Impact of Increased Body Mass Index on Outcomes of Elective Spinal Surgery

Andreea Seicean, MPH, PhD; Nima Alan, BS; Sinziana Seicean, MD, PhD, MPH; Marta Worwag, BA; Duncan Neuhauser, PhD; Edward C. Benzel, MD; Robert J. Weil, MD

Disclosures

Spine. 2014;39(18):1520-1530.

Abstract and Introduction

Abstract

Study Design. Observational retrospective cohort study of prospectively collected database.

Objective. To determine whether overweight body mass index (BMI) influences 30-day outcomes of elective spine surgery.

Summary of Background Data. Obesity is prevalent in the United States, but its impact on the outcome of elective spine surgery remains controversial.

Methods. We used National Surgical Quality Improvement Program, a prospective clinical database with proven validity and reproducibility consisting of 256 perioperative standardized variables from surgical patients at nearly 400 academic and nonacademic hospitals nationwide. We identified 49,314 patients who underwent elective fusion, laminectomy or both between 2006 and 2012. We divided patients according to BMI (kg/m²) as normal (18.5–24.9), preobese (25.0–29.9), obese I (30.0–34.9), obese II (35.0–39.9), and obese III (≥40). Relationship between increased BMI and outcome of surgery measured as prolonged hospitalization, complications, return to the operating room, discharged with continued care requirement, readmission, and death was determined using logistic regression before and after propensity score matching.

Results. All overweight patients (BMI ≥25 kg/m²) showed increased odds of an adverse outcome compared with normal patients in unmatched analyses, with maximal effect seen in obese III group. In the propensity-matched sample, obese III patients continued to show increased odds for complications (odds ratio, 1.6; 95% confidence interval, 1.1–2.3), readmission (odds ratio, 2.3; 95% confidence interval, 1.1–4.9), and return to the operating room (odds ratio, 1.8; 95% confidence interval, 1.1–3.1).

Conclusion. Impact of obesity on elective spine surgery outcome is mediated, at least in part, by comorbidities in patients with BMI between 25.0 and 39.9 kg/m². However, BMI itself is an independent risk factor for adverse outcomes in morbidly obese patients.

Level of Evidence: 3

Introduction

Obesity is prevalent in United States, and associated with numerous comorbidities.^[1,2] In several surgical specialties, including spine surgery, relationships between obesity and surgical outcome have been investigated,^[3–8] although the results have been conflicting. Because patient selection contributes to the success of elective spine surgery,^[9] it is important to elucidate more definitively the relationship between obesity and surgical outcome.

We studied the impact of increased body mass index (BMI) on outcome of elective spine surgery during a recent, 7-year period, using the National Surgical Quality Improvement Program.

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Table 1. Baseline Characteristics in the Unmatched Cohorts, Stratified by Body Mass Index (N = 49,314)
	Normal (n = 10,088)	Preobese (n = 17,305)	ASD	Obese I (n = 12,647)	ASD	Obese II (n = 5938)	ASD	Obese III (n = 3606)	ASD
Age, yr, mean ± SD	57 ± 16	58 ± 15	0.07	57 ± 14	0.05	56 ± 14	0.07	53 ± 13	0.24
Female	56.9%	41.0%	0.32	44.5%	0.25	53.1%	0.08	61.8%	0.10
Caucasian	82.8%	81.6%	0.03	81.6%	0.03	80.9%	0.05	79.9%	0.08
Admitted from home	98.8%	99.1%	0.03	99.1%	0.03	98.8%	0.01	98.8%	0.00
Smoking status
Current	30.9%	24.2%	0.16	22.1%	0.21	21.0%	0.23	20.0%	0.25
Previous	5.9%	7.7%	0.16	7.9%	0.21	7.4%	0.23	7.2%	0.25
> 2 alcoholic drinks per day	4.4%	3.9%	0.03	2.8%	0.09	2.5%	0.11	0.9%	0.22
Dependent functional status	3.2%	2.7%	0.03	2.9%	0.02	3.3%	0.00	4.0%	0.04
ASA classification
1 + 2	69.8%	67.1%	0.06	57.7%	0.25	46.5%	0.49	30.4%	0.86
3 + 4	30.2%	32.9%	0.06	42.3%	0.25	53.5%	0.49	69.6%	0.86
Hypertension requiring medication	35.0%	45.7%	0.22	56.0%	0.43	61.7%	0.55	65.7%	0.64
Diabetes mellitus	6.8%	11.6%	0.17	17.9%	0.34	24.7%	0.51	32.0%	0.67
Cerebrovascular comorbidities*	4.0%	4.1%	0.00	4.5%	0.01	4.0%	0.02	4.0%	0.01
Cardiopulmonary comorbidities†	5.3%	4.9%	0.02	6.0%	0.03	7.2%	0.08	9.4%	0.16
Renal comorbidities‡	0.3%	0.2%	0.00	0.2%	0.01	0.4%	0.02	0.2%	0.01
Bleeding risk factors§	2.6%	3.1%	0.03	3.3%	0.04	3.0%	0.02	2.7%	0.01
Anemia	22.3%	17.5%	0.12	17.8%	0.12	20.0%	0.06	22.6%	0.06
Transfusion	5.9%	6.3%	0.02	7.1%	0.05	8.1%	0.09	8.4%	0.10
Steroid use for chronic condition	3.5%	3.3%	0.01	3.2%	0.01	3.1%	0.02	3.0%	0.02
Sepsis or SIRS	0.5%	0.5%	0.00	0.5%	0.01	0.6%	0.02	0.6%	0.02
Prior operation within 30 d	0.8%	0.7%	0.02	0.6%	0.03	0.9%	0.01	0.7%	0.02
Abnormal WBC count	14.0%	12.5%	0.04	12.2%	0.05	12.4%	0.05	14.5%	0.02
Abnormal LFT¶	11.9%	10.6%	0.04	9.1%	0.09	9.6%	0.08	9.2%	0.09
Resident in OR	32.8%	31.9%	0.02	30.6%	0.05	29.2%	0.08	28.9%	0.09
Neurosurgery	66.6%	66.5%	0.00	65.7%	0.02	64.8%	0.04	65.0%	0.03

*History of transient ischemic attacks or cerebrovascular accident with or without residual neurological deficits.
†Pulmonary and/or cardiovascular disease, dyspnea.
‡Renal failure, dialysis, or abnormal blood urea nitrogen or creatinine.
§ Bleeding diathesis, abnormal international normalized ratio, or activated partial thromboplastin time or platelet count.
¶Abnormal bilirubin, alkaline phosphatase, aspartate transaminase, or albumin.
Boldfaced absolute standardized difference (> 0.20) denotes significance. Patients in each overweight category are compared with those with normal BMI.
ASA indicates American Association of Anesthesiologists; ASD, absolute standardized difference; BMI, body mass index; OR, operating room; SD, standard deviation; SIRS, systemic inflammatory response syndrome; LFT, liver function test; WBC, white blood cell.

Table 2. Baseline Characteristics in the Matched Cohorts, Stratified by Body Mass Index
	Normal	Preobese	ASD	Normal	Obese I	ASD	Normal	Obese II	ASD	Normal	Obese III	ASD
	(n = 10,088)		ASD	(n = 8778)		ASD	(n = 4834)		ASD	(n = 1372)		ASD
Age, yr, mean ± SD	57 ± 16	56 ± 15	0.01	56 ± 15	56 ± 16	0.00	55 ± 16	55 ± 14	0.04	53 ± 16	54 ± 13	0.02
Female	56.9%	56.9%	0.00	53.8%	51.8%	0.04	55.7%	53.9%	0.04	53.9%	62.9%	0.18
Caucasian	82.8%	81.5%	0.03	82.4%	82.1%	0.01	80.8%	81.5%	0.02	79.6%	77.9%	0.04
Admitted from home	98.8%	99.1%	0.03	98.7%	99.1%	0.03	98.5%	99.2%	0.06	99.2%	98.5%	0.07
Smoking status
Current	30.9%	25.1%	0.13	28.1%	26.9%	0.03	24.0%	23.3%	0.02	22.5%	22.2%	0.04
Previous	5.9%	6.9%	0.13	6.3%	6.4%	0.03	7.5%	7.2%	0.02	13.9%	12.5%	0.04
> 2 alcoholic drinks per day	4.4%	3.2%	0.07	4.3%	2.5%	0.10	4.3%	2.7%	0.09	1.2%	1.2%	0.01
Dependent functional status	3.2%	2.5%	0.04	3.4%	2.6%	0.05	4.0%	2.9%	0.06	5.7%	4.2%	0.07
ASA classification
1 + 2	69.8%	70.3%	0.01	67.7%	66.6%	0.02	56.0%	54.5%	0.03	47.2%	43.7%	0.07
3 + 4	30.2%	29.8%	0.01	32.3%	33.4%	0.02	44.0%	45.6%	0.03	52.8%	56.3%	0.07
Hypertension requiring medication	35.0%	35.0%	0.00	39.4%	40.7%	0.03	51.4%	54.3%	0.06	55.3%	55.7%	0.01
Diabetes mellitus	6.8%	9.7%	0.11	7.7%	8.3%	0.03	12.7%	14.7%	0.06	18.2%	17.5%	0.02
Cerebrovascular comorbidities*	3.2%	2.8%	0.02	3.5%	2.9%	0.03	3.9%	2.5%	0.08	4.7%	2.8%	0.10
Cardiopulmonary comorbidities†	5.3%	4.6%	0.03	5.4%	5.7%	0.01	6.3%	7.0%	0.03	4.7%	4.5%	0.01
Renal comorbidities‡	0.3%	0.2%	0.02	0.3%	0.1%	0.04	0.5%	0.3%	0.04	0.6%	0.2%	0.06
Bleeding risk factors¶	2.6%	2.6%	0.00	2.7%	2.8%	0.01	2.5%	2.7%	0.01	2.2%	2.9%	0.04
Anemia	22.3%	19.3%	0.08	22.1%	17.5%	0.12	24.5%	18.7%	0.14	26.2%	22.5%	0.12
Transfusion	5.9%	6.2%	0.02	5.9%	6.7%	0.03	6.5%	7.9%	0.06	6.8%	8.7%	0.07
Steroid use for chronic condition	3.5%	3.4%	0.00	3.5%	3.1%	0.02	4.3%	2.9%	0.08	4.7%	3.2%	0.08
Sepsis or SIRS	0.5%	0.5%	0.00	0.5%	0.5%	0.01	0.6%	0.6%	0.00	0.6%	0.7%	0.01
Prior operation within 30 d	0.8%	0.7%	0.01	0.7%	0.5%	0.03	0.9%	0.9%	0.01	1.1%	0.8%	0.03
Abnormal WBC	14.0%	12.6%	0.04	14.2%	12.2%	0.06	14.1%	12.2%	0.06	14.4%	15.5%	0.03
Abnormal LFT\|\|	11.9%	9.6%	0.08	12.4%	8.4%	0.13	13.4%	9.3%	0.13	12.0%	7.8%	0.14
Resident in OR	32.8%	31.2%	0.04	32.7%	30.4%	0.05	33.2%	28.9%	0.09	33.3%	28.9%	0.10
Neurosurgery	66.6%	65.8%	0.02	66.5%	65.5%	0.02	66.7%	64.2%	0.05	71.6%	65.2%	0.14

*History of transient ischemic attacks or cerebrovascular accident with or without residual neurological deficits.
†Diagnosis of pulmonary and/or cardiovascutlar disease, dyspnea.
‡Diagnosis of renal disease, abnormal blood urea nitrogen or creatinine.
§Disseminated cancer, weight loss more than 10% within 6 months of surgery, preoperative chemo/radiotherapy.
¶Diagnosis of bleeding diathesis, abnormal international normalized ratio or platelet count.
||Abnormal bilirubin, alkaline phosphatase, aspartate transaminase, or albumin.
ASA indicates American Association of Anesthesiologists; ASD, absolute standardized difference; BMI, body mass index; OR, operating room; SD, standard deviation; SIRS, systemic inflammatory response syndrome; LFT, liver function test; WBC, white blood cell.

Table 3. Distribution of Outcomes in the Unmatched Cohorts, Stratified by Body Mass Index
	Normal (n = 10,088)	Preobese (n = 17,305)	P *	Obese I (n = 12,647)	P *	Obese II (n = 5938)	P *	Obese III (n = 3606)	P *
Total length of hospital stay, d
Mean ± SD	3 ± 9	3 ± 7	0.03	3 ± 6	< 0.01	3 ± 7	< 0.01	3 ± 5	< 0.01
Median	2	2	0.03	2	< 0.01	2	< 0.01	2	< 0.01
Prolonged LOS (>4 d)	21.8%	22.2%	0.43	23.8%	< 0.01	27.6%	< 0.01	29.8%	< 0.01
Minor complications†	2.1%	2.2%	0.65	2.8%	< 0.01	3.2%	< 0.01	4.6%	< 0.01
Major complications‡	3.8%	4.2%	0.14	4.2%	0.17	4.7%	< 0.01	6.7%	< 0.01
Any complications§	5.3%	5.7%	0.22	6.2%	< 0.01	6.8%	< 0.01	9.4%	< 0.01
30-day return to the operating room	2.3%	2.5%	0.23	2.5%	0.32	2.9%	0.02	3.6%	< 0.01
Discharge with continued care requirement¶	9.6%	9.9%	0.52	10.5%	0.07	12.2%	< 0.01	14.1%	< 0.01
Readmission within 30 d	3.5%	4.6%	< 0.01	4.4%	< 0.01	5.0%	< 0.01	5.9%	< 0.01
30-day mortality rate	0.1%	0.1%	0.50	0.2%	0.82	0.1%	0.51	0.2%	0.47

*P values that are boldfaced are significant.
†Any one or more of the following complications within 30 days postoperatively: superficial surgical site infection, urinary tract infection, deep venous thrombosis and/or thrombophlebitis.
‡Any one or more of the following complications within 30 days postoperatively: deep incision surgical site infection, organ or space surgical site infection, wound disruption, pneumonia, unplanned intubation, pulmonary embolism, more than 48-hour postoperative ventilator-assisted respiration, progressive renal insufficiency, acute renal failure, cardiovascular accident with neurological deficit, coma of more than 24 hours, peripheral nerve injury, cardiac arrest requiring cardiopulmonary resuscitation, myocardial infarction, graft, prosthesis or flap failure, sepsis, septic shock, and/or 30-day return to the operating room.
§Any one or more minor or major complications.
¶Discharged to continued care facility, unless patient was originally admitted from such facility.
LOS indicates length of stay; SD, standard deviation; BMI, body mass index.

Table 4. Distribution of Outcomes in the Matched Cohorts, Stratified by Body Mass Index
	Normal	Preobese	P *	Normal	Obese I	P *	Normal	Obese II	P *	Normal	Obese III	P *
	(n = 3411)		P *	(n = 8778		P *	(n = 4834)		P *	(n = 1372)		P *
Total length of hospital stay, d
Mean ± SD	3 ± 7	3 ± 9	0.04	3 ± 9	3 ± 6	<0.01	3 ± 11	3 ± 5	< 0.01	3 ± 15	3 ± 5	< 0.01
Median	2	2	0.04	2	2	<0.01	2	2	< 0.01	2	2	< 0.01
Prolonged LOS (>4 d)	21.8%	22.4%	0.29	22.1%	22.5%	0.61	23.7%	26.3%	<0.01	25.6%	30.2%	0.01
Minor complications†	2.1%	2.2%	0.66	2.2%	2.7%	0.03	2.5%	2.9%	0.17	3.3%	5.1%	0.02
Major complications‡	3.8%	4.1%	0.37	3.7%	4.0%	0.22	4.5%	4.6%	0.73	5.3%	7.1%	0.05
Any complications§	5.3%	5.6%	0.42	5.6%	5.8%	0.65	6.3%	6.6%	0.53	7.4%	10.3%	0.01
30-day return to the operating room	2.3%	2.5%	0.31	2.4%	2.2%	0.36	2.5%	2.9%	0.31	2.8%	4.2%	0.06
Discharge with continued care requirement¶	9.6%	9.5%	0.89	10.1%	9.2%	0.09	10.4%	11.6%	0.11	7.7%	14.1%	<0.01
Readmission within 30 d	3.5%	4.5%	0.01	3.6%	4.0%	0.37	4.1%	4.8%	0.13	4.5%	7.1%	0.08
30-day mortality	0.1%	0.1%	0.41	0.2%	0.1%	0.69	0.2%	0.1%	0.11	0.2%	0.1%	0.56

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Impact of Increased Body Mass Index on Outcomes of Elective Spinal Surgery

Abstract and Introduction

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