APPLICATION OF LOGISTIC REGRESSION FOR RISK FACTORS AFFECTING THE OUTCOME OF SURGERY UNDER EXTRACORPOREAL CIRCULATION

Аnnotation. This article discusses risk factors for cardiac surgery under extracorporeal circulation. Advance statistical analysis was performed using the nonparametric Van der Wanda, Kruskal-Wallis and median criterion over the entire volume of data. Assessment of the intensity relations between the selected risk factors affecting the outcome of the operation, performed on V-Cramer coefficient. The signs and symptoms of significantly interrelated and affect the outcome of operations. Statistical analysis was performed using a logistic regression model with step by step algorithm of inclusion and exclusion of predictors for the overall group of patients. To interpret the structure of the equations used in the analysis of contingency tables and the results of the comparison groups for the central action of the dependent variable. For dependent characteristics of the two grades on the basis of the equations of logistic regression was performed ROC-analysis with the construction of ROC-curves.

Objective. To estimate the probability of lethal outcome of operations in the condition of cardiopulmonarybypass. Resolving this task for operations in the condition of extracorporeal circulation is associated withdetermining main risk factors of lethal outcome. Having substantiated the choice of important factors frommedical point of view the subsequent stage of task resolving was performed using statistical calculation.

Material and methods. Within the period 2006 to 2009 in V. I. Shumakov Federal Scientific Center forTransplantation and Artificial Organs the data base was formed concerning the cardiac surgery patients whowere operated in the condition of cardiopulmonary bypass. The analysis was focused on 1731 patients. The fol-lowing factors were outlined: a) preoperative – presence/absence of repeated operations and bacterialendocarditis, age; b) intraoperative – presence/absence of chronic source of infection, performance of re-thoracotomy and blood loss more than 500 ml and cardiopulmonary bypass duration; c) postoperative – presence/absence of polyorganic insufficiency developing in the first days after the surgery, performance of intra-aortic balloon contrarpulsation and duration of artificial ventilation of lungs that was performed within days.Preliminary statistical analysis was performed with the help of non-parametrical criteria. Evaluation of intensity ofconnections between the outlined risk factors influencing on operation outcome was performed according to V-coefficient of Cramer.The subsequent statistical analysis was performed with the help of logistic regression model.

Results. The adequate equations of logistic regression were received for intra-aortic balloon con-trarpulsation factor and polyorganic insufficiency factor in which the preoperative and intraoperative riskfactors of the lethal outcome represent the variables of the equation. In 78.3 % of cases it is possible topredict the probability of presence of intra-aortic balloon contrarpulsation factor and in 84.6 % – poly-organic insufficiency factor. These figures represent the percentage of concordance. The adequatemodel with concordance percentage of 93.9 % was received for the death factor. The importance is notonly receiving the equation in accordance with which it is possible to accurately compute the probabilityof death but also establishing connections between risk factors leading to it.

Conclusion. Long length artificial lungs ventilation has been a statistically proven risk factor for developmentof polyorganic insufficiency. In order to decrease the probability of intra-aortic balloon contrarpulsation per-formance it is necessary not allowing the re-thoracotomy. The same might permit decreasing the probability of presence of polyorganic insufficiency factor as it depends on the performed re-thoracotomy via the factor when the blood loss is more than 500 ml. The precursor factor affecting the surgery outcome is thepolyorganic insufficiency which is often associated with the artificial lungs ventilation performed longer than2 days. The factor of duration of cardiopulmonary bypass in its quantity form plays the same role. The thirdplace is occupied by the group of factors regarding the patient's age expressed in quantity form and theintraoperative associated factors such as performance of re-thoracotomy and blood loss more than 500 ml.