Peripheral Nerve Blocks

A peripheral nerve block deposits local anaesthetic around a peripheral nerve or plexus, away from the neuraxis, to anaesthetise the territory that nerve supplies. Peripheral blocks are the non-neuraxial branch of regional anaesthesia and are widely used for surgical anaesthesia and analgesia of the limbs and trunk, increasingly placed under ultrasound guidance.

Definition

A peripheral nerve block is the deposition of local anaesthetic at or around a peripheral nerve or plexus, outside the neuraxis, to interrupt conduction and anaesthetise the sensory and motor territory supplied by that nerve.

Scope

This topic covers the principle of perineural deposition, the distinction between single-nerve and plexus blocks, the guidance methods used to locate the target — ultrasound and electrical nerve stimulation — and the comparative evidence between them, together with the principal safety concern of neurologic complications. It is a reference topic and provides no procedural technique or dosing.

Core questions

• Which peripheral nerve or plexus supplies the region to be anaesthetised?
• How is the nerve located — by ultrasound, electrical stimulation, or landmarks?
• How do guidance methods compare for block success and safety?

Key concepts

• Perineural deposition
• Plexus versus single-nerve block
• Electrical nerve stimulation
• Ultrasound localisation
• Block success and onset time
• Local anaesthetic systemic toxicity
• Nerve injury and neurologic complications

Mechanisms

Local anaesthetic placed around a peripheral nerve diffuses into the nerve and blocks voltage-gated sodium channels, halting conduction in the axons and producing loss of sensation and motor function in that nerve's distribution. Accurate deposition close to, but not within, the nerve is central to efficacy and safety; the nerve is located by ultrasound visualisation, by the motor response evoked with electrical nerve stimulation, or by surface landmarks. The extent of the block follows the anatomy of the targeted nerve or plexus.

Clinical relevance

Peripheral nerve blocks are a reference concept for understanding how regional analgesia is produced away from the spinal cord and how the target is located. The entry summarises the comparative evidence and safety advisories for educational orientation, not as instruction for performing blocks or for patient management.

Evidence & guidelines

Systematic reviews and meta-analyses by Munirama and McLeod and by Wang and colleagues compare ultrasound with electrical nerve stimulation for peripheral nerve location and blockade. The ASRA practice advisory on neurologic complications addresses the safety of regional techniques including peripheral nerve blocks, and Marhofer and colleagues review the role of ultrasound guidance.

History

Peripheral nerve blockade developed alongside injectable local anaesthetics and was long performed using surface landmarks and, later, electrical nerve stimulation; the adoption of ultrasound guidance, reviewed by Marhofer and colleagues, reshaped how peripheral targets are located.

Debates

Ultrasound versus nerve stimulation for peripheral nerve blocks

Meta-analyses comparing ultrasound guidance with electrical nerve stimulation examine differences in block success, onset, and complications; the relative benefit depends on the specific block and the outcome assessed, and evidence continues to accumulate.

Seminal works

• marhofer-2005
• munirama-2015
• wang-2017
• neal-2015

Frequently asked questions

How is a peripheral nerve block different from a spinal or epidural?

A peripheral nerve block targets a specific nerve or plexus away from the spine to numb that nerve's territory, whereas spinal and epidural techniques act on spinal nerve roots within the neuraxis to produce a segmental block.

How is the target nerve found?

The nerve is located by ultrasound imaging, by the motor response evoked with electrical nerve stimulation, or by anatomical landmarks; ultrasound and stimulation have been compared in meta-analyses.