Simultaneous monitoring of force, acceleration and electromyogram during computer-controlled infusion of atracurium in sheep

Abstract

Five sheep were anaesthetised with sodium thiopentone, nitrous oxide and oxygen, and the lungs ventilated artificially. A computer-controlled infusion of atracurium employing feedback from isometric force measurement was set to maintain 15, 50 and 85% depth of neuromuscular block. Each was held constant for 30 minutes, while isometric force and electromyogram were measured on the left forelimb and acceleration on the right. The acceleration transducer records at the three levels of block were practically identical with those from force measurements: mean differences (SD) between simultaneous measurements being 3.6 (5.4)%. EMG value was 10.1 (12.0)% different from force measurement. Correlation between simultaneous force and either acceleration or EMG was excellent (r = 0.986 and 0.938 respectively). In clinical practice all three techniques measure block comparably. In the sheep forelimb, EMG wa a less reliable method of measuring block.