Achieving glycemic control is imperative for patients with diabetes undergoing tests and procedures, many of which require dietary restrictions. For these patients, mismanagement of diabetes medications during fasting periods can have dangerous consequences including hypo- or hyperglycemia. This chapter will review glycemic management and guidelines for patients with type 1 diabetes (T1D) and type 2 diabetes (T2D) undergoing tests and procedures in both the inpatient and outpatient settings.
General Approach to Glycemic Management While NPO
The glycemic management of patients who are nil per os (NPO or “nothing by mouth”) should begin with plasma blood glucose checks every 4–6 hours. Basal insulin should still be administered, but with a 20%–40% reduction. Patients with T1D require daily basal insulin to avoid diabetic ketoacidosis, a life-threatening complication of hyperglycemia. Basal insulin products are intermediate or long-acting which include insulin glargine, insulin detemir, and insulin degludec. While bolus premeal insulin should be held to avoid potential hypoglycemic episodes, correctional bolus insulin should be made available in the instance of hyperglycemia. Bolus insulin for before meals or as a correctional is rapid-acting and included insulin aspart, insulin lispro, and insulin glulisine.
An Overview of Inpatient Diabetes
INPATIENT GLYCEMIC TARGETS
Persistent hyperglycemia is associated with a range of adverse outcomes in hospitalized patients. According to the American Diabetes Association, all patients with diabetes or hyperglycemia (blood glucose ≥140 mg/dL or 7.8 mmol/L) should have a hemoglobin A1c (HbA1c) test upon admission if one was not performed within 3 months preceding admission. Injectable insulin, not oral or noninsulin subcutaneous (SQ) agents, should be prescribed in patients with pre-existing diagnoses or those with a HbA1c ≥6.5%, allowing for dosage adjustments based on blood glucose fluctuations. Once insulin therapy has been initiated, an inpatient glycemic target of 140–180 mg/dL or 7.8–10 mmol/L should be maintained. Tighter glycemic control, maintaining a target of 110–140 mg/dL or 6.1–7.8 mmol/L, is recommended only for critically ill postsurgical patients and those undergoing cardiac surgery, taking care to avoid hypoglycemia. Tight glycemic control in patients outside of these categories has been linked to increased mortality and should be avoided. Bedside glucose monitoring should occur before meals and at bedtime in patients who are eating, and every 4–6 hours in NPO patients.
INPATIENT INSULIN MANAGEMENT
In hospital settings, basal insulin or basal-bolus insulin regimens with corrective sliding scales are preferred for management of diabetes and hyperglycemia. If previous oral agents were discontinued during admission, they should be restarted 1–2 days prior to discharge, as home oral antihyperglycemic agents have been shown to exacerbate medical comorbidities in the hospital setting. , Basal insulin in conjunction with rapid-acting insulin allows for meal coverage and correction for hyperglycemic episodes unrelated to nutrition. This balance of basal-bolus insulin is designed to mimic physiologic insulin release. Long-acting basal insulin should provide up to 24 hours of constant insulin supply, effectively suppressing liver and renal gluconeogenesis between meals, while bolus insulin provides insulin coverage for meals and prevents postprandial glucose elevations, reaching its peak effect within an hour. Rapid-acting insulin should be given up to 15 minutes prior to a meal, sooner than regular insulin, which should be given 30 minutes prior to a meal as it has a slower onset of action. However, in the case of preprandial hypoglycemia below 70 mg/dL, bolus insulin should not be administered until hypoglycemia is corrected and the patient is eating. The amount of total insulin administered daily will depend on the patient’s weight, renal function, and nutritional intake but will generally be divided equally between the basal and total bolus doses.
Presurgical Targets and Medication Adjustments
According to the American Diabetes Association, presurgical glycemic targets should be maintained at 80–180 mg/dL or 4.4–10 mmol/L, although higher levels may be preferred per anesthesia guidelines. All oral antihyperglycemic agents should be discontinued the day of surgery, whereas sulfonylureas and sodium-glucose cotransporter-2 (SGLT2) inhibitors need to be held longer. The Food and Drug Administration (FDA) has recommended that SGLT2 inhibitors should be held 3 (canagliflozin, dapagliflozin, empagliflozin) or 4 days (ertugliflozin) prior to surgery in order to avoid diabetic ketoacidosis. Sulfonylureas cause the pancreas to produce more insulin, with effects lasting 1–2 days, but the effect can be even longer in those with renal disease. Therefore, they should be discontinued 1–2 days prior to the procedure. If prescribed on the day of surgery, half the dosage of NPH (an intermediate-acting insulin) should be administered and 60%–80% of other basal insulins should be given preceding surgery. Patients should be monitored for 4–6 hours prior to surgery if NPO, and levels should be adjusted using a corrective scale.
Surgical NPO Management
Coronary artery bypass grafting (CABG): Insulin infusions are often used in the perioperative care of patients undergoing a CABG, as patients will often have increased insulin requirements during surgery due to the stress of the procedure and increased insulin resistance from their NPO status. Proper glycemic control allows for improved outcomes. A glycemic target of 125–200 mg/dL results in greater survival and improved wound healing compared with the more lenient target of <250 mg/dL. Evidence suggests that trying to impose tighter glycemic control (90–120 mg/dL) leads to more hypoglycemia as opposed to those with a goal of 120–180 mg/dL, with no improvements in morbidity or mortality. See Chapter 20: Coronary Artery Bypass Grafting for more details about this procedure.
Transcatheter aortic valve replacement (TAVR): A TAVR is a much shorter procedure (about 1 hour). Insulin infusion is less likely to be used. See Chapter 56: Transcatheter Aortic Valve Replacement for more details about this procedure.
Esophagogastroduodenoscopy (EGD)/colonoscopy: In preparation for gastrointestinal procedures, patients should not eat for 8 hours prior. Clear liquids are permitted until 2 hours beforehand. In some cases, patients are required to have a full day of clear liquids or bowel prep the day before their procedure, in which case they will need to adjust their medications both the day before and day of the procedure. See Chapter 32: Gastrointestinal Endoscopy, Upper and Chapter 31: Gastrointestinal Endoscopy, Lower for more details about these procedures.
Percutaneous endoscopic gastrostomy (PEG) placement: In patients with newly established PEG tubes, feedings should not be initiated until 24 hours after placement. Both before tube placement and following initiation of diabetic-specified formula feedings, these patients should receive SQ premeal bolus insulin every 4–6 hours to correct hyperglycemia. All regimens should include basal, bolus, and correctional requirements. Patients with T1D and those with T2D should still receive SQ basal-bolus insulin even if feedings are discontinued. Each patient’s basal insulin requirement can be estimated using their preadmission long- or intermediate-acting dosages, or, alternatively, weight-based dosing can be used at 0.4–0.6 units/kg, with half given as a basal dosage and the other half divided over three meals daily as short-acting nutritional doses. See Chapter 47: Percutaneous Endoscopic Gastrostomy Tube for more details about this procedure.
Enhanced recovery procedure (ERP): ERP has been used to decrease surgical stress and decrease length of stay for several types of surgery, including colorectal and hepatic surgeries. , It allows patients to drink clear liquids up until 2 hours prior to anesthesia. According to the American Society of Anesthesiologists, clear liquids include but are not limited to water, fruit juices without pulp, carbonated beverages, carbohydrate (CHO)-rich nutritional drinks, clear tea, and black coffee. Following consumption, patients are specifically required to drink 45 g CHO 2 hours prior to the surgery, decreasing insulin resistance via increasing endogenous insulin production, leading to less perioperative hyperglycemia. As a result, patients with T1D and those with T2D who use bolus insulin will require a bolus dose for the CHO load. The bolus dosage to account for this load can be calculated by dividing 45 by the patient’s insulin-to-CHO ratio (ICR) (which is determined by dividing 450 by their usual total daily insulin dose).
Postoperative corticosteroid regimens have been noted to induce consistent hyperglycemia until discontinuation. Likewise, transplant medications, specifically tacrolimus, sirolimus, and cyclosporine, have been shown to induce hyperglycemia via increased jejunal glucose absorption and/or increased insulin resistance. As steroids preferentially affect postprandial glycemic control, adjustments to premeal insulin should be made first. Rather than a 50:50 basal:bolus regimen, a bolus-heavy regimen should be used in a 40:60 or 30:70 basal:bolus ratio.
An Overview of Outpatient Diabetes
The management of blood glucose levels begins with two techniques—self-monitoring of blood glucose (SMBG) and continuous glucose monitoring (CGM). Regular use of these tools may reduce complications and provide insight into the efficacy of glycemic control for patients and providers. With the information provided by SMBG and CGM, individualized guidance with regard to medication, nutrition, and physical activity can be better achieved. For nonpregnant adults, HbA1c of <7% is within the parameters of the goal, but this value may range from 6.5% to 8% depending on the patient’s clinical scenario. An acceptable glycemic status is considered to be 80–130 mg/dL preprandially and can reach up to 180 mg/dL postprandially. As with HbA1c, these targets may fluctuate depending on the individual. See Chapter 18: Continuous Glucose Monitoring for details about these devices and practices.
Medication Management for Same-Day NPO Procedures
Oral antihyperglycemic agents should be held the day of any NPO-requiring procedures, and some agents, such as sulfonylureas and SGLT2 inhibitors, should be held for a longer period of time. Sulfonylureas are a class of medications that cause the pancreas to release insulin with an effect that lasts 1–2 days, or longer in those with renal disease, which can lead to hypoglycemia, especially if a patient is not eating. It is suggested that these agents (e.g., glipizide, glyburide, glimepiride) be held 1–2 days prior to the same-day procedure. SGLT2 inhibitors can induce euglycemic ketoacidosis or diabetic ketoacidosis in the perioperative period and need to be held for 3–4 days prior to procedures, and not restarted until the patient resumes oral intake. ,
Patients who use metformin should hold this medication the day of the procedure. However, if the procedure requires intravenous contrast such as that used with computed tomography scanning or cardiac catheterizations and has acute kidney injury (AKI), metformin should be held for 48 hours after the use of the intravenous contrast. Those without AKI and with an estimated glomerular filtration rate (eGFR) ≥30 mL/min/1.73m 2 can resume metformin when they resume eating even if earlier than 48 hours postcontrast. Metformin does not cause an increase in the risk of AKI but can accumulate in the setting of AKI, causing a higher risk of adverse effects (e.g., lactate accumulation). There are no interactions when gadolinium contrast is used. See Chapter 17: Computed Tomography for more details about the effects of contrast.
For patients using insulin, the recommendations given for inpatients would apply—reduce the basal dose of insulin by 20%–40% the night before. The same dose reduction should be applied for persons who take their basal insulin twice daily. The dose the night before and the morning of the procedure should be both reduced by 20%–40%.
Diabetes medication management in NPO patients requires that the provider be aware of the type of diabetes, renal function, diabetes medications, and procedure. All patients with T1D and some of those with T2D require basal-bolus insulin, with dosage reductions of 20%–40% the night before the procedure if their basal insulin is once daily and both the night before and the morning of the procedure if their basal insulin is twice daily. In the case of some gastrointestinal procedures in which the patient drinks only clear liquids the day before, insulin adjustments may have to be made starting 2 days before the procedure. For those with T2D who use oral or SQ noninsulin agents, the medication should be held the day of the procedure. Patients on SGLT2 inhibitors should hold these medications for 3–4 days, and patients on sulfonylureas should consider holding their medications for 1–2 days, depending on their renal function, in an effort to avoid hypoglycemia.