Delayed onset of alcuronium effect in children with cyanotic congenital heart disease

The effect of alcuronium dichloride (0.3 mg/kg) was studied in seven normal children (Group A), nine with acyanotic congenital heart disease (Group B) and eight with cyanotic disease (Group C). The onset of action was recorded using an integrated electromyograph and blood samples taken for later estimation of plasma concentrations of the drug. The mean time (SD) taken to 75% suppression of twitch height was 1.3(0.8), 1.7(1.0) and 3.8(2.8) minutes, respectively, in each of the three groups. This was significantly slower in Group C compared with both other groups (P < 0.05). While six of the Group A patients and seven from Group B reached 95% paralysis within ten minutes, only two of the cyanosed children achieved this level of relaxation. However, if times to 95% relaxation were extrapolated, there was no significant difference between the groups at 4.5(3.9), 5.8(5.7) and 10.9(6.5) minutes respectively. There was a weak but statistically significant relationship between haematocrit and time to 75% blockade. Maximum twitch depression was similar in all three groups with plasma concentrations at this time being 1.6(0.7), 1.8(0.5) and 2.3(1.4) micrograms/ml respectively. Again, there was no statistically significant difference between these values. These results confirm that the clinical onset of relaxation is delayed in children with cyanotic congenital heart disease, possibly because of delayed distribution of alcuronium.