Miscellaneous Articles

Postop hyperglycemia called the primary risk factor for surgical site infection

By Mary Ann Moon, writer for MD/Consult (www.mdconsult.com)

September 21, 2010

Postoperative hyperglycemia, independent of the presence of diabetes, appears to be the single most important risk factor for surgical site infection in general and colorectal procedures, according to a report in the September issue of the Archives of Surgery.

Hyperglycemia is a recognized risk for infection in cardiac and surgical intensive care units, and intensive insulin therapy is frequently used to prevent infection in those settings. This study found that serum glucose levels higher than 110 mg/dL also increased the rate of surgical site infection (SSI) in patients undergoing general and colorectal surgery and that the risk of infection rose dramatically at even higher glucose levels, said Dr. Ashar Ata and associates at Albany (N.Y.) Medical Center.

The investigators examined the relationship between hyperglycemia and SSI using information in the American College of Surgeons’ National Surgical Quality Improvement Program database. They assessed the records of 2,090 surgery patients aged 16 years and older who were treated at the medical center between 2006 and 2009.

The rate of superficial, deep incisional, or organ space infection was 1.8% among patients with postoperative glucose levels of 110 mg/dL or less. That rate rose with increasing glucose levels to a high of 17.7% in patients with levels of 220 mg/dL or higher.

Compared with patients whose first postoperative glucose level was 110 mg/dL or less, those whose first level was 111-140 mg/dL had 3.6 times the risk of developing SSI, and those whose first level was 220 mg/dL or higher had 12 times the risk.

Analysis of the subgroup of patients without diabetes showed similar results: increasing postoperative glucose levels were significantly associated with increasing risk of SSI in a dose-response fashion.

Similarly, analysis of the subgroup of patients undergoing colorectal surgery showed that postoperative serum glucose levels of 140 mg/dL or higher were the only significant predictor of surgical site infection. The rate of infection was three times higher in patients with that level of hyperglycemia (21%) than in patients with serum glucose levels below 140 mg/dL (7%).

Initial analysis showed that several other variables – including patient age, severity of illness, need for emergency surgery, need for transfusion, and operative time – also raised the risk of SSI. However, after the data were adjusted to account for serum glucose levels, all those risk factors except for operative time ceased to be significant predictors of SSI. This suggests that the effect of these other risk factors may be exerted through the alteration of serum glucose levels, Dr. Ata and colleagues said.

In contrast to the findings with general and colorectal surgery, postoperative serum glucose level showed no association with infection risk in vascular surgery. The reason for this discrepancy is not yet known, they said (Arch. Surg. 2010;145:858-64).

For vascular surgery, the rates of SSI were relatively high across all categories of serum glucose level, from 13.2% in the lowest category to 20% in the highest category. After adjustment, the likelihood of SSI in vascular surgery patients increased by 6% for every 10 minutes increase in operative time. Patients with diabetes were 1.84 times more likely to develop SSI in vascular surgery than were nondiabetic patients.

These results must be confirmed in larger, prospective, multicenter studies, the researchers noted. Meanwhile, “based on the results of this study, a revised protocol targeted at achieving glucose levels less than 140 mg/dL will be considered for a future prospective study.”

If the findings are confirmed, it is possible that clinicians may be able to reduce the risk of postsurgical infection by managing perioperative hyperglycemia, they added.

According to Dr. Joseph H. Frankhouse, who was not involved with this study, this report supports the conclusion that postoperative hyperglycemia is not benign and dispels the notion that surgical site infections are beyond our control.

However, he says there are two problems with the study design.

First, only 75% of patients had reliable data on postoperative glucose levels and in only half of those cases were those levels obtained within 12 hours of surgery. Much of the data was derived from routine lab tests done the day after surgery, so “there is quite a variance as to when glucose monitoring began, how it was performed, and when, or even if, attempts at glycemic control began,” noted Dr. Frankhouse of Legacy Health System, Portland, Ore.

Second, the failure to find any association between serum glucose levels and site infection after vascular surgery was “striking.” This patient group is the very one that presumably has the highest rates of diabetes. They also had a higher rate of surgical site infection than did patients undergoing general or colorectal surgery. So a lack of association “leads one to wonder whether factors such as hemoglobin A1c level, nutrition, tobacco use, obesity, operative time, and tissue perfusion/oxygenation may be more powerful factors in the equation,” Dr. Frankhouse said.

Dr. Frankhouse reported no financial disclosures. These comments were taken from his Invited Critique, which accompanied Dr. Ata’s report (Arch. Surg. 2010;145:864).