PvO2 changes in cutaneous veins during regression of spinal anaesthesia.

Following transurethral resection of the prostate under spinal anaesthesia, 26 patients were divided into two groups according to the sensory levels measured in the recovery room: Group A: 20 patients with sensory level T10 or above, and Group B: six patients with sensory level T11 or T12. Through an intravenous catheter placed preoperatively in a superficial vein of the foot, serial blood samples were drawn to measure the PvO2. In Group A, the PvO2 increased significantly after spinal anaesthesia compared with preoperative control values, then decreased when the sensory level receded to T11 or T12. In Group B, the changes in PvO2 from control to postspinal and to motor recovery were not significant. The authors postulate that sympathetic denervation induced by spinal anaesthesia increases the PvO2 by the opening of arteriovenous anastomoses in the cutaneous circulation, and the PvO2 decreases with sympathetic recovery. These findings confirm that significant sympathetic denervation of the lower limbs can be expected at a sensory level of T10 or above, and sympathetic recovery begins when the sensory level recedes below T10.