DESCRIPTION

Local anesthetics are used for minor surgical procedures, regional anesthesia, spinal anesthesia, and treatment of cardiac dysrhythmias.

FORMS AND USES

• Local anesthetics are available in a wide variety of formulations, including chloroprocaine (Nesacaine), procaine (Anuject, Novacaine), proparacaine, propoxycaine (Rovocaine), tetracaine (Pontocaine, Niphaoid, Ak-taine, Kainaii, Occucaine, Opthaine, Opthetic, Fluorocaine, Ocufluorocaine), bupivacaine (Marcaine, Sensorcaine), etidocaine (Duranest), lidocaine (Xylocaine), mepivacaine (Carbocaine), prilocaine (Citanest), pramoxine (Tronolane, Fleet Relief, Proctofoam, Prax, Tronothane, Itch-X, Pramagel), and dyclonine (Dyclone, Tanaco, Sucrets).
• Dosage varies with each specific agent.
• Agents used for infiltrative anesthesia may be mixed with epinephrine to prolong action and provide local hemostasis.
• Agents used only as topical agents include benzocaine (Unguentine, Foille, Aerocaine, Aerotherm, Americaine, Burntame, Dermoplast, Lanacaine, Solarcaine, Benzocol, Ivarest, Rhulicream, Bicozeze, Chiggarex, Anacaine, Chiggertox, Campophenique), butanilicaine, carticaine, and dibucaine (Nupercainal).

TOXIC DOSE

Lidocaine

• Ingestion of more than 5 mg/kg (e.g., 3.0 ml of 2% solution in a 15-kg child) may result in seizure.
• Skin infiltration greater than approximately 4.0 mg/kg should be avoided (amount may be increased to 7.0 mg/kg if epinephrine-containing solution is used).

PATHOPHYSIOLOGY

• Local anesthetic agents interrupt electrical impulse transmission by blocking sodium channels in nerves.
• Systemic absorption of local anesthetics may lead to suppression of inhibitory centers in the brain, resulting in agitation, anxiety, and seizures.
• Blockade of the cardiac sodium channels may cause progressive heart block and asystole; however, cardiac effects only occur when levels are above those that produce neurologic effects (although bupivacaine reportedly produces cardiovascular collapse without warning signs of CNS toxicity).
• Methemoglobinemia has been reported frequently as a side effect of benzocaine use and occasionally with prilocaine, tetracaine, or lidocaine.
• Systemic effects of coadministered epinephrine may cause agitation or anxiety and mimic toxicity.
• Allergic reactions may occur, but most are due to paraben added to multidose vials as a preservative; when true allergic reaction occurs, agents in another class (e.g., amide instead of ester) may be used.

EPIDEMIOLOGY

• Poisoning from local anesthetics is uncommon and often iatrogenic.
• Toxic effects are usually mild to moderate and self-limited.
• Neonates and infants are at increased risk for methemoglobinemia.

CAUSES

• Most poisonings result from inadvertent injection of a therapeutic dose into a blood vessel, repeated use of therapeutic dose, or unintentional administration of a toxic dose.
• Child neglect or abuse should be considered if the patient is less than 1 year of age, suicide attempt if the patient is over 6 years of age.

RISK FACTORS

Advanced age and liver disease increase the likelihood of toxicity.

DRUG AND DISEASE INTERACTIONS

• Use of lidocaine with other class Ib antidysrhythmic agents (phenytoin, tocainide) may produce additive cardiac depression.
• Lidocaine and beta-blockers produce additive cardiac effects.

PREGNANCY AND LACTATION

• Lidocaine. US FDA Pregnancy Category B. Animal studies indicate no fetal risk, and there are no controlled human studies, or animal studies show an adverse fetal effect, but well-controlled studies in pregnant women do not.
• Bupivacaine. US FDA Pregnancy Category C. The drug exerts animal teratogenic or embryocidal effects, but there are no controlled studies in women, or no studies are available in either animals or women.
• Toxicity may develop in mother or fetus following paracervical or pudendal block.

Section Outline:

• DESCRIPTION
• FORMS AND USES
• TOXIC DOSE
  • Lidocaine
• PATHOPHYSIOLOGY
• EPIDEMIOLOGY
• CAUSES
• RISK FACTORS
• DRUG AND DISEASE INTERACTIONS
• PREGNANCY AND LACTATION

DIFFERENTIAL DIAGNOSIS

• Other toxicologic agents that cause agitation and seizure include sympathomimetic drugs (cocaine, ephedrine, etc.), type 1 antiarrhythmics, theophylline, and a variety of stimulants, among others.
• Nontoxicologic causes of agitation and seizure include allergic reactions, hypoxia from any cause, and withdrawal from alcohol or sedative-hypnotics.

SIGNS AND SYMPTOMS

• Severe overdose may involve abrupt onset of CNS depression and seizure, sometimes accompanied by dysrhythmia and hypotension.
• Methemoglobinemia has been reported frequently with high doses of benzocaine and occasionally with tetracaine and lidocaine.

Vital Signs

Tachycardia and hypertension are initial signs of toxicity but may be quickly followed by bradycardia and hypotension in severe overdose.

HEENT

• Vision loss has been reported after intranasal local anesthesia.
• Tinnitus may occur with toxic doses.

Cardiovascular

• Mild intoxication may cause tachycardia and hypertension.
• Overdose may cause bradycardia, ventricular dysrhythmia, and hypotension.

Pulmonary

Respiratory depression occurs with severe overdose.

Gastrointestinal

Nausea and vomiting are common.

Hematologic

Methemoglobinemia may occur.

Fluids and Electrolytes

Hyponatremia has been reported after ingestion.

Neurologic

• Agitation, anxiety, seizures, and, ultimately, coma may develop.
• Parasthesias may occur.
• Abrupt onset of numbness and seizures occur in severe overdose.

PROCEDURES AND LABORATORY TESTS

Essential Tests

ECG and cardiac monitoring are performed to detect dysrhythmia.

Recommended Tests

• Serum electrolytes, BUN, and creatinine should be obtained to assess the cause of cardiac dysrhythmia.
• Methemoglobin level should be obtained in symptomatic patients with cyanosis; serial levels may be needed if methemoglobinemia is present.

Section Outline:

• DIFFERENTIAL DIAGNOSIS
• SIGNS AND SYMPTOMS
  • Vital Signs
  • HEENT
  • Cardiovascular
  • Pulmonary
  • Gastrointestinal
  • Hematologic
  • Fluids and Electrolytes
  • Neurologic
• PROCEDURES AND LABORATORY TESTS
  • Essential Tests
  • Recommended Tests

• Treatment should focus on airway management, blood pressure support, treatment of seizures, and dysrhythmias.
• Dose and time of exposure should be determined for all substances involved.

DIRECTING PATIENT COURSE

The health-care professional should call the poison control center when:

• Hypotension or other severe effects occur.
• Signs and symptoms are not consistent with local anesthetic poisoning.
• Coingestant, drug interaction, or underlying disease presents an unusual problem.

The patient should be referred to a health-care facility when:

• Attempted suicide or homicide is possible.
• The patient or caregiver seems unreliable.
• Any toxic effects develop.
• Coingestant, drug interaction, or underlying disease presents an unusual problem.

Admission Considerations

Inpatient management is warranted for patients who develop altered mental status, seizure, or dysrhythmia.

DECONTAMINATION

Out of Hospital

Ipecac-induced emesis is not recommended because of the potential for seizures.

In Hospital

• Decontamination is not needed for parenteral exposure.
• Gastric aspiration with a nasogastric tube should be performed in patients with large ingestion presenting within 1 hour of ingestion or if serious effects are present.
• One dose of activated charcoal (1-2 g/kg) should be administered without a cathartic if a substantial ingestion has occurred within the previous few hours.

ANTIDOTES

There is no specific antidote for local anesthetic poisoning.

ADJUNCTIVE TREATMENT

• Cardiopulmonary bypass has been used successfully to treat massive lidocaine exposure with refractory dysrhythmia, allowing hepatic metabolism of lidocaine despite hypotension.
• Symptomatic methemoglobinemia is treated with methylene blue (see SECTION III, Methylene Blue chapter).
• Dialysis has been used to increase clearance of lidocaine.

Seizure

• A patent airway must be ensured.
• A benzodiazepine is administered for initial control. If seizures persist or recur, another anticonvulsant such as phenobarbital may be added.

Dysrhythmias or Conduction Abnormalities

• Seizures must be controlled and acidemia corrected.
• Treatment for stable patients begins with drug therapy; unstable patients receive defibrillation followed by pharmacologic therapy.
• Sodium bicarbonate should be administered in a 1 to 2 mEq/kg intravenous bolus and repeated as needed to maintain a narrow QRS interval.
  • Arterial pH should not exceed 7.55.
  • Simultaneous hyperventilation and bicarbonate therapy must be undertaken cautiously because it may cause severe alkalemia.
  • Seizure control should continue during sodium bicarbonate therapy.
• Cardiac bypass may be used to maintain perfusion and allow continued lidocaine metabolism in patients with refractory dysrhythmia or hypotension.
• Bretylium should be avoided because its alpha-blocking effects may worsen hypotension.
• Other class I antiarrhythmic agents should be avoided because they may worsen dysrhythmias.

Hypotension

• Primary treatment for hypotension in local anesthetic poisoning is correction of dysrhythmia.
• In addition, 10 to 20 ml/kg 0.9% saline may be administered followed by a vasopressor, if needed. Dopamine is preferred, and norepinephrine may be added for refractory hypotension.

Section Outline:

• DIRECTING PATIENT COURSE
  • Admission Considerations
• DECONTAMINATION
  • Out of Hospital
  • In Hospital
• ANTIDOTES
• ADJUNCTIVE TREATMENT
  • Seizure
  • Dysrhythmias or Conduction Abnormalities
  • Hypotension

PATIENT MONITORING

Cardiac and respiratory monitoring should be performed continuously.

EXPECTED COURSE AND PROGNOSIS

• Toxic effects develop rapidly within minutes of iatrogenic parenteral overdose.
• Recovery generally occurs within minutes to hours, except in massive overdose, unless sequelae of hypoxia and hypotension intercede.

DISCHARGE CRITERIA/INSTRUCTIONS

• From emergency department. Asymptomatic patients without CNS or cardiac affects for 4 to 6 hours may be discharged after gastrointestinal decontamination and psychiatric evaluation, if needed.
• From the hospital. Patients may be discharged after mental status and cardiac conduction return to normal, and gastrointestinal decontamination and psychiatric evaluation, if needed.

Section Outline:

• PATIENT MONITORING
• EXPECTED COURSE AND PROGNOSIS
• DISCHARGE CRITERIA/INSTRUCTIONS

DIAGNOSIS

• Cardiac toxicity may develop suddenly with bupivacaine, whereas it is heralded by neurotoxicity with lidocaine.
• It is important to consider local anesthetic toxicity in patients who develop neurologic symptoms during minor procedures.

TREATMENT

It is important to manage the airway adequately to avoid hypoxia and aspiration.

FOLLOW-UP

To avoid toxic exposure, maximal recommended doses of local anesthetics should be determined prior to administration.

Section Outline:

• DIAGNOSIS
• TREATMENT
• FOLLOW-UP

Intravenous anesthetics.

See Also: SECTION II, Hypotension, Methemoglobinemia, and Seizure chapters; and SECTION IV, Benzocaine chapter.

RECOMMENDED READING

Cardiotoxicity of local anesthetic drugs. Lancet 1986;2:1192-1194.

Noble J, Kennedy J, Latimer RD, et al. Massive lignocaine overdose during cardiopulmonary bypass. Br J Anaesth 1984;56:1439-1441.

Norris RL. Local anesthetics. Emerg Med Clin North Am 1992;10:707-717.

Author: Kennon Heard

Reviewer: Luke Yip