Sunday, May 31, 2009

Local Anesthetics


Duration of Action

Maximum Dosage Guidelines (Total Cumulative Infiltrative Injection Dose per Procedure*)


Procaine (Novocain)

Short (15-60 min)

7 mg/kg; not to exceed 350-600 mg

Chloroprocaine (Nesacaine)

Short (15-30 min)

Without epinephrine: 11 mg/kg; not to exceed 800 mg total dose With epinephrine: 14 mg/kg; not to exceed 1000 mg


Lidocaine (Xylocaine)

Medium (30-60 min)

Without epinephrine: 4.5 mg/kg; not to exceed 300 mg

Lidocaine with epinephrine

Long (120-360 min)

With epinephrine: 7 mg/kg

Mepivacaine (Polocaine, Carbocaine)

Medium (45-90 min) Long (120-360 min with epinephrine)

7 mg/kg; not to exceed 400 mg

Bupivacaine (Marcaine)

Long (120-240 min)

Without epinephrine: 2.5 mg/kg; not to exceed 175 mg total dose

Bupivacaine with epinephrine

Long (180-420 min)

With epinephrine: Not to exceed 225 mg total dose

Etidocaine (Duranest) No longer available in United States

Long (120-180 min)

Without epinephrine: 0.4 mg/kg; not to exceed 300 mg total dose With epinephrine: 8 mg/kg

Prilocaine (Citanest)

Medium (30-90 min)

Body weight <70 kg: 8 mg/kg; not to exceed 500 mg Body weight >70 kg: 600 mg

Ropivacaine (Naropin)

Long (120-360 min)

5 mg; not to exceed 200 mg for minor nerve block

*Xylocaine spray 10%: contains 50ml (500 sprays), each 1ml = 10mg xylocaine with maximum dose 20 sprays. (50 ml of 1% lidocaine with epinephrine 1:100,000 contains lidocaine 500 mg and epinephrine 0.5 mg). *Administer the smallest dose and concentration required to achieve desired effect; avoid rapid injection.

-Side Effects: Local and Systemic, caused by high plasma concentrations of local anesthetic drug that result from:

  • Inadvertent intravascular injection,
  • Excessive dose or exposure or rate of injection,
  • Delayed drug clearance,
  • Administration into vascular tissue.
    1. Central nervous system signs:
  • Initial symptoms
    • Lightheadedness
    • Dizziness
    • Visual and auditory disturbances (difficulty focusing and tinnitus)
    • Disorientation
    • Drowsiness
  • Higher-dose symptoms
    • Often occur after an initial CNS excitation followed by a rapid CNS depression
    • Muscle twitching
    • Convulsions à ttt with diprivan but not phenytoin
    • Unconsciousness
    • Coma
    • Respiratory depression and arrest à CPR (it's rev.)
    • Cardiovascular depression and collapse à CPR
    1. Cardiovascular signs:
  • Direct cardiac effects
    • Toxic doses of local anesthetic agents can cause myocardial depression (tetracaine, etidocaine, and bupivacaine), cardiac dysrhythmias (bupivacaine), and cardiotoxicity in pregnancy.
    • Several anesthetics also have negative inotropic effects on cardiac muscle that lead to hypotension. Bupivacaine is especially cardiotoxic.
  • Peripheral effects
    • Vasoconstriction at low doses
    • Vasodilatation at higher doses (hypotension)
  • The range of signs and symptoms of cardiovascular toxicity include the following:
    • Chest pain
    • Shortness of breath
    • Palpitations
    • Lightheadedness
    • Diaphoresis
    • Hypotension
    • Syncope
    1. Hematological signs:

Methemoglobinemia with benzocaine, lidocaine and prilocaine; O-toluidine, the liver metabolite of prilocaine, is a potent oxidizer of hemoglobin to methemoglobin. At low levels (1-3%), methemoglobinemia can be asymptomatic, but higher levels (10-40%) may be accompanied by any of the following complaints:

  • Cyanosis
  • Cutaneous discoloration (gray)
  • Tachypnea
  • Dyspnea
  • Exercise intolerance
  • Fatigue
  • Dizziness and syncope
  • Weakness
    1. Allergic manifestations:

.Amino esters are derivatives of para -aminobenzoic acid (PABA), which have been associated with acute allergic reactions.

.However, preparations of amide anesthetics may sometimes contain methylparaben, which is structurally similar to PABA and, thus, may result in allergic reactions like: rash and urticaria, rarely anaphylaxis (should be considered if the patient is wheezing or in respiratory distress following administration). Patients who report an allergy to lidocaine are likely allergic to the methylparaben preservative.

N.B. Preservative-free lidocaine is now present to prevent allergy.

    1. Local tissue manifestations:

· Numbness and paresthesias (in the normal range)

· Irreversible conduction block within 5 minutes (with v high doses) Peripheral neurotoxicity, such as prolonged sensory and motor deficits (due to combination of low pH and sodium bisulfite in the mixture)

· Reversible skeletal muscle damage (rare)

6. Topical application:

A variety of anesthetics are available for topical or mucosal application (e.g., tetracaine, benzocaine, lidocaine)

Typically, this is caused by application to abraded or torn skin. The following adverse effects may occur:

  • Local burning or stinging may occur.
  • Oral viscous lidocaine may cause systemic toxicity, particularly with repeated use in infants or children.
  • CNS
    • High plasma concentration initially produces CNS stimulation (including seizures), followed by CNS depression (including respiratory arrest); CNS stimulatory effects may be absent in some patients, particularly when amides (e.g., tetracaine) are administered.
    • Epinephrine-containing solutions may add to the CNS stimulatory effect.
  • Cardiovascular
    • High plasma levels typically depress the heart and may include bradycardia, dysrhythmias, hypotension, cardiovascular collapse, and cardiac arrest
    • Epinephrine-containing local anesthetics may cause hypertension, tachycardia, and myocardial ischemia.
  • Gag-reflex suppression with oral administration
  • Other adverse effects include the following:
    • Transient burning sensation
    • Skin discoloration
    • Swelling
    • Neuritis
    • Tissue necrosis and sloughing
    • Methemoglobinemia with prilocaine

*Note that toxicity of anesthetics may be potentiated in patients with renal or hepatic compromise, respiratory acidosis, preexisting heart block, or heart conditions. Toxicity may be potentiated during pregnancy, at the extremes of age, or in those with hypoxia. However, inadvertent intravascular injection is the most common cause of local anesthetic toxicity even if anesthetic was administered within the recommended dose range.

*Download From: Local Anesthetics.doc

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