Monitoring of neuromuscular transmission in organophosphate pesticide-poisoned patients

Thirty-four adult patients with severe organophosphorus compounds (OP) poisoning requiring artificial ventilation were enrolled in a clinical study and received atropine and obidoxime (250 mg i.v., followed by 750 mg/24 h) as antidotal treatment. Here, we re-analyzed the cholinesterase status (red blood cell acetylcholinesterase (RBC-AChE) activity, reactivatability of RBC-AChE, and plasma butyrylcholinesterase (Pl-BChE) activity) in relation to the neuromuscular transmission (NMT) data. When RBC-AChE activity ranged between 100% and 30% NMT was unimpaired after tetanic stimulation with frequencies up to 50 Hz. A further decrease in RBC-AChE activity was accompanied by a marked disturbance of NMT, being strongly impaired at AChE activities <5% of normal. Higher stimulation frequencies (>30 Hz) facilitated the discrimination of the types of impairment. The neuromuscular transmission was the best quantified by using the ratio of the ninth to the first amplitude, while the standard method was less discriminative. At RBC-AChE levels higher than 40% of normal weaning from the ventilator may be considered. Completely aged RBC-AChE as indicated by loss of reactivatability loses its guidance function. Then, steadily increasing Pl-BChE activity suggests lack of circulating poison. One-week later, neuromuscular transmission may be largely normal and patients could be weaned from the respirator if other complications are not withstanding.