Impact of Procedure on the Post-Operative Infection Risk of Patients after Elective Colon Surgery

Abstract

Background:

Post-operative infection impacts the quality of patient care, prolongs the length of hospital stay, and utilizes more health care resources. The purpose of this study was to compare the rates of surgical site infection among three major surgical procedures for treating patients with colon pathology.

Hypothesis:

The location of colon resection impacts the post-operative infection rate.

Methods:

A retrospective cohort study was conducted by using the 2006 Nationwide Inpatient Sample. Adult patients (age ≥18 yr) with colon diseases are the population of interest. The disease status and procedures were categorized according to the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM). Patients with a primary diagnosis of diverticulosis of the colon without hemorrhage (ICD-9-CM codes: 562.11 and 562.12) or malignant neoplasm of the colon (ICD-9-CM codes: 153.x, where x represents the possible digits within this ICD-9-CM code category), with procedures of open and other right hemicolectomy (ORH; ICD-9-CM code: 45.73) or open and other left hemicolectomy (OLH; ICD-9-CM code: 45.75), or open and other sigmoidectomy (OS; ICD-9-CM code: 45.76) were included for this study. The primary measured outcome for the study was surgical site infection.

Results:

There were an estimated 26,381 ORH procedures, 9,558 OLH procedures, and 31,656 OS procedures performed in 2006. There was a significant difference among procedures with respect to their age distributions (mean [standard error]: ORH vs. OLH vs. OS=70.5 [0.2] vs. 63.8 [0.3] vs. 59.5 [0.2] yr, p<0.0001) and the gender distributions (female percentage ORH vs. OLH vs. OS=56.1% vs. 51.5% vs. 50.9%, p<0.0001). There was a significant difference among the surgical procedures (infection rates: ORH vs. OLH vs. OS=2.9% vs. 5.6% vs. 4.9%, p<0.0001). From a logistic regression model, after controlling for age, gender, primary diagnosis, comorbidities, and hospital teaching status, OLH had a higher chance of SSI (adjusted odds ratio [AOR] [95% confidence interval {CI}]=1.54 [1.16–2,05], p=0.003) compared with ORH. However, OS did not have different SSI rates (AOR [95% CI]=1.18 [0.90–1.54], p=0.234) compared with ORH. There was a higher rate of infection for OLH (AOR [95% CI]: 1.31 [1.04–1.64], p=0.02) compared with OS.

Conclusions:

Different sites of colon operations were associated with different risks of surgical site infections. Accordingly, appropriate pre-operative measures should address these differences.

Surgical site infections (SSIs) are the most common nosocomial infections in surgical patients and are a substantial cause of morbidity, as well as other negative outcomes [1,2]. Indeed, post-operative infections lead to a number of adverse outcomes, such as prolonged length of stay (LOS) in the hospital, lower health-related quality of life, and markedly increased hospital spending and resource utilization per patient [3 –5]. Colorectal resections in particular present an increased risk for SSIs (in addition to the consequent adverse outcomes) relative to other surgical procedures, most likely as a result of the extremely high density of bacteria in the colon [6 –8]. Accordingly, a great deal of research has focused on identifying risk factors, comparing procedures, and developing protocols to reduce SSI rates after colorectal surgery.

A number of risk factors have been identified that increase the likelihood of SSIs. For example, higher than normal blood glucose concentration, obesity, intra-operative transfusion of red blood cell concentrates, sarcopenia, and operative time are all positively associated with SSI rate [8 –13]. Moreover, the invasiveness of the surgery plays a crucial role in SSI rate; laparoscopic procedures, relative to open procedures, reduce the incidence of post-operative infections [9,14,15].

Despite our progress in understanding the multiple variables involved in determining the risk of SSIs and subsequent morbidities, few studies have explored the impact of the site of colorectal resection on infection rate. Therefore, the purpose of this study was to analyze data pertaining to SSI rates in colorectal resection patients, grouped by the surgical site (open right hemicolectomy [ORH], open left hemicolectomy [OLH], and open sigmoid colectomy [OS]), from the Nationwide Inpatient Sample [NIS] database.

Patients and Methods

Data source

This retrospective cohort study examined SSI rates in 2006 using discharge data from the Nationwide Inpatient Sample [NIS], Healthcare Cost and Utilization Project (HCUP), Agency for Healthcare Research and Quality [16]. The NIS is the largest all-payer inpatient care database in the United States and contains approximately a 20% stratified sample of U.S. community hospitals. The stratification is based on five hospital characteristics: Geographic region (northeast, midwest, west, and south), control (government non-federal [public], private not-for-profit [voluntary], and private investor-owned [proprietary]), location (urban or rural), teaching status (teaching or non-teaching), and bed size (small, medium, and large). It contains data from approximately eight million hospital stays each year.

Diseases and procedures of interest

The population of interest included adult patients (age ≥18 yr) with colon disease in 2006. The disease status and procedures were categorized according to the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM).

ICD-9-CM codes

Patients were included who had undergone elective colon surgery following a primary diagnosis of diverticulosis of the colon without hemorrhage (ICD-9-CM codes: 562.11 and 562.12) or malignant neoplasm of the colon (ICD-9-CM codes: 153.x, where x represents the possible digits within this ICD-9-CM code category), with procedures of open and other right hemicolectomy (ORH; ICD-9-CM code: 45.73) or open and other left hemicolectomy (OLH; ICD-9-CM code: 45.75) or open and other sigmoidectomy (OS; ICD-9-CM code: 45.76).

Outcome variables

The primary measured outcome for this study was SSI as defined by a patient who had a record of cellulitis or abscess of the trunk (ICD-9-CM code: 682.2), peritoneal abscess (ICD-9-CM code: 567.22), infected post-operative seroma (ICD-9-CM code: 998.51), or other post-operative infection (ICD-9-CM code: 998.59).

Statistical methods

The SSI rate was calculated for the three groups of procedures: ORH, OLH, and OS. The weighted number of procedures and rates were calculated to take into consideration the stratified sampling design of NIS data. A Rao-Scott χ² test was used to compare the discrete variables among these three groups. Multivariable logistic regression models were used to assess the association between SSI and types of procedures while controlling for potential confounding variables. Only the comorbidities that were reported in more than 5% of the patients were considered in the regression models. The adjusted odds ratio (AOR) and its 95% confidence interval (CI) were reported. The analysis was conducted using R language with the “survey” package [16 –21]. For evaluating the model fitting further, the Nagelkerke R² and c-statistic were calculated using the PROC SURVEYLOGISTIC procedure with SAS 9.3 software (SAS Institute, Cary, NC), and the Hosmer-Lemeshow goodness-of-fit test was performed using the “svy” and “estat gof” functions with STATA 13.1 (StataCorp, College Station, TX).

Results

In 2006, there were an estimated 26,381 ORHs, 9,558 OLHs, and 31,656 OSs. The patients within these three cohorts differed significantly with respect to age (mean [standard error]: ORH vs. OLG vs. OS=70.5 [0.2] vs. 63.8 [0.3] vs. 59.5 [0.2] years, p<0.0001) and gender distribution (female percentage: ORH vs. OLG vs. OS=56.1% vs. 51.5% vs. 50.9%, p<0.0001) (Table 1). SSI rates were significantly different between procedures: ORH versus OLH versus OS=2.9% versus 5.6% versus 4.9%, p<0.0001) (Table 2). After controlling for age, gender, hospital teaching status, primary diagnosis, and comorbidities, the chance of developing a SSI following OLH was higher than ORH and OS (AOR [95% CI]=1.54 [1.16–2.05], p=0.003; and AOR [95% CI]=1.31 [1.04–1.64], p=0.02, respectively). (Nagelkerke R²=0.0645, c-statistic=0.649, Hosmer-Lemeshow test of goodness of fit F=1.78, p=0.069). Additionally, there was no significant difference between the likelihood of SSI after OS versus ORH (AOR [95% CI]=1.18 [0.90–1.54], p=0.234) (Table 3).

Table 1.

Patient Data

Characteristic (%)	Right hemicolectomy (n=26,281)	Left hemicolectomy (n=9,558)	Sigmoidectomy (n=31,656)	p Value
Age in years: mean (standard error)	70.5 (0.2)	63.8 (0.3)	59.5 (0.2)	<0.0001
Female	56.1	51.5	50.9	<0.0001
Teaching hospital	45.8	45.4	44.4	0.62
Iron deficiency anemia	25.7	12	6.8	<0.0001
Chronic pulmonary disease	15.6	14.1	13.5	0.003
Diabetes mellitus	17.7	16.7	11.5	<0.0001
Hypertension	55.5	48.9	43.5	0.18
Fluid and electrolyte disorders	16	15.5	11.6	<0.0001
Metastatic cancer	30.5	20.1	10.1	<0.0001
Obesity	5.2	7.3	7.3	<0.0001
Congestive heart failure	7.8	4.7	3.3	<0.0001
Primary diagnosis
Diverticulosis	1.9	39.5	69.3	<0.0001
Malignant neoplasm	98.1	60.5	30.7	<0.0001

Table 2.

Surgical Site Infection Rates

Outcome (%)	Right hemicolectomy (n=26,281)	Left hemicolectomy (n=9,558)	Sigmoidectomy (n=31,656)	p Value
Overall infection	2.9	5.6	4.9	<0.0001
Infection by primary diagnosis
Diverticulosis	0.1	3.0	3.9	<0.0001
Malignant neoplasm	2.8	2.6	1.1	<0.0001

Table 3.

Adjusted Risk of Infection for All Variables in the Multiple Logistic Regression Model

Comparison	Adjusted odds ratio	95% confidence interval	p Value
OLH vs. ORH	1.54	[1.16–2.05]	0.003
OLH vs. OS	1.31	[1.04–1.64]	0.020
OS vs. ORH	1.18	[0.90–1.54]	0.234
Patient and hospital characteristics
Age in years	1.004	[0.997–1.01]	0.282
Female	0.72	[0.60–0.86]	0.000
Teaching hospital	1.42	[1.17–1.73]	0.000
Iron deficiency anemia	0.92	[0.71–1.19]	0.509
Chronic pulmonary disease	1.21	[0.96–1.52]	0.104
Diabetes mellitus	1.06	[0.83–1.35]	0.635
Hypertension	0.75	[0.63–0.91]	0.003
Fluid and electrolyte disorders	2.02	[1.63–2.50]	0.000
Metastatic cancer	1.10	[0.86–1.41]	0.435
Obesity	1.37	[1.01–1.87]	0.044
Congestive heart failure	1.36	[0.94–1.97]	0.106
Diverticulosis	1.90	[1.49–2.42]	0.000

OLH=open left hemicolectomy; ORH=open right hemicolectomy; OS=open sigmoidectomy.

Discussion

The NIS data from 2006 show that the risk for developing SSIs was significantly higher after OLH relative to ORH or OS. Moreover, there was no difference in risk for SSIs between ORH and OS patients. Few studies have compared post-operative infection rates separately for different areas of the colon. The NIS data were used to compare perioperative complications between 50,779 right hemicolectomy and left hemicolectomy/sigmoidectomy patients [22]. Their results showed that the latter group presented a higher risk for post-surgical abdominal abscess and anastomotic leak (AOR=1.12). In another study using the National Surgical Quality Improvement Program (NSQIP) database, 4,875 patients were identified who underwent colectomy for colon cancer between 2005–2008. The results showed that right-side colectomy patients were less likely to develop superficial SSIs than left-side colectomy patients (odds ratio=0.68), which supports the data presented here [23]. Surgeons have believed that left-side colon surgery results in a higher post-surgical infection rate [23]. Although the specific causative factors remain unclear, the variety and number of bacteria that inhabit the colon play major roles. Indeed, the distribution of bacteria has been studied using genetic methods, which have identified a large number of bacteria that adhere to the mucosa of the proximal and distal colon [6,24 –26]. The results of these studies show generally that the density of particular genera and species is not distributed uniformly, e.g., lactobacilli are most prominent in the distal colon [6], yet the overall quantity of bacteria is not significantly different in various portions of the colon [6,24,25,27], nor is the prevalence of potentially pathogenic species [26]. However, in contrast to bacteria that adhere to the mucosa, the bacteria found in feces are generally less diverse and greater in quantity, including a higher prevalence of pathogenic species [26]. This is a potential factor contributing to the observed increase in SSI rate in the left colon, because fecal matter does not solidify until it reaches the distal colon.

Regardless of the underlying pathophysiology, it is important to use the most effective measures to minimize SSIs. Whereas there are many risk factors that increase the likelihood of SSIs (e.g., obesity, diabetes mellitus, elevated white blood cell count, intra-operative blood loss, and blood transfusion), most cannot be controlled prior to surgery [9,10,12,13,28]. Conversely, pre-operative bowel preparation, another significant predictor of post-operative infections, can be optimized [28,29]. For example, the Surgical Care Improvement Project (SCIP) guidelines mandate that systemic antibiotics (SABs) be given 60 min prior to incision. However, as a result of these guidelines, administration of oral antibiotics (OABs) has been reduced greatly in recent years [28], even though OABs in conjunction with SABs reduce significantly the rate of post-operative infections by approximately 50% compared with SABs alone [29 –32]. Indeed, in spite of this national mandate, infection rates have increased rather than decreased [33]. Therefore, pre-operative bowel preparation guidelines should continue to be refined to minimize post-operative infection rates.

The NIS data used for the present study contain several inherent problems, e.g., the data were entered retrospectively from patients' charts after their discharge. Moreover, it is impossible to follow-up on patients after discharge and on readmission because all patient information is de-identified. Accordingly, and because most SSIs present after day 10 or 11 [34], the SSI rate in our study was much lower than data presented from prospective studies. In addition, the 2006 NIS data did not include separate coding schemes for laparoscopic and open procedures, or information regarding pre-operative bowel preparation, including OABs, so we were unable to account for these variables in our analyses.

The results of the present study indicate that the location of colon resection is indeed an important risk factor for developing post-surgical infections, particularly for patients undergoing procedures on the distal colon. Accordingly, prophylactic measures, including OABs and SABs, should be routinely administered to optimize prevention against post-operative infections.

Footnotes

Author Disclosure Statement

No competing financial interests exist.

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