This guideline outlines the indications and contraindications to local anaesthetic use, a guide to LA selection, maximal doses and administration advice.
- Local anaesthesia for painful procedures such as wound debridement, suturing, foreign body retrieval and relocation of a dislocated joint such as a finger or toe.
- Do not use lignocaine with adrenaline to infiltrate areas with an end arterial supply such as fingers, toes, pinna and nose.
- Local anaesthetic allergy (actually quite uncommon).
- Antiseptic swab
- Skin cleansing solution (e.g. chlorhexidine)
- Local anaesthetic agent (e.g. lignocaine)
- Syringe: 5 mL or 10 mL
- Needle: 25G and 21G.
Choose your local anaesthetic agent
- Lignocaine is a short-acting, amide-type local anaesthetic agent. It is supplied in 0.5%, 1% and 2% concentrations without (plain) or with adrenaline. Onset of action is within 1–2 minutes and duration 1–2 hours.
- Small volumes of more concentrated solution (i.e. 2%) are used for small areas of infiltration (e.g. interphalangeal joint relocation).
- Use a larger volume of a less concentrated solution (e.g. 1 %) around larger joints (e.g. knee joint aspiration).
- Use lignocaine with adrenaline for vascular sites or sites where the skin needs to be incised because adrenaline causes vasoconstriction.
- Never use lignocaine with adrenaline for nerve blocks of an extremity (fingers, toes, nose, pinna).
- Bupivacaine or ropivacaine are long-acting, amide-type local anaesthetic agents. Onset of action is slightly longer than lignocaine, but duration of action is much longer (6–8 hours). These agents are typically used for epidural anaesthesia and nerve blocks (e.g. femoral nerve block), but can also be used instead of lignocaine to provide a longer anaesthetic effect for painful conditions.
Calculating the maximum dose of local anaesthetic agent
- Maximum dose of lignocaine without adrenaline is 3 mg/kg.
- Maximum dose of lignocaine with adrenaline is 7 mg/kg.
- Lignocaine concentration in solution:
- Lignocaine 1% = 1 g/100mL or 10 mg/mL
- Lignocaine 2% = 2 g/100mL or 20 mg/mL
- Thus, in a 70-kg patient do not use more than:
- 20 mL 1% plain lignocaine
- 10 mL 2% plain lignocaine
- 48 mL 1% lignocaine with adrenaline
- 24 mL 2% lignocaine with adrenaline.
- Attach a 25G needle to a syringe filled with local anaesthetic, after checking dilution, dose and safety related to body weight.
- Enter the dermis of the skin at 45 degrees and aspirate to ensure not in a blood vessel. Infiltrate 1–2 mL local anaesthetic to raise a subdermal ‘bleb’ on the skin.
- Exchange the 25G needle for a 21G needle and enter the skin through the previously anaesthetised skin site.
- Advance the needle into the deeper tissues. Aspirate for blood before injecting any tissue. If you draw blood, withdraw a little and try again.
- Infiltrate the area to be anaesthetised and remove the needle.
- Direct the 25G needle along the line of the incision at the level of the dermis to extend the area of superficial anaesthesia, if an incision is to be made in the skin.
- Wait at least 2 minutes for the local anaesthetic to take effect.