Date of Award

6-2024

Degree Type

Thesis

Degree Name

MS in Epidemiology & Biostatistics

First Advisor

Dr. Bilal Ahmed Usmani

Second Advisor

Dr. Adil Haider

Third Advisor

Mr. Iqbal Azam

Department

Community Health Sciences

Abstract

Introduction: One of the leading causes of increased morbidity, length of stay in the hospital, cost of care, and mortality amongst surgical patients is surgical site infections (SSIs). While there are many factors that can be associated with SSIs, one of them is comorbidities. Literature highlights that with increasing severity of comorbidities, the risk of post-operative complications and mortality significantly increases. It is of utmost importance in patients undergoing exploratory laparotomies due to highest prevalence of SSIs in this cohort. The prognostication of surgical outcomes can be significantly improved in exploratory laparotomy using the Charlson comorbidity index (CCI) and Charlson age-comorbidity index (CACI) that can be used to quantify comorbidity severity through a unified index. Thus, the study aims to assess relationship between CCI/CACI and the 30-day incidence of SSIs amongst exploratory laparotomy patients at a tertiary care hospital in Karachi, Pakistan.
Methods: A retrospective cohort study design was employed to obtain data of adult patients (aged > 18 years) using ICD-9 CM procedure codes defined for exploratory laparotomy at a tertiary teaching hospital. The records were taken for primary index admissions only, presenting between 2010 and 2019. The primary exposure was the severity of comorbidity using the CCI, categorized into no comorbidity (CCI score= 0) classified as the unexposed group, and mild (CCI score = 1-2), moderate (CCI score = 3-4) and severe (CCI score > 5) comorbidities classified as the exposed group. A similar index that accounted for age was also calculated, which was CACI. The criteria for calculating it remained the same with 1 point added to the score for every one decade increase in age after 40 years to classify patients as unexposed and exposed. The outcome of interest was incidence of SSIs within 30 days of surgery. A sub-group analysis was also performed for patients admitted with primary abdominal conditions only (upper gastrointestinal [GI], lower GI, hepatic-pancreatic[1]biliary, peritoneal cavity). There was no information on time to developing SSIs. Multiple logistic regression was performed to obtain adjusted odds ratio along with 95% CI for all significant predictors. Effect modification was also tested between plausible factors with a p-value of 0.1 considered eligible for the inclusion in the model.
Results: Analysis of 2,267 exploratory laparotomy patients at primary index admission showed that 45.57% had no comorbidity, and 54.43% were classified as having comorbidity (including mild, 14 moderate, and severe CCI). Across CCI, the highest incidence of SSIs was seen in patients with moderate CCI (25.68%). In case of CACI, there was no such difference noted in incidence of SSIs amongst no CACI (15.88%), and patients with mild, moderate, and severe CACI (18.49%, 18.94%, and 17.42%). For sub-group analysis, 43.09% had no CCI. The incidence of SSIs in patients with no comorbidity was 14.60% compared to patients with mild, moderate, and severe CCI (17.53%, 26.04%, and 11.81%). In case of CACI, there was no major difference in incidence of SSIs amongst no CACI (14.60%), and patients with mild, moderate, and severe CACI (18.62%, 17.62%, and 16.24%). In the entire cohort and sub-group analysis, upper-GI related diagnosis was most common across groups. The multivariable analysis showed that CCI/CACI had an effect modification with gender. Amongst females, CCI/CACI was not significantly associated with SSIs. Amongst males, a dose-response relationship was observed with severe CACI having the highest odds of developing SSIs (AOR 2.04; 95% CI 1.35, 3.05) compared to patients with no CACI in entire cohort when adjusted for primary diagnosis, admission status, days after surgery, and residency. The odds remained similar for severe CACI in sub-group analysis (AOR 2,03; 95% CI 1.28, 3.21) after adjusting for primary diagnosis, admission status, and days after surgery.
Conclusion: The findings suggested that increasing CACI severity showed the highest odds of developing surgical site infections amongst males. This shows that comorbidity index is valuable in prognosticating surgical outcomes in exploratory laparotomy patients with age being an integral part of the index. Managing comorbid conditions during hospital admission can reduce the occurrence of developing SSIs, particularly amongst males.

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