Joeky Senders

73 Thromboprophylaxis after craniotomy Analysis Univariableanalysiswasperformedtoexploretherelationshipbetweenthe independent variables and the occurrence of VTE and ICH. Chemotherapy and radiotherapy were not included in the analysis of VTE within 21 days since these adjuvant therapies were generally started six weeks after surgery. Similarly, KPS score, immobility, and length of stay were not included in the analysis of ICH since these variables were assessed after the occurrence of all ICH events. We considered this to be a result rather than a cause of the occurrence of ICH. Subsequent multivariable analysis was aimed at determining the independent contribution of each variable to the risk of postoperative VTE or ICH. Chi-square test and independent sample t-test were used in the univariable analysis for categorical and continuous data, respectively. Mann-Whitney U test was used for non- parametric continuous data. Variables associated with VTE in the univariable analysis were included in the multivariable logistic regression analysis, with a liberal threshold (p<0.20) in order to include all determinants with potential value. Firth regression analysis was performed if one of the cells in the multivariable analysis contained zero events. Given our interest in the duration of LMWH thromboprophylaxis, this variable was included in the multivariable analysis automatically. A probability level below 0.05 was considered as statistically significant. The β-coefficients of the continuous variables in the final multivariable models were multiplied to represent the odds ratios and confidence intervals of meaningful and interpretable units for age (per ten years increase) and BMI (per five kg/m2 increase). All statistical analyses were performed by means of the Statistical Package for Social Science (IBM, version 24) software. Results A total of 313 patients underwent craniotomy for a HGG between 2007 and 2013. Twelve patients were excluded because of a previous craniotomy (n = 10) or age under 18 years at time of surgery (n = 2); therefore, 301 patients were included in the analysis. The cumulative number of patients that developed a VTE within 21 and 90 days were six (2.0%) and 20 (6.6%) patients, respectively. Nine patients (3.0%) had an ICH that required surgical evacuation, all within 10 days after surgery. Hundred-sixty six patients received short prophylaxis, and 135 received prolonged prophylaxis. Baseline characteristics compared by thromboprophylactic regimen are shown in Table 1. In the univariable analysis for the occurrence of VTE, prolonged compared to short prophylaxis was not significantly associated with the rate of VTE within 21 days (3.0% for the group that received 21 days of dalteparin versus 1.2% for the group that received