insulin, often in combination with periodic doses of correctional short- or rapid-acting insulin during a surgical procedure to avoid hyperglycemia.3–5,7 Withholding insulin in patients with T1D or insulin-treated T2D increases risk for diabetic ketoacidosis (DKA) or hyperosmolar hyperglycemic state (HHS) with high risk for perioperative complications.15
To calculate the percentage of basal insulin to be administered to patients during periods of fasting, consider the degree of preoperative glycemic control as determined from measures of HbA1c and results of bedside BG monitoring, patient characteristics, type of diabetes, and analysis of their home regimen (physiologic vs. basal heavy). In one study, patients with T1D were given their full dose of basal insulin (glargine) on a day when they were maintained in a fasting state with a low incidence of hypoglycemia.32 Similar studies with detemir or NPH insulin have not been performed. The pharmacokinetics of NPH insulin with a peak time of action at 6–10 h following administration would support reductions in dose of 25–50% of usual doses.33,34 The pharmacokinetics of detemir can vary from a flat profile at lower doses (<0.3 units/kg/day) to a more pronounced peak action time at higher doses, again supporting recommendations for dose modifications in some patients during periods of fasting.35
One general guideline is to provide 50–75% of the usual basal insulin dose before a surgical procedure.3–5,7,15,17 In one study that employed this recommendation in 585 patients with diabetes admitted to a same-day surgical center, 21% of patients arrived at the center with BG >200 mg/dL and 2% had BG <70 mg/dL.15 This study reveals the wide variability in insulin requirements in patients during periods of fasting. Patients who are under what is considered “tight” glycemic control may require reductions in their doses of basal insulin to avoid hypoglycemia, whereas those who are under fair or poor control may require the full dose to avoid significant hyperglycemia.
Given that the patient in this case was under suboptimal control with BBI as an outpatient, she likely will require the full dose of detemir insulin before surgery. It also is likely that administration of detemir 40 units will not be sufficient to maintain glycemic control during this surgical procedure for which she will receive general anesthesia. General anesthesia is associated with increases in counterregulatory hormones and insulin resistance, often increasing insulin requirements.7,36,37 This differs from regional or spinal anesthesia in which insulin requirements often remain unchanged.7,36,37 The responsibility for glucose monitoring with administration of subcutaneous or intravenous (IV), which is preferred, doses of regular or rapid-acting insulin analogs will fall to the anesthesiologist.15,37,38
Basal-heavy insulin refers to the (usually inappropriate) use of high doses of a single daily injection of basal insulin (glargine, detemir, or NPH) to cover both prandial and basal insulin requirements. Patients on these regimens often receive >0.6 to >1 unit/kg/day of basal insulin each day. Although not recommended by endocrinologists, in reality, this is a fairly common practice. When carbohydrate intake is decreased or eliminated in the NPO state, more aggressive decreases in basal insulin doses of ≥50% are required.
Perioperative Management of Patients Receiving Noninsulin Diabetes Therapy
Evidence is insufficient regarding the best ways to manage patients receiving noninsulin diabetes therapy.7,15,17 It is generally accepted that on the morning before surgery, although patients are consuming a normal diet, all usual diabetes medications should be continued. For patients on a clear liquid diet such as the patient in this case, or those who are receiving dietary preparation for a colonoscopy, we recommend holding sulfonylurea agents because of the risk of hypoglycemia.39 Short-acting insulin secretogogues such as repaglinide and nateglinide can be continued in reduced doses. Other noninsulin therapies usually can be continued until a patient is in the fasted (NPO) state. On the morning of surgery, we recommend holding all oral and injectable noninsulin diabetes medications.15
Suboptimal HbA1c and High-Risk for Postoperative Complications
Although some evidence links preoperative glycemic control with the risk for postoperative complications, available evidence is more suggestive than absolute.40,41 In the patient in this case, there is no need to delay surgery based on her HbA1c. Two days in the hospital preoperatively allows time for insulin adjustments and for the institution of a reasonable level of glycemic control, defined as maintaining BG values between 140 and 180 mg/dL.6,7
For elective procedures (e.g., joint replacement surgery, hernia repair), patients with previous poor diabetes control can be encouraged to improve their metabolic status with the motivating factor being that this will reduce risk for postoperative complications.40,42 The optimal level of “improved control” is not defined, but the authors of this chapter recommend HbA1c values of <8.5%, which correspond to a mean BG of <200 mg/dL, the level at which risk for perioperative complications increases most significantly.43–46
Not all patients will have the ability to achieve this level of glycemic control. In these situations, personal experience and judgment are important. For example, a patient with chronically uncontrolled insulin requiring T2D with HbA1c values >12% resulting from personal chaos and stress may be encouraged to reduce their HbA1c to <10% in preparation for elective surgery, but they may have difficulty getting to lower values. In some cases, allowing an elective surgical procedure to take place has the potential to contribute to improved glycemic control by addressing issues such as chronic pain that interfere with self-management. For patients who are unable to achieve desired levels of glycemic control or for whom a procedure is urgent, glycemic control can be achieved rapidly with the use of an IV insulin infusion before, during, and following the surgical procedure.15,47
Metabolic Effects Associated with NPO Status
Prolonged fasting is associated with reductions in insulin sensitivity in patients with and without diabetes.48,49 In the absence of diabetes, fasting is associated with a decline in insulin levels and an increase in glucagon, with associated increases in circulating free fatty acids that further impair insulin sensitivity.49 Although it is beyond the scope of this chapter, the reader is referred to several recent publications that explore the continued administration of carbohydrates in preparation for surgical procedures as a way to avoid potentially harmful increases in counterregulatory hormones.49–52
For prolonged procedures, the IV administration of glucose- or dextrose- containing IV fluids may help to limit perioperative changes in insulin sensitivity. Administration of glucose-containing IV fluids contributes to elevated BG. One liter of D5%-containing IV fluid has 50 g of glucose or ~200 calories. If this is infused at a rate of 100 cc/h, this provides 5 g of glucose or 20 calories/h. This calculates to ~1.2 mg/kg/min for an individual who wieghts 70 kg. Although this amount may seem trivial, personal experience indicates that in some cases, this is sufficient to contribute to mild elevations in BG that prompt administration of additional insulin. No published studies have investigated the effect of these low glucose infusion rates on hyperglycemia in hospitalized patients. In one study, glucose infusion rates of ≤4 mg/kg/min were not associated with hyperglycemia in patients without diabetes receiving total parenteral nutrition.53
Preventing Hypoglycemia When NPO Status Is Imposed Abruptly
Some patients may be abruptly placed in the fasting state after full doses of a weight-based BBI regimen has been administered, placing patients at increased risk for hypoglycemia.39 We generally recommend that infusions of D5% or D10% be initiated with more frequent glucose monitoring as a way to reduce this risk.54
Patients Who Experience Hypoglycemia while NPO for a Procedure
Little data have addressed the issue of patients who experience hypoglycemia while NPO.7 Studies that discuss the benefit of
