Pulmonary Medicine Made Easy: Local Anesthetics

Agent	Duration of Action	Maximum Dosage *Guidelines (Total Cumulative Infiltrative Injection Dose per Procedure)**
Esters
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
Amides
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.

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

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

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

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.

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