Modulatory effects of topically administered lidocaine and pentobarbital on traumatic vasospasm in the rabbit ear artery

The effect of topical administration of 2 or 20% lidocaine and of 3% pentobarbital on traumatic vasospasm was studied in the central ear artery of the rabbit. The inner diameter of the artery was measured by in vivo microscopy. Vasospasm was induced by a standardised pinch of a 3.2 mm long arterial segment and lasted for 10-20 min. The drugs were given locally at maximal spasm, 1 min after spasm induction. All treatments caused prompt resolution of the vasospasm. This was followed by a plateau phase when the vessel diameter was reduced to about 60% of the initial pre-spasm value as a result of drug-induced vasoconstriction. The vasoconstriction lasted between 40 min and 24 h, depending on the treatment. Twenty per cent lidocaine was most effective, but caused thrombosis in microvessels surrounding the central ear artery. It is concluded that topical lidocaine and pentobarbital are both effective in resolving traumatic vasospasm but should only be used after careful consideration, since they also cause a general decrease in vascular diameter.