[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Anaesthesia and ICU](https://durgical.com/en/anaesthesia/) › [Regional anaesthesia](https://durgical.com/en/anaesthesia/areas/regional/) › Peripheral nerve blocks in principle

# Peripheral nerve blocks in principle

- Technique

Numbing medicine placed next to a nerve or plexus so that one limb or body area stops feeling pain, for surgery or for pain relief afterwards.

Updated Nov 13, 2026

## Key points

- Ultrasound guidance shows nerve, needle, vessels and spread; it lowers the amount of local anaesthetic needed and the risk of vascular puncture.
- Every local anaesthetic has a maximum safe dose by weight; aspirate and inject in small increments, watching the patient.
- Interscalene blocks almost always paralyse the phrenic nerve on that side: caution in severe lung disease.
- Pain or high resistance on injection suggests an intraneural needle: stop and reposition.
- Femoral blocks weaken the quadriceps, so patients are at risk of falls; the adductor canal block largely spares motor power.

On this page

- The basics Key points
- What it is
- Indications
- Equipment and preparation
- Step by step (and why)
- Common blocks and what they cover
- Next step
- Elsewhere in DurgiPedia

- Clinical Complications

- Safety Contraindications and precautions

- Study Test yourself

- Connections Connections

## What it is

A peripheral nerve block is the injection of local anaesthetic around a single nerve, a plexus or a fascial plane that carries nerves, so that the region it supplies loses sensation and, depending on the block, movement. Blocks can be the sole anaesthetic for limb surgery in an awake or lightly sedated patient, be combined with general anaesthesia, or be used purely for analgesia, for example a fascia iliaca or femoral block for a hip fracture. Their main benefits are excellent pain relief, fewer opioids and their side effects, less nausea, and avoiding general anaesthesia in high-risk patients. Today most blocks are guided by ultrasound, which shows the nerve, the needle tip, nearby vessels and pleura, and the spread of the injected solution; a nerve stimulator may be added to confirm the target. Local anaesthetics block voltage-gated sodium channels in the nerve membrane; thin pain and autonomic fibres are blocked before thick motor fibres. Common examples are the interscalene, supraclavicular, infraclavicular and axillary blocks of the brachial plexus for the upper limb; the femoral, adductor canal, sciatic and popliteal blocks for the lower limb; and plane blocks of the trunk such as the transversus abdominis plane and erector spinae blocks. The main serious risks are local anaesthetic systemic toxicity and nerve injury, so blocks are done with monitoring, resuscitation equipment and lipid emulsion at hand.

## Indications

- Surgical anaesthesia for limb surgery, alone or with sedation, especially when general anaesthesia carries high risk.
- Postoperative analgesia that reduces opioid use, nausea and sedation (shoulder, knee, hip, hand and foot surgery).
- Analgesia for injuries such as hip and femoral fractures before surgery, helping positioning and reducing delirium.
- Trunk plane blocks for abdominal and chest wall surgery when neuraxial blocks are not possible or wanted.
- Continuous catheters for prolonged analgesia after major limb surgery.

## Contraindications and precautions

- Absolute: refusal by a competent patient, infection at the puncture site, and true allergy to the local anaesthetic class.
- Coagulopathy and anticoagulants: weigh the risk most for deep, non-compressible blocks; superficial blocks are more forgiving.
- Pre-existing neuropathy or nerve deficit: examine and document it before the block.
- Respiratory reserve: avoid interscalene and supraclavicular blocks if the patient could not tolerate a paralysed hemidiaphragm.
- Compartment syndrome risk (for example tibial fractures): agree with the surgeon, since a dense block may mask the pain.

## Equipment and preparation

- Standard monitoring, intravenous access, oxygen and full resuscitation equipment, including lipid emulsion, in the block area.
- Ultrasound machine with a sterile probe cover and gel; nerve stimulator if used.
- Short-bevel, insulated block needles of a suitable length; extension tubing so an assistant can aspirate and inject.
- The chosen local anaesthetic, calculated against the maximum safe dose by weight and labelled.
- Consent, marking of the surgical side and a «stop before you block» check immediately before the needle.

## Step by step (and why)

- Explain the block and its risks and obtain consent — the patient should know about numbness, weakness and rare nerve injury.
- Attach monitors and secure intravenous access — toxicity and vasovagal reactions need immediate treatment.
- Do «stop before you block»: confirm patient, side and site against the marking — wrong-side blocks happen when this is skipped.
- Position the patient, clean the skin and scan to identify the nerve, vessels and pleura — knowing the anatomy prevents punctures.
- Advance the needle in plane, keeping the tip in view — a visible tip avoids vessels, pleura and the nerve itself.
- Aspirate, then inject small increments while watching the spread — repeated aspiration and slow injection detect intravascular placement.
- Stop if the patient feels pain or the pressure is high — this suggests the needle is inside the nerve.
- Talk to the patient during injection about numbness of lips, metallic taste or ringing ears — these are early signs of toxicity.
- Test sensation and movement before surgery — confirms the block works or shows that a rescue plan is needed.

## Common blocks and what they cover

| Block | Covers | Watch for |
| --- | --- | --- |
| Interscalene (brachial plexus roots) | Shoulder and upper arm | Phrenic palsy, Horner syndrome, hoarseness |
| Supraclavicular | Arm below the shoulder | Pneumothorax, phrenic palsy |
| Axillary | Forearm and hand | Vascular puncture (axillary artery) |
| Femoral / fascia iliaca | Anterior thigh, femur, hip | Quadriceps weakness and falls |
| Adductor canal (saphenous) | Medial knee and leg | Less motor block; incomplete knee cover |
| Popliteal sciatic | Lower leg, ankle and foot | Numb, weak foot: protect the heel and skin |

## Complications

- Local anaesthetic systemic toxicity from intravascular injection or absorption: from perioral numbness to seizures and cardiac arrest.
- Nerve injury: usually transient numbness or tingling; permanent damage is rare.
- Vascular puncture and haematoma, mainly in deep blocks or in anticoagulated patients.
- Pneumothorax with blocks near the pleura, such as supraclavicular and infraclavicular blocks.
- Phrenic nerve palsy, Horner syndrome and hoarseness after interscalene blocks.
- Failed or patchy block, falls from a weak leg and rebound pain when the block wears off.

## Next step

- Protect the numb limb: sling for the arm, fall precautions and crutches or supervision for the leg until power returns.
- Start regular oral analgesia before the block wears off to soften rebound pain, and tell the patient when to expect it.
- Keep the patient monitored for a period after a large-volume block, because toxicity can appear late.
- Call a senior for new shortness of breath, a block lasting much longer than expected, or signs of toxicity.
- Numbness or weakness persisting beyond the expected time needs examination, documentation and referral, sometimes with nerve conduction studies.

## Test yourself

Think of the answer, then tap the question to see it.

## Why do pain fibres lose function before motor fibres during a nerve block?

Thin, lightly myelinated or unmyelinated fibres need a shorter length of nerve exposed to local anaesthetic to be blocked than thick motor fibres.

## Which nerve is almost always blocked by an interscalene block, and why does it matter?

The phrenic nerve on the same side; the hemidiaphragm is paralysed, which patients with severe lung disease may not tolerate.

## What should you do if the patient reports severe pain or you feel high resistance while injecting?

Stop injecting and withdraw or reposition the needle: these suggest intraneural injection, which can injure the nerve.

## Why is the adductor canal block often preferred over a femoral block after knee surgery?

It blocks the saphenous nerve with much less quadriceps weakness, so patients can mobilise earlier with a lower risk of falls.

[Add to my cards (4)](https://durgical.app/estudiar/?add=/en/anaesthesia/peripheral-nerve-blocks-in-principle/)

## Elsewhere in DurgiPedia

- [Ultrasound-guided vascular access](https://durgical.com/en/clinical-skills/ultrasound-guided-vascular-access/)
- [Infiltrating local anaesthetic and digital blocks](https://durgical.com/en/clinical-skills/infiltrating-local-anaesthetic-and-digital-blocks/)
- [Types of nerve fibers](https://durgical.com/en/physiology/types-of-nerve-fibers/)
- [Peripheral nerve: endoneurium, perineurium, epineurium; myelin](https://durgical.com/en/histology/peripheral-nerve-endoneurium-perineurium-epineurium-myelin/)
- [Consent for anaesthesia](https://durgical.com/en/anaesthesia/consent-for-anaesthesia/)

## Connections

## Related 6

- [Local anaesthetic systemic toxicity: the crisis](https://durgical.com/en/anaesthesia/local-anaesthetic-systemic-toxicity-the-crisis/)
- [Postoperative pain: multimodal analgesia](https://durgical.com/en/anaesthesia/postoperative-pain-multimodal-analgesia/)
- [Orthopaedic surgery: tourniquets, cement and blood loss](https://durgical.com/en/anaesthesia/orthopaedic-surgery-tourniquets-cement-and-blood-loss/)
- [General, regional, local and sedation: what each one is](https://durgical.com/en/anaesthesia/general-regional-local-and-sedation-what-each-one-is/)
- [Anticoagulants, antiplatelets and neuraxial blocks](https://durgical.com/en/anaesthesia/anticoagulants-antiplatelets-and-neuraxial-blocks/)
- [Standard intraoperative monitoring](https://durgical.com/en/anaesthesia/standard-intraoperative-monitoring/)

## Related conditions 6

- [Local anaesthetic systemic toxicity (LAST)](https://durgical.com/en/conditions/local-anaesthetic-systemic-toxicity/)
- [Femoral Neck Fracture](https://durgical.com/en/conditions/femoral-neck-fracture/)
- [Distal radius fracture (Colles)](https://durgical.com/en/conditions/distal-radius-fracture/)
- [Brachial plexus injury](https://durgical.com/en/conditions/brachial-plexus-injury/)
- [Pneumothorax](https://durgical.com/en/conditions/pneumothorax/)
- [Horner syndrome](https://durgical.com/en/conditions/horner-syndrome/)

## In Pharmacology 5

- [Local anesthetics](https://durgical.com/en/pharmacology/classes/local-anesthetics/)
- [Lidocaine](https://durgical.com/en/pharmacology/lidocaine/)
- [Bupivacaine](https://durgical.com/en/pharmacology/bupivacaine/)
- [Ropivacaine](https://durgical.com/en/pharmacology/ropivacaine/)
- [Dexmedetomidine](https://durgical.com/en/pharmacology/dexmedetomidine/)

[← All of anaesthesia](https://durgical.com/en/anaesthesia/)

Educational content; it does not replace supervised training, your institution's protocols or the anaesthetist's or intensivist's decision. It contains no doses and no ventilator or infusion settings.

Sources: [Peripheral Nerve Blocks](https://www.ncbi.nlm.nih.gov/books/NBK459210/) (StatPearls (NCBI Bookshelf), 2025).

## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake

Representative model, for educational purposes only.

---
Source: https://durgical.com/en/anaesthesia/peripheral-nerve-blocks-in-principle/
License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/anaesthesia/peripheral-nerve-blocks-in-principle/