 Patient characteristics and anesthetic and operative variables are compared with the t-test for independent samples continuous variables, or the Mann-Whitney U-test and 2-test Pearson or Fishers exact test when appropriate categorical variables. Cannulation time differences between the groups will be compared with the t-test for independent samples after tests for homoscedasticity and normality or Mann-Whitney U-test if appropriate. Success of cannulation will be compared with 2-test Pearson or Fishers exact test when appropriate. A p value less than 0.05 is considered statistically significant. Results are given as mean SD or number of patients. All statistical analyses will be performed with SPSS version 11.01 software SPSS Inc, Chicago, IL, USA. 