Heart Surgery May Induce Sustained High Glucose Levels

A new study has found that nearly half of all heart surgery patients may experience stress-induced hyperglycemia (SIH), with blood glucose levels high enough to require temporary insulin treatment after the operation.

Researchers at the University of Michigan (U-M, Ann Arbor, USA) conducted a retrospective study based on data from 1,362 patients who underwent different heart and vascular operations in 2006 and 2007. These included coronary artery bypass graft (CABG) operations, heart valve operations, or an operation on the superior section of their aorta. The researchers found that 662 of the surgery patients developed SIH, and 87 still needed medication to control blood glucose levels after they were discharged from the hospital. The most telling sign that a person was likely to need treatment, both in the hospital and later on at home, was their average blood sugar level two days after surgery. Those patients whose glucose levels were still high at this point were more than two and a half times more likely to need post-hospital medication, even after other factors were considered. The researchers found that patients who had a body mass index (BMI) over 35 were also somewhat more likely to develop SIH, as were older patients. However, these factors were not nearly as strongly predictive of SIH as was the glucose level on the second day after surgery. The study was presented at the American Diabetes Association Scientific Sessions, held during June 2008 in San Francisco (CA, USA).

"High blood sugar in non-diabetic patients after surgery hasn't been fully studied,” said study presenter Sima Saberi, M.D., a U-M endocrinology fellow. "Stress-induced hyperglycemia occurs when the body reacts to the double insults of having an operation on the heart or major blood vessels, and of being cooled down by the heart-bypass machine to protect the heart muscle during surgery.”

One of the most sweeping changes in intensive care unit (ICU) and post-surgical care in recent years is the trend toward more aggressive treatment of SIH. A number of research studies have demonstrated that even mildly elevated blood glucose levels in a hospital ICU can measurably increase the morbidity and mortality of such patients. Controlling patients' blood glucose below 110 mg/dL or 6.1 mmol/L was shown in several studies to decrease significantly patient mortality compared to conventional treatment, and decrease morbidity from bloodstream infections, acute renal failure requiring dialysis, or hemofiltration and critical illness polyneuropathy. On the other hand, other studies failed to show benefit or demonstrated harmful effects (mainly from induced hypoglycemia) of intensive insulin therapy in critically ill patients.


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