The optimal and safe intensity for facial nerve stimulation during intraoperative neuromonitoring in middle ear surgery

Olfactory Evoked Potential Produced by Electrical Stimulation for Monitoring Olfactory Function During Endonasal Endoscopic Surgery: A Preliminary Study

PURPOSE

The aim of this study is to develop an intraoperative olfactory monitoring system using olfactory evoked potential produced by electrical stimulation. Furthermore, the study seeks to ascertain the feasibility and safety of olfactory evoked potential. This study lays the groundwork for safeguarding olfactory function during surgical procedures.

METHODS

We provided a detailed description of the procedure involving electrical stimulation of the olfactory mucosa to induce olfactory evoked potentials during endonasal endoscopic surgery under general anesthesia. This study enrolled 20 patients undergoing endonasal endoscopic surgery. Before surgery, all patients reported no olfactory complaints, and T&T olfactometry did not detect any olfactory disorders. Olfactory evoked potentials were recorded from various regions of the nasal mucosa and followed by analysis of waveform differentiation, latencies, and amplitudes.

RESULTS

Typical "N1-P1-N2" three-phase waves, consistent with the waveforms of olfactory evoked potentials recorded in previous studies, were collected from the olfactory mucosa in each case. No significant alteration was observed in the patients' olfactory function pre- and postsurgery. The latencies of the "N1-P1-N2" waves recorded during the operation were 12.2 ± 6.9 ms, 28.9 ± 10.0 ms, and 47.1 ± 11.6 ms, respectively, whereas the amplitudes of the "N1-P1" and "P1-N2" waves measured 0.9 and 0.6 μV, respectively.

CONCLUSIONS

Intraoperative olfactory monitoring through olfactory evoked potential produced by electrical stimulation is achievable and safe.

Effect of total intravenous anesthesia versus sevoflurane anesthesia on intraoperative facial nerve monitoring: a randomized controlled trial

PURPOSE

Intraoperative facial nerve monitoring (IFNM) facilitates effective nerve preservation during ear and head and neck surgeries. Quantitative differences in the timely feasibility of IFNM during total intravenous anesthesia (TIVA) vs sevoflurane anesthesia have not been investigated.

METHODS

We conducted a randomized controlled trial in which 98 patients undergoing ear surgery were allocated to either the TIVA or sevoflurane group. We used quantitative neuromuscular monitoring of train-of-four (TOF) responses to assess achievements of IFNM-feasible conditions, and recorded the TOF count (TOFC) or TOF ratio of T4/T1 (TOFR). The primary outcome was the time interval between a TOFR of 0.25 and 0.75 (recovery index). The most important secondary outcome was the time to reach a TOFR of 0.25. We also recorded the quality of IFNM, intubation condition, patient-ventilator dyssynchrony, surgeon's satisfaction, and postoperative analgesic and antiemetic requirements.

RESULTS

Ninety-two patients completed the study. The median [interquartile range] recovery index was significantly shorter in the TIVA group (9 [7-11] min) than in the sevoflurane group (34 [24-53] min), with a difference in medians of 25 min (95% confidence interval, 20 to 31; P < 0.001). Before IFNM requests, the time to TOFR of 0.25 was achieved earlier in the TIVA group (34 [29-41] min) than in the sevoflurane group (51 [43-77] min) (P < 0.001). Both groups achieved neuromuscular recovery in time for IFNM without a need for reversal agents.

CONCLUSIONS

Intraoperative facial nerve monitoring was feasible earlier and faster under TIVA than under sevoflurane anesthesia. We suggest that TIVA may be a preferable choice over sevoflurane to meet a surgeon's request for an earlier IFNM.

STUDY REGISTRATION

CRIS.nih.go.kr ( KCT0006676 ); first submitted 7 October 2021.

A full-head model to investigate intra and extracochlear electric fields in cochlear implant stimulation

Objective.Despite the widespread use and technical improvement of cochlear implant (CI) devices over past decades, further research into the bioelectric bases of CI stimulation is still needed. Various stimulation modes implemented by different CI manufacturers coexist, but their true clinical benefit remains unclear, probably due to the high inter-subject variability reported, which makes the prediction of CI outcomes and the optimal fitting of stimulation parameters challenging. A highly detailed full-head model that includes a cochlea and an electrode array is developed in this study to emulate intracochlear voltages and extracochlear current pathways through the head in CI stimulation.Approach.Simulations based on the finite element method were conducted under monopolar, bipolar, tripolar (TP), and partial TP modes, as well as for apical, medial, and basal electrodes. Variables simulated included: intracochlear voltages, electric field (EF) decay, electric potentials at the scalp and extracochlear currents through the head. To better understand CI side effects such as facial nerve stimulation, caused by spurious current leakage out from the cochlea, special emphasis is given to the analysis of the EF over the facial nerve.Main results.The model reasonably predicts EF magnitudes and trends previously reported in CI users. New relevant extracochlear current pathways through the head and brain tissues have been identified. Simulated results also show differences in the magnitude and distribution of the EF through different segments of the facial nerve upon different stimulation modes and electrodes, dependent on nerve and bone tissue conductivities.Significance.Full-head models prove useful tools to model intra and extracochlear EFs in CI stimulation. Our findings could prove useful in the design of future experimental studies to contrast FNS mechanisms upon stimulation of different electrodes and CI modes. The full-head model developed is freely available for the CI community for further research and use.