Changes in percutaneous oxygen tension induced by spinal anesthesia

To check the level of spinal anesthesia is sometimes difficult in patients with dementia. In spinal anesthesia, peripheral oxygen tension may increase in the anesthetized area because of vasodilatation due to sympathetic block. The purpose of this study was to determine whether changes in percutaneous oxygen tension (tcPO(2)) were suitable for checking the level of spinal anesthesia.

Thirty patients, aged 40 to 70 years, scheduled for surgery of the lower extremities under spinal anesthesia, were enrolled. Spinal anesthesia was performed at L4-5 with hyperbaric 0.5% tetracaine 10 to 12 mg, administered with the patient in the lateral position; the patients were then immediately returned to the supine position. The anesthesia level was checked by cold test 10 min after the spinal anesthesia, and it was confirmed that the upper level was between T3 and T11. Then oxygen 6 l x min(-1) was administered by mask. Six electrodes of a tcPO(2) monitor, (TCM 400) were attached before anesthesia, three electrodes at the right, center, and left side of the T3 level, and the other three at the right, center, and left at the T11 level. TcPO(2) was measured before and 10 min after spinal anesthesia, and 5 min after starting oxygen inhalation.

TcPO(2) increased significantly after spinal anesthesia only at T11, and was increased by oxygen administration at both T3 and T11. The increase of tcPO(2) after oxygen administration was larger at T3 than T11, without any differences in absolute values.

Measurement of TcPO(2) might be useful as one of the objective methods to distinguish anesthetized and nonanesthetized areas in spinal anesthesia.