A novel non-invasive nociceptive monitoring approach fit for intracerebral surgery: a retrospective analysis.

Background: Measuring depth of anesthesia during intracerebral surgery is an important task to guarantee patient safety, especially while the patient is fixated in a Mayfield-clamp. Processed electro-encephalography measurements have been established to monitor deep sedation. However, visualizing nociception has not been possible until recently and has not been evaluated for the neurosurgical setting. In this single-center, retrospective observational analysis, we routinely collected the nociceptive data via a nociception level monitor (NOL®) of 40 patients undergoing intracerebral tumor resection and aimed to determine if this monitoring technique is feasible and delivers relevant values to potentially base therapeutic decisions on. Methods: Forty patients (age 56 ± 18 years) received total intravenous anesthesia and were non-invasively connected to the NOL® via a finger clip as well as a bispectral-index monitoring (BIS®) to confirm deep sedation. The measured nociception levels were retrospectively evaluated at specific time points of nociceptive stress (intubation, Mayfield-positioning, incision, extubation) and compared to standard vital signs. Results: Nociceptive measurements were successfully performed in 35 patients. The largest increase in nociceptive stimulation occurred during intubation (NOL® 40 ± 16) followed by Mayfield positioning (NOL® 39 ± 16) and incision (NOL® 26 ± 12). Correlation with BIS measurements confirmed a sufficiently deep sedation during all analyzed time points (BIS 45 ± 13). Overall, patients showed an intraoperative NOL® score of 10 or less in 56% of total intervention time. Conclusions: Nociceptive monitoring using the NOL® system during intracerebral surgery is feasible and might yield helpful information to support therapeutic decisions. This could help to reduce hyperanalgesia, facilitating shorter emergence periods and less postoperative complications. Prospective clinical studies are needed to further examine the potential benefits of this monitoring approach in a neurosurgical context. Trial registration: German trial registry, registration number DRKS00029120.

Motoneurons of the stapedius muscle in the guinea pig middle ear: afferent and efferent transmitters.

The objective of the present study was to identify efferent and afferent transmitters of motoneurons of the stapedius muscle of the middle ear in order to gain more insight into the neuronal regulation of the muscle. To identify motoneurons, we injected the fluorescent neuronal tracer Fluorogold (FG) into the muscle after preparation of the middle ear in adult guinea pigs. Upon terminal uptake and retrograde neuronal transport, we observed FG in neurons located medial and ventral to the nucleus of the facial nerve ipsilateral to the injection site. Immunohistochemical studies of these motoneurons showed that the majority contains calcitonin gene-related peptide. Our data further demonstrate close spatial relationships of motoneurons to structures immunoreactive to either serotonin, substance P or neuronal nitric oxide and reveal that these neurons are under neuropeptidergic and nitrergic influence.