Find out more about each anaesthetic type.
Lidocaine
- Type – amide
- No inherent vasodilatation/constriction
- Can be used with a vasoconstrictor e.g. adrenaline*
- Infiltration normally 1-2%
- Painful on injection which can be improved by buffering with sodium bicarbonate or warming to 37C [2]
Topical preparations such as LAT (lidocaine, adrenaline and tetracaine) gel are available and can be useful as an adjunct to anaesthetise small wounds such as those on the face or scalp prior to closure.
Dosing [3]
- Should not exceed 4.5mg/kg (up to 200mg) [4] in adults/over 12s
- Should not exceed 3mg/kg in children under 12
- In adrenaline-containing preparations, should not exceed 7mg/kg (up to 500mg) in all patients
- Onset around 5 minutes (so it is important to give it time to work)
- Duration of action around 2 hours (or 3 hours with adrenaline)
Bupivacaine
- Type – amide
- No inherent vasodilatation/constriction
- Can be used with a vasoconstrictor e.g. adrenaline*
- Infiltration normally 0.25-0.5%
- Long duration, reducing the possibility of the need for a top-up
- More toxic than lidocaine, but remains safe within the recommended doses
Dosing [5]
- Should not exceed 2mg/kg as a single dose, or 400mg over 24 hours in adults
- Should not exceed 2mg/kg in children
- In adrenaline-containing preparations, should not exceed 2mg/kg (150mg max dose) [6]
- There are limited safety data in children under 1 year of age
Tetracaine
- Type – ester
- Used as part of a topical preparation such as LAT gel (see above) or on its own for topical administration for anaesthetic of the eye
- Should not be used in patients taking sulphonamides such as co-trimoxazole (septrin) [7]
Ethyl chloride
- This is a liquid with a boiling point lower than room temperature. When stored in a glass bottle, a saturated vapour develops within the container with a pressure of 30-40mmHg. This means when the stopper is opened, the liquid is forced out under pressure
- It is used by squirting on the skin from 15-20cm away. As it hits the skin, it vaporises, and the subsequent cooling produces an anaesthetic effect
- Ethyl chloride was first used in the 1800s for general and local anaesthesia. It is no longer used for the former, but still occasionally used for the latter
- In clinical practice, ethyl chloride has limited use. Lasting only seconds from the time spraying finishes and with effects confined to the very upper level of the skin, it may only be used for very quick superficial procedures such as removing small splinters, or facilitating venepuncture or cannulation
Learning bite
Choose the best drug and formulation for the job.
*Adrenaline has always been traditionally contraindicated in digits, however the evidence behind this is weak. A recent Cochrane review [8] found insufficient evidence to make a recommendation for or against adrenaline in digital nerve blocks.