Ultrasound for Neuraxial Anesthesia

The patients will be allocated to 2 groups: the ultrasound group and the palpation group. Ultrasound detection of the puncture site will be performed to the patients of the one group (group U). The puncture site will be determined by palpation of the landmarks at the patients of the other group (group L). The main purpose of the study is to determine if the ultrasound scan of the lumbar spine can facilitate spinal, epidural and combined spinal-epidural anesthesia, increase the success and decrease the complication rate of these techniques. The secondary purpose of the study is to evaluate if the lumbar ultrasound scan can be used to determine accurately the depth of the epidural space.