Should Insulin Therapy Be Adjusted for a Cardiac Stress Test?

Darrell T. Hulisz, PharmD

Disclosures

May 20, 2009

Question

A patient on insulin glargine with brittle diabetic control is scheduled for a cardiac stress test. Should the insulin regimen be changed before the procedure?

Response from Darrell T. Hulisz, PharmD
Associate Professor, Department of Family Medicine, Case Western Reserve University School of Medicine, University Hospitals, Case Medical Center, Cleveland, Ohio

Whether to hold, continue, or modify an existing insulin regimen in a patient undergoing a cardiac stress test is a complicated decision. The concern is that some percentage of these patients will undergo emergent and perhaps prolonged cardiac surgery. Sustained hyperglycemia worsens morbidity and mortality in patients undergoing coronary artery bypass grafting.[1] Perioperative and postoperative hypoglycemia is clearly undesirable and can complicate management.

In some patients, long-acting insulin may be replaced using standardized hospital protocols for continuous infusion of regular insulin or rapid-acting insulin (eg, insulin aspart [NovoLog®] or glulisine [Apidra®]) given either intermittently or by continuous infusion. Short-acting insulin regimens are readily adapted to individual patients' needs in situations that require tight glucose control, such as emergent cardiac surgery, changing nutritional status, and critical care.[2] A recent study found that tight blood glucose control can be achieved during cardiac bypass surgery with minimal risk for hypoglycemia.[3] However, in 1 controlled trial, intensive insulin therapy during cardiac surgery did not reduce perioperative death or morbidity.[4]

It is often impossible to predict, a priori, which patients undergoing a stress test will end up in the catheterization laboratory or in the operating room. Thus, several factors should be considered in choosing an appropriate insulin regimen:

  1. Adequacy of prior glycemic control. Previous values of glycemic control, duration, and type of diabetes will help determine a patient's need for tight control.

  2. The presence or absence of microvascular and/or macrovascular disease. Physiologic evidence of poor glycemic control may be manifested by the development of cardiovascular disease, diabetic nephropathy, neuropathy, or retinopathy.

     

  3. Predicted nutritional intake. Patients often are fasting before a stress test, due to the possibility of having a subsequent, emergent cardiac procedure. It is important to know how long the patient has been fasting. Different types of cardiac stress tests may require patients to fast for just a few hours while others require an overnight fast.

  4. Type of insulin, dosage, and administration. In this case, the patient is receiving insulin glargine, which is a type of basal insulin that somewhat mimics endogenous insulin activity with an approximate 24-hour duration of action. One advantage of basal insulin products is that they do not produce a substantial peak plasma concentration. Controlled studies have demonstrated that insulin glargine is less likely to cause hypoglycemic episodes relative to equipotent doses of neutral protamine Hagedorn (NPH) insulin.[5]

  5. The cardiologist's level of comfort with varying degrees of hyperglycemia. In this scenario, a reasonable approach would be to consult the cardiologist and/or surgeon to determine both the likelihood of this patient needing an emergent procedure and the level of hyperglycemia that would be acceptable. This may also be done in consultation with the patient's primary care physician or endocrinologist.

In some health centers, patients are instructed to take half their usual dose of morning insulin before a stress test, although this practice is empiric and not based on evidence. In the event that insulin is given, patients should be instructed to inform the technologist if any symptoms of hypoglycemia develop during the stress test, including lightheadedness, tachycardia, nervousness, or profuse sweating.

One must consider many variables before deciding to hold, continue, or modify an existing insulin regimen in a patient undergoing a cardiac stress test. As in other situations where caloric intake and metabolic demands are unpredictable, perhaps the best advice is to individualize the insulin dose in an informed manner. Frequent blood glucose monitoring should be used to guide insulin dosing, perhaps every 2 to 4 hours during the stress test and during any subsequent surgical intervention.

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