2.1 ETHICAL STATEMENT
The study did not aim to change or modify existing clinical or laboratory practices. Steps were taken to ensure data collection was anonymous. Data collected was not used for making clinical decisions.
This study was reviewed and cleared by the Institutional ethics committee prior to the study as it was carried out as a thesis project for post graduate degree certification.
2.2 Study design and setting
The study was a prospective observational cohort study carried out at Department of Surgery, University College of Medical Sciences and GTB Hospital, Delhi between December 2018 and March 2020. The hospital is a 1800 bedded multi-specialty tertiary care facility with facilities for acute and emergency surgery and dedicated surgical ICU. Approximately 600-800 surgeries for gastrointestinal emergencies are carried out per year with the bulk being made up of secondary peritonitis followed by bowel obstruction.
The intention behind the study was to evaluate three different risk scoring systems in current use for accuracy of prediction.
The study has been written in conformation with STROBE Guidelines for cohort studies.
2.3 INCLUSION AND EXCLUSION CRITERIA
All consecutive patients of non traumatic secondary peritonitis undergoing emergency laparotomy by three different general surgical units in this period were included in the study. Secondary Peritonitis was defined as intra-abdominal infection that extended beyond the organ of origin and caused either a localized or diffuse inflammation of the peritoneum with soiling of the peritoneal cavity.
The exclusions were
- Patients with traumatic perforations due to blunt or penetrating trauma
- post operative peritonitis due to leaks who had undergone index surgery elsewhere
- those who could not be taken up for surgery either due to lack of consent or preoperative death were excluded from the study.
2.4 OUTCOME MEASURES
The primary outcome measure was in hospital mortality or discharge to home. Secondary outcome measures were need for postoperative ICU care and overall length of stay.
2.5 TREATMENT
Every patient followed the same standard pathway using Surviving Sepsis Guidelines(22). Clinical and biochemical assessment was carried out to determine and classify presence of sepsis, septic shock and organ dysfunction according to internationally accepted criteria(2)(23) (22). After confirmation of diagnosis and adequate resuscitation, patients were taken up for exploratory laparotomy after preanaesthetic assessment by the anaesthesia team on duty. The procedure performed was decided by the operating surgeon, either The Consultant on Duty or Senior Resident after discussion with Consultants.
2.6 DATA COLLECTION
The clinical findings were recorded from hospital pre-operative notes, operative notes, anaesthetic charts and postoperative ward notes. After the initial registry, patients were followed till the end of stay in hospital ( discharge or mortality).
The data collected was of the following types :
1. Preoperative Data including demographic data, co-morbid history, examination findings, laboratory investigations and radiological findings.
2. Intraoperative findings i.e. degree of contamination, aetiology of perforation, source of contamination, intraoperative blood loss, method of abdomen closure and need for blood transfusion.
3. Postoperative course including need for ICU stay, course of disease, any postoperative complications.
Final etiology was defined by intraoperative findings, histopathological and microbiological examination.
Postoperative mortality was defined as intrahospital death.
To reduce bias, all consecutive patients wih secondary peritonitis who underwent laparotomy were included in the study. All the data points required for calculation of scores were collected from patient records and verified by two different investigators.
2.7 STATISTICAL ANALYSIS AND SCORING SYSTEMS
Using the patient data and variables, risk scores for every patient, under each of the three systems to be assessed were calculated. The scoring systems used were p-POSSUM (Portsmouth modification to Physiological and operative severity score for enumeration of mortality )(19) , MPI ( Mannheim Peritonitis Index)(20) and Jabalpur Peritonitis Index (JPI)(21).
Receiver operator characteristic curves were constructed for sensitivity analysis for each of the 3 risk scoring systems used to determine diagnostic performance and compare the three scores based on the area under the curve (AUC)(24). The receiver operator characteristic curve was also used to define a cutoff score, using the Youden Index(25)beyond which patients were considered to be high risk(25).
After cutoff scores were calculated using ROC, further calibration of scores was done using Chi Square test for observed to expected mortality rates(26) to ensure applicability of results.
p-Value of <0.05 was considered significant.
2.8 SCORING SYSTEMS
The scoring systems to be evaluated were chosen on the basis of clinical utility and common usage. Both p-POSSUM and MPI have been reported to have high accuracy based on the area under the curve in receiver operator characteristic curves(27)(28,29) with AUC greater than 80 % indicating good diagnostic ability(25)(30). The Jabalpur peritonitis index is easy to use with few components and perhaps more suited to Indian populations as the original patient cohort was based in India. Due to its simplicity, it may also be suited for usage in low resource settings.
p-POSSUM
p-POSSUM, standing for Portsmouth modification to Physiological and Operative Severity Score for the enUmeration of Mortality was devised by Prytherch et al(19). The system uses a 12 factor physiological score for patient condition prior to surgery and a 6 factor operative severity score, both of which were derived from earlier observations on 1372 patients(31). The physiological and operative scores are used to give a predicted percentage risk of mortality for a patient by calculating via the p-POSSUM equation
ln [R / (1 - R)] = - 9.065 (0.1692 x physiological score) + (0.1550 x operative severity score)
where R is the predicted risk of mortality.
MANNHEIM PERITONITIS INDEX (MPI)
Based on the clinical observations and risk factors from 1243 patients of purulent peritonitis, Linder et al(20) devised the Mannheim peritonitis index for predicting mortality in patients of perforation peritonitis. A total of 8 factors are included in the scoring system covering demographic, physiological and disease specific factors. Total score possible is 47. In the original study, with a cutoff value of > 26, MPI helped in identifying patients at increased risk of mortality with good sensitivity ( 84 %), specificity (79 %) and overall accuracy ( 81 %).
JABALPUR PERITONITIS INDEX
Mishra, Sharma et al (21) devised the Jabalpur peritonitis index for perforation peritonitis as a simplified system for use in resource poor situations where extensive preoperative investigations may not be available. 140 patients were studied prospectively and multiple regression analysis employed to identify 6 factors which had a high association with mortality. Using 9 as a cutoff value, beyond which 50% mortality was observed, the authors determined the system to have sensitivity of 87 % and specificity of 85 %.