Long-term survival of equine surgical colic cases. Part 2: modelling postoperative survival.

The study aimed to identify factors influencing long-term survival rates of horses post colic surgery by using a comprehensive, penalised Cox regression model. The study determined significant variables as an increase in packed cell volume (PCV), intestinal resection length, time to surgery, duration of surgery, and epiploic foramen entrapment.

Research Design and Findings

• The study was conducted over 321 horse years of postoperative survival. The data was used to model postoperative survival probability after recovery from colic surgery.
• Continuous variables such as increase in packed cell volume (PCV), intestinal resection length, time from colic onset to surgery, and the duration of surgery were examined using a penalised, six-variable Cox regression model.
• The model indicated a linear correlation between survival and these continuous variables. However, age and heart rate were not significant factors in this model.
• The categorical variable of epiploic foramen entrapment was found to significantly influence survival rates. No other categorical variable showed a significant relationship with survival.

Use of Cox Proportional Hazards Model

• A final Cox proportional hazards model was applied that incorporated the significant variables, each adjusted for a non-linear relationship with the time to surgery. The variables included were PCV increase, resection length, duration of surgery, and epiploic foramen entrapment.
• This model aimed to minimize the impact of those variables which were found to exhibit non-linearity when correlated with survival, thus ensuring a more accurate prognosis.

Investigation of Residual Variation

• Other potential influences on postoperative survival, particularly attributable to professional personnel (including the referring veterinary surgeon, the anaesthetist, and the primary surgeon), were explored by fitting each as a random effects term in the model.
• However, the residual variation could be attributed to almost none of these personnel categories, indicating the limited impact of individual healthcare providers on the long-term survival post-surgery.

Model Diagnostics and Evaluation

• The influence of individual outliers on the model parameters was found to be minimal and there was a scant evidence that any subjects were particularly poorly forecasted by the final model.
• Thus, the study concludes with a reliable model that effectively highlights the factors influencing the long-term survival of horses after colic surgery. It can be used to inform prognosis and aid in clinical decision-making.