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Scarborough JE, Schumacher J, Kent KC, Heise CP, Greenberg CC. Associations of Specific Postoperative Complications With Outcomes After Elective Colon Resection: A Procedure-Targeted Approach Toward Surgical Quality Improvement. JAMA Surg. 2017;152(2):e164681. doi:10.1001/jamasurg.2016.4681
Which postoperative complications have the greatest effect on clinical and economic outcomes after elective colorectal surgery?
In this cohort study using American College of Surgeons National Surgical Quality Improvement Program data, anastomotic leak and postoperative ileus had significantly higher associations with 30-day patient and health care resource use outcomes than complications such as surgical site infection, urinary tract infection, or venous thromboembolism.
Existing federal quality improvement programs are not targeting the complications that matter the most in colorectal surgery.
Numerous quality initiatives have been implemented in an effort to minimize the onus of postoperative complications on clinical and economic outcomes after major surgery. It is unknown which complications have the greatest overall effect on these outcomes.
To quantify the associations of specific postoperative complications with outcomes after elective colon resection.
Design, Setting, and Participants
Patients undergoing elective colon resection between January 1, 2012, and December 31, 2013, who were included in the Colectomy-Targeted American College of Surgeons National Surgical Quality Improvement Program were assessed for the development of specific types of postoperative complications. The overall contributions of these complications to subsequent clinical and resource use outcomes were assessed.
Main Outcomes and Measures
The main outcomes were 30-day mortality, end-organ dysfunction, reoperation, prolonged hospitalization, nonroutine discharge status, and hospital readmission. Risk-adjusted population attributable fractions were estimated for each complication-outcome pair. The population attributable fractions for a specific complication represented the percentage reduction in a given outcome that would be expected if exposure to that complication was completely eliminated.
A total of 26 682 patients undergoing elective colon resection were included for analysis; 13 870 patients were women (52.0%) and 15 088 (56.5%) were younger than 65 years. The most common index complications were ileus (n = 3140; 11.8%), bleeding (n = 2032; 7.6%), and incisional surgical site infection (n = 1873; 7.0%). Anastomotic leak was associated with the incidence of end-organ dysfunction, mortality, reoperation, and hospital readmission, with estimated population attributable fractions of 33.3% (95% CI, 29.6-36.8), 20.0% (95% CI, 14.0-25.7), 48.4% (95% CI, 45.7-51.0), and 20.6% (95% CI, 19.1-22.1) for each of these respective outcomes. The effect of complications, such as urinary tract infection, venous thromboembolism, and myocardial infarction, on these outcomes was comparatively small.
Conclusions and Relevance
Anastomotic leak has a large overall effect on 30-day clinical and economic outcomes after elective colon resection. The findings of our study support the adoption of a procedure-targeted approach to surgical quality improvement and describe a practical method for assessing complication effect.
Surgical complications have a profound effect on the US health care industry. Occurrence of a complication after major surgery is the single most important determinant of adverse patient outcome, surpassing both preoperative comorbid risk profile and intraoperative factors in the magnitude of its effect on short- and long-term postoperative survival.1,2 In addition, complications substantially increase the costs of surgical care, with most of this excess being passed on to third-party payors.3-7 When the downstream effects of postoperative complications are also considered, including the costs associated with morbidity-related hospital readmission and the lost wages that result from prolonged patient disability, their overall financial burden to society is substantial.8,9
In an effort to reduce the clinical and economic burden imposed by surgical complications, the Centers for Medicare and Medicaid Services (CMS) partnered in 2006 with other key stakeholder organizations to implement the Surgical Care Improvement Project (SCIP).10 The Surgical Care Improvement Project comprised a set of evidence-based process measures believed to be important for the prevention of surgical morbidity. The specific postoperative complications that were targeted by SCIP included surgical site infection (SSI), venous thromboembolism (VTE), myocardial infarction, and catheter-associated urinary tract infection.11 Although this program has since been replaced by newer initiatives, the original complications that were targeted by SCIP continue to serve as the primary focus of complication-associated federal quality public reporting and pay-for-performance efforts.12-14 As a result, hospitals continue to devote considerable time and resources toward tracking their compliance with SCIP-related process and outcome measures.15
Numerous studies have sought to determine whether hospital compliance with SCIP measures has resulted in a decrease in the incidence of the complications which the measures were designed to prevent.16-18 A larger and ultimately more relevant question is whether the complications targeted by SCIP and federal quality programs are the complications with the greatest effect on surgical mortality and the costs associated with surgical care. While SCIP was designed based on the best available evidence at the time, we need a more empirical population-based approach to prioritizing targets for quality improvement interventions in surgery.10 The population attributable fraction (PAF) is an epidemiologic method used to estimate the proportion of cases of a disease that can be attributed to a specific risk factor and thus to assist policymakers in assigning priorities for public health action.19 We sought to use the PAF to identify the highest-value complications relative to surgical mortality and resource use to inform development and prioritization of future quality improvement interventions in surgery.
Patients whose data were contained within the 2012 to 2013 Colectomy-Targeted American College of Surgeons National Surgical Quality Improvement Program (ACS NSQIP) participant use files were included in this analysis.20-22 The Colectomy-Targeted participant use files contain prospectively collected information on 22 perioperative variables that are considered to be particularly relevant to outcomes after colorectal surgery. A total of 121 accredited centers across the United States contributed patient data to the data source in 2012 and 152 centers in 2013.20
The University of Wisconsin institutional review board waived review board review of our study because it included deidentified patient data. The primary clinical outcome measures for our analysis included 30-day mortality and end-organ dysfunction (EOD). End-organ dysfunction was defined as postoperative coma, septic shock, or postoperative renal insufficiency (with or without the need for hemodialysis), and/or mechanical ventilation for more than 48 hours.23 The primary dichotomous resource use outcome measures for our analysis were 30-day reoperation, 30-day hospital readmission, and prolonged postoperative hospitalization. Prolonged postoperative hospitalization was defined as a postoperative length of hospital stay that exceeded the 75th percentile value for the surgical approach that was used during the index procedure (>5 days for minimally invasive surgical approach, >8 days for MIS-converted-to-open approach, or >8 days for open approach).24
The primary predictor variables for our analysis were the presence or absence of the following index complications within 30 days after colorectal surgery: incisional SSI (includes superficial and/or deep incisional infections), bleeding, anastomotic leak, ileus, pneumonia, VTE (includes deep venous thrombosis and/or pulmonary embolism), urinary tract infection, and myocardial infarction. A patient was classified by ACS NSQIP as having a postoperative leak if “...a leak of endoluminal contents through an anastomosis occurred...The presence of infection/abscess thought to be related to an anastomosis, even if the leak cannot be definitively identified as visualized during an operation, or by contrast extravasation, [was] still considered an anastomotic leak if indicated by the surgeon.”20 For the purpose of our study, we also included patients who sustained an organ/space SSI as having an anastomotic leak. Additional predictors included an array of patient demographic, comorbidity, and procedure-related characteristics (Tables 1 and 2). It is important to note that all of the outcome and predictor variables used in the analysis are strictly defined by ACS NSQIP to ensure uniformity of reporting across participating hospitals.20,25
Patients with an American Society of Anesthesiologists Physical Status Classification of 6 (indicating moribund condition) were excluded from our analysis. Multiple imputation using chained equations was used for observations for missing data for 1 or more variables, with 10 data sets being imputed, averaging predictions, and adjusting standard errors for uncertainty owing to imputation.26 Those variables with missing data for 1 or more observations included age (n = 1 missing observation), body mass index (n = 121), preoperative functional status (n = 91), American Society of Anesthesiologists classification (n = 24), surgical approach (n = 17), indication for surgery (n = 30), preoperative albumin (n = 9357), bowel preparation status (n = 6880), prolonged postoperative hospitalization (n = 13), postoperative leak (n = 92), and postoperative ileus (n = 112).
Continuous patient- and procedure-related measures are described using mean or median values as appropriate. Frequencies of index complications and of the 5 adverse outcomes are likewise reported. Multivariable poisson regression with log link and robust error variance was used to produce relative risk estimates (ratios of the probability of a given outcome occurring for persons with a particular surgical complication to the probability of the same event occurring for patients without the complication). Covariates that were used for risk adjustment in these models included all of the variables listed in Table 1.
Two approaches were used for these models: (1) using a separate regression model for each complication-outcome pair, with the pool of potential predictor variables including patient- and procedure-related factors and the specific index complication of interest and (2) 1 regression model for each outcome, with all 8 index complications included as potential predictors. The rationale for using 2 different approaches stems from the fact that some patients in our study population had more than 1 index complication, and we are unable to determine whether these coexisting complications were causally related.
We used PAF to quantify the overall contribution of each complication to each of our 5 outcomes (mortality, EOD, readmission, reoperation, and resource use).19 The unadjusted PAF was calculated as PAF = [Pc × (RR − 1)] / [Pc × (RR − 1) + 1], with Pc denoting complication prevalence and RR denoting risk ratio of the outcome given the complication.27 In the context of our study, the PAF for a specific complication will represent the estimated percentage decrease in an outcome that would be expected if exposure to the complication were fully prevented within the study population. Using the estimated relative risks derived from the previously described regression models, we estimated PAF for each complication-adverse outcome pair in a manner that accounts for other known patient- and procedure-related variables.28 Adjusted PAF is reported as the percentage reduction in the incidence of a given adverse outcome measure (with 95% confidence intervals) that would be anticipated if the specific complication were completely prevented, controlling for other variables. The 2 different approaches to Poisson regression generation resulted in relatively small differences in our PAF estimates (data not shown), so we have presented the results of the models that include only 1 index complication in the pool of predictor variables. Stata, version 14.0 (StataCorp) was used for all statistical analyses.
A total of 26 682 patients undergoing elective colon resection at 1 of 152 hospitals that participated in 2012-2013 Colectomy-Targeted ACS NSQIP were included for analysis. The demographic, comorbid, and procedure characteristics of these patients are summarized in Table 1.
The frequency of index complications in our study population is shown in the Figure. The most common complications after elective colon resection were ileus (n = 3140; 11.8%), bleeding (n = 2032; 7.6%), and incisional surgical site infection (n = 1873; 7.0%). The least frequent complications were VTE (n = 365; 1.4%), pneumonia (n = 379; 1.4%), and myocardial infarction (n = 132; 0.5%).
The 30-day mortality rate for our study population was 0.9% (233 of 26 682 patients), and the 30-day EOD incidence was 2.7% (729 patients). The 30-day reoperation rate for our study population was 4.4% (1177 patients), and 22.0% (5867 patients) required prolonged postoperative hospitalization. The rate of hospital readmission for 30-day survivors was 9.4% (2514 patients).
Pneumonia was the index complication that was associated with the greatest relative risk of EOD and mortality (Table 2), while anastomotic leak was the complication associated with the largest relative risk of reoperation and readmission (Table 3).
To characterize each complication effect, we estimated the risk-adjusted PAF for each complication-outcome pair (Table 4). A complication’s PAF for a given adverse outcome represents the percentage reduction in the incidence of that outcome that would occur if exposure to the complication were completely eliminated within the study population.
Anastomotic leak was the complication with the largest overall effect on the 30-day occurrence of EOD and the third-largest effect on mortality after elective colon resection. If it were possible to completely prevent this complication, the incidence of EOD and death would decrease by 33.3% and 20.0%, respectively. Based on the size of their risk-adjusted PAFs, ileus, pneumonia, and bleeding also demonstrated relatively large effects on the clinical outcomes of study population (32.0%, 19.1%, and 19.5%, respectively, for EOD and 22.6%, 18.5%, and 20.1%, respectively, for mortality). Conversely, urinary tract infection, incisional SSI, and VTE all had estimated PAFs of less than 8% for both EOD and mortality, indicating that the effect of these complications on the physiologic outcomes of elective colon resection patients is relatively small. Anastomotic leak was also the complication that contributed the most to the incidence of reoperation and hospital readmission, while ileus was the complication with the largest overall effect on length of postoperative hospitalization.
Using a novel method to quantify the contribution of specific postoperative complications toward subsequent surgical outcomes, we have demonstrated that anastomotic leak has a large overall effect on 30-day mortality and resource use after elective colon resection. The PAF is a simple yet attractive indicator of complication effect because it incorporates information about both the frequency of a complication and the likelihood that the complication will result in a given adverse outcome.27 The parameter can therefore be used to facilitate comparison of low-frequency/high-severity complications with high-frequency/low-severity complications in terms of their overall effect on outcomes for a given surgical population to prioritize targets for intervention.19
In this study, anastomotic leak was the largest contributor to 3 of the 5 assessed outcome measures, and the only complication besides postoperative ileus that demonstrated a relatively sizeable effect on all 5 measures. Complete prevention of this complication would result in an estimated 33.3% reduction in the incidence of EOD, a 20.0% reduction in the incidence of postoperative death, a 48.4% reduction in the rate of reoperation, and a 20.6% reduction in the need for hospital readmission after elective colon resection. These findings suggest that any effort to reduce the burden of complications on the colorectal surgical population must target the prevention of anastomotic leak to achieve maximal yield.
In addition to providing strong evidence for the inclusion of anastomotic leak as a target of CMS-driven quality efforts in colorectal surgery, the findings of our study also raise concern about the continued focus of federal quality initiatives on SCIP-associated complications such as urinary tract infection, myocardial infarction, and VTE. Most of these complications demonstrated estimated PAFs of less than 10% for all of the outcome measures of our study, indicating that their effect on the colorectal surgical population is relatively small. Although our analysis is confined to elective colon resection procedures, a previous examination of patients undergoing emergency general surgery revealed bleeding and pneumonia complications to have the largest effect on subsequent patient outcomes.29 Similar to this study, that analysis demonstrated SCIP-associated complications to have little if any effect on most outcome measures in the EGS population. Thus, even if efforts to reduce the incidence of SCIP-associated complications were successful, the estimated effect of these efforts on clinical and economic outcomes of colorectal and emergency general surgery patients would be anticipated to be relatively small. Because these procedures collectively account for a disproportionate and sizeable share of surgical morbidity in the United States, the overall effectiveness of existing complication-associated process and outcome measures in being able to achieve meaningful reductions in complication-associated mortality and excess resource use seems limited at best.23,30-34 However, because SCIP-associated complications remain the primary focus of CMS public reporting and pay-for-performance programs, hospitals have strong financial motivation to devote quality improvement efforts toward prevention of these complications. As a result, the pool of resources that are available for initiatives that target higher-effect complications might be insufficient.15,35 Thus, by endorsing process and outcome measures that target ubiquitous but low-effect complications, CMS may inadvertently be diverting valuable resources away from more meaningful quality efforts.
The findings of our study provide a strong argument for a more purposeful, empirically driven approach to surgical quality improvement. The Centers for Medicare and Medicaid Services and other national quality stakeholders should promote and support further investigation into the effect of both ubiquitous and specialty-specific complications on specific surgical populations. For example, the methods described in our analysis can easily be applied to existing national data sources to determine the overall effect of pancreatic fistula to patients undergoing pancreaticoduodectomy or of bronchopleural fistula to patients undergoing lung resection. Once the highest-effect complications have been identified for a given procedure type, evidence-based interventions and quality measures can be developed. Although the application of different quality metrics to different surgical populations may appear at first to be less practical than the “procedure-nonspecific” approach that is used by CMS, the procedure-targeted approach will ultimately result in a more efficient and effective allocation of hospital quality improvement resources by ensuring that hospitals are measuring what matters the most.
The literature supports our identification of anastomotic leak after elective colon resection as a critical target for quality improvement and measurement. The relevance of this complication has been confirmed by leaders of the American Society of Colon and Rectal Surgeons and the American Board of Colon and Rectal Surgery.36 The complication has also been included as an outcome measure in several regional and national colorectal surgical registries, including the Dutch Surgical Colorectal Audit, the Surgical Clinical Outcomes Assessment Program in Washington state, and the Colectomy-Targeted ACS NSQIP.37,38 Several strategies have been shown in the literature to offer protection against postoperative anastomotic leak, including preoperative bowel preparation with mechanical catharsis and oral antibiotics, performance of an intraoperative air leak test, and selective use of a proximal defunctioning stoma.39-41 The proven import of this complication to the outcomes of colorectal surgery patients would seem to justify redirection of quality improvement resources toward further investigation of these and other strategies as potential process measures. Until best practices for the construction of colorectal anastomoses can be further developed, the simple use of anastomotic leak rate as a public reporting and pay-for-performance outcome measure for colectomy patients may provide hospitals with sufficient impetus to further explore processes for preventing this complication.
An important limitation of our use of PAF to estimate complication effects is that we have assumed that the index complications that we have analyzed are at least in part causative of the subsequent adverse outcomes and that our risk-adjustment algorithm for estimating PAFs has completely accounted for the influence of other potential confounding factors on this causative relationship. In addition, we are unable to determine the temporal associations between index complications in those patients from our study population who sustained more than 1 type of index complication. As a result, our PAF estimates may be subject to some degree of adjustment error. In addition, these estimates may not necessarily be generalizable to hospitals that do not participate in the Colectomy-Targeted ACS NSQIP program, and the absence of hospital identifiers in the participant use files prevented us from adjusting for possible hospital-related effects. Also, we selected outcome measures based on the data that were available in ACS NSQIP and made no attempt to prioritize these measures. Finally, by including organ/space SSI in our study definition of postoperative leak, our analysis may overestimate the frequency with which this complication has occurred in our study population.
Our study identified anastomotic leak to be the complication with the greatest overall effect on 30-day clinical and economic outcomes after elective colon resection. Given the significant contribution of anastomotic leak to these outcomes and the relatively small effect of other complications that are currently targeted by CMS-endorsed process measures, the findings of our study provide strong support for the adoption of process and/or outcome measures that focus on this complication. Extension of the methods described in our analysis to other surgical populations will facilitate the development of a more targeted and thus more effective national approach to surgical quality improvement.
Corresponding Author: John E. Scarborough, MD, Surgery, G5/340 Clinical Science Center, 600 Highland Ave, Madison, WI 53792 (firstname.lastname@example.org).
Accepted for Publication: September 30, 2016.
Published Online: December 7, 2016. doi:10.1001/jamasurg.2016.4681
Author Contributions: Dr Scarborough had full access to all the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Concept and design: Scarborough, Kent, Greenberg.
Acquisition, analysis, or interpretation of data: Scarborough, Schumacher, Heise.
Drafting of the manuscript: Scarborough, Kent.
Critical revision of the manuscript for important intellectual content: All authors.
Statistical analysis: Scarborough, Schumacher.
Administrative, technical, or material support: Scarborough, Greenberg.
Conflict of Interest Disclosures: None reported.