Local Anaesthetics

For any patient about to be sutured, attention must be given to obtaining adequate analgesia and ensuring overall comfort. After documenting the neurovascular status of adjacent structures, which must be done in every case, a local anaesthetic can be injected into the tissue in and around the wound. A 1% solution (10 mg/cc) of lidocaine can be used for most wounds.

Lidocaine 1% is very safe when used in the small quantities usually required for simple lacerations. The physician should not use in excess of 3mg/kg of lidocaine. Its onset of action when infiltrated locally is within seconds and its duration of action is generally 30 to 60 minutes. Lidocaine is also available in 0.5% (5 mg/cc) and 2.0% (20 mg/cc). The 0.5% is useful in pediatric patients, whereas the 2.0% solution is rarely necessary.

Epinephrine is added to some of the commercially available lidocaine solutions. It is a potent vasoconstrictor and functions to prolong anaesthesia by slowing vascular uptake of the lidocaine, and to reduce the bleeding into the wound, which can impair visualization of structures. Solutions containing epinephrine are best avoided by inexperienced physicians as there are risks associated with their use.

Lidocaine causes an intense burning sensation when injected locally. The burning is dependent on the rate of injection and the acidity of the solution. The burning can be minimized by slow injection using a small gauge needle (#25, #27, or #30). An experienced physician can inject local anaesthetic with virtually no discomfort if time and care are taken.
Recently, it has been shown that the addition of bicarbonate to buffer the lidocaine solution can reduce some of the burning sensation at the injection site. However, this buffered solution is not available commercially and must be made up in the Emergency Department as it has a short shelf life.