[Electrical nerve stimulation for peripheral nerve blocks. Ultrasound-guided needle positioning and effect of 5%...

The use of nerve stimulation is a common standard procedure for peripheral nerve blocks. However, ultrasound guidance is increasingly being used as an alternative. This study explored the relationship between needle positioning defined by ultrasound guidance and the electrical nerve stimulation before and after injection of 5% glucose solution (G5%).

After obtaining permission from the ethics committee, 60 patients were enrolled in the study and the results from 51 patients could be analyzed. For sonographically defined correct needle placement the lowest electrical threshold of the elicited motor responses before and after injection of 1 ml G5% was determined.

In 76% of cases nerve structures could be visualized with high quality and 90% of the blocks were successful. Only 29% of patients with a successful block showed a motor response with a stimulation current < or = 0.5 mA. There was a relationship only between the quality of the visualization and the success of the blockade. Addition of G5% did not result in significant changes in stimulation thresholds.

With the protocol used the success of a blockade depends only on the quality of visualization. With correct ultrasound-guided needle tip positioning the electrical information seems to be skewed and doubtful.