Patient factors, comorbidities, and surgical characteristics that increase mortality and complication risk after spinal arthrodesis: a prognostic study based on 5,887 patients

Background context: The impact of patient factors and medical comorbidities on the risk of mortality and complications after spinal arthrodesis has not been well described. Prior works have been limited by small sample size, single center data, or the inability to be broadly generalized.

Purpose: To determine if there is an association between the patient demographic factors, comorbidities, nutritional status, and surgical characteristics and the occurrence of mortality and complications after spinal arthrodesis.

Study design: Retrospective review of prospectively collected data in the National Surgical Quality Improvement Program (NSQIP).

Patient sample: Patients who underwent spinal arthrodesis and had data registered with the NSQIP between 2005 and 2010.

Outcome measures: Primary outcomes were death or any complication after spinal arthrodesis. Secondary measures were the development of a specific complication, including wound infection, thromboembolic disease, or cardiac arrest/myocardial infarction.

Methods: The data set of the NSQIP from 2005 to 2010 was queried to identify all patients who underwent spinal arthrodesis. Demographic information, body mass index (BMI), medical comorbidities, arthrodesis procedure, operative time, American Society of Anesthesiologists (ASA) classification, and preoperative albumin were recorded for all patients identified. Mortality, the development of postoperative complications, and the presence of specific complications were also abstracted. Risk factors for mortality and complications were initially evaluated using chi-square and univariate logistic regression analyses. The risk factors that maintained p values less than .2 in univariate analysis were then combined in a multivariate fashion that identified significant, independent, predictors of mortality and complications while controlling for other factors present in the model. Sensitivity analysis was also performed, discriminating between the impact of risk factors on major and minor complications and the relative contribution to overall risk of morbidity. Multivariate analysis resulted in odds ratios (ORs) with 95% confidence intervals (CIs) for each risk factor. Only those predictors with ORs and 95% CI exclusive of 1.0 and p values less than .05 were considered statistically significant.

Results: In all, 5,887 patients who underwent spinal arthrodesis were identified. The average age of patients was 55.9 (±14.5) years. Twenty-five (0.42%) patients died after surgery, whereas 608 (10%) sustained a complication. Wound infection was the most common specific complication occurring in 2% of the cohort. Age (p=.03) and pulmonary conditions (p=.002) were found to have a significant association with the risk of mortality. Age exceeding 80 years was found to carry the highest risk of mortality. Age, pulmonary conditions, BMI, history of infection, ASA classification more than 2, neurologic conditions, resident (i.e., trainee) involvement, and procedural times exceeding 309 minutes increased the risk of complications. Body mass index, ASA classification more than 2, resident involvement, and procedural times exceeding 309 minutes were associated with the risk of infection. Although limited to univariate analysis, serum albumin 3.5 g/dL or less increased the risk of mortality, complications, wound infection, and thromboembolic disease. The OR for postoperative mortality among patients with albumin 3.5 g/dL or less was 13.8 (95% CI, 4.6-41.6; p<.001).

Conclusions: Several factors, including patients' age, BMI, ASA classification more than 2, pulmonary conditions, procedural times, and nutritional status likely influence the risk of postoperative morbidity to varying degrees. The risk factors identified here may be more generalizable to the American population as a whole because of the design and methodology of the NSQIP in comparison with previously published studies.