the day before the procedure, the healthcare provider will need to know the details to guide dosage suggestions. Diabetic patients should be scheduled early in the day to avoid hypoglycemia. Patients with NPH insulin will likely take the same dose the evening before surgery but half the usual dose on the day of surgery.6
Self-management
Patients who use intensive self-management-a continuous insulin infusion (CII) with rapid-acting insulin or those using a basal bolus insulin regimen (long-acting analogue with short-acting analogue)-will generally be more independent and may minimize the need to consult with their healthcare provider. Let the patient know that although the goal is to facilitate self-care, it's necessary that his or her healthcare providers be aware of any situation that may require guidance. Make sure a notation is made about the settings on the pump and location of the site and pump. In some facilities, the patient will not be allowed to use an insulin pump. Tell your patient to check with his or her healthcare provider to determine if he or she can be given a long-acting analogue or an infusion of dextrose with insulin on admission. The anesthesia provider may prefer the infusion because it best affords glucose control with hourly assessment of glucose.7
Monitoring glucose
Surgical facilities should have a protocol outlining glucose targets and interventions so standards of care are followed. Depending on the length of procedure, glucose needs to be monitored every 1 to 2 hours. Sepsis and hyperthermia can cause the patient to return to a catabolic state requiring more insulin, so monitor glucose levels during the entire hospitalization. Other reasons to monitor are the progression of hyperglycemia related to stress in the recovery period, hypoglycemia from a miscalculation of a correction dose of rapid-acting insulin or the prolonged effect of either short- or long-acting insulin when renal function is compromised.
The key to any management regimen is to monitor plasma glucose levels frequently and appreciate the variation between patients. Patients with brittle type 1 diabetes may need their glucose measured every hour, although every 2 or 3 hours is sufficient for many patients with type 2 diabetes. Some type 2 diabetic patients will tolerate minor, brief surgical procedures without any exogenous insulin. The incretin effect explains why some patients who required large dosages of insulin have lower insulin requirements while N.P.O. The stepwise protocol identifies the correct dosages based on insulin sensitivity; however, the dosages may be changed the longer your patient is hospitalized based on physiologic changes and the half-life of preadmission medications.
For example, if your patient was on a thiazolidinedione, it may be several weeks until the effect is diminished, compared with a meglitinide, whose effect lasts 4 to 6 hours. Doherty suggests the following medication considerations: Metformin and sulfonylureas should not be used 24 to 48 hours before surgery because of their long half-lives.5 The medications can be restarted when the patient is taking oral medications postoperatively only if the renal and hepatic function remain adequate. The author also suggests that patients with diabetes be evaluated for temporomandibular joint and cervical spine mobility to anticipate difficulty in intubation, which occurs in obese patients and in 30% of persons with type 1 diabetes. Patients with diabetes may also experience diabetic autonomic neuropathy symptoms. They can include nausea and vomiting, irregular heart rhythm, and unstable BP.6
Postoperatively, patients receiving less than 900 calories/day will be in a calorie-wasting state. Previously stored endogenous carbohydrate is used quickly, resulting in a reduction of muscle masses because amino acids can be derived from muscle and converted to fuel by the liver. A low rate of D5W (less than 1.5 mL/kg/hour) or 0.9% sodium chloride doesn't provide sufficient calories to prevent catabolism. D10W is administered in 1 liter every 6 to 8 hours. Some facilities find it useful to mix short-acting insulin into 0.9% sodium chloride and "piggyback" into the glucose solution so the setting on the I.V. infusion pump can be adjusted based on the insulin needed. Although it may seem counter-intuitive to give glucose to someone who is already hyperglycemic, the infusion provides a ready source of glucose for I.V. insulin until the patient is able to resume caloric intake sufficient enough to exceed 1,000 calories/day. After using this type of regimen for those who used NPH or long-acting insulin analogues (insulin detemir [Levemir] or insulin glargine), the insulin can be resumed at a slightly lower dosage than preoperatively and the patient's response to the drug monitored.6
Calories and sliding scales
Lavin suggests there are two common mistakes in the treatment of diabetic patients during the perioperative phase: insufficient calories and regular insulin sliding scale corrections of hyperglycemia.7 Sliding scale corrections commonly used in hospitals set the stage for hyperglycemia, leading to complications and impaired healing processes because they are set too high. Sliding scales don't provide basal insulin, which contributes to the metabolic dysregulation. The patient should be given a dosage of NPH or long-acting analogue.7 The patient using a CII may resume pump use provided there is an accessible, nonedematous site and necessary support for frequent monitoring. This may mean allowing the patient to use his own glucose monitor that connects to the insulin pump to determine the doses of correction.
The American Association of Clinical Endocrinolo-gists recommends the use of standardized protocols with specific guidelines for identifying patients at risk for hypoglycemia and actions to prevent and treat hypoglycemia. Standard sliding scale insulin should be avoided because it makes no provision to avoid hypoglycemia and often causes "roller-coaster" glycemic control.
Trence and colleagues8 have an algorithm for dosing and adjusting insulin infusions based on response. It's a stepwise increase, thereby lessening the chance of hypoglycemia. This, along with proper caloric intake, will also prevent starvation ketosis. Of course, lab tests should be checked daily to monitor for hypokalemia, creatinine abnormalities, and acidosis.
Switching from I.V. to subcutaneous insulin
If your patient is on I.V. insulin and has been on insulin therapy in the past, a key principle when switching to subcutaneous insulin is to make sure there is no interruption of insulin delivery. The half-life of I.V. insulin is only a few minutes. A patient with type 1 diabetes can quickly become hyperglycemic. To maintain glucose levels within target range when switching from I.V. to subcutaneous insulin, proper timing must be considered. The I.V. stop time will depend on which insulin is being used as basal insulin. Premeal dosages should be given before the patient has the meal and aren't based on the medication time at the facility. If the patient needs NPH insulin, mealtime should be considered to ensure appropriate timing and cessation of I.V. therapy. The patient's glucose monitoring will guide dosage adjustments. Caution should be taken in those who have undergone abdominal surgery, which may prevent them from tolerating normal meals. Continue insulin infusion for a day or two after the patient starts eating with mealtime coverage until it's confirmed that the meals are tolerated. This isn't always possible in a managed-care environment, however.
Special consideration must be made for pregnant patients. Surgery on a pregnant patient will require consultation with a perinatologist and endocrinologist. Different insulin replacement regimens will be necessary during surgery and postoperatively, especially for a cesarean section, based on metabolic needs related to type 1, type 2, or gestational diabetes. Gestational diabetic patients may not need any medication by their discharge or they may actually have been an unrecognized type 2 diabetic patient. If this is the case, target ranges will be different and additional education will be necessary. They may be at a higher risk for postpartum depression due to the diagnosis of diabetes in addition to recovering from a cesarean section. Suggest that your patient attend diabetes education classes or have an education session with a certified diabetes educator if available. Women with preexisting diabetes will likely require different dosages of insulin or oral medication than during prepregnancy. Women should continue with glucose monitoring and schedule a follow-up appointment with their healthcare provider within a few weeks.
Resuming therapy
When a patient begins sufficient oral intake and blood chemistries return to normal, oral medications or insulin therapy can be resumed (see Oral antidiabetic drugs). Some of the medication will require several days or weeks to take full effect. Insulin timing will be based on the type of insulin. All patients should know their glucose target ranges and how to treat hypoglycemia based on the glucose data. In most cases, patients can continue home glucose monitoring and contact their primary care provider or endocrinologist to schedule a follow-up appointment. OR
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