Risk prediction models in emergency surgery: Protocol for a scoping review

BACKGROUND

Risk prediction models are used for many purposes in emergency surgery, including critical care triage and benchmarking. Several risk prediction models have been developed, and some are used for purposes other than those for which they were developed. We aim to provide an overview of the existing literature on risk prediction models used in emergency surgery and highlight knowledge gaps.

METHODS

We will conduct a scoping review on risk prediction models used for patients undergoing emergency surgery in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR). We will search Medline, EMBASE, and the Cochrane Library and include all study designs. We aim to answer the following questions: (1) What risk prediction models are used in emergency surgery? (2) Which variables are used in these models? (3) Which surgical specialties are the models used for? (4) Have the models been externally validated? (5) Where have the models been externally validated? (6) What purposes were the models developed for? (7) What are the strengths and limitations of the included models? We will summarize the results descriptively. The certainty of evidence will be evaluated using a modified Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach.

CONCLUSION

The outlined scoping review will summarize the existing literature on risk prediction models used in emergency surgery and highlight knowledge gaps.

Validation of the NELA risk prediction model in emergency abdominal surgery

Risk prediction models are frequently used to identify high-risk patients undergoing emergency laparotomy. The National Emergency Laparotomy Audit (NELA) developed a risk prediction model specifically for emergency laparotomy patients, which was recently updated. In this study, we validated the updated NELA model in an external population. Furthermore, we compared it with three other risk prediction models: the original NELA model, the Portsmouth Physiological and Operative Severity Score for the enUmeration of Mortality and morbidity (P-POSSUM) model, and the American Society of Anesthesiologists Physical Status (ASA-PS). We included adult patients undergoing emergency laparotomy at Zealand University Hospital, from March 2017 to January 2019, and Herlev Hospital, from November 2017 to January 2020. Variables included in the risk prediction models were collected retrospectively from the electronic patient records. Discrimination of the risk prediction models was evaluated with area under the curve (AUC) statistics, and calibration was assessed with Cox calibration regression. The primary outcome was 30-day mortality. Out of 1226 included patients, 146 patients (11.9%) died within 30 days. AUC (95% confidence interval) for 30-day mortality was 0.85 (0.82-0.88) for the updated NELA model, 0.84 (0.81-0.87) for the original NELA model, 0.81 (0.77-0.84) for the P-POSSUM model, and 0.76 (0.72-0.79) for the ASA-PS model. Calibration showed underestimation of mortality risk for both the updated NELA, original NELA and P-POSSUM models. The updated NELA risk prediction model performs well in this external validation study and may be used in similar settings. However, the model should only be used to discriminate between low- and high-risk patients, and not for prediction of individual risk due to underestimation of mortality.

Long-term mortality in the Intermediate care after emergency abdominal surgery (InCare) trial-A post-hoc follow-up study

BACKGROUND

Patients undergoing emergency abdominal surgery are at high risk of post-operative complications. Although post-operative treatment at an intermediate care unit may improve early outcome, there is a lack of studies on the long-term effects of such therapy. The aim of this study was to assess the long-term effect of intermediate care versus standard surgical ward care on mortality in the Intermediate Care After Emergency Abdominal Surgery (InCare) trial.

METHODS

We included adult patients undergoing emergency major laparoscopy or laparotomy with an Acute Physiology and Chronic Health Evaluation (APACHE) II score of 10 or more, who participated in the InCare trial from October 2010 to November 2012. In the InCare trial, patients were randomized to either post-operative intermediate care or standard surgical ward care. The primary outcome was time to death within 6 years after surgery. We assessed mortality with Coxregression analysis.

RESULTS

A total of 286 patients were included. The all-cause 6-year landmark mortality was 52.8% (76 of 144 patients) in the intermediate care group and 47.9% (68 of 142 patients) in the ward care group. There was no statistically significant difference in mortality risk between the two groups (hazard ratio 1.06 (95% confidence interval 0.76-1.47), P = .73).

CONCLUSION

We found no statistically significant difference in 6-year mortality between patients randomized to post-operative intermediate care or ward care after emergency abdominal surgery. However, we detected an absolute mortality risk reduction of 5% in favour of ward care, possibly due to random error.

APACHE II score validation in emergency abdominal surgery. A post hoc analysis of the InCare trial

BACKGROUND

Patients undergoing emergency abdominal surgery are at high risk of morbidity and mortality. Accurate identification of high-risk patients is important. The Acute Physiology and Chronic Health Evaluation (APACHE) II score needs to be validated in a larger heterogeneous population before implementation. We aimed to assess the predictive value of the APACHE II score in emergency abdominal surgical patients. Furthermore, we compared the APACHE II score with the American Society of Anesthesiologists (ASA) physical status score and the Charlson Comorbidity Index (CCI).

METHODS

We included adult patients undergoing emergency abdominal surgery screened for enrolment in the InCare trial from October 2010 to November 2012. The APACHE II score was evaluated with area under the receiver operating characteristics curve (AUROC) statistics. The primary outcome was 30-day mortality. Secondary outcomes included 90-day mortality and admission to the intensive care unit.

RESULTS

We included a total of 885 patients. All-cause 30-day mortality was 5.0%, 90-day mortality was 8.9%, and a total of 7.9% of the patients were admitted to the intensive care unit. The AUROC (95% confidence interval) of the APACHE II score was 0.72 (0.65-0.80) for 30-day mortality, 0.70 (0.64-0.76) for 90-day mortality and 0.65 (0.59-0.71) for admission to the intensive care unit. The CCI performed better in prediction of 90-day mortality (P = .04). All other results for the ASA score and CCI were comparable with the APACHE II score.

CONCLUSION

The APACHE II score predicted mortality moderately and admission to intensive care unit poorly in emergency abdominal surgical patients.