RESUMEN
BACKGROUND: Congenital pseudocholinesterase (pChe) deficiency is a rare genetic abnormality which may lead to prolonged duration of action of muscle relaxants that are hydrolysed by pChe. We describe two cases in which mivacurium resulted in neuromuscular block lasting several hours. CASE REPORTS: Two non-related male patients, aged 26 and 7 years, scheduled for elective ENT surgery, received propofol, desflurane, remifentanil and mivacurium. At the end of the surgery it was not possible to reverse the neuromuscular blockade, and there were no responses to TOF or post-tetanic stimulation. Neuromuscular transmission returned spontaneously after 7, and 4 h, respectively. Postoperative assay revealed severe pChe deficiency in both patients, with values of 3393 UL(-1)and 2558 UL(-1), respectively (normal range 5100-11700 UL(-1). Family screening confirmed the presence of pChe deficiency in both cases. CONCLUSION: In any case of unexpected prolonged muscle relaxation after mivacurium, pChe deficiency should be considered and its activity measured.When confirmed, careful family screening is mandatory.