There are multiple topical anesthetics that we use in the ED. The common theme is that all of these drugs with -caine cause sodium channel inhibition in nerves, which blocks axonal transmission leading to the typical numbness and and localized weakness. I admit that it can be a bit confusing as to which one you should use and when. The aim of this post is therefore to help provide some clarity.
This gel contains 4% Lidocaine, 0.1% epinephrine and 0.5% tetracaine. It is used for topical laceration repair and according to some studies can provide adequate local anesthesia for scalp and facial lacerations in up to 90% of patients. Apply 1-3mL to the open wound. It should then remain there for 20-30 minutes to allow for absorption. Cover the wound with an occlusive bandage and tell the patient not to remove it. LET is great for lacs of the face of the scalp. It is generally contraindicated in areas with end arterial supply digits, penis, nose, and ears because pi is a vasoconstrictor. In large wounds the amount needed to cover can be toxic. You can also see excess absorption if it is applied to mucous membranes – so don’t do that. However, in most uses it is very safe. A trial of 203 children by Harman et al, in 2013 involving kids 3 mos to 17 years saw no toxicity when 3mL of LET was applied to a wound prior to tissue adhesive. The amount of lido in 3 mL of LET is approximately 135 mg – but the amount absorbed is generally way less than this and is limited by the size of the lac. Epi will lead to less absorption locally due to the vasoconstriction.
You may be familiar with 5mg/kg at the ceiling for lidocaine dosing. The lack of toxicity with LET means that this number does not need to be slavishly followed. Finally, since lidocaine can lead to methemoglobinemia be cautious in using it in infants under age 1 month.
EMLA stands for eutectic mixture of local anesthetics and is comprised of 2.5% lidocaine and 2.5% prilocaine in a cream. This cream consists of microscopic droplets that penetrate intact skin up to a depth of 2-3mm via diffusion down the concentration gradient. It can reduce the pain of venous/arterial puncture, lumbar puncture, access of ports and in wound repair/abscess I&D (prior to subcutaneous injection of lidocaine).
The usual dose is 1-2 grams applied per 10 square cm of skin. Cover with an occlusive dressing for 45-60 minutes.
Per Gajraj et al, the maximum area for usage is: The maximum application areas recommended for children are