The predictive value of available scoring systems, in particular those that can be assessed sequentially, for ongoing abdominal infection needing relaparotomy is not known. In clinical practice changes in organ functions are seen as useful triggers to expand diagnostic tools or intervention. However, only the SOFA score and APS had equally modest discriminatory ability for predicting ongoing infection needing relaparotomy. Furthermore, they showed an extremely low specificity for a 90% sensitivity. Broadening the definition of ongoing abdominal infection by patients needing reintervention (relaparotomy or percutaneous drainage) did not enhance identification of patients with persistent peritonitis.
The RELAP trial concludes that the on-demand strategy is preferred . Stringent monitoring of patients is a vital component of this strategy. A scoring system can aid in adequate and timely identification of patients for relaparotomy. Ideally, such a prediction model should be a sequential score. Changes in organ failure may be of better value in objectifying the clinical course of the disease, in particular since postoperative (follow-up) variables are more predictive than variables that become available during index laparotomy .
We were surprised by the low performance of these well-known scoring systems, as most of these scores quantify organ function. However, none of the evaluated scoring systems were originally developed to predict the need of a relaparotomy for ongoing peritonitis following emergency laparotomy in the acute phase of the disease [2–7]. All scores, except the MPI, have been developed to predict death for ICU patients in general and for groups of patients (strata) rather than predicting death for individual patients [2, 3, 6, 7]. Although the MPI is specifically developed for patients with abdominal sepsis, it is focused on prediction of death rather than occurrence of ongoing infection . Also, the MPI largely consists of peritonitis-related data, determined at the initial emergency laparotomy . These variables are described to be less predictive than physiological post-operative variables . All scores, indeed, did better at predicting death, as they are developed and validated to do.
Prognostic relevance of the SOFA score in combination with inflammatory parameters was also found in a recent study conducted by Zügel et al., even though results were based on only a small number of events . Torer et al. and Tan et al. identified possible prognostic relevance for the MPI in retrospective cohorts with patients with secondary peritonitis due to postoperative complications and community acquired perforations of small bowel and colon [17–20]. However, quantification of or changes in organ failure does not seem to differentiate between ongoing organ failure due to abdominal sepsis despite source control of the initial causative focus and ongoing abdominal infection.
For the non-reoperated patients, the time frame in which the predictor status of the sequential scoring systems was assessed was less precise. Our best deduction was to evaluate the scores during the clinical phase in which the dilemma of early relaparotomy is most prominent; day 1 and day 2 after the initial emergency laparotomy, for all included patients. In view of the disappointing predictive values, it is unlikely that extension of assessment after day 2 would have revealed completely different results.
Patients included in this study were randomized to the on-demand or the planned strategy . This enhances the generalizability of the results but foremost eliminates selection bias in choice of practiced treatment strategies. Differences in these treatment arms did lead to differential verification, but not necessarily to verification bias. Another option would have been to use only the planned arm of the trial, as all these patients were reoperated and had uniform outcome verification. Instead, all existing scoring systems were tested for the assumption that both the on-demand and planned strategy could be combined for the above analyses and we found no significant interaction between treatment strategies and predictive ability of the various scoring systems. This means that the predictive ability of existing scoring systems is comparable for both on-demand and planned treated patients. Importantly, also the proportion of events (positive findings at relaparotomy) was comparable for both strategies (29% for on-demand vs. 32% for planned) .
For clinical purposes, discriminatory power is more important than stratification. A 90% level of sensitivity was employed, as it is considered worse to mistakenly not re-operate a patient with ongoing infection needing relaparotomy than it is to reoperate a patient on the suspicion of ongoing infection but with negative findings [15, 21]. The approximate of 90% sensitivity was chosen to determine a cut-off for adequate scoring systems, reflecting the trade-off between a false positive prediction of peritonitis (negative relaparotomy) and a false negative prediction of peritonitis (no relaparotomy although one is needed). Nevertheless, performing too many negative relaparotomies should be avoided . None of the scoring systems had a clinical important predictive value nor demonstrated a clinically useful discriminatory ability. In order not to withhold relaparotomy from too many patients who need treatment for ongoing infection, an unacceptable high proportion of inappropriate relaparotomies would be performed based on the scores.
All presented, existing scoring systems lack the additional information derived from diagnostic imaging techniques which is likely valuable for selection of patients with ongoing infection needing reintervention. For patients suspected of abdominal infection following elective abdominal surgery, CT imaging has a high diagnostic accuracy . The exact value of diagnostic imaging in operated peritonitis patients with suspected ongoing abdominal infection is not known, as consequences from management decisions based on CT results have not been evaluated yet. Future research is needed to determine the exact accuracy of CT scanning in on-demand treated peritonitis patients who are suspected of ongoing infection.