Relationship between neuromuscular block induced by cisatracurium for tracheal intubation during anesthesia induction and types of myasthenia gravis

Objective To determine the relationship between neuromuscular block induced by cisatracurium for tracheal intubation during anesthesia induction and types of myasthenia gravis(MG). Methods Sixty-five patients of both sexes with MG, aged 20-75 yr, weighing 53-92 kg, with body height of 155-185 cm, of American Society of Anesthesiologists physical status Ⅰ or Ⅱ, undergoing elective video-assisted thoracoscopic thymectomy, were enrolled in the study.Among the 65 patients, there were 8 patients with ocular MG(typeⅠ), 19 patients with mild generalized MG(typeⅡa), 33 patients with subacute generalized MG(typeⅡb), 2 patients with acute MG(type Ⅲ) and 3 patients with late severe MG(type Ⅳ). Neuromuscular monitoring was initiated when the patients lost consciousness after induction of anesthesia.Cisatracurium was administrated with the initial dose of 0.05 mg/kg, and if T1 depression was less than 95% within 6 min, cisatracurium 0.015 mg/kg was intravenously injected until T1 depression was more than 95%.The patients were then tracheally intubated.The amount of cisatracurium consumed for intubation, onset time(from the beginning of cisatracurium injection to T1 depression >95%) and recovery time(recovery of T4/T1 to 25% of control height) of neuromuscular block were recorded.T1 depression > 95% within 6 min after administration of 1-fold ED95 cistracurium was defined as sensitivity to muscle relaxants.The requirement for cistracurium > 1-fold ED95 when T1 depression > 95% was defined as insensitivity to muscle relaxants.The proportion of sensitivity/insensitivity was calculated. Results There was no significant difference in the amount of cisatracurium consumed for intubation and onset time and recovery time of neuromuscular block between patients with typeⅠ and those with typeⅡa(P>0.05). Compared with patients with typeⅠ and type Ⅱa, the amount of cisatracurium consumed for intubation was significantly decreased, the proportion of sensitivity/insensitivity was increased, the onset time was shortened, and the recovery time was prolonged in patients with typeⅡb(P<0.05). Conclusion With the severity of MG, the consumption of cisatracurium is gradually decreased when used for tracheal intubation during anesthesia induction, and the sensitivity is gradually increased in the patients with MG. Key words: Androstanes; Myasthenia gravis; Intubation, intratracheal; Dose-response relationship, drug