Influence of acute normovolaemic haemodilution on the dose–response relationship, time-course of action and pharmacokinetics of rocuronium bromide

Background Acute normovolaemic haemodilution (ANH) is an effective strategy for avoiding or reducing allogeneic blood transfusion. We aimed to study its effect on the pharmacological profile of rocuronium. Methods In two study centres, 28 patients undergoing major surgery with ANH were matched with 28 control patients. In the dose–response groups, using the mechanomyograph, neuromuscular block of six consecutive incremental doses of rocuronium 50 μg kg −1 , followed by 300 μg kg −1 , was evaluated. In the pharmacokinetics groups, serial arterial blood samples were withdrawn for rocuronium assay after a single dose of rocuronium 600 μg kg −1 . Results ANH resulted in a shift to the left of rocuronium dose–response curve. Rocuronium effective dose 95 (ED 95 ) was 26% lower ( P −1 ] compared with the control group [383.5 (127.3) μg kg −1 ]. Times from administration of last incremental dose until 25% of first response of train-of-four (TOF) recovery (Dur 25 ) and 0.8 TOF ratio recovery (Dur 0.8 ) were 28% longer in the ANH group [39.9 (8.4), 66.7 (14.2) min] compared with the control group [31.1 (6.6), 52.1 (15.8) min] ( P P P P P −1 , 4.70 (0.94) ml kg −1 min −1 , 77.29 (12.25) min] compared with the control group [181.22 (35.73) ml kg −1 , 5.71 (1.29) ml kg −1 min −1 , 56.86 (10.05) min, respectively]. Conclusion ANH resulted in prolongation of rocuronium time-course of action, thus careful monitoring of neuromuscular block is recommended in patients who undergo ANH.