Equipment and Safety Conditions (con't)

Selection of the local anesthetic solution

Local anesthetics of the amide type are the most commonly used local anesthetics. Usual solutions and doses (according to patient's weight) are displayed in the following table. The limited duration of action of local anesthetics can be significantly prolonged by a sound selection of additives mixed with the injected solution. Alpha2-adrenergic agonists have long been added to local anesthetics. Epinephrine is the most commonly used of such agents, usually in concentrations ranging from 1:200,000 to 1:400,000; when not contraindicated, this addition offers two main advantages: 1) vascular absorption is decreased; 2) detection of inadvertent intravascular injection is facilitated by monitoring the electrocardiographic tracing. Provided that adequate time is allowed (20 seconds), and at least 0.5 µg/Kg of epinephrine is used, intravascular injection can be recognized by ST segment elevation, T wave change [34] and, occasionally, heart rate change.[35]

Clonidine, an a2-adrenergic agonist, is now commonly added to local anesthetics. Adminis-tered at doses ranging from 1 to 1.5 µg/Kg, clonidine consistently increases the duration of nerve blockade [36,37] with no perceptible hemodynamic effects in children. This dose may produce a slight sedation for 1 to 3 hours, a beneficial effect that allows for a smoother emergence from general anesthesia. While the addition of sodium bicarbonate aiming at increasing the non-ionized form of the local anesthetic has not proved to be of significant clinical relevance [38], the addition of ketamine appears promising.[39] However, more clinical studies are needed before ketamine can be suggested for routine use in peripheral nerve blockade.