Intravascular injection of local anaesthetic drugs can produce serious or life-threatening effects at much smaller doses than the maxima quoted. Local anaesthetic injections at any site can form part of balanced analgesia where a mixture of techniques provides pain relief. This has the advantage of decreasing the dosage of each drug needed and diminishing the likelihood of side effects. The small delay that results from performance of the blocks is outweighed by the benefit to the patient. Toxicity The most important factor in the prevention of local anaesthetic toxicity is the avoidance of intravascular injection.
Careful aspiration is vital especially if the needle is moved.
However, a negative aspiration test is not an absolute guarantee of correct needle placement. Inject slowly and watch carefully for signs of toxicity such as buzzing in the ears, a feeling of numbness in the face and lips and a feeling of muscle twitching. If toxicity is suspected the injection should be stopped and the patient's respiration and circulation assessed. Provided hypoxia is avoided little other treatment is needed. Cardiovascular depression should be treated by raising the legs, giving intravenous fluids and administering a vasopressor such as ephedrine.