Local anaesthesia for minor procedures

What it is

The dose limit that is written down is for lidocaine without epinephrine: max dose 4.5 mg/kg. Since 1% lidocaine is 10 mg/mL, always multiply the % by 10 to get mg/mL. Then max volume (mL) = [4.5 x weight (kg)] divided by [concentration in mg/mL].

The worked example is a patient of 100 kg given lidocaine 4%, which is 40 mg/mL: max dose is 4.5 x 100 = 450 mg, and max volume is 450 divided by 40 = 11.25 mL.

How it is treated

For a laceration of a finger, the block of choice is a digital block at the base of the proximal phalanx, which blocks the digital nerves and allows appropriate anesthesia: the needle is inserted into the web space on either side, anesthesia is deposited anteriorly and posteriorly, and the same is repeated on the opposite side of the affected digit. Local infiltration through the wound margins does provide adequate anesthesia, but it may interfere with good wound approximation and so may lead to a poor cosmetic result. Irrigating a wound with anesthetic does not provide adequate anesthesia at all.

For a laceration of the lower lip, a mental nerve block is the most appropriate way to anesthetize the patient given his lip swelling. The mental nerve is a continuation of the inferior alveolar nerve; it emerges from the mental foramen below the second premolar and innervates the mucosa and skin of the lower lip.

For a laceration of the face crossing the vermilion border, a nerve block is required because local anesthesia would distort tissue anatomy thereby limiting appropriate approximation. Infiltration with local anesthesia will distort the tissue anatomy and may make proper alignment unreliable, and it should only be used if the patient fails nerve block.