Results
Patient Characteristics
Among the 1,879 patients undergoing intra-abdominal procedures during the study period 56 patients were included in the validation group; the patients developed wound dehiscence during the postoperative period and represented 2.9% of all operations performed. The group consisted of 37 men and 19 women; there was a statistically significant difference with regard to gender, men accounted for more of the cases (p = 0.034). The mean age was 66.8 ± 12.6 years. Abdominal wound dehiscence occurred on average at the 9.8 ± 6.5 postoperative day (median: 8 days). The mortality of patients in this group was 25%. In addition, more patients were operated on as a emergency procedures 45 (80.4%) vs. 11 patients in the elective group, this difference was statistically significant (p <0.001). There were 168 patients in the control group based on the above mentioned criteria. The baseline characteristics of the patients are reported in Table 1.
The patients that developed abdominal wound dehiscence had a higher rate of wound infection, circulatory insufficiency, increased length of hospitalization and were more likely admitted to the ICU; these differences were statistically significant. The other factors studied did not show statistically significant differences.
Comparison of Predicted Dehiscence Risk
Calculation of risk scores for all patients revealed significantly higher scores in both abdominal wound dehiscence groups (p < 0.001). The median scores were 24 (range: 3–46) and 4.95 (range: 2.2–7.8) vs. 10 (range: -3–45) and 3.3 (range: 0.4–6.9), for the VAMC and Rotterdam abdominal wound dehiscence risk score in the dehiscence and control groups, respectively (p < 0.001). Table 2 and Table 3 are showing the VAMC and Rotterdam scores variables and characteristics of the validation population.
The relationship between all scores was statistically significant. The area under the curve, in the ROC plot, was 0.84 and 0.76 respectively, showing a good and moderate predictive value of the risk scores (Table 4). However, the VAMC score more successfully predicted patients that would develop dehiscence.
The odds ratio as risk coefficient was examined using a binary logistic regression model. When the VAMC and Rotterdam scores increased by one unit the predicted odds changed by a multiplicative factor of 1.1 and 2.2, respectively. This indicates that for an increase of 1 point, on both risk scores, the risk of abdominal wound dehiscence increases 1.1 and 2.2 times (Table 4).
The efficacy of both scores for predicting abdominal wound dehiscence during the postoperative period can be defined as sensitivity and its efficacy in predicting a complication free course (in terms of dehiscence) defined as specificity. The values of the VAMC and Rotterdam scores are shown in Table 5. These results are presented at optimal cut off values and at the values used in primary publications. In the calculations, two types of errors of abdominal wound dehiscence scores were investigated. These can be referred to as the false positive and negative results (Table 5).
Comparison of Discrimination
Table 6 shows that the overall area under the receiver operating characteristic curve for wound dehiscence was 0.84 and 0.76, for VAMC and Rotterdam scores, respectively. The AUC under the VAMC curve was significantly higher than the Rotterdam curve (p < 0.001), indicating a better discriminatory ability.
Calibration of Prediction Scores
The fit of the model was good in both cases, as shown by the Hosmer and Lemeshow test (p = 0.461 and p = 0.083, respectively, as it is shown in Table 6). However, in the case of the VAMC score the calibration was significantly better.