Local anaesthetic is useful in many procedures, ranging from the excision of skin lesions to post-operative analgesia in major surgery, to improve pre-operative or post-operative analgesia.
Often local anaesthetic is used with adrenaline to increase the amount of local anaesthetic that can be used*, as well as aiding to reduce bleeding from the operation site.
*Remember that adrenaline must never be used in areas with an end-arterial supply, such as digits, the pinna, penis, or nose, as the vasoconstriction can cause ischaemia and gangrene of the area
Procedure
When administering local anaesthetic, the theory to bear in mind is to infiltrate around the whole planned surgical field, allowing the anaesthetic to act on the nerve endings that supply the area from all directions.
Before Starting
- Check the expiry date and concentration of the anaesthetic. If the patient is awake, warm the anaesthetic in your hand, as this has been shown to significantly reduce the pain of injection.
- Start with a fine bore needle. A subsequent change to a longer and wider needle can be used after initial infiltration once the injection site is numbed.
Methods of Infiltration
Two methods of infiltration can be performed, both with the aim to infiltrate subcutaneously:
- Static – Insert the needle, aspirate to ensure no flashback of blood, then inject* (as shown in the video)
- Continuous – Insert the needle, inject continuously into the surrounding area with continuous movement
Aim to penetrate the skin as little number of times as possible. Rotate the angle of the needle to allow maximal infiltration through one puncture site. If required, additional punctures should be through an area already infiltrated.
Prior to any procedure, check that the area has been anaesthetised adequately by checking sensation, such as by pinching gently using toothed forceps.
*Inadvertent injection of local anaesthetic into the circulation can lead to paraesthesia, light-headedness, cardiac arrhythmias, and even cardiac arrest
Maximum Dosage of Local Anaesthetic
It is very important to know the safe dosage of local anaesthetic. The table below is a guide for adults, however you should check local protocols before administering.
| Anaesthetic | Without adrenaline | With adrenaline |
| Lidocaine | 3mg / kg | 7mg / kg |
| Bupivicaine | 2mg / kg | 2.5mg / kg |
Key Points
- Local anaesthetic is useful in many procedures to improve post-operative analgesia
- When administering local anaesthetic, attempt to infiltrate around the whole planned surgical field
- Two methods of subcutaneous infiltration can be performed, either static or continuous
- Prior to any procedure, check that the area has been anaesthetised adequately by checking sensation