The Journal of Bone & Joint Surgery

The Journal of Bone & Joint Surgery, Volume 93, Issue 17

Scientific Articles | September 07, 2011

Risk Factors for Immediate Postoperative Complications and Mortality Following Spine Surgery: A Study of 3475 Patients from the National Surgical Quality Improvement Program

Andrew J. Schoenfeld, MD¹; Leah M. Ochoa, MD¹; Julia O. Bader, PhD²; Philip J. Belmont, Jr, MD¹

¹ Department of Orthopaedic Surgery, William Beaumont Army Medical Center, Texas Tech University Health Sciences Center, 5005 North Piedras Street, El Paso, TX 79920
² Department of Mathematical Sciences, University of Texas at El Paso, 500 West University Avenue, El Paso, TX 79968

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Disclosure: One or more of the authors received payments or services, either directly or indirectly (i.e., via his or her institution), from a third party in support of an aspect of this work. In addition, one or more of the authors, or his or her institution, has had a financial relationship, in the thirty-six months prior to submission of this work, with an entity in the biomedical arena that could be perceived to influence or have the potential to influence what is written in this work. No author has had any other relationships, or has engaged in any other activities, that could be perceived to influence or have the potential to influence what is written in this work. The complete Disclosures of Potential Conflicts of Interest submitted by authors are always provided with the online version of the article.

Disclosure statement for author(s): PDF

Investigation performed at Department of Orthopaedic Surgery, William Beaumont Army Medical Center, El Paso, Texas

A commentary by Raj D. Rao, MD, is linked to the online version of this article at jbjs.org.

Disclaimer: Some of the authors are employees of the U.S. Federal Government and the United States Army. The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or reflecting the views of William Beaumont Army Medical Center, the Department of Defense, or United States government. The American College of Surgeons National Surgical Quality Improvement Program and the hospitals participating in the ACS NSQIP are the source of the data used herein; they have not verified and are not responsible for the statistical validity of the data analysis or the conclusions derived by the authors.

J Bone Joint Surg Am, 2011 Sep 07;93(17):1577-1582. doi: 10.2106/JBJS.J.01048

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Abstract

Background:

This investigation sought to identify risk factors for immediate postoperative morbidity and mortality among a large series of patients undergoing spine surgery who were prospectively entered into a national registry.

Methods:

The database of the National Surgical Quality Improvement Program was queried to identify all patients undergoing spine surgery in the years 2005 to 2008. Demographic data, comorbidities, medical history, body-mass index, and the type of procedure performed were obtained for all patients. Postoperative complications and mortality within thirty days after the spinal procedure were also documented. The chi-square test and univariate and multivariate logistic regression analyses were used to evaluate the effect of individual risk factors on mortality, as well as the probability of the development of complications.

Results:

From 2005 to 2008, 3475 patients undergoing spine surgery were registered in the database. The average age of patients was 55.5 years (range, sixteen to ninety years), and 54% of the cohort were men. Ten patients (0.3%) died after surgery, and there were 407 complications in 263 patients (7.6%). Increased patient age and contaminated or infected wounds were identified as independent predictors of mortality. Increased patient age, cardiac disease, preoperative neurologic abnormalities, prior wound infection, corticosteroid use, history of sepsis, American Society of Anesthesiologists classification of >2, and prolonged operative times were independent predictors for the development of one or more complications.

Conclusions:

Patient age, female sex, longer procedural times, and several types of medical comorbidities influenced the risk of postoperative complications or mortality. This information enhances estimates of morbidity and mortality following spine surgery and may improve patient selection for spine surgery as well as preoperative discussions related to the risks of spine surgery.

Level of Evidence:

Prognostic Level II. See Instructions to Authors for a complete description of levels of evidence.

Figures in this Article

Introduction

As a result of the advances in diagnostic capabilities, surgical techniques, and spinal instrumentation, the indications for spine surgery have broadened and the rates of spine surgery have increased dramatically over the last twenty years^1-5. While the advantages of successful spine surgery are recognized, it is also understood that complications may lessen the likelihood of a satisfactory outcome and can result in further disability and even death^2-5. It is in the best interest of patients and surgeons contemplating spine surgery to understand the types of complications that may present in the early postoperative period, as well as potential risk factors for their development. Such knowledge would be useful to minimize the risk of postoperative complications. Comparatively little research has been conducted regarding the influence of variables, such as age, sex, body-mass index (BMI), and medical comorbidities, on the risk of complications following spine surgery^1-3,6-9. Most prior research has focused on wound infection^10-17, and few investigations have documented the impact of risk factors on other potential complications, or on mortality^4,7,9,18,19.

The goal of this investigation was to identify risk factors for mortality and complications among patients undergoing spine surgery who were registered in the American College of Surgeons National Surgical Quality Improvement Program (ACS NSQIP) database. The NSQIP assembles deidentified patient-related data on preoperative medical characteristics and postoperative morbidity and mortality from participating hospitals across the United States^20-23. The authors thought that the use of the NSQIP database would allow estimations for risks of morbidity and mortality following spine surgery from a cohort of >3000 patients.

Materials and Methods

Following the approval of our institution's investigational review board, the NSQIP database was obtained from the ACS for the years 2005 to 2008. The NSQIP prospectively collects preoperative patient medical data and documents postoperative morbidity and mortality for patients undergoing surgical interventions at participating medical facilities throughout the United States^20-22. Risk-assessment nurses, assigned to each participating center, are responsible for assembling patient-level data and entering them into the NSQIP system. All risk-assessment nurses undergo rigorous uniform training²¹. Data integrity measures, including site visits, conference calls, an annual meeting of participants, and auditing, are regularly performed to ensure reliability and validity of the system's data^21,22. Interrater reliability is calculated for all NSQIP variables, and a disagreement rate of >5% automatically triggers corrective action²².

Patients undergoing surgical procedures at a participating institution are included in the database. Individuals are prospectively observed for a period of thirty days postoperatively in order to document complications and/or mortality. Additional procedures, both surgical and nonsurgical, performed within thirty days after an index surgery are not recorded in the database as new cases. Individuals under the age of sixteen and patients receiving surgery as a result of acute trauma are not entered in the database.

For this study, the NSQIP database was queried, with use of the Current Procedural Terminology codes (see Appendix), for all patients receiving one or more operations on the spine. Demographic data, medical comorbidities, medical history, BMI, preoperative serum albumin, preoperative white blood-cell count, and surgical characteristics, including the type of procedure performed and operative time, were obtained for all identified patients. The complete list of preoperative characteristics, operative times, and type of surgery performed are detailed in Table I and the Appendix.

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TABLE I Patient Demographic and Preoperative Characteristics

Characteristic	No. with Available Data on Characteristic	Value
Age*(yr)	3475	55.5 ± 15.5
Gender (no. [%])	3475	—
Male	—	1871 (54)
Female	—	1604 (46)
Race (no. [%])	3475	—
White	—	2650 (76)
Black	—	221 (6)
Hispanic	—	238 (7)
Unknown	—	301 (9)
Other	—	66 (2)
Body-mass index* (range)	3457	29.8 ± 6.3 (10.8-94.7)
Underweight (no. [%])	—	90 (3)
Normal (no. [%])	—	638 (18)
Overweight (no. [%])	—	1255 (36)
Obese (no. [%])	—	1474 (43)
Preop. albumin*(g/dL)	1420	4.1 ± 0.5
Preop. white blood-cell count*(cells/mL)	3090	7.7 ± 2.7
Wound classification (no. [%])	3475	—
Clean	—	3394 (98)
Clean/contaminated	—	49 (1)
Contaminated	—	12 (0.4)
Dirty or infected	—	20 (0.6)
ASA classification†(no. [%])	3474	—
1	—	249 (7)
2	—	1955 (56)
3	—	1183 (34)
4	—	86 (2)
5	—	1 (0.03)
Medical comorbidities (no. [%])	3475	—
Diabetes	—	496 (14)
Smoking	—	904 (26)
Regular alcohol use	—	116 (3)
Chronic obstructive pulmonary disease	—	129 (4)
Cardiac issues (myocardial infarction and/or chronic heart failure)	—	25 (1)
Peripheral vascular disease	—	34 (1)
Renal insufficiency	—	16 (0.5)
Preop. neurologic issue	—	78 (2)
History of wound infection	—	19 (0.6)
Steroid use	—	128 (4)
History of sepsis	—	64 (2)

*The values are given as the mean and the standard deviation.
†ASA = American Society of Anesthesiologists.

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TABLE I Patient Demographic and Preoperative Characteristics

Characteristic	No. with Available Data on Characteristic	Value
Age*(yr)	3475	55.5 ± 15.5
Gender (no. [%])	3475	—
Male	—	1871 (54)
Female	—	1604 (46)
Race (no. [%])	3475	—
White	—	2650 (76)
Black	—	221 (6)
Hispanic	—	238 (7)
Unknown	—	301 (9)
Other	—	66 (2)
Body-mass index* (range)	3457	29.8 ± 6.3 (10.8-94.7)
Underweight (no. [%])	—	90 (3)
Normal (no. [%])	—	638 (18)
Overweight (no. [%])	—	1255 (36)
Obese (no. [%])	—	1474 (43)
Preop. albumin*(g/dL)	1420	4.1 ± 0.5
Preop. white blood-cell count*(cells/mL)	3090	7.7 ± 2.7
Wound classification (no. [%])	3475	—
Clean	—	3394 (98)
Clean/contaminated	—	49 (1)
Contaminated	—	12 (0.4)
Dirty or infected	—	20 (0.6)
ASA classification†(no. [%])	3474	—
1	—	249 (7)
2	—	1955 (56)
3	—	1183 (34)
4	—	86 (2)
5	—	1 (0.03)
Medical comorbidities (no. [%])	3475	—
Diabetes	—	496 (14)
Smoking	—	904 (26)
Regular alcohol use	—	116 (3)
Chronic obstructive pulmonary disease	—	129 (4)
Cardiac issues (myocardial infarction and/or chronic heart failure)	—	25 (1)
Peripheral vascular disease	—	34 (1)
Renal insufficiency	—	16 (0.5)
Preop. neurologic issue	—	78 (2)
History of wound infection	—	19 (0.6)
Steroid use	—	128 (4)
History of sepsis	—	64 (2)

*The values are given as the mean and the standard deviation.
†ASA = American Society of Anesthesiologists.

Postoperative complications and death occurring within thirty days after the operative procedure were recorded for each patient. Complications were grouped into major and minor categories on the basis of previously published protocols^7,9,19,24. The complete list of major and minor complications can be found in Tables II and III.

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TABLE II Mortality and Major Complications*

Characteristic	Value†
Death	10 (0.3)
Deep wound infection	30 (1)
Cardiopulmonary complication	28 (1)
Thromboembolic disease	37 (1)
Pulmonary embolism	12 (0.4)
Deep venous thrombosis	25 (0.7)
Cerebrovascular accident	3 (0.1)
Postop. neurologic deficit	5 (0.1)
Postop. sepsis	46 (1)
Return to operating room	106 (3)

*The occurrence of death and major complications was assessed for all 3475 patients.
†The values are given as the number of patients, with the percentage in parentheses.

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TABLE II Mortality and Major Complications*

Characteristic	Value†
Death	10 (0.3)
Deep wound infection	30 (1)
Cardiopulmonary complication	28 (1)
Thromboembolic disease	37 (1)
Pulmonary embolism	12 (0.4)
Deep venous thrombosis	25 (0.7)
Cerebrovascular accident	3 (0.1)
Postop. neurologic deficit	5 (0.1)
Postop. sepsis	46 (1)
Return to operating room	106 (3)

*The occurrence of death and major complications was assessed for all 3475 patients.
†The values are given as the number of patients, with the percentage in parentheses.

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TABLE III Minor Complications*

Characteristic	Value†
Wound dehiscence	11 (0.3)
Superficial wound infection	35 (1)
Pneumonia	29 (1)
Urinary tract infection	58 (2)
Bleeding complication	9 (0.3)

*The occurrence of minor complications was assessed in all 3475 patients.
†The values are given as the number of patients, with the percentage in parentheses.

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TABLE III Minor Complications*

Characteristic	Value†
Wound dehiscence	11 (0.3)
Superficial wound infection	35 (1)
Pneumonia	29 (1)
Urinary tract infection	58 (2)
Bleeding complication	9 (0.3)

*The occurrence of minor complications was assessed in all 3475 patients.
†The values are given as the number of patients, with the percentage in parentheses.

The influence of potential risk factors on postoperative complications and mortality was initially evaluated with use of univariate logistic regression analysis and the chi-square statistic. Multivariate logistic regression analysis was then conducted for factors with p < 0.2 in the initial univariate and/or chi-square testing and the variables previously identified as significant predictors for complications and/or mortality in prior publications. Significance was predetermined for p values of <0.05.

Source of Funding

No outside funding was received in support of this research or in the preparation of the manuscript.

Results

From 2005 to 2008, 3475 patients who underwent spine surgery were registered in the NSQIP database. The average age of the cohort was 55.5 years (range, sixteen to ninety years), and 54% of the cohort were men. Seventy-six percent of the patients were white. Sixty-three percent of the patients were graded as class 1 or 2 according to the system of the American Society of Anesthesiologists (ASA), while the remaining patients were graded ASA class 3 or higher. Diabetes was the most commonly encountered medical comorbidity and was present in 14% of the patients (Table I). Twenty-six percent of the cohort reported that they smoked. Disc herniation was the most common preoperative diagnosis (39%), followed by spinal stenosis (23%) and degenerative disc disease (13.5%). Lumbar decompression or discectomy procedures were the most common intervention, occurring in 2338 patients (67%). Spinal arthrodesis was performed in 1016 individuals (29%), and lumbar arthrodesis was done in 832 patients (24%). The average surgical time was 153.8 minutes (range, eight to 901 minutes).

In the acute postoperative period, 407 complications (Tables II and III) were documented in 263 individuals (7.6%). Two hundred and sixty-five major complications were seen in 179 patients (5.2%), 142 minor complications occurred in 128 patients (3.7%), and ten patients (0.3%) died. Urinary tract infections occurred in 2% of the patients, and wound infections (superficial or deep) occurred in 2%. The prevalence of cardiopulmonary complications, thromboembolic disease, and sepsis was 1% for each. The ten patients who died had nineteen complications, with the most common being pneumonia and myocardial infarction, each of which occurred in four patients.

The univariate and/or chi-square analyses identified significant risk factors for mortality, one or more complications, and one or more major complication (Table IV). Female sex (odds ratio [OR], 1.54; 95% confidence interval [CI], 1.08 to 2.19), BMI (OR, 1.04; 95% CI, 1.01 to 1.07), arthrodesis procedure (OR, 1.85; 95% CI, 1.30 to 2.64), diabetes (OR, 2.1; 95% CI, 1.40 to 3.15), chronic obstructive pulmonary disease (OR, 2.24; 95% CI, 1.15 to 4.38), cardiac issues (OR, 8.40; 95% CI, 3.30 to 21.4), renal insufficiency (OR, 13.24; 95% CI, 4.46 to 39.3), preoperative neurological abnormalities (OR, 3.0; 95% CI, 1.34 to 6.66), prior wound infection (OR, 7.0; 95% CI, 2.29 to 21.36), corticosteroid use (OR, 3.1; 95% CI, 1.69 to 5.65), history of sepsis (OR, 5.04; 95% CI, 2.51 to 10.13), ASA classification of >2 (OR, 3.83; 95% CI, 2.64 to 5.57), preoperative albumin of <3 g/dL (OR, 6.34; 95% CI, 3.16 to 12.71), increasing age (OR, 1.02; 95% CI, 1.01 to 1.04), and longer operative times (OR, 1.005; 95% CI, 1.004 to 1.006) significantly increased the risk of sustaining one or more minor complications in the univariate and/or chi-square analysis.

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TABLE IV Results of Univariate and/or Chi-Square Analyses for the Influence of Risk Factors on Mortality, One or More Complications, and One or More Major Complications

	Mortality		One or More Complications		One or More Major Complications
Risk Factor	P Value	Odds Ratio (95% Confidence Interval)	P Value	Odds Ratio (95% Confidence Interval)	P Value	Odds Ratio (95% Confidence Interval)
Sex (female vs. male)	0.12	3.4 (0.72-16.2)	0.03	1.32 (1.02-1.69)	0.5	1.11 (0.82-1.5)
Body-mass index	0.28	0.94 (0. 84-1.05)	0.001	1.03 (1.01-1.05)	0.01	1.03 (1.01-1.05)
Procedure (arthrodesis vs. nonarthrodesis)	0.46	1.61 (0.45-5.74)	<0.001	1.76 (1.37-2.29)	<0.001	1.77 (1.3-2.4)
Diabetes	0.03	4.03 (1.13-14.33)	<0.001	1.79 (1.31-2.44)	<0.001	2.1 (1.47-2.96)
Smoking	0.77	1.22 (0.78-17.8)	0.84	0.97 (0.73-1.3)	0.72	0.94 (0.66-1.32)
Regular alcohol use	0.98	<0.01 (<0.01-999)	0.94	1.03 (0.52-2.06)	0.68	1.17 (0.54-2.56)
Chronic obstructive pulmonary disease	0.02	6.57 (1.38-31.26)	<0.00	2.65 (1.64-4.27)	<0.001	3.2 (1.88-5.34)
Cardiac issues (myocardial infarction and/or congestive heart failure)	0.01	15.93 (1.94-130.70)	<0.001	8.42 (3.75-18.94)	<0.001	10.73 (4.68-24.63)
Peripheral vascular disease	0.99	<0.01 (<0.01-999)	0.03	2.66 (1.1-6.48)	0.02	3.2 (1.22-8.36)
Renal insufficiency	<0.001	66.39 (12.85-343.05)	<0.00	10.95 (3.94-30.44)	<0.001	16.53 (5.93-46.11)
Preoperative neurologic issue	0.99	<0.01 (<0.01-999)	<0.001	3.54 (1.97-6.36)	<0.001	4.74 (2.4-8.34)
History of wound infection	0.005	21.28 (2.56-176.78)	<0.001	11.35 (4.57-28.17)	<0.001	17.19 (6.89-42.84)
Steroid use	0.02	6.62 (1.39-31.52)	<0.001	4.1 (2.66-6.29)	<0.001	4.97 (3.12-7.91)
History of sepsis	0.09	6.0 (0.75-48.1)	<0.001	5.48 (3.16-9.52)	<0.001	5.99 (3.29-10.9)
Wound classification (not clean vs. clean)	<0.001	18.6 (4.72-73.31)	<0.001	3.4 (1.96-5.89)	<0.001	4.4 (2.47-7.91)
ASA classification* (1 or 2 vs. ≥3)	0.01	15.72 (1.99-124.25)	<0.001	3.19 (2.46-4.14)	<0.001	3.12 (2.28-4.25)
Preop. albumin (<3 vs. ≥3 g/dL)	0.007	9.47 (1.86-48.15)	<0.001	7.68 (4.25-13.90)	<0.001	9.1 (4.88-16.86)
Preop. white blood-cell count (<5 vs. ≥5 cells/mL)	0.94	0.93 (0.12-7.36)	0.86	0.96 (0.63-1.48)	0.83	0.95 (0.57-1.58)
Age†	<0.001	1.13 (1.1-1.2)	<0.001	1.02 (1.01-1.03)	<0.001	1.03 (1.02-1.04)
Operative time	0.025	1.004 (1.001-1.008)	<0.001	1.005 (1.004-1.006)	<0.001	1.004 (1.003-1.005)

*ASA = American Society of Anesthesiologists.
†The odds ratio for age indicates the elevation in risk per year.

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TABLE IV Results of Univariate and/or Chi-Square Analyses for the Influence of Risk Factors on Mortality, One or More Complications, and One or More Major Complications

	Mortality		One or More Complications		One or More Major Complications
Risk Factor	P Value	Odds Ratio (95% Confidence Interval)	P Value	Odds Ratio (95% Confidence Interval)	P Value	Odds Ratio (95% Confidence Interval)
Sex (female vs. male)	0.12	3.4 (0.72-16.2)	0.03	1.32 (1.02-1.69)	0.5	1.11 (0.82-1.5)
Body-mass index	0.28	0.94 (0. 84-1.05)	0.001	1.03 (1.01-1.05)	0.01	1.03 (1.01-1.05)
Procedure (arthrodesis vs. nonarthrodesis)	0.46	1.61 (0.45-5.74)	<0.001	1.76 (1.37-2.29)	<0.001	1.77 (1.3-2.4)
Diabetes	0.03	4.03 (1.13-14.33)	<0.001	1.79 (1.31-2.44)	<0.001	2.1 (1.47-2.96)
Smoking	0.77	1.22 (0.78-17.8)	0.84	0.97 (0.73-1.3)	0.72	0.94 (0.66-1.32)
Regular alcohol use	0.98	<0.01 (<0.01-999)	0.94	1.03 (0.52-2.06)	0.68	1.17 (0.54-2.56)
Chronic obstructive pulmonary disease	0.02	6.57 (1.38-31.26)	<0.00	2.65 (1.64-4.27)	<0.001	3.2 (1.88-5.34)
Cardiac issues (myocardial infarction and/or congestive heart failure)	0.01	15.93 (1.94-130.70)	<0.001	8.42 (3.75-18.94)	<0.001	10.73 (4.68-24.63)
Peripheral vascular disease	0.99	<0.01 (<0.01-999)	0.03	2.66 (1.1-6.48)	0.02	3.2 (1.22-8.36)
Renal insufficiency	<0.001	66.39 (12.85-343.05)	<0.00	10.95 (3.94-30.44)	<0.001	16.53 (5.93-46.11)
Preoperative neurologic issue	0.99	<0.01 (<0.01-999)	<0.001	3.54 (1.97-6.36)	<0.001	4.74 (2.4-8.34)
History of wound infection	0.005	21.28 (2.56-176.78)	<0.001	11.35 (4.57-28.17)	<0.001	17.19 (6.89-42.84)
Steroid use	0.02	6.62 (1.39-31.52)	<0.001	4.1 (2.66-6.29)	<0.001	4.97 (3.12-7.91)
History of sepsis	0.09	6.0 (0.75-48.1)	<0.001	5.48 (3.16-9.52)	<0.001	5.99 (3.29-10.9)
Wound classification (not clean vs. clean)	<0.001	18.6 (4.72-73.31)	<0.001	3.4 (1.96-5.89)	<0.001	4.4 (2.47-7.91)
ASA classification* (1 or 2 vs. ≥3)	0.01	15.72 (1.99-124.25)	<0.001	3.19 (2.46-4.14)	<0.001	3.12 (2.28-4.25)
Preop. albumin (<3 vs. ≥3 g/dL)	0.007	9.47 (1.86-48.15)	<0.001	7.68 (4.25-13.90)	<0.001	9.1 (4.88-16.86)
Preop. white blood-cell count (<5 vs. ≥5 cells/mL)	0.94	0.93 (0.12-7.36)	0.86	0.96 (0.63-1.48)	0.83	0.95 (0.57-1.58)
Age†	<0.001	1.13 (1.1-1.2)	<0.001	1.02 (1.01-1.03)	<0.001	1.03 (1.02-1.04)
Operative time	0.025	1.004 (1.001-1.008)	<0.001	1.005 (1.004-1.006)	<0.001	1.004 (1.003-1.005)

*ASA = American Society of Anesthesiologists.
†The odds ratio for age indicates the elevation in risk per year.

Multivariate logistic regression analysis determined that increased patient age (OR, 1.14; 95% CI 1.05 to 1.25) and contaminated or infected wounds (OR, 8.31; 95% CI, 1.04 to 66.67) significantly increased the risk of death, while increasing age (OR, 1.01; 95% CI, 1.001 to 1.02), cardiac disease (OR, 2.88; 95% CI, 1.07 to 7.72), preoperative neurologic abnormalities (OR, 2.24; 95% CI, 1.16 to 4.32), prior wound infection (OR, 4.34; 95% CI, 1.49 to 12.65), corticosteroid use (OR, 3.37; 95% CI, 2.1 to 5.45), history of sepsis (OR, 3.56; 95% CI, 1.81 to 6.97), ASA classification of >2 (OR, 1.87; 95% CI, 1.37 to 2.55), and prolonged operative times (OR, 1.004; 95% CI, 1.003 to 1.005) were independent predictors for the development of one or more postoperative complications, as well as one or more major complications (Table V). Female sex (OR, 1.54; 95% CI, 1.06 to 2.25), corticosteroid use (OR, 2.18; 95% CI, 1.10 to 4.32), history of sepsis (OR, 3.65; 95% CI, 1.57 to 8.47), ASA classification of >2 (OR, 2.17; 95% CI, 1.41 to 3.36), and prolonged operative times (OR, 1.005; 95% CI, 1.003 to 1.006) significantly affected the risk for one or more minor complications (Table V).

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TABLE V Significant Risk Factors for Mortality, Major Complications, Minor Complications, and Any Complication as Determined by Multivariate Logistic Regression Analysis

Risk Factor*	P Value	Odds Ratio (95% Confidence Interval)
Mortality
Age†	0.002	1.14 (1.05-1.25)
Wound classification	0.046	8.31 (1.04-66.67)
One or more complications
Age†	0.034	1.01 (1.001-1.02)
Cardiac issues (myocardial infarction and/or congestive heart failure)	0.036	2.88 (1.07-7.72)
Preop. neurologic issue	0.016	2.24 (1.16-4.32)
History of wound infection	0.007	4.34 (1.49-12.65)
Steroid use	<0.001	3.37 (2.1-5.45)
History of sepsis	<0.001	3.56 (1.81-6.97)
ASA classification	<0.001	1.87 (1.37-2.55)
Operative time	<0.001	1.004 (1.003-1.005)
One or more major complications
Age†	0.026	1.01 (1.002-1.03)
Cardiac issues (myocardial infarction and/or congestive heart failure)	0.045	2.95 (1.02-8.48)
Preop. neurologic issue	0.003	2.88 (1.42-5.83)
History of wound infection	<0.001	6.54 (2.17-19.72)
Steroid use	<0.001	4.02 (2.38-6.79)
History of sepsis	<0.001	3.11 (1.44-6.71)
ASA classification	0.011	1.61 (1.11-2.34)
Operative time	<0.001	1.004 (1.003-1.005)
One or more minor complications
Sex	0.025	1.54 (1.06-2.25)
Steroid use	0.026	2.18 (1.10-4.32)
History of sepsis	0.003	3.65 (1.57-8.47)
ASA classification	<0.001	2.17 (1.41-3.36)
Operative time	<0.001	1.005 (1.003-1.006)

*ASA = American Society of Anesthesiologists.
†The odds ratio for age indicates the elevation in risk per year.

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TABLE V Significant Risk Factors for Mortality, Major Complications, Minor Complications, and Any Complication as Determined by Multivariate Logistic Regression Analysis

Risk Factor*	P Value	Odds Ratio (95% Confidence Interval)
Mortality
Age†	0.002	1.14 (1.05-1.25)
Wound classification	0.046	8.31 (1.04-66.67)
One or more complications
Age†	0.034	1.01 (1.001-1.02)
Cardiac issues (myocardial infarction and/or congestive heart failure)	0.036	2.88 (1.07-7.72)
Preop. neurologic issue	0.016	2.24 (1.16-4.32)
History of wound infection	0.007	4.34 (1.49-12.65)
Steroid use	<0.001	3.37 (2.1-5.45)
History of sepsis	<0.001	3.56 (1.81-6.97)
ASA classification	<0.001	1.87 (1.37-2.55)
Operative time	<0.001	1.004 (1.003-1.005)
One or more major complications
Age†	0.026	1.01 (1.002-1.03)
Cardiac issues (myocardial infarction and/or congestive heart failure)	0.045	2.95 (1.02-8.48)
Preop. neurologic issue	0.003	2.88 (1.42-5.83)
History of wound infection	<0.001	6.54 (2.17-19.72)
Steroid use	<0.001	4.02 (2.38-6.79)
History of sepsis	<0.001	3.11 (1.44-6.71)
ASA classification	0.011	1.61 (1.11-2.34)
Operative time	<0.001	1.004 (1.003-1.005)
One or more minor complications
Sex	0.025	1.54 (1.06-2.25)
Steroid use	0.026	2.18 (1.10-4.32)
History of sepsis	0.003	3.65 (1.57-8.47)
ASA classification	<0.001	2.17 (1.41-3.36)
Operative time	<0.001	1.005 (1.003-1.006)

*ASA = American Society of Anesthesiologists.
†The odds ratio for age indicates the elevation in risk per year.

Discussion

This study sought to characterize risk factors for mortality and complications following spine surgery among a series of patients whose perioperative data had been obtained from hospitals across the United States. The robust patient-based data available in the NSQIP facilitates a broad analysis regarding the potential for multiple demographic, medical, and surgical characteristics to influence complications and mortality following spine surgery. Because of the large patient numbers available in the NSQIP dataset, as well as the fact that patient data are entered from facilities throughout the United States, estimates of postoperative complications after spine surgery with use of this system may be more applicable to the American population as a whole than estimates derived from sets of patients treated by one surgeon, or at a single center^15,19.

In our multivariate logistic regression analysis, increasing patient age and contaminated or infected wounds were independent factors significantly increasing the risk of death (Table V). Increasing patient age also independently increased the risk of one or more complications and major complications, as did cardiac disease preoperative neurologic abnormalities, a history of a spinal wound infection, corticosteroid use, a history of sepsis, an ASA classification of >2, and longer operative times (Table V).

The average age of our cohort approximates that of most other studies^{11,13,15,16,18,19,24}, as does the overall estimation of complications for cohorts exceeding 1000 patients^4,19. Similarly, the perioperative mortality rate identified in this study approximates the rate previously reported^4,5,19.

Few studies have attempted to estimate the effect that patient-based factors have on the risk of morbidity and mortality following spine surgery^4,7,9,19. Deyo et al. reported that increasing age, male sex, and spinal arthrodesis procedures increased the risk of complications, while increasing age and male sex affected mortality⁴. Kalanithi et al. reported that increasing age and the number of medical comorbidities influenced the risk of complications¹⁹. They found no effect of sex on the risk of complications. Patel et al. confirmed the effect of BMI on complication risk in their investigation of eighty-four patients receiving spine surgery at a single center⁹. A similar study, conducted by Yadla et al., among eighty-seven patients who had spine surgery, reported that age, hypertension, and spinal arthrodesis procedures increased the risk of complications, but the authors found no association between obesity and the prevalence of postoperative morbidity⁷.

The results presented in this investigation appear to support many of these prior reported conclusions. Most of the factors identified in previous investigations were noted to increase the risk of complications in our univariate analysis, although significance was lost for several variables once multivariate testing was performed. Increasing age remained a significant predictor for complications, however, as did an ASA classification of >2, which is usually associated with the presence of medical comorbidities. Likewise, the effect of operative time on complication risk in this study could reflect the previously reported impact of more extensive procedures, such as spinal arthrodesis^4,7,15,18.

This study was limited by the fact that it was performed with use of information obtained from a database. The majority of contributing institutions are large academic centers, and a minority participates in the multispecialty program that captured the data from spine surgery cases. Thus, such interventions are a small proportion of the entire dataset²⁵. The NSQIP is also not specifically designed to create predictive models of mortality or postoperative complications.

Furthermore, patients treated at NSQIP-participating hospitals, as well as those specifically enrolled in the dataset, may not be representative of all individuals undergoing spinal surgery. For example, only 29% of the cases in this study entailed arthrodesis-based spinal procedures and no individuals sustaining acute spinal trauma were enrolled. Disc herniation was the most common preoperative diagnosis in the cohort, and discectomies and simple decompressions have been shown to carry lower complication risks than spinal arthrodesis^2-4,7,18. This fact may have skewed our results to a certain degree, meaning that the prevalence of complications after spine surgery might be underestimated, and our findings are not necessarily generalizable to patients undergoing surgery for conditions such as spinal tumors, trauma, or complex deformity.

While recognizing these potential drawbacks, it should be emphasized that our use of the NSQIP dataset enabled a comprehensive characterization of risk factors for postoperative morbidity and mortality following spine surgery in a large series of patients. The previously established validity of the NSQIP dataset^20-23, as well as the fact that it is derived from multiple institutions throughout the United States, may indicate that findings in the present report represent some of the best available evidence on this topic. The results of this study can potentially enhance patient care and safety by informing preoperative discussions, patient selection, and medical optimization in the preoperative and perioperative periods.

Appendix

Tables showing the Current Procedural Terminology codes used to identify patients for inclusion in this study and the operative times and types of surgery performed are available with the online version of this article as a data supplement at jbjs.org.

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Yadla S; Malone J; Campbell PG; Maltenfort MG; Harrop JS; Sharan AD; Vaccaro AR; Ratliff JK. Obesity and spine surgery: reassessment based on a prospective evaluation of perioperative complications in elective degenerative thoracolumbar procedures. Spine J. 2010;10:581-7.[CrossRef][PubMed]

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Guigui P; Devyver B; Rillardon L; Ngounou P; Deburge A; Ghosez JP. [Intraoperative and early postoperative complications of lumbar and lumbosacral fusion: prospective analysis of 872 patients]. Rev Chir Orthop Reparatrice Appar Mot. 2004;90:5-15. French.[PubMed]

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Topics

postoperative complications ; mortality ; quality improvement ; spinal procedure

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Andrew J. Schoenfeld, Leah M. Ochoa, Julia O. Bader, Philip J. Belmont, Jr; Risk Factors for Immediate Postoperative Complications and Mortality Following Spine Surgery: A Study of 3475 Patients from the National Surgical Quality Improvement Program. The Journal of Bone & Joint Surgery. 2011 Sep;93(17):1577-1582.

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