Clinical recovery and train-of-four ratio measured mechanically and electromyographically following atracurium

Abstract

Indices of clinical recovery were compared with mechanically (adductor pollicis muscle) and electromyographically (first dorsal interosseal muscle) recorded train-of-four (TOF) ratios during antagonism of atracurium blockade in 23 healthy neurolept anesthetized patients. Clinical recovery was evaluated from the ability to lift the head, sustain headlift for 5 or 10 s, protrude the tongue, open the eyes, and the presence of ptosis of the eyelids. In all patients mechanical TOF ratio was recorded. In 17 patients TOF ratios based on measurements of the potential area and the amplitude of the major negative deflection of the compound EMG response were recorded as well. At each TOF ratio interval of 0.05 from a TOF ratio of 0.5-0.85, the number of patients being able to perform the individual tests was recorded. Further, the mechanical TOF ratio during recovery was compared with the EMG TOF ratios. Headlift could not be sustained for 5 s in any patient at a TOF ratio of 0.5, whether recorded mechanically or by EMG, and TOF ratio had to recover to 0.8 before all patients could sustain headlift for 5 s. All patients could open the eyes and protrude the tongue at a TOF ratio of 0.65, and ptosis remained present during the entire testing period. There was no statistically significant difference between the mechanical and the EMG methods with regard to the TOF ratios at which the tests could be performed. During recovery a linear relationship was found between mechanical TOF ratios and the square root of the EMG TOF ratios. It is concluded that the TOF ratio, whether recorded mechanically or by EMG, must exceed 0.8 to exclude residual curarization from atracurium blockade.