BackgroundThis retrospective study assessed the onset and duration of the neuromuscular block (NMB) induced by cis-atracurium 0.15 mg/kg intravenously with and without fentanyl or lidocaine infusions in 45 isoflurane-anaesthetised dogs.MethodsDogs with neuromuscular function assessed by a calibrated train-of-four (TOF) monitor with stimulation (every 13 s) of the peroneal nerve were included. The onset and duration of the NMB were defined as the time from cis-atracurium administration until TOF=0 and the time during TOF=0 display, respectively.ResultsThe NMB onset was shorter during fentanyl (mean±sd) (1.9±0.7 minutes; P=0.0042) and lidocaine (2.0±0.7 minutes; P=0.0154) compared with control (2.9±0.8 minutes). The NMB duration was shorter in the fentanyl (27.5±7.3 minutes; P=0.0491), but not in the lidocaine group (32.3±6.9 minutes; P=0.0790), compared with control (33.7±9.1 minutes). The NMB onset was poorly but significantly correlated with the dose of fentanyl and lidocaine administered before cis-atracurium (r=−0.3396; P=0.0225). The fentanyl and lidocaine groups received more crystalloid and colloid boluses than the control.ConclusionsFentanyl and lidocaine shortened the NMB onset and the former decreased the NMB duration. Further prospective studies are required to clarify whether this was associated with an indirect decrease in blood pressure or a direct interaction between cis-atracurium and fentanyl and lidocaine.