Interference between muscle relaxation and facial nerve monitoring during parotidectomy

There is a worst case scenario involving a small risk of facial nerve injury and dysfunction of facial nerve monitoring. With regard to patient safety the use of a short-acting muscle relaxant and the analysis of neuromuscular blockade are necessary because these permit documentation of the temporal course of relaxation and the progress of surgery.

The use of muscle relaxant may disturb facial nerve monitoring during parotidectomy. The aim of the study was to analyze the duration of muscle relaxation in relation to the progress of surgery.

Twenty-one patients who underwent parotidectomy were enrolled in this prospective study, where the short-acting muscle relaxant mivacurium (0.2 mg/kg) was used. The neuromuscular blockade was monitored on the basis of train-of-four (TOF) peripheral stimulation. The time of intubation, skin incision, facial nerve identification and the end of surgery were documented.

The mean times of the TOF ratios (2/4; 3/4; 4/4), skin incision, and facial nerve identification differed significantly (chi(2)=0.05; df=1; p>0.05). For the earliest skin incision (21 min), 14.3% of patients have a TOF ratio smaller than 2/4 at which a neuromuscular block of the facial nerve is possible.