P‐POSSUM and the NELA Score Overpredict Mortality for Laparoscopic Emergency Bowel Surgery: An Analysis of the NELA Database

Abstract

Background Risk stratification has become a key part of the care processes for patients having emergency bowel surgery. This study aimed to determine if operative approach influences risk‐model performance, and risk‐adjusted mortality rates in the United Kingdom. Methods A prospectively planned analysis was conducted using National Emergency Laparotomy Audit (NELA) data from December 2013 to November 2018. The risk‐models investigated were P‐POSSUM and the NELA Score, with model performance assessed in terms of discrimination and calibration. Risk‐adjusted mortality was assessed using Standardised Mortality Ratios (SMR). Analysis was performed for the total cohort, and cases performed open, laparoscopically and converted to open. Sub‐analysis was performed for cases with ≤ 20% predicted mortality. Results Data were available for 116 396 patients with P‐POSSUM predicted mortality, and 46 935 patients with the NELA score. Both models displayed excellent discrimination with little variation between operative approaches (c‐statistic: P‐POSSUM 0.801–0.836; NELA Score 0.811–0.862). The NELA score was well calibrated across all deciles of risk, but P‐POSSUM over‐predicted risk beyond 20% mortality. Calibration plots for operative approach demonstrated that both models increasingly over‐predicted mortality for laparoscopy, relative to open and converted to open surgery. SMRs calculated using both models consistently demonstrated that risk‐adjusted mortality with laparoscopy was a third lower than open surgery. Conclusion Risk‐adjusted mortality for emergency bowel surgery is lower for laparoscopy than open surgery, with P‐POSSUM and NELA score both over‐predicting mortality for laparoscopy. Operative approach should be considered in the development of future risk‐models that rely on operative data.

Novel predictors of mortality in emergency bowel surgery: a single‐centre cohort study

“…P‐POSSUM had a similar c‐statistic to SORT (0.796) but overpredicted mortality; this was consistent with previous reports. This can be explained by the fact the model was developed around 20 years ago when surgical mortality was higher [23, 26]. P‐POSSUM had much better discrimination in the study by Wong et al.…”

“…This could therefore reduce PRE‐OP accuracy in data on exclusively open surgery. However, a recently published analysis of national NELA data has found that P‐POSSUM and the NELA score consistently overpredict mortality for laparoscopic surgery [26]. Thus, it may be of benefit that PRE‐OP has been developed on a more even mix of operative approaches, allowing it to provide a more balanced, if slightly less accurate, prediction.…”

Serum Biomarkers of Inflammation in the Identification and Prognostication of Frail Patients Undergoing Emergency Laparotomy

“…The risks associated with emergency laparotomy, such as wound and secondary infections, long-term morbidity and mortality are widely recognised [13]. The elderly and frail represent a patient cohort with reduced physiological reserve, impairing their ability to tolerate the intense burden of emergency laparotomy; as a result, the likelihood and severity of adverse outcomes is significantly increased [7].…”

“…These clinical composite scoring systems utilise descriptive parameters such as baseline functional status and co-morbidities to generate a numerical output of risk expressed as a percentage [4][5][6]. These techniques require a comprehensive clinical history which may not be available in the emergency setting and are subjective in nature, risking the under-or over-estimation of morbidity and mortality in certain patient groups [7].…”

Quality of life after emergency laparotomy: a systematic review

“…It was also shown that patients and clinicians had different views on what defined a positive outcome after emergency laparotomy. Current pre-operative scoring and risk stratification systems for emergency laparotomy such as the National Emergency Laparotomy Audit (NELA) score or Portsmouth Physiological and Operative Severity Score for the 2 numeration of Mortality and morbidity (P-POSSUM) do not take into account or provide prediction tools for post-operative QoL [ 5 ].…”