Caudal: System Toxicity
Basic, Clinical Sciences: Anesthesia Procedures, Methods, and Techniques
Caudal Block is a technique most commonly utilized in neonates, infants and small children (typically <5 or 6 years of age). Dose and injection site influence the plasma concentration and peak levels. Rate of absorption at different sites is, from highest to lowest: intercostal, intratracheal, caudal, epidural, brachial plexus and subcutaneous. In general, higher vascularized areas have higher rates of absorption. Epinephrine is added to the solution to vasoconstrict and decrease absorption from the site of injection.
Allowable safe levels of local anesthetic for adults are extrapolated from animal studies and then fitted for infants and children. Maximum safe doses of Lidocaine are 5 mg/kg and with epinephrine 1:200,000 are 7 mg/kg. Bupivacaine and ropivacaine are 3 mg/kg and does NOT change with the addition of epinephrine.
Dose For Caudals: Bupivacaine 2.5 mg/kg; Ropivacaine 2 mg/kg.
Toxicity levels: Bupivacaine 2-4 mcg/ml.
When injecting a test dose with epinephrine, monitor for increases in HR > 10 bpm or increase in T-wave amplitude in lead II. When using a TIVA, increased BP (>30% within 2 minutes) has been shown to be more consistent.
Symptoms of toxicity: CNS toxicity levels tend to be higher than cardiac toxicity levels, thus Cardiac symptoms appear first. This is opposite as compared to adults. The first sign of toxicity may be cardiac collapse. Can be muscle rigidity, hypoxia, tachycardia or dysrhythmias.