Is the change of percutaneous oxygen pressure available to judge the effects of brachial plexus block?

To know the objective methods of the effects of the brachial plexus block, we studied the changes in percutaneous oxygen pressure (tcPO₂) with the hypothesis that tcPO₂ increases significantly on the blocked arm in comparison with the non-blocked arm, a phenomenon which is connected with vasodilation following the brachial plexus block.Fifteen patients scheduled for upper extremity surgery, aged 20 to 70 years, with ASA physical status I or II were included. Before anaesthesia, the electrodes used to measure tcPO₂ were put on the radial side of the forearm and upper arm of both the right and left sides (a total of 4 electrodes). Oxygen at 6 L min⁻¹ was administered by a facial mask. Once midazolam 1-2 mg and fentanyl 50 μg had been administered intravenously, a propofol infusion was started at a dose of 2 mg kg⁻¹ h⁻¹. The interscalene block was performed by means of a nerve stimulator, using 20 mL of 1% lidocaine solution combined with 20 mL of 0.75% ropivacaine solution. TcPO₂ was measured just before the block and 30 minutes after the block.TcPO₂ in both forearm and upper arm significantly increased after the block in both sides namely, blocked and non-blocked. No difference was observed in tcPO₂ between the blocked side and non-blocked side.Changes of tcPO₂ are not useful in order to assess the effects of the interscalene block under oxygen administration.