SPINE Volume 39, Number 10, pp 798-804 ©2014, Lippincott Williams & Wilkins

CLINICAL CASE SERIES

Body Mass Index as a Predictor of Complications and Mortality After Lumbar Spine Surgery Alejandro Marquez-Lara, MD, Sreeharsha V. Nandyala, BA, Sriram Sankaranarayanan, MD, Mohamed Noureldin, MD, and Kern Singh, MD

Study Design. Retrospective analysis. Objective. A national population-based database was analyzed to characterize the risks of postoperative complications and mortality associated with the patient’s body mass index (BMI) after lumbar spinal surgery. Summary of Background Data. Obesity has been associated with greater perioperative complications and worsened surgical outcomes after lumbar spinal surgery. However, the stratified BMI risks of postoperative complications relative to normal weight patients have not been well characterized. Methods. The American College of Surgeons National Surgical Quality Improvement Program database was queried to identify patients who underwent lumbar spinal surgery between 2006 and 2011. Patients were stratified into BMI cohorts: normal (18.5– 24.99 kg/m2), overweight (25.00–29.99 kg/m2), class 1 (30.00–34.99 kg/m2), class 2 (35.00–39.99 kg/m2), and class 3 (≥40 kg/m2) obesity. Preoperative patient characteristics and perioperative outcomes were assessed. The relative risks of 30-day postoperative complications and mortality for each BMI cohort were calculated in reference to the normal weight cohort using a 95% confidence interval. Results. A total of 24,196 patients underwent lumbar spine surgery between 2006 and 2011 of which 19,195 (79.3%) were overweight or obese. The risk for deep vein thrombosis increased beginning with overweight patients and compounded for the subsequent obesity classes. The risk for superficial wound infection and pulmonary embolism increased beginning with the class 1 obesity cohort. Furthermore, the relative risk increase for urinary tract infection, acute renal failure, and sepsis was significantly increased only among class 3 obesity patients. Lastly, there was no relative risk increase in 30-day mortality in any cohort after lumbar spine surgery. From the Department of Orthopaedic Surgery, Rush University Medical Center, Chicago, IL. Acknowledgment date: December 10, 2013. First revision date: January 2, 2014. Acceptance date: January 9, 2014. The manuscript submitted does not contain information about medical device(s)/drug(s). No funds were received in support of this work. Relevant financial activities outside the submitted work: board membership, consultancy, and royalties. Address correspondence and reprint requests to Kern Singh, MD, Department of Orthopaedic Surgery, Rush University Medical Center, 1611 W. Harrison St, Suite 300, Chicago, IL 60612; E-mail: [email protected] DOI: 10.1097/BRS.0000000000000232

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Conclusion. Overweight and obese patients demonstrated an increased risk of postoperative complications relative to normal weight patients. Despite these findings, a BMI 25 kg/m2 or more was not associated with a greater risk of mortality. Further studies are warranted to characterize the impact of postoperative complications associated with overweight and obese patients on hospital resource utilization and costs after lumbar spine surgery. Key words: obesity, body mass index, lumbar spine surgery, relative risk, perioperative outcomes, postoperative complications. Level of Evidence: 4 Spine 2014;39:798–804

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besity (BMI >30 kg/m2) is associated with significant medical and financial implications1 including a greater risk of lower back pain and injury.2–6 Despite greater public health awareness, 69.2% of American adults are estimated to be overweight or obese.7 The surgical outcomes of lumbar spine surgery with regard to the patient’s weight has been subject to considerable scrutiny.8 Although several reports demonstrate that obesity is associated with greater perioperative complications and worsened surgical outcomes,9–15 other studies have not demonstrated significant differences in these parameters as a function of the patient’s weight.16–19 The purpose of this study was to analyze a large, multicenter, population-based database to determine the perioperative outcomes associated with overweight and obese patients and to characterize the stratified BMI risks of postoperative complications relative to normal weight patients.

MATERIALS AND METHODS The American College of Surgeons National Surgical Quality Improvement Program (ACS NSQIP) provides a large population-based database that aims to measure and improve the quality of surgical care in the private sector.20 This database was created in 1994 by the Veterans Administration Health System, and now expands more than 300 hospitals in the United States.21 The ACS NSQIP database is unique in that it collects clinical data from 135 variables related to patient demographics and comorbidities, perioperative parameters, and risk-adjusted outcomes up to the 30th postoperative day.21 Annual audits are performed to assure reliability of the

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CLINICAL CASE SERIES

BMI and Postoperative Complications • Marquez-Lara et al

data collection to at least 95%.21 Each variable is subject to a logistic regression to determine its predictability of complications. Patients younger than 16 years and trauma patients are excluded from the database. The ACS NSQIP issues Current Procedural Terminology codes for the primary and concurrent procedures.

Data Collection The ACS NSQIP database was queried from 2006 to 2011. Current Procedural Terminology codes were used to identify patients undergoing elective primary lumbar spine procedures (Table 1). The selected cohort was stratified into the following BMI groups: normal (18.5–24.99 kg/m2), overweight (25.00– 29.99 kg/m2), class 1 (30.00–34.99 kg/m2), class 2 (35.00– 39.99 kg/m2), and class 3 (≥40 kg/m2) obesity. Underweight patients (BMI

Body mass index as a predictor of complications and mortality after lumbar spine surgery.

Retrospective analysis...
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