Spread of epidural blockade in the anaesthetised pig using technetium99 and sensory-evoked potentials

Our objective was to determine the extension and duration of a stable segmental thoracic or lumbar epidural blockade by lidocaine in the 20 to 25-kg pig. Fourteen anaesthetised pigs were investigated. The radioactive isotope technetium99 (Tc99) was added to lidocaine to evaluate the spread in the epidural space. One ml of this solution was administered via an epidural catheter either at the Th(6-7) or L6-S1 level. Sensory-evoked potentials (SEPs) were measured following peripheral nerve stimulation, to determine duration and sensory extension of the epidural blockade. The thoracic anatomical mean spread was 14.2 vertebrae. The end points of the spread were C3-C7 and Th8-Th13 and the lumbar anatomical mean spread was 10.2 vertebrae. The end points were Th10-Th12 and L6-S1. It was possible to abolish the SEPs with 2 and 4% lidocaine. A smaller volume of lidocaine was needed if a second dose was administered within 20 min. With 4% lidocaine it was possible to abolish the SEPs for more than 180 min. The use of 1 ml of 4% lidocaine repeated after 20 and 60 min at the Th(6-7) or L6-S1 level achieved a stable thoracic or lumbar epidural blockade.