Interactive diabetes case 12: Perioperative management of a 67-year-old patient with type 2 diabetes who undergoes coronary artery bypass surgery – Comment

COMMENT — The patient with diabetes presented in this case, who underwent coronary artery bypass surgery and received postoperative care in an intensive care unit (ICU), compels us to consider the relationship between inpatient glycemia and outcome in patients in an ICU and maintenance of glycemic management in the transition between ICU care and floor care in the hospitalized patient.

Numerous studies have assessed the appropriate targets for patients with preexisting diabetes mellitus who are critically ill (in an ICU setting). Some early trials showed that achieving normoglycemia (80 to 110 mg/dL [4.4 to 6.1 mmol/L]) in cardiac surgery patients or those requiring postoperative surgical ICU settings may reduce mortality. However, subsequent trials in mixed populations of critically ill patients did not show a benefit of targeting a blood glucose of 80 to 110 mg/dL (4.4 to 6.1 mmol/L) and revealed an increased incidence of severe hypoglycemia and increased mortality rates. These trials are discussed elsewhere. (See "Glycemic control in critically ill adult and pediatric patients".)

As a result of these trials, current guidelines specify that in critically ill patients, insulin should be initiated for persistent hyperglycemia starting at a threshold of >180 mg/dL (10 mmol/L) and blood glucose levels should be kept between 140 and 180 mg/dL (7.8 to 10 mmol/L) [1].

The achievement of these goals generally requires the use of intravenous insulin, both for patients with diabetes and for patients without preexistent diabetes who develop glucose values above 180 mg/dL (10 mmol/L). This can be done safely, with minimal risk of hypoglycemia, with properly trained personnel and the use of a suitable protocol. Many insulin algorithms have been published and are in widespread use. Because there are no direct comparisons between these algorithms, no one protocol can be recommended. (See "Management of diabetes mellitus in hospitalized patients", section on 'Insulin infusion'.)

In general, an insulin infusion protocol should consider both the measured glucose level and the rate of change and should have appropriate adjustments to prevent hypoglycemia, including reductions in the insulin infusion rate and an intravenous glucose infusion. The target range should approximate the currently recommended target values (see above) and should be acceptable to the nurses and clinicians involved in the care of the patients after appropriate education about current standards.

It cannot be emphasized too strongly that successful implementation of an insulin infusion algorithm requires the willing and active participation of the staff, which depends in turn on appropriate education including discussion about the prevention and treatment of hypoglycemia.

Patients move quickly from the ICU to the medical or surgical floor. It is important to manage the transition from intravenous to subcutaneous insulin effectively. The transition should provide a suitable overlap of intravenous insulin and subcutaneous insulin to prevent an interval of insulin deficiency. The intravenous insulin infusion should continue for two to four hours after the first injection of a basal subcutaneous insulin (eg, glargine or NPH).

One advantage of using intravenous insulin in the ICU is that it allows the clinician to estimate the patient's basal subcutaneous insulin requirement once the patient is stable and the insulin infusion rate is relatively constant. When one uses a peakless basal subcutaneous insulin such as glargine, one can start with approximately 80 percent of the estimated 24-hour intravenous insulin infusion rate. As an example, if the patient's basal insulin infusion rate is 2 units an hour, as in the patient under consideration, the estimated 24-hour insulin infusion rate is 2 units/hour x 24 hours = 48 units. The initial dose of glargine insulin would then be 0.8 x 48 = 38 units (rounded to the nearest full unit). When one uses a basal subcutaneous insulin with a peak of action such as NPH, the initial dose should be smaller to minimize the risk of hypoglycemia. As an example, one might start with approximately 50 percent of the estimated 24-hour insulin infusion rate, or 24 units in the present example.

The management of diabetes is an iterative process. The effect of the initial subcutaneous dose of basal insulin must be assessed on a daily basis and adjustments made as dictated by the blood glucose values. Correction doses of a short- or very short-acting insulin should be added as needed.

This patient was not on insulin before admission to the hospital, so it is not known whether he will need prandial insulin doses. Also, he is not eating. It would be inappropriate (with high risk of hypoglycemia) to use a prandial dose at this time. As food intake resumes, one can determine whether he needs prandial insulin doses. If the basal insulin dose controls the fasting or another pre-meal glucose value, but not all pre-meal glucose values, then prandial (pre-meal) doses of a short or very short-acting insulin should be added at the appropriate times.