Methods of Nerve Localization
Despite the fact that people have been performing brachial plexus blocks for over a hundred years, there is as yet no clear evidence to support the assertion that one method of nerve localization is better than another. There are however numerous case reports documenting cases in which use of a portable ultrasound scanning device has detected abnormal anatomy that would otherwise not have been evident using a "blind" approach. On the other hand, use of ultrasound may create a false sense of security in the operator, which may lead to errors, especially if the needle tip is not adequately visualized at all times.
For interscalene block, it is not clear whether nerve stimulation provides a better interscalene block than elicitation of paresthesiae. However, a recent study using ultrasound to follow the spread of local anesthetic demonstrated an improved success rate of the block (relative to blocks done with nerve stimulator alone) even at the inferior roots of the plexus.
For supraclavicular block, nerve stimulation with a minimal threshold of 0.9 mA can offer a dependable block. Although ultrasound-guided supraclavicular block has been shown to be a safe alternative to the peripheral nerve stimulator guided technique, there is little evidence to support that ultrasound guidance provides a better block, or is associated with fewer complications. There is some evidence to suggest that the use of ultrasound guidance in combination with nerve stimulation can shorten the performance time of supraclavicular block.
For axillary block, success rates are greatly improved with multiple injection techniques whether using nerve stimulation or ultrasound guidance.
Read more about this topic: Anesthesia Of The Brachial Plexus
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