The mean procedure times for groups A and B were 24.09 minutes 8.05 ( standard deviation ) ( range , 14-68 minutes ) and 18.62 minutes 6.34 ( range , 12-81 minutes ) , respectively ( P = .001 ) , and the numbers of patients in each group who required multiple puncture attempts were six ( 3.9 % ) of 154 and 23 ( 13.6 % ) of 169 ( P = .003 ) , respectively .