Common peripheral nerve blocks (conceptual)

What is a peripheral nerve block (PNB)?

• Injection of local anaesthetic (LA) near a peripheral nerve or nerve bundle to reduce pain (and sometimes movement) in a specific body region.
• Goal: excellent analgesia with less opioid, earlier mobilisation, and better patient experience.
• Blocks can be single-shot (one injection) or continuous (catheter infusion).
• “Sensory block” = numbness/analgesia; “motor block” = weakness/paralysis; most blocks give some of both depending on site and LA dose.
• Regional anaesthesia is a team activity: patient selection, consent, monitoring, and rescue plans matter as much as needle placement.

Common blocks you will meet early (conceptual map)

• Upper limb: interscalene (shoulder), supraclavicular (arm), infraclavicular/axillary (forearm/hand).
• Lower limb: femoral or fascia iliaca (hip/anterior thigh), adductor canal (knee analgesia with less weakness), popliteal sciatic (below-knee/foot).
• Trunk: TAP block (abdominal wall), rectus sheath (midline abdominal wall), erector spinae plane (thoracic/abdominal analgesia).
• Rule of thumb: more proximal brachial plexus blocks cover more of the arm but can have more respiratory/nerve-related side effects.
• Many “plane blocks” (e.g., TAP, ESP) target nerves in tissue planes rather than a single named nerve.

Indications and benefits (when blocks help most)

• Surgery with significant postoperative pain (e.g., shoulder, rib fractures, major knee/foot surgery, abdominal wall incisions).
• Patients where opioid minimisation is helpful: obstructive sleep apnoea, frailty, nausea/vomiting history, opioid sensitivity.
• Day-case pathways: good analgesia can reduce unplanned admissions and improve mobilisation.
• Trauma: can facilitate positioning, imaging, splinting, and reduce distress (ensure neurovascular assessment is documented first).

Contraindications and cautions (intro level)

• Absolute: patient refusal; infection at injection site; true LA allergy (rare—often preservative-related).
• Relative: anticoagulation/coagulopathy (site-dependent bleeding risk—follow local/regional guidance); severe sepsis; inability to cooperate; raised compartment syndrome risk where pain is a key sign (discuss with seniors).
• Pre-existing neuropathy: not an absolute contraindication, but document baseline symptoms and counsel about uncertainty of postoperative nerve symptoms.
• Respiratory compromise: some upper limb blocks (especially interscalene) can affect breathing—seek senior input.
• Always consider whether the block will cause problematic weakness (e.g., femoral block and falls risk).

Consent and communication (what to cover simply)

• Explain purpose: “to reduce pain during and after surgery; you may still need other pain relief.”
• Set expectations: numbness and weakness are common; duration varies; protect the limb until sensation returns.
• Discuss common risks: bruising, failure/partial block, temporary nerve symptoms, infection, bleeding.
• Discuss serious but rare risks: local anaesthetic systemic toxicity (LAST), long-term nerve injury, pneumothorax (certain upper chest blocks).
• Confirm laterality and site with the patient and the surgical team; mark the correct side per local policy.

Safety essentials before you start (the ‘block checklist’ mindset)

• Correct patient, correct side, correct procedure; allergies checked; anticoagulation status reviewed.
• Baseline neuro exam documented (sensation/movement) and pain score recorded.
• IV access in place; standard monitoring (ECG, NIBP, SpO2) and oxygen available.
• Resuscitation equipment immediately available; intralipid (lipid emulsion) accessible for LAST.
• Time-out immediately before needle insertion: confirm block type, side, LA drug and dose, and plan for complications.
• Use aseptic technique: hand hygiene, sterile gloves, skin prep, sterile probe cover/gel if using ultrasound.

Local anaesthetic basics (practical, exam-relevant)

• Think in TOTAL dose (mg), not just volume: check concentration and calculate maximum safe dose for the patient.
• Use the lowest effective dose/volume, especially for high-risk sites or small patients.
• Incremental injection with frequent aspiration reduces intravascular injection risk (but does not eliminate it).
• Adrenaline-containing LA can reduce systemic absorption and acts as a marker of intravascular injection (tachycardia), but is not suitable for all patients.
• Additives (e.g., dexamethasone) may prolong analgesia—use only if within local policy and with senior agreement.

Ultrasound vs nerve stimulation (conceptual)

• Ultrasound helps identify anatomy, needle tip position, and spread of LA; it does not guarantee safety.
• Nerve stimulation can help confirm proximity to motor nerves; absence of twitch does not guarantee correct placement.
• Best practice often combines ultrasound guidance with careful technique: visualise needle tip, inject small test aliquots, watch spread, and stop if pain/paraesthesia occurs.
• Never inject against high resistance; stop and reassess needle position.

Block assessment and postoperative advice

• Assess sensory change in the expected distribution (cold/light touch) and motor function where relevant; document findings.
• If block is incomplete: consider time (some take 20–40 minutes), top-up options, or alternative analgesia—escalate early.
• Protect numb limbs: sling for upper limb; falls precautions for lower limb; avoid heat sources (burn risk).
• Give clear discharge advice for day-case patients: expected duration, when to start oral analgesia, and when to seek help.

Complications you must recognise early

• LAST: tinnitus, metallic taste, agitation, seizures, reduced consciousness, arrhythmias, cardiovascular collapse—treat as an emergency.
• Nerve injury: severe pain on injection, persistent numbness/weakness beyond expected duration, new neuropathic pain—stop injection and seek senior review.
• Bleeding/haematoma: increased risk with anticoagulants; swelling, pain, neurological changes—urgent assessment.
• Infection: rare with single-shot; higher with catheters—monitor for redness, fever, discharge.
• Site-specific: pneumothorax risk with some upper chest blocks; diaphragmatic weakness with interscalene; falls with femoral-type blocks.