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Invasiveness Index as a Predictor of Surgical Site Infection after Spinal Fusion, Revision Fusion, or Laminectomy

Published online by Cambridge University Press:  09 November 2016

Brian L. Hollenbeck*
Affiliation:
Division of Infectious Diseases, New England Baptist Hospital, Boston, Massachusetts
Kevin J. McGuire
Affiliation:
Beth Israel Deaconess Medical Center, Department of Orthopaedic Surgery, Boston, Massachusetts
Andrew P. White
Affiliation:
Beth Israel Deaconess Medical Center, Department of Orthopaedic Surgery, Boston, Massachusetts
David S. Yassa
Affiliation:
Beth Israel Deaconess Medical Center, Division of Infection Control/ Hospital Epidemiology, Silverman Institute for Health Care Quality and Safety, Boston, Massachusetts
Sharon B. Wright
Affiliation:
Beth Israel Deaconess Medical Center, Division of Infection Control/ Hospital Epidemiology, Silverman Institute for Health Care Quality and Safety, Boston, Massachusetts
*
Address correspondence to Brian L. Hollenbeck, MD, New England Baptist Hospital, Division of Infectious Diseases, 125 Parker Hill Ave, Converse #600, Boston, MA 02120 (bhollenb@nebh.org).
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Abstract

OBJECTIVE

To evaluate invasiveness index as a potential predictor of spine surgical site infection (SSI) after spinal fusion, revision fusion, or laminectomy.

DESIGN

Retrospective cohort study.

SETTING

Single, large, academic medical center.

PATIENTS

Adults undergoing spinal fusion, revision fusion, or laminectomy.

METHODS

Data were obtained from electronic hospital databases; cases of SSI were extracted from the infection control database using National Healthcare Safety Network (NHSN) definitions. For each case, an invasiveness index, determined by surgical approach, procedure, and number of spine levels treated, was calculated using current procedural terminology (CPT) billing codes. Statistical analyses were performed using univariate and multivariate logistic regression models.

RESULTS

In total, 3,143 patients met inclusion criteria, and 43 of these developed SSI. Multivariate regression showed that advanced age (odds ratio [OR], 1.03; 95% confidence interval [CI], 1.005–1.05, for each year of life) and invasiveness index (medium invasiveness index OR, 5.36; 95% CI, 1.92–14.96; high invasiveness index OR, 14.1; 95% CI, 4.38–45.43) were significant predictors of infection. In subgroup analyses of spinal fusion patients, morbid obesity (OR, 2.542; 95% CI, 1.08–5.99), trauma (OR, 2.41; 95% CI, 1.05–5.55), and invasiveness index (medium invasiveness index OR, 5.39; 95% CI, 1.56–18.61; high invasiveness index OR, 13.44; 95% CI, 3.28–55.01) were significant predictors of SSI. Models containing invasiveness index were compared to NHSN models and demonstrated similar performance.

CONCLUSIONS

Invasiveness index is a predictor of SSI after spinal fusion and performs similarly to NHSN models. Invasiveness index shows promise as a potential risk stratification tool that is easily calculated and is available preoperatively.

Infect Control Hosp Epidemiol 2016:1–7

Information

Type
Original Articles
Copyright
© 2016 by The Society for Healthcare Epidemiology of America. All rights reserved 
Figure 0

FIGURE 1The invasiveness Index is a sum of surgical approach, procedure, and number of spine levels treated, and it has been independently associated with increased risk for surgical site infection. At each spinal level treated, points are assigned for anterior decompression, instrumentation and arthrodesis and posterior decompression, instrumentation, and arthrodesis. Results are summed to generate an invasiveness index score. This measure can be calculated preoperatively based on planned procedure or retrospectively through case review or electronic review of billing codes. Image reproduced courtesy of “Regional Vertebral Characteristics,” Boundless Anatomy and Physiology. Boundless, July 3, 2014.

Figure 1

FIGURE 2Patient disposition. There were 5,673 patient encounters (*including staged anterior/posterior procedures). A total of 2,530 patients were excluded because of incomplete billing information used to calculate invasiveness index and other variables. Patients with superficial infection were excluded from the final analysis (n=22). The cohort under analysis consisted of 3,100 controls and 43 deep or organ/space infections.

Figure 2

FIGURE 3The invasiveness index calculated by manual chart review (Y-axis) versus the invasiveness index calculated using current procedural terminology (CPT) codes (X-axis). When divided into tertials (low invasiveness [<10], medium invasiveness [10–20], high invasiveness [>20]), the 2 measures demonstrated good reliability with κ=0.72 (95% CI, 0.65–0.80) and weighted κ=0.77 (95% CI, 0.71–0.83).

Figure 3

TABLE 1Univariate Comparisons of Demographic, Clinical and Procedural Characteristics of Cases and Controls

Figure 4

TABLE 2Multivariate Models of Predictors for SSI Among the Full Cohort (All Procedures) and Stratified by Fusion Procedures

Figure 5

TABLE 3Goodness-of-Fit of Surgical Site Infection Prediction Models for All Procedures and Stratified by Procedure Type

Figure 6

FIGURE 4Risk predicted by the National Healthcare Safety Network Standardized Infection Ratio (NHSN SIR) (X-axis) versus invasiveness index (Y-axis) for all procedures. Dots represent surgical site infection cases; grey crosses represent controls. Spearman correlation coefficient demonstrated modest positive correlation between the variables (correlation coefficient=0.42).

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