Accidental i.v. injection of local anaesthetics: an avoidable event?

In this issue of the British Journal of Anaesthesia, Abouleish and colleagues 1 report a case in which accidental injection of ropivacaine into an extradural vein resulted in central nervous system toxicity and a seizure. The extradural catheter was inserted while the patient was in labour, but she delivered before it was used. She was then to undergo tubal ligation. In spite of a negative aspiration test and fractionating the total dose of ropivacaine 120 mg over 11 min, the patient had a tonic-clonic seizure. Fortunately, there were no life-threatening cardiac arrhythmias, the ECG indicating only a mild sinus tachycardia, and she came to no harm. The catheter tip was found to contain blood when it was removed. This is one of the first case reports of systemic toxicity with the clinical use of this recently introduced local anaesthetic agent and it raises several issues. Is a negative aspiration test, particularly when done several hours after the extradural catheter has been placed, reassuring? The catheter had presumably entered an extradural vein, but the blood in the tip of it had clotted. This is the most likely reason for the negative aspiration test. Perhaps an initial flush of the catheter with saline followed by aspiration would have revealed the problem in this case, although it is interesting that a second aspiration test (always a wise precaution after the initial injection), done after the third bolus of ropivacaine, was negative. This suggests that the clot in the tip of the catheter was causing a flap valve effect, allowing injection of local anaesthetic into a vein, but preventing aspiration of blood. Should an extradural catheter that has been inserted several hours before be " re-used " to establish a block? The answer is probably a guarded yes, but adequate tests must be used to determine if the catheter is within a vessel or has pierced the dura before the therapeutic dose of local anaesthetic is injected. What constitutes an " adequate " test to exclude catheter mis-placement? The authors of the report used a test dose of ropivacaine 15 mg followed by a further 22.5 mg, 3 min later, but unfortunately this failed to warn that the catheter was within an extradural vessel. Is a test dose of 2 ml of ropivacaine 0.75% (to exclude accidental subarachnoid block) followed 3 min later by a further 3 ml of the same solution likely to …