Objective Stimulus rate (SR) affects auditory brainstem response (ABR) latencies; however, its segment-specific effects under standardized intraoperative total intravenous anesthesia (TIVA) remain incompletely characterized. We investigated whether SR differentially affects early and late brainstem conduction segments. Methods Intraoperative ABRs were recorded in 23 patients undergoing microvascular decompression under standardized propofol–remifentanil TIVA. SRs of 17, 29, 37, and 43 Hz were applied in a standardized sequence. Interpeak latencies (IPLs) for the I–III and III–V segments were analyzed using linear mixed-effects models to distinguish within-patient SR effects from between-patient variability. Fixed-effect slopes and 95% confidence intervals were estimated. Results Although the absolute wave V latency increased with increasing SR, the III–V interpeak interval remained unchanged. The I–III IPL showed a significant positive association with SR when SR was modeled as a continuous variable (β = 0.00521 ms/Hz, 95% CI 0.00307–0.00735, p < 0.001), corresponding to an approximately 0.052-ms prolongation per 10-Hz increase. The III–V IPL was not significantly associated with SR (β = 0.00033 ms/Hz, 95% CI −0.00201 to 0.00267, p = 0.782). Individual trajectories showed a consistent effect in the early segment, with no systematic trend in the late segment. Conclusions Under standardized TIVA conditions, SR selectively prolongs conduction time in the early brainstem segment (I–III), while showing a limited observable effect in the later segment (III–V). This rate-dependent pattern was consistent across patients over the tested SR range. Significance Recognition of segment-specific SR-dependent modulation may improve the interpretation of intraoperative ABR monitoring and support the concept of a rate-sensitive processing stage in early auditory brainstem pathways.
Objective Somatosensory evoked potentials (SSEPs) are objective neurophysiological measures of sensory pathway integrity that may serve as biomarkers of neurological recovery after spinal cord injury (SCI). This scoping review synthesized SSEP methodologies used in SCI research to identify methodological gaps, support protocol harmonization, and facilitate their integration into personalized rehabilitation. Methods MEDLINE, EBM Reviews and EMBASE were searched using terms related to SCI, peripheral nerve stimulation, and evoked potentials. Extracted data included study design, participant characteristics, stimulation and recording parameters, and primary SSEP outcomes. The review followed Joanna Briggs Institute methodology and PRISMA-ScR guidelines. Results Seventy studies published between 1964 and 2023 met the inclusion criteria. SSEPs were most commonly recorded from the contralateral somatosensory cortex, with N20 and P40 components used as primary outcomes for upper- and lower-limb stimulation, respectively. Considerable heterogeneity was observed in stimulation intensity determination, pulse width (0.1–0.5 ms), stimulation frequency (0.5–7 Hz), electrode montage, filtering, and sampling rate. Complete SCI was frequently associated with absent SSEPs, whereas incomplete injuries showed prolonged latency and/or reduced amplitude. Conclusions Despite methodological heterogeneity, SSEPs have been used to assess sensory pathway integrity and monitor recovery after SCI. Greater standardization of acquisition and reporting protocols is needed to improve comparability across studies and facilitate clinical translation. Significance This review maps how the literature has used SSEPs to assess sensory pathway integrity and monitor recovery after SCI, while highlighting the need for standardized acquisition and reporting practices to improve comparability and support future clinical research.
