Four-Factor Model Predicts Vascular Surgery Site Infection

ATLANTA — Preoperative patient factors were moderately predictive of surgical site infection risk in a retrospective case-control study of 253 patients undergoing elective vascular surgery.

Previous scoring systems also have been predictive of risk for surgical site infections (SSIs), but these are based on a combination of pre-, peri-, and postoperative factors. Thus, the scores aren't helpful for gauging risk in individual patients prior to surgery.

Knowing risk before surgery could allow the pursuit of nonsurgical options as well as guide infection prevention processes in patients who are shown to be at high risk, Dr. Surbhi Leekha and her associates said in a poster at the Decennial International Conference on Healthcare-Associated Infections.

Further, the most commonly used risk stratification tool, the National Nosocomial Infections Surveillance System (NNIS) risk index (Am. J. Med. 1991;91:152S-7S), does not perform well for “clean” procedures such as cardiovascular surgery, said Dr. Leekha and her associates, of the Mayo Clinic, Rochester, Minn.

The study population included patients who had undergone elective vascular (abdominal aortic and peripheral arterial) surgery at the Mayo Clinic from 2003 through 2007. A total of 87 patients who developed SSIs requiring hospitalization were included, and were matched with 166 controls who had undergone the same type of procedure on the same day but did not develop an infection.

There were no significant differences between cases and controls in age, sex, diabetes, smoking, alcohol use, chronic kidney disease, liver disease, weight loss, immunosuppressive therapy, and presence of skin ulcers. In multivariate analysis, preoperative variables that were significantly associated with SSI risk included critical ischemia (odds ratio 2.91), previous SSI (OR 6.29 with previous surgery, OR 1.40 with no previous surgery), previous peripheral revascularization (OR 2.55), and chronic obstructive pulmonary disease (OR 2.22).

A preop score model was developed in which 1 point each was given for COPD, critical ischemia, and previous peripheral revascularization and 2 points for previous SSI. The concordance statistic (c-statistic) for the preop score model was 0.73, compared with 0.50 for the NNIS score, Dr. Leekha and her associates reported.

A c-statistic of 1.0 indicates that the predictions are perfectly concordant with the actual outcomes, while 0.5 indicates that the predictions are no better than random chance. Thus, “based on these data, NNIS performs no better than a coin toss,” Dr. Leekha said in a follow-up interview.

The NNIS, the national standard for all types of surgeries, has been shown to perform poorly for cardiac surgery. Its performance for vascular surgery appears to be similar, possibly because the patients are similar in two of the three NNIS components—type of surgery (type 1/clean) and American Society of Anesthesiologists score of III or IV, she explained in the interview.

In their poster, Dr. Leekha and her associates recommended that patients predicted to be at high risk should be observed for wound problems and early intervention/wound care, but added that prospective validation of this tool is still required.

Disclosures: Dr. Leekha stated she had nothing to disclose.

ATLANTA — Preoperative patient factors were moderately predictive of surgical site infection risk in a retrospective case-control study of 253 patients undergoing elective vascular surgery.

Previous scoring systems also have been predictive of risk for surgical site infections (SSIs), but these are based on a combination of pre-, peri-, and postoperative factors. Thus, the scores aren't helpful for gauging risk in individual patients prior to surgery.

Knowing risk before surgery could allow the pursuit of nonsurgical options as well as guide infection prevention processes in patients who are shown to be at high risk, Dr. Surbhi Leekha and her associates said in a poster at the Decennial International Conference on Healthcare-Associated Infections.

Further, the most commonly used risk stratification tool, the National Nosocomial Infections Surveillance System (NNIS) risk index (Am. J. Med. 1991;91:152S-7S), does not perform well for “clean” procedures such as cardiovascular surgery, said Dr. Leekha and her associates, of the Mayo Clinic, Rochester, Minn.

The study population included patients who had undergone elective vascular (abdominal aortic and peripheral arterial) surgery at the Mayo Clinic from 2003 through 2007. A total of 87 patients who developed SSIs requiring hospitalization were included, and were matched with 166 controls who had undergone the same type of procedure on the same day but did not develop an infection.

There were no significant differences between cases and controls in age, sex, diabetes, smoking, alcohol use, chronic kidney disease, liver disease, weight loss, immunosuppressive therapy, and presence of skin ulcers. In multivariate analysis, preoperative variables that were significantly associated with SSI risk included critical ischemia (odds ratio 2.91), previous SSI (OR 6.29 with previous surgery, OR 1.40 with no previous surgery), previous peripheral revascularization (OR 2.55), and chronic obstructive pulmonary disease (OR 2.22).

A preop score model was developed in which 1 point each was given for COPD, critical ischemia, and previous peripheral revascularization and 2 points for previous SSI. The concordance statistic (c-statistic) for the preop score model was 0.73, compared with 0.50 for the NNIS score, Dr. Leekha and her associates reported.

A c-statistic of 1.0 indicates that the predictions are perfectly concordant with the actual outcomes, while 0.5 indicates that the predictions are no better than random chance. Thus, “based on these data, NNIS performs no better than a coin toss,” Dr. Leekha said in a follow-up interview.

The NNIS, the national standard for all types of surgeries, has been shown to perform poorly for cardiac surgery. Its performance for vascular surgery appears to be similar, possibly because the patients are similar in two of the three NNIS components—type of surgery (type 1/clean) and American Society of Anesthesiologists score of III or IV, she explained in the interview.

In their poster, Dr. Leekha and her associates recommended that patients predicted to be at high risk should be observed for wound problems and early intervention/wound care, but added that prospective validation of this tool is still required.

Disclosures: Dr. Leekha stated she had nothing to disclose.

ATLANTA — Preoperative patient factors were moderately predictive of surgical site infection risk in a retrospective case-control study of 253 patients undergoing elective vascular surgery.

Previous scoring systems also have been predictive of risk for surgical site infections (SSIs), but these are based on a combination of pre-, peri-, and postoperative factors. Thus, the scores aren't helpful for gauging risk in individual patients prior to surgery.

Knowing risk before surgery could allow the pursuit of nonsurgical options as well as guide infection prevention processes in patients who are shown to be at high risk, Dr. Surbhi Leekha and her associates said in a poster at the Decennial International Conference on Healthcare-Associated Infections.

Further, the most commonly used risk stratification tool, the National Nosocomial Infections Surveillance System (NNIS) risk index (Am. J. Med. 1991;91:152S-7S), does not perform well for “clean” procedures such as cardiovascular surgery, said Dr. Leekha and her associates, of the Mayo Clinic, Rochester, Minn.

The study population included patients who had undergone elective vascular (abdominal aortic and peripheral arterial) surgery at the Mayo Clinic from 2003 through 2007. A total of 87 patients who developed SSIs requiring hospitalization were included, and were matched with 166 controls who had undergone the same type of procedure on the same day but did not develop an infection.

There were no significant differences between cases and controls in age, sex, diabetes, smoking, alcohol use, chronic kidney disease, liver disease, weight loss, immunosuppressive therapy, and presence of skin ulcers. In multivariate analysis, preoperative variables that were significantly associated with SSI risk included critical ischemia (odds ratio 2.91), previous SSI (OR 6.29 with previous surgery, OR 1.40 with no previous surgery), previous peripheral revascularization (OR 2.55), and chronic obstructive pulmonary disease (OR 2.22).

A preop score model was developed in which 1 point each was given for COPD, critical ischemia, and previous peripheral revascularization and 2 points for previous SSI. The concordance statistic (c-statistic) for the preop score model was 0.73, compared with 0.50 for the NNIS score, Dr. Leekha and her associates reported.

A c-statistic of 1.0 indicates that the predictions are perfectly concordant with the actual outcomes, while 0.5 indicates that the predictions are no better than random chance. Thus, “based on these data, NNIS performs no better than a coin toss,” Dr. Leekha said in a follow-up interview.

The NNIS, the national standard for all types of surgeries, has been shown to perform poorly for cardiac surgery. Its performance for vascular surgery appears to be similar, possibly because the patients are similar in two of the three NNIS components—type of surgery (type 1/clean) and American Society of Anesthesiologists score of III or IV, she explained in the interview.

In their poster, Dr. Leekha and her associates recommended that patients predicted to be at high risk should be observed for wound problems and early intervention/wound care, but added that prospective validation of this tool is still required.

Disclosures: Dr. Leekha stated she had nothing to disclose.