Acute emergencies from local anesthetics are generally related to high plasma
levels encountered during therapeutic use of local anesthetics or to unintended
subarachnoid injection of local anesthetic solution. (See ADVERSE
REACTIONS, WARNINGS, and PRECAUTIONS.)
Management of Local Anesthetic Emergencies
The first consideration is prevention, best accomplished by careful and constant
monitoring of cardiovascular and respiratory vital signs and the patient's state
of consciousness after each local anesthetic injection. At the first sign of
change, oxygen should be administered.
The first step in the management of systemic toxic reactions, as well as
underventilation or apnea due to unintentional subarachnoid injection of drug
solution, consists of immediate attention to the establishment and maintenance
of a patent airway and effective assisted or controlled ventilation with 100%
oxygen with a delivery system capable of permitting immediate positive airway
pressure by mask. This may prevent convulsions if they have not already
occurred.
If necessary, use drugs to control the convulsions. A 50 mg to 100 mg bolus
IV injection of succinylcholine will paralyze the patient without depressing
the central nervous or cardiovascular systems and facilitate ventilation. A
bolus IV dose of 5 mg to 10 mg of diazepam or 50 mg to 100 mg of thiopental
will permit ventilation and counteract central nervous system stimulation, but
these drugs also depress central nervous system, respiratory, and cardiac function,
add to postictal depression and may result in apnea. Intravenous barbiturates,
anticonvulsant agents, or muscle relaxants should only be administered by those
familiar with their use. Immediately after the institution of these ventilatory
measures, the adequacy of the circulation should be evaluated. Supportive treatment
of circulatory depression may require administration of intravenous fluids,
and when appropriate, a vasopressor dictated by the clinical situation (such
as ephedrine or epinephrine to enhance myocardial contractile force).
Endotracheal intubation, employing drugs and techniques familiar to the clinician
may be indicated after initial administration of oxygen by mask, if difficulty
is encountered in the maintenance of a patent airway or if prolonged ventilatory
support (assisted or controlled) is indicated.
Recent clinical data from patients experiencing local anesthetic induced convulsions
demonstrated rapid development of hypoxia, hypercarbia, and acidosis within
a minute of the onset of convulsions. These observations suggest that oxygen
consumption and carbon dioxide production are greatly increased during local
anesthetic convulsions and emphasize the importance of immediate and effective
ventilation with oxygen which may avoid cardiac arrest.
If not treated immediately, convulsions with simultaneous hypoxia, hypercarbia,
and acidosis, plus myocardial depression from the direct effects of the local
anesthetic may result in cardiac arrhythmias, bradycardia, asystole, ventricular fibrillation, or cardiac arrest. Respiratory abnormalities, including apnea,
may occur. Underventilation or apnea due to unintentional subarachnoid injection
of local anesthetic solution may produce these same signs and also lead to cardiac
arrest if ventilatory support is not instituted. If cardiac arrest should occur,
standard cardiopulmonary resuscitative measures should be instituted and maintained
for a prolonged period if necessary. Recovery has been reported after prolonged
resuscitative efforts.
The supine position is dangerous in pregnant women at term because of aortocaval compression by the gravid uterus. Therefore during treatment of systemic toxicity,
maternal hypotension, or fetal bradycardia following regional block, the parturient
should be maintained in the left lateral decubitus position if possible, or
manual displacement of the uterus off the great vessels be accomplished.
The mean seizure dosage of mepivacaine in rhesus monkeys was found to be 18.8
mg/kg with mean arterial plasma concentration of 24.4mcg/mL. The intravenous
and subcutaneous LD50 in mice is 23 mg/kg to 35 mg/kg and 280 mg/kg respectively.