Overview
Definition:
Local anesthetics (LAs) are drugs used to temporarily block nerve conduction, producing localized loss of sensation
In children, precise dosing is critical due to physiological differences and higher risk of systemic toxicity compared to adults.
Epidemiology:
Pediatric procedural sedation and regional anesthesia are common
Overdosing of LAs, though preventable, can lead to serious adverse events including seizures and cardiovascular collapse
Accurate weight-based calculations are paramount.
Clinical Significance:
Safe and effective use of local anesthetics is fundamental in pediatric procedural care, including minor surgeries, dental procedures, and diagnostic investigations
Understanding dosing limits prevents toxic reactions and ensures patient safety, a key concern for DNB and NEET SS candidates.
Age Considerations
Neonates:
Neonates (0-1 month) have immature hepatic metabolism and reduced protein binding, potentially increasing LA plasma concentrations and toxicity risk
Dosing should be conservative.
Infants:
Infants (1-12 months) and young children have a higher ratio of total body water to fat, affecting drug distribution
Dosing requires careful adherence to weight-based calculations.
Older Children:
Older children and adolescents generally tolerate LAs similarly to adults, but age-appropriate physiological assessments and adherence to standard dosing guidelines remain crucial.
Weight Based Dosing:
All pediatric LA dosing must be calculated on a weight-based (mg/kg) principle to ensure safety and efficacy
Always double-check calculations.
Local Anesthetic Agents And Limits
Lidocaine:
Maximum dose for plain lidocaine is typically 4 mg/kg
With epinephrine, the maximum dose can be increased to 7 mg/kg, though epinephrine use in young infants requires caution due to potential cardiovascular effects.
Bupivacaine:
Maximum dose for bupivacaine is 2 mg/kg (plain)
Bupivacaine has a slower onset but longer duration of action, making it suitable for prolonged procedures
Toxicity can be severe and harder to manage.
Ropivacaine:
Maximum dose for ropivacaine is 3 mg/kg (plain)
Ropivacaine is a pure S-enantiomer with a better safety profile than bupivacaine regarding CNS and cardiac toxicity.
Mepivacaine:
Maximum dose for mepivacaine is 4-5 mg/kg (plain)
It has a faster onset and intermediate duration, often used in dental anesthesia.
Epinephrine Considerations:
Epinephrine is added to prolong duration and reduce peak plasma levels by causing vasoconstriction
However, it should be used cautiously in neonates and infants due to potential for systemic effects like hypertension and bradycardia.
Factors Influencing Dosing
Injection Site:
Vascularity of the injection site impacts absorption
Highly vascular areas (e.g., scalp, intercostal) lead to faster systemic absorption
Dilution with epinephrine can mitigate this.
Type Of Procedure:
Minor procedures with less systemic absorption risk may allow for closer adherence to maximum doses, while major procedures or those with potential for intravascular injection require greater caution.
Patient Factors:
Co-existing medical conditions such as hepatic or renal dysfunction, cardiac arrhythmias, or seizure disorders can significantly affect LA metabolism and tolerance, necessitating dose reduction.
Metabolism And Excretion:
LAs are primarily metabolized by the liver (amides) or plasma esterases (esters)
Impaired hepatic or renal function can lead to drug accumulation and toxicity.
Signs And Symptoms Of Toxicity
Central Nervous System Effects:
Early signs include circumoral numbness, dizziness, tinnitus, blurred vision, and metallic taste
Progression can lead to slurred speech, muscle twitching, tremors, confusion, and ultimately seizures.
Cardiovascular Effects:
Following CNS effects, cardiac effects can occur, including bradycardia, hypotension, arrhythmias (ventricular tachycardia, fibrillation), and cardiovascular collapse
These are life-threatening.
Other Effects:
Hypoxia, hypercarbia, and methemoglobinemia (especially with certain agents like benzocaine) can also occur.
Management Of Toxicity
Immediate Recognition:
Prompt identification of early CNS signs is crucial
Discontinue LA administration immediately.
Airway Management:
Secure the airway and provide supplemental oxygen
Assist ventilation as needed
Hyperventilation may worsen CNS toxicity.
Seizure Management:
Intravenous benzodiazepines (e.g., diazepam, midazolam) are first-line for seizure control
Avoid barbiturates if possible as they can depress cardiovascular function.
Lipid Emulsion Therapy:
Intralipid 20% emulsion is the antidote for systemic LA toxicity (LAST)
It acts by sequestering the LA and providing energy to the myocardium
Administer 1.5 mL/kg bolus, followed by an infusion of 0.25 mL/kg/min, potentially repeated.
Cardiovascular Support:
Manage hypotension with fluid boluses and vasopressors
Avoid epinephrine if possible in early stages due to potential for exacerbating arrhythmias
if used, use low doses
Amiodarone may be used for arrhythmias.
Key Points
Exam Focus:
Always calculate LA doses on a mg/kg basis for children
Memorize maximum recommended doses for common agents like lidocaine and bupivacaine, with and without epinephrine
Recognize early signs of toxicity and the role of Intralipid.
Clinical Pearls:
Use the lowest effective concentration and volume
Consider dilute LAs for larger volumes
Always have resuscitation equipment and Intralipid readily available when administering LAs
Double-check calculations with another provider.
Common Mistakes:
Extrapolating adult doses to children, neglecting weight-based calculations, failing to account for factors affecting absorption, and delaying treatment of toxic reactions.