Intraoperative monitoring of olfactory function: a feasibility study.

Intraoperative neuromonitoring of the chemical senses (smell and taste) has never been performed. The objective of this study was to determine if olfactory-evoked potentials could be obtained intraoperatively under general anesthesia. A standard olfactometer was used in the surgical theater with hydrogen sulfide (4 ppm, 200 msec). Olfactory-evoked potentials were recorded in 8 patients who underwent neurosurgery for resection of cerebral lesions. These patients underwent routine target-controlled propofol and sufentanil general anesthesia. Frontal, temporal, and parietal scalp subdermal electrodes were recorded ipsilaterally and contralaterally at the site of the surgery. Evoked potentials were computed if at least 70 epochs (0.5-100 Hz) satisfying the artifact rejection criterion (threshold 45 μV) could be extracted from signals of electrodes. Contributive recordings were obtained for 5 of 8 patients (3 patients had fewer than 70 epochs with an amplitude < 45 μV). Olfactory-evoked potentials showed N1 responses (mean 442.8 ± 40.0 msec), most readily observed in the patient who underwent midline anterior fossa neurosurgery. No component of later latencies could be recorded consistently. The study confirms that olfactory-evoked potentials can be measured in response to olfactory stimuli under general anesthesia. This demonstrates the feasibility of recording olfactory function intraoperatively and opens the potential for neuromonitoring of olfactory function during neurosurgery.