Postoperative Hyperglycemia May Predict Surgical Site Infection

Postoperative hyperglycemia may predict surgical site infection (SSI), according to the results of a retrospective medical record review reported in the September issue of Archives of Surgery.

“Postoperative …SSI is a well known cause of morbidity in the United States,” write Ashar Ata, MBBS, MPH, from Albany Medical College in Albany, New York, and colleagues. “It has been well established that patients with diabetes mellitus are more prone to surgical and other nosocomial infections. Although the mechanism by which diabetes predisposes to SSI is not well understood, hyperglycemia has been proposed as a causative factor for the higher infection rates in diabetic patients.”

Between November 1, 2006, and April 30, 2009, a total of 2090 patients undergoing general or vascular surgery at an academic tertiary referral center were included in an institutional quality improvement database. The primary study endpoint was postoperative SSI.

Of 1561 patients (74.7.0%) for whom postoperative glucose levels were available, 803 (51.4%) underwent measurement within 12 hours of surgery. SSI occurred in 7.42% of patients overall, including 14.11% of those who had colorectal surgery, 10.32% of those who had vascular surgery, and 4.36% of those who had other general surgery.

In patients undergoing general surgery, the significant univariate predictors of SSI were increasing age, emergency status, American Society of Anesthesiologists physical status classes P3 to P5, time in surgery, transfusion of more than 2 units of red blood cells, preoperative glucose level exceeding 180 mg/dL, diabetes mellitus, and postoperative hyperglycemia.

Of these factors, increasing age, emergency status, American Society of Anesthesiologists classes P3 to P5, time in surgery, and diabetes remained significant predictors of SSI for patients who underwent general surgery, based on multivariate adjustment. However, after further adjustment for postoperative glucose level, these other factors were no longer found to be significant predictors of SSI and only incremental postoperative glucose level remained a significant predictor of infections.

Subanalysis showed that the only significant predictor of SSI for patients who had colorectal surgery was a serum glucose level exceeding 140 mg/dL (odds ratio, 3.2; 95% confidence interval [CI], 1.4 – 7.2 times). Compared with patients who received general surgery, patients receiving vascular surgery were 1.8 times (95% CI, 1.3 – 2.5 times) more likely to have SSI. Among patients who had vascular surgery, the only significant univariate predictors of SSI were operative time and diabetes mellitus, and postoperative hyperglycemia was not associated with SSI.

“Postoperative hyperglycemia may be the most important risk factor for SSI,” the study authors write. “Aggressive early postoperative glycemic control should reduce the incidence of SSI.”

Limitations of this study include retrospective design and use of a single hospital, reducing generalizability. In addition, the first postoperative serum glucose value was available within 12 hours for only 51.3% of patients and within 24 hours for 96.0% of patients.

“In conclusion, we found postoperative hyperglycemia to be the most important risk factor for SSI in general and colorectal cancer surgery patients, and serum glucose levels higher than 110 mg/dL were associated with increasingly higher rates of postsurgical infection,” they continue. “If hyperglycemia is confirmed in future prospective studies with better postoperative glucose data to be an independent risk factor for postsurgical infection in general surgery patients, this would give surgeons a modifiable variable to reduce the incidence of postoperative infection.”

In an accompanying comment, Joseph H. Frankhouse, MD, from Legacy Health System in Portland, Oregon, notes that postoperative hyperglycemia is independently associated with SSI in patients who underwent general or colorectal surgery; that the relationship is linearly related to infection; and that a glucose level of less than 140 mg/dL is the threshold that should be achieved to minimize the risk for SSI.

“These 3 principles will form the foundation for future work in this area,” Dr. Frankhouse writes. “This group’s work also stimulates us to consider techniques with more effective glycemic control, such as the liberal use of insulin glargine. Succeeding work will need to focus on preoperative, intraoperative, and postoperative glucose control; techniques for glucose management; and in which patients such efforts are necessary.”

The study authors and Dr. Frankhouse have disclosed no relevant financial relationships.

Arch Surg. 2010;145:858-864. Abstract

Additional Resource
The Institute for Healthcare Improvement offers clinicians some online resources on surgical site infections.

Postoperative SSI is the most common nosocomial infection in the United States, accounting for 38% of all hospital-acquired infections, and they can prolong hospital stays and increase rehospitalization rates and healthcare costs. Patients with diabetes mellitus are more prone to SSI, and intensive insulin therapy has been used to reduce the risk for SSI, but the benefit of glycemic control in different postsurgical patients is not known.

This is a retrospective medical record review study to examine the role of postoperative hyperglycemia on the risk for SSI in different surgical patients, independent of the existence of diabetes.

Study Highlights

• The study was conducted on surgical patients 16 years or older within the database of a 630-bed hospital.
• The American College of Surgeons’ National Surgical Quality Improvement Program database was used to abstract information from the period 2006 to 2009 on 3129 patients.
• Included were patients who underwent colorectal surgery, noncolorectal (general) surgery, and vascular surgery.
• Colorectal surgeries were open or laparoscopic and included partial or complete removal of the colon or rectum.
• The sampling strategy for the database consisted of reporting 40 consecutive eligible cases on an 8-day cycle, starting on different weekdays. Surgical patients were identified with use of the subspecialty variable.
• Information on preoperative and postoperative blood glucose levels was obtained by medical record review by 2 researchers.
• Serum glucose information was available on 74.7% of patients, of which 51.4% were obtained within 12 hours of surgery.
• Postoperative glucose values were available for 776 noncolorectal surgical patients, 559 vascular surgical patients, and 226 colorectal surgical patients.
• The primary outcome was postoperative infection, defined as a postoperative occurrence of a superficial, deep incisional, or organ space SSI.
• Variables included American Society of Anesthesiologists physical status classification, red blood cell transfusion, operative time, and postoperative glucose level.
• Risk factors were separately determined for patients who underwent general and vascular surgery.
• The overall SSI rate in the study sample was 7.42%, higher for patients who underwent colorectal (14.11%) and vascular (10.32%) surgery vs those who had noncolorectal general surgery (4.36%).
• Colorectal surgical patients were 3.6 times more likely and vascular surgical patients 2.5 times more likely than noncolorectal surgical patients to have SSI.
• Compared with patients with a first postoperative glucose level of 110 mg/dL or less, the likelihood of SSI increased progressively for patients with higher serum glucose levels, ranging from 1.8% in the category of less than 110 mg/dL to 17.7% in the category of 220 mg/dL.
• The likelihood increased from 3.61 times in the lower category (110 – 140 mg/dL) to 12.13 times in the highest category (> 220 mg/dL) of postoperative glucose level vs less than 110 mg/dL.
• Although risk factors for SSI in patients who underwent general surgery included higher American Society of Anesthesiologists class, older age, red blood cell transfusion, postoperative glucose level, and operative time, only high postoperative glucose level remained as a significant predictor of SSI after adjustment.
• In patients who underwent colorectal surgery, postoperative glucose levels of 140 mg/dL or higher were associated with a 3.2 times increased risk for SSI vs postoperative glucose levels of less than 140 mg/dL.
• In vascular surgical patients, postoperative glucose level was not a significant predictor of SSI risk, and the risk for SSI was high in all categories of glucose level (from 13.2% for < 110 mg/dL to 20% for > 220 mg/dL).
• In patients who had vascular surgery, operative time and diabetes were the significant predictors of SSI.
• For every 10-minute increase in operative time, the likelihood of SSI increased by 6%.
• Diabetic patients had 1.84 times the risk for SSI vs nondiabetic patients.
• The authors concluded that colorectal and noncolorectal surgical patients with postoperative hyperglycemia were at increased risk for SSI.

Clinical Implications

• Elevated postoperative glucose level is a predictor of SSI among general and colorectal surgical patients.
• Among patients who underwent vascular surgery, operative time, and diabetes mellitus, but not postoperative glucose level, are predictors of SSI.

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