Adverse Reactions/Side Effects
Systemic adverse reactions involving the central
nervous system and the cardiovascular system usually result from high
plasma levels due to excessive dosage, rapid absorption, or inadvertent
intravascular injection. In addition, use of inappropriate doses or
techniques may result in extensive spinal blockade leading to hypotension
and respiratory arrest.
A small number of reactions
may result from hypersensitivity, idiosyncrasy, or diminished tolerance
to normal dosage.
Excitatory CNS effects (nervousness, dizziness, blurred
vision, tremors) commonly represent the initial signs of local anesthetic
systemic toxicity. However, these reactions may be very brief or absent
in some patients in which case the first manifestation of toxicity
may be drowsiness or convulsions merging into unconsciousness and
respiratory arrest.
Cardiovascular system reactions include depression of the
myocardium, hypotension (or sometimes hypertension), bradycardia,
and even cardiac arrest.
Allergic reactions are characterized
by cutaneous lesions of delayed onset, or urticaria, edema, and other
manifestations of allergy. The detection of sensitivity by skin testing
is of limited value. As with other local anesthetics, hypersensitivity,
idiosyncrasy and anaphylactoid reactions have occurred rarely. The
reaction may be abrupt and severe and is not usually dose related.
The following adverse reactions may occur with spinal
anesthesia: Central Nervous System: postspinal headache, meningismus, arachnoiditis, palsies, or spinal
nerve paralysis. Cardiovascular: hypotension due to vasomotor paralysis and pooling of the blood
in the venous bed. Respiratory: respiratory impairment or paralysis due to the level of anesthesia
extending to the upper thoracic and cervical segments. Gastrointestinal: nausea and vomiting.
Treatment of Reactions. Toxic effects of local anesthetics require symptomatic treatment:
there is no specific cure. The physician should be prepared to maintain
an airway and to support ventilation with oxygen and assisted or controlled
respiration as required. Supportive treatment of the cardiovascular
system includes intravenous fluids and, when appropriate, vasopressors
(preferably those that stimulate the myocardium, such as ephedrine).
Convulsions may be controlled with oxygen and by the intravenous administration
of diazepam or ultrashort-acting barbiturates or a short-acting muscle
relaxant (succinylcholine). Intravenous anticonvulsant agents and
muscle relaxants should only be administered by those familiar with
their use and only when ventilation and oxygenation are assured. In
spinal and epidural anesthesia, sympathetic blockade also occurs as
a pharmacological reaction, resulting in peripheral vasodilation and
often hypotension. The extent
of the hypotension will usually depend on the number of dermatomes
blocked. The blood pressure should therefore be monitored in the early
phases of anesthesia. If hypotension occurs, it is readily controlled
by vasoconstrictors administered either by the intramuscular or the
intravenous route, the dosage of which would depend on the severity
of the hypotension and the response to treatment.
