local anaesthetics
Oct 09, 2025
The building blocks of blocks
The primary function of local anaesthetics in nerve blocks is to prevent the transmission of painful stimuli by blocking sodium channels, thereby inhibiting action potentials and producing sensory and/or motor blockade to a particular area or region of the body. 🧠
When it comes to selecting a particular local anaesthetic agent, considerations for choice include onset time, duration of blockade, potency, toxicity profile, and patient/surgery factors. ⚖️
Let’s look at some common agents used in blocks, and why they might be chosen:
🔹 Lignocaine:
Onset – rapid, typically within 2–5 minutes after administration ⏱️
Duration – short to intermediate, roughly 30–90 minutes. Duration can be extended up to 3 hours when combined with adrenaline
Indications
🔸 Infiltration for small procedures (e.g. cannulation, wound suturing)
🔸 Peripheral blocks where short duration is sufficient
🔸 Intravenous regional anaesthesia (Bier’s block)
🔸 Topical anaesthesia (sprays, gels, viscous solutions)
Potency – moderate, less likely to cause profound or prolonged blockade, well suited for rapid anaesthesia
Toxicity – generally well tolerated, but risk increases with rapid absorption, excessive dosing, or accidental intravascular injection ⚠️
🔹 Ropivacaine:
Onset – moderate, typically 10–20 minutes depending on dose, site, and concentration
Duration – long acting, between 2–8 hours for anaesthesia, and up to 12 hours for analgesia ⏳
Indications
🔸 Epidural anaesthesia
🔸 Peripheral nerve blocks
🔸 Wound infiltration
🔸 Continuous peripheral nerve and epidural infusions
Potency – high, similar to bupivacaine, but produces less motor blockade at similar concentrations allowing better patient mobility
Toxicity – has a favourable safety profile compared to bupivacaine, less cardio- and neurotoxic ❤️
🔹 Bupivacaine:
Onset – similar to ropivacaine, 10–20 minutes
Duration – longer acting, typically 4–12 hours for anaesthesia, and up to 18 hours for analgesia
Indications
🔸 Epidural and spinal anaesthesia
🔸 Peripheral nerve and plexus blocks
🔸 Wound infiltration
🔸 Continuous epidural infusions
Potency – high, approximately four times that of lignocaine
Toxicity – higher risk of systemic toxicity compared with ropivacaine and lignocaine. It binds strongly to sodium channels, making resuscitation difficult in overdose situations 🚫
Local anaesthetics are essential, opioid-sparing tools in regional and neuraxial anaesthesia, offering targeted and profound pain relief. 🏥
While lignocaine, bupivacaine, and ropivacaine are among the most commonly used agents in practice, a range of other formulations and adjuncts exist — each with unique properties that allow for individualised care and optimal patient outcomes. 🌿
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References:
Australian and New Zealand College of Anaesthetists. Guidelines for the Management of Major Regional Analgesia (PS03). Australian & New Zealand College of Anaesthetists. https://hdl.handle.net/11055/21
“Local Anaesthetics – Austin Health Clinical Guideline.” Austin Health, Melbourne. https://www.austin.org.au/Assets/Files/Local%20Anaesthetics.July%202023%5B1%5D.pdf
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