Does the ACS NSQIP Surgical Risk Calculator Accurately Predict Complications Rates After Anterior Lumbar Interbody Fusion Procedures?

Ankur S. Narain, MD; Alexander Z. Kitto, MD; Benjamin Braun, MD; Matthew J. Poorman, MD; Patrick Curtin, MD; Justin Slavin, MD; Giles Whalen, MD; Christian P. DiPaola, MD; Patrick J. Connolly, MD; Michael P. Stauff, MD


Spine. 2021;46(12):E655-E662. 

In This Article

Materials and Methods

ACS NSQIP Surgical Risk Calculator

The ACS NSQIP Surgical Risk Calculator was developed using a cohort of 4.3 million cases from 780 participating hospitals from 2013 to 2017.[2] The ACS NSQIP Surgical Risk Calculator requires input of common demographic and comorbidity data and produces preoperative risk estimates for 13 categories. The online interface with all input variables is presented in Figure 1. The complication categories and data output is presented in Figure 2. For clarification, cardiac complications included cardiac arrest and myocardial infarction. Surgical site infection included superficial, deep, and organ space infections. Serious complications encompassed cardiac arrest, myocardial infarction, pneumonia, progressive renal insufficiency, acute renal failure, pulmonary embolism, deep venous thrombosis, reoperation, deep incision surgical site infection, organ space surgical site infection, systemic sepsis, unplanned intubation, urinary tract infection, and wound dehiscence.

Figure 1.

ACS NSQIP Surgical Risk Calculator data input interface.

Figure 2.

ACS NSQIP Surgical Risk Calculator data output interface.

Patient Identification and Data Abstraction

All patients undergoing anterior lumbar interbody fusion either as a stand-alone or as part of a staged procedure at our institution from 2009 to 2019 were included. Patients were excluded if they had incomplete preoperative or postoperative records (up to 30 days postoperatively), or if they underwent surgery for nondegenerative indications (trauma or oncologic indications). Retrospective chart review was performed for each patient. The data abstracted from the database included all necessary demographic and comorbidity information as required for entry into the ACS NSQIP surgical risk calculator, as described previously. Additional operative variables were collected including surgery type (stand-alone, staged), operative levels, total number of levels, additional procedures and type, length of hospital stay, and discharge destination. After inputting all necessary variables into the ACS NSQIP surgical risk calculator, the percentage risk for each complication category was collected. To obtain the predicted complication incidence, the risk percentage for each category was averaged across the entire study sample and that percentage was used to determine the predicted number of complications. The number of predicted complications was then rounded to the nearest whole integer to obtain the final predicted complication incidence for each category.

Perioperative and postoperative medical records were then reviewed to determine incidence of complications as categorized by the ACS NSQIP Surgical Risk Calculator. Criteria for incidence of complication was based off the ACS NSQIP user guide.[6] Additionally, medical records were thoroughly reviewed to capture all complications as noted by the list of diagnoses in the chart, including but not limited by the complications that meet the criteria as listed in the ACS NSQIP user guide. Length of stay was tabulated in the form of days, with integer values being utilized. Length of stay was characterized as long when above the 75th percentile (>4 days). Length of stay analysis was only performed on stand-alone ALIF procedures and not staged procedures. This was performed to ensure that the observed length of stay was attributed only to the ALIF procedure, and not affected by supplemental posterior fusion done during the index procedure or staged at a later date within the same admission. Hospital readmission was defined as any admission to the emergency department observation unit or any inpatient unit within 30 days postoperatively. Return to the operating room was defined as any unplanned reoperation within 30 days postoperatively. Admissions and operations as part of planned two-stage procedures were not designated as readmissions or reoperations.

Statistical Analysis

Statistical analysis was performed using STATA/MP 13.1 for Mac (StataCorp, College Station, TX). Demographic, comorbidity, and operative variables were summarized with descriptive statistics. To evaluate the predictive ability of the ACS NSQIP surgical risk calculator, logistic regression models were fitted for each complication type. Receiver operator characteristic curve (ROC) and area under the curve (AUC) analysis was then performed comparing observed complication rates versus predicted risks from the ACS NSQIP surgical risk calculator. AUC analysis produces a c-statistic value, with c = 0.5 associated with prediction no better than chance. A c-value of 0.6 to 0.69 designates poor predictive ability, 0.7 to 0.79 fair predictive ability, and ≥0.80 good predictive ability. Ninety five percent confidence intervals were also produced from AUC analysis. Statistical significance was set at P < 0.05 in all appropriate analyses.