Facial Nerve Monitoring under Different Levels of Neuromuscular Blockade with Cisatracurium Besilate in Parotid Tumour Surgery

Abstract

Background: Anaesthesia can alter neuronal excitability and vascular reactivity and ultimately lead to neurovascular coupling. Precise control of the skeletal muscle relaxant doses is the key in reducing anaesthetic damage.

Methods: A total of 102 patients with the normal functioning preoperative facial nerve who required parotid tumour resection were included in this study. Facial nerve monitoring was conducted intraoperatively. The surgeon stimulated the facial nerve at different myorelaxation intervals at TOF% (T4/T1) and T1% (T1/T0) and recorded the responses and the amplitude of electromyogram (EMG). Body movements (BM) or patient-ventilator asynchrony (PVA) was recorded intraoperatively.

Results: In parotid tumour resection, T1% should be maintained at a range of 30 to 60% while TOF% should be maintained at a range of 20 to 30%. Analysis of the decision tree model for facial nerve monitoring suggests a partial muscle relaxation level of 30% < T1% ≤ 50% and TOF ≤ 60%. A nomogram prediction model, while incorporating factors such as sex, age, BMI, TOF%, and T1%, was constructed to predict the risk of BM/PVA during surgery, showing good predictive performance.

Conclusions: This study revealed an adequate level of neuromuscular blockade in intraoperative parotid tumour resection while conducting facial nerve monitoring. A visual nomogram prediction model was constructed to guide anaesthetists in improving the anaesthetic plan.

Figure 1

Relationship between T1% and the degree of muscle relaxation with skeletal muscle relaxants in facial nerve monitoring: (a) T1% and body movement score relationship; (b) T1% and patient-ventilator asynchrony relationship; (c) estimated T1% with/without BM/PVA; (d) T1% and positive facial nerve EMG reaction relationship; (e) comparison of estimated T1% between positive EMG reaction and negative EMG reaction.

Figure 2

Relationship between TOF% and the cut-off value for the effect of facial nerve anaesthesia for muscle relaxation: (a) the relationship between TOF% and body movement score; (b) the relationship between TOF% and patient-ventilator asynchrony; (c) comparison of estimated TOF% with/without BM/PVA; (d) the relationship between TOF% and positive EMG reaction of the facial nerve; (e) comparison of estimated TOF% between positive EMG reaction and negative EMG reaction.

Figure 3

ROC curves of TOF% and T1% for predicting the effect of facial nerve anaesthesia on muscle relaxation: (a) ROC curve of TOF% and T1% for body movement or patient-ventilator asynchrony; (b) ROC curve of TOF% and T1% for body movement or positive EMG reaction of the facial nerve; (c) correlation of EMG values with TOF% and T1%.

Figure 4

Visualization of the decision tree. (a) A decision tree-heat map for predicting the occurrence of BM or PVA during surgery. MRVC: movement or ventilation confrontation has occurred; ASA: American Society of Anesthesiologists. (b) A decision tree-heat map for predicting a positive EMG response of the facial nerve during surgery. EMG: electromyogram. Note: the heat map colours present the relative value of a sample compared to the rest of the group.

Figure 5

A visual nomogram prediction model. (a) Nomogram prediction model for predicting the occurrence of BM or PVA during surgery. (b) Calibration curve of the BM/PVA model for predicting the occurrence of BM/PVA during surgery. The closer the solid line to the dashed line, the better the predictive power.