To Map Human Lower Thoracic Dermatomes by Epidural Block

Background: The tract for percutaneous nephrolithotomy is typically established in the 11th intercostal space or in the subcostal area. According to Keegan and Garrett's dermatome map, the somatic pain could be controlled if the 11th and 12th the spinal nerve been blocked. However, the investigators found that if the 11th and the 12th spinal nerve had been blocked by evaluating the landmarks of ventral landmarks (xiphoid process , umbilicus and pubic symphysis), the somatic pain of percutaneous nephrolithotomy could not be controlled. In order to find the reason, the investigators compared the four main dermatome maps created by Henry Head, Foerster, Keegan and Lee. There are significant differences of dermatome among these maps. In addition, there were no landmarks to evaluate the dermatome at the back.

Objectives: To map the sensory innervations of lower thoracic nerves and find the dorsal landmarks to evaluate sensory innervations by epidural block.

Methods: Adult patients undergoing elective percutaneous nephrolithotomy, ureteroscopic lithotripsy, transuretheral resection of prostate and transuretheral resection of bladder tumor will receive epidural block with 0.5% ropivacaine. Complete Sensory loss to ice will be evaluated at anterior median line as soon as the surgery was completed. The superior border of complete sensory loss to ice will be identified by ventral landmaks (xiphoid process , umbilicus and pubic symphysis). Fifty patients with superior border of complete sensory loss to ice from T9 to T12 will be included in this study. The sensory loss to ice will be evaluated at anterior median line, midclavicular line, anterior axillary line, posterior axillary line, scapular line and posterior median line. The level of vertebrae will be identified and marked by ultrasound. The superior border of complete sensory loss to ice form anterior median line to posterior median line will be drawn and recorded for every patient. The dermatome map from T9 to T12 will be drawn. The landmarks of sensory innervations at posterior median line will be established using vertebrae..

Inclusion criteria

• Patients scheduled for percutaneous nephtolithotomy, ureteroscopy lithotripsy, transurethral resection of bladder tumor or transurethral resection of the prostate
• American Society of Anesthesiologists physical statusⅠ-Ⅲ
• Informed consent

Exclusion criteria

• Coagulopathy, on anticoagulants
• History of surgery on spine
• Spine deformity
• A known allergy to the drugs being used
• Tumer or infection at the site of puncture
• refusal to participate in the study