Table 1. The standard procedures of IONM.

Procedures	Note
Record vocal cord movement before surgery	Use of fiberoptic laryngoscope
Recommended anesthesia method for IONM	Intermediate- or short-acting muscle relaxant is recommended for preoperative anesthesia induction. The dosage of intermediate-acting muscle relaxant is smaller than that used for routine anesthesia induction. 1x ED95 intermediate-acting non-depolarizing muscle relaxant is recommended; avoid adding muscle relaxant before the termination of intraoperative monitoring
Body position and tube placement	Anesthesia intubation is performed after positioning (intubation under video laryngoscope is recommended)
Device connections and checking
The ground electrodes are routinely placed under the skin at the shoulders or xiphoid
Confirm the monitoring system has been effectively established
Check electrode impedance and differences in impedance values	Electrode impedance <5 kΩ, with deviations <1 kω
Check initial EMG	Initial fluctuations: about 10 μV
Set up event thresholds	Typically 100 μV
The current intensity of stimulator probe should be routinely set at 1-3 mA
The monitoring device should be placed far away from electro-surgical devices and be connected with anti-jamming silence detectors
The recording electrode positions should be confirmed during surgery	Directly detect, locate, and record the electrode depth at the antemedial laryngeal line using stimulator probe
IONM four-step method
Step 1: V1 signal	Obvious bipolar EMG signal is obtained at the ipsolateral vagus nerve at the plexas thyreoidea inferior level (point B), confirming the successful establishment of the monitoring system. If signal is absent at point B, detect the vagus nerve at the plexas thyroid superior level (point A); the presence of signal at point A confirms the presence of non-recurrent laryngeal nerve (25) (Figure 4)
Step 2: R1 signal	Before the exposure of RLN, its EMG signal is located using the Cross method by applying the probe vertical to trachea at its traveling area and then parallel to trachea
Step 3: R2 signal	Continuous monitoring is applied during the dissection of RLN and the signal change is compared in a real-time manner. After the RLN is exposed, the most proximal end of the exposed part is detected for EMG signal
Step 4: V2 signal	After complete hemostasis is achieved at the surgical field, the EMG signal of the vagus nerve is detected before closing the incision
Signal analysis
Basic EMG parameters	The biphasic waveform should be differentiated from the monophasic non-EMG artifacts
No obvious decrease in R2 and V2 signals	The basic EMG parameters include amplitude, latency and duration (26) (Figure 5); the RLN has intact function
Loss of R2 and V2 signals	If the RLN is injured during the surgical operation, detect the “injury site” and search for the injury cause*
Photo recording the exposed RLN during surgery	To confirm the RLN continuity (visual integrity)
Postoperative laryngoscopy

*, If no “injury site” is detected, it is important to determine whether there is a “real” loss of signal. (I) stimulate the nerve and then observe the contact between endotracheal tube electrode and vocal cord via a laryngoscope; (II) detect signals at vagus nerve and RLN again before closing the incision. IONM, intraoperative neuromonitoring; RLN, recurrent laryngeal nerve.