Postoperative Hyperglycemia Important Risk Factor for SSI

A recent study reported in the Archives of Surgery [2010;145(9):858-864] found that postoperative hyperglycemia is the most important independent risk factor for surgical site infection (SSI) in general surgery patients. Previous studies have shown that postoperative SSI is a common cause of morbidity, accounting for 14% to 17% of all hospital-acquired infections. Hyperglycemia has been proposed as a causative factor for the higher infection rates in diabetic patients and is associated with increased morbidity and mortality rates in nondiabetic patients. Researchers of this current study analyzed data from the nationwide American College of Surgeons National Surgical Quality Improvement Program database and found that patients with diabetes had increased rates of SSI. The study comprised 2090 patients who underwent general and vascular surgery at Albany Medical Center between November 1, 2006, and April 30, 2009. Patients were required to be ≥16 years of age at the time of admission. The study sample was a randomized selection of noncolorectal general surgery and vascular surgery patients. The researchers also used medical records to gain information on the patients’ postoperative glucose levels. Postoperative infection was the primary outcome of interest and was defined by the researchers as a postoperative occurrence of a superficial, deep incisional, or organ space SSI. The researchers also examined other risk factors, including age at hospital admission, sex, race and ethnicity, diabetes mellitus, emergency versus elective surgery, the most recent preoperative serum glucose level within 3 months of surgery, the patient’s preoperative status as indicated by the American Society of Anesthesiologists’ physical status classification (P1 through P5 indicating none to mild systemic disease through life-threatening to moribund systemic disease) and the number of red blood cell units given intraoperatively (≤2 or >2 U), operative time, and first postoperative serum glucose level. The overall SSI rate in the patient sample was 7.42%. Infection rates were significantly higher for colorectal (14.11%) and vascular (10.32%) surgery patients than for noncolorectal general surgery patients, where there was an SSI rate of 4.36% (P<.001 for both). The likelihood of getting an SSI increased progressively for patients with higher serum glucose levels compared with patients with a first postoperative glucose level of ≤110 mg/dL. The incidence of SSI ranged from 1.8% in the ≤110-mg/dL category to 17.7% in the ≥220-mg/dL category. After adjustment for postoperative serum glucose level, all risk factors ceased to be significant predictors of SSI. Colorectal surgery patients in the general surgery group with postoperative serum glucose levels >140 mg/dL had an incidence of infection that was 3.2 times that of those with serum glucose levels of ≤140 mg/dL (95% confidence interval [CI], 1.4-7.2 times). This study also found that postoperative serum glucose level was not significantly associated with the likelihood of postoperative SSI in vascular surgery patients. Diabetic patients were 1.84 times more likely to develop SSI in vascular surgery patients than nondiabetic patients (95% CI, 1.20-2.82 times). Overall, the likelihood of infection was positively associated with operative time in vascular and general surgery patients. The researchers concede that they could be speculating that hyperglycemia is the cause of increased SSI rate, as it is also possible that the accumulation of the other SSI risk factors could lead to hyperglycemia. Therefore, treating hyperglycemia may not reduce the risk of SSI. The researchers note that further investigation of this issue is necessary. A larger, prospective, multiplehospital study would provide even more solid results, they said. Another limitation cited by the researchers is that the first postoperative serum glucose value was available within 12 hours for only 51% of the patient population and in 96% of the patients within a 24-hour period. Overall, serum glucose levels ≥110 mg/dL were associated with increasingly higher rates of postsurgical infection. Further investigation on this issue could give surgeons a modifiable variable to reduce the incidence of postoperative infection, according to the researchers.