The quantitative distinction between train-of-four "counts of 2" and posttetanic "counts of 2" evidenced by a stable paralysis/stable infusion rate method in anesthetized patients receiving mivacurium.

Abstract

In this study we quantitatively evaluated, by a stable paralysis/stable infusion rate method, the difference between two standardized paralysis levels--train-of-four (TOF) count of 2 responses and posttetanic count (PTC) of 2. Ten ASA physical status I-II consenting adult patients scheduled for elective surgery were anesthetized (sufentanil/propofol), tracheally intubated, mechanically normoventilated with a fixed O(2)/air mixture, and normothermic; oropharynx and thenar temperatures were maintained above 36 degrees and 32.5 degrees C, respectively. After partial recovery from 200 microg/kg mivacurium (MIV), stable tactile TOF and PTC counts of 2 paralysis levels were induced on the adductor pollicis muscle by manual adjustments of an infusion pump containing MIV. The paralysis levels and the infusion rates were considered as stable once they remained constant at 4 consecutive time points separated by 5 min each. Infusion rates observed were: TOF count 2-6 (2-11) and PTC 2-17 (3-18) microg . kg(-1) . min(-1) (P < 0.001; Wilcoxon's paired comparison test). Under the present conditions, obtaining and maintaining a PTC of 2 requires MIV infusion rates far in excess of the "standard" recommendations mentioned in the literature for MIV infusion management.