Local anesthesia/anesthetics adverse effects

In 165 children receiving caudal anesthesia with fenta-nyl 1 mg/kg and bupivacaine 4 mg/kg, there were adverse effects in only six, two of whom required postoperative ventilation. This was felt to be due to their pathology and not the anesthetic. However, there was no comment on the presence or absence of specific local anesthetic adverse effects, and an unusually high dose of... 

Amide-type agents include articaine, lidocaine, bupivacaine, prilocaine, mepivacain and ropiva-caine. These are metabolized in the liver by microsomal enzymes with amidase activity. The amide group is preferred for parenteral and local use. If by accident rapidly administered intravascularly these agents, especially bupivacaine but also lidocaine, can produce serious and potentially lethal adverse effects including convulsions and cardiac arrest. They can more easily accumulate after multiple administrations. Intravenous lidocaine is sometimes used for regional anesthesia, for infiltration procedures, for the induction of nerve blockade and for epidural anesthesia. However, it is also used as an antiarrhythmic. Bupivacaine is a long-acting local anesthetic used for peripheral nerve blocks and epidural anesthesia. 

Mechanism-specific adverse effects. Since local anesthetics block Na+ influx not only in sensory nerves but also in other excitable tissues (A and p.206), they are applied locally. Depression of excitatory processes in the heart, while undesired during local anesthesia, can be put to therapeutic use in cardiac arrhythmias (p.138). 

The addition of fentanyl 1 pg/ml to ropivacaine 7.5 mg/ml did not improve nerve blockade by axillary brachial plexus anesthesia in a double-blind, randomized study in 30 patients undergoing orthopedic procedures (31). In another double-blind, randomized study, 60 patients receiving axillary brachial plexus blockade were given 0.25% bupivacaine 40 mg, 0.25% bupivacaine 40 mg plus fentanyl 2.5 pg/ml, or 0.125% bnpivacaine 40 mg plus fentanyl 2.5 pg/ml (32). The addition of fentanyl 2.5 pg/ml prolonged sensory and motor blockade without any improvement in the onset of anesthesia and no significant increase in adverse effects. These two studies have reaffirmed the current position of conflicting results in studies of the benefits of adding fentanyl to local anesthetics for peripheral nerve blockade. 

Systemic hypersensitivity reactions are not a frequent problem in local anesthesia. Systemic toxicity or allergy to additives (hyaluronidase, bisulfate, parabens) has sometimes been mistakenly classified as hypersensitivity to local anesthetics (SEDA-17,135) (29). WeU-documented case reports are very few, relating particularly to the older aminoesters this appears to be because these agents have the highly antigenic para-aminobenzoic acid as a metabolite (SEDA-13, 98). The incidence of true allergy is actually very low, probably less than 1% of all the adverse effects attributable to these substances (SEDA-20, 123). 

Phenol is a benzyl alcohol and a major oxidized metabolite of benzene that was introduced into medicine as an antiseptic (1). Although it can be prepared in an aqueous solution or in glycerine, it appears to be more effective when mixed in aqueous compounds. At a concentration of 0.2% it is bacteriostatic and at over 1% bactericidal (2). In addition to its uses as an antiseptic and disinfectant, phenol is also used as a sclerosant, as a local anesthetic on the skin, and as an analgesic, by injection into nerves or spinally, but its use was limited by severe adverse effects. Current medical uses include cosmetic face peeling, nerve injections, and topical anesthesia. It is also an ingredient of various topical formulations, and is used as an environmental disinfectant. 

Convulsions have occurred after inadvertent intravenous injection of ropivacaine during regional anesthesia (4,5). CNS adverse effects from ropivacaine occur before or without severe cardiovascular toxicity, as there have been several similar reports of CNS toxicity, but not yet one with severe or fatal cardiotoxicity. This reinforces the claim of increased safety from cardiovascular toxicity with this enantiomeric local anesthetic compared with racemic bupivacaine. 

---