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

 

BACKGROUND: 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.

METHODS: 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.

RESULTS: 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.

CONCLUSION: Changes of tcPO₂ are not useful in order to assess the effects of the interscalene block under oxygen administration.

 

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