Intravenous injection local anaesthetics

Local anaesthetics can be applied topically, deposited around peripheral nerves, or infiltrated into tissues. Central neural blockade can be produced by injection into the subarachnoid or epidural spaces. Less common uses are for intravenous regional anaesthesia and attenuation of cardiovascular responses to tracheal intubation. The membrane-stabilising effect of local anaesthetics has been utilised in the treatment of myocardial arrhythmias. 

Parenteral administration can be associated with pain at the injection site. The so-called injection fear may be diminished by applying topically anaesthetics prior to injection. Eutectic mixtures of local anaesthetics (e.g. lidocaine/ prilocaine cream or a tetracaine gel) have proven to be effective and well-tolerated in the relief of pain associated with intramuscular injections, venepuncture or intravenous injection in adults and children. 

Inadvertent intravenous injection of the local anaesthetic agent (especially possible in the thin-walled and engorged epidural veins during labour) can lead to acute systemic toxicity convulsions occurring within 30 seconds of epidural injection of bupi-vacaine have been described in 4 obstetric cases (5 ). 

One case of anaphylactic shock (27 ) and one of generalized exfoliative dermatitis (28 ) after the use of lidocaine as a local anaesthetic have been described. The intravenous administration of lidocaine in patients with myocardial infarction sometimes also leads to undesirable side effects, of which hypotension is the best known. The problem is mainly one for the cardiologist, but since inadvertent intravenous injection during local anaesthesia may occur, the anaesthetist must be aware of it. A case of sinusbradycar-dia after a bolus injection of 50 mg (29 -) and an atrioventricular block after 800 mg, given in the course of 12 hours (30 ) have been described. Two fatalities, one due to ventricular fibrillation after 50 mg and one to sinus arrest after 100 mg, have been re-... 

Twenty patients undergoing surgery were given repeated 1-mg intravenous doses of midazolam as induction anaesthesia every 30 seconds until they failed to respond to three repeated commands to squeeze the anaesthetist s hand. This was considered as the induction end-point titrated dose. It was found that the 10 who had been given prior spinal anaesthesia with tetracaine 12 mg needed only half the dose of midazolam (7.6 mg) than the 10 other patients who had not received tetracaine (14.7 mg). The reasons are not known. The authors of this report simply advise care in this situation. In another study in which patients were given intravenous midazolam following an intramuscular injection of either bupivacaine, lidocaine or saline, it was found that both anaesthetics enhanced the effect of midazolam. This effect was dose-dependent and it was concluded that the use of lidocaine or bupivacaine for regional blocks or local infiltration could alter the effect of midazolam from sedative to hypnotic. ... 

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