Misconceptions in IONM Part III: Stimulation Repetition Rate Effects on Intraoperative Somatosensory Evoked Potential Amplitude and Latency

The rate at which stimulation is applied to peripheral nerves is critical to generating high-quality intraoperative somatosensory evoked potentials (SSEPs) in a timely manner. Guidelines based on a limited study and anecdotal evidence present differing, incorrect, or incomplete stimulation rate recommendations. We examined the effect stimulating the ulnar and tibial nerves at 1.05, 2.79, 5.69, and 8.44 Hz had on cortical, subcortical, and peripheral response amplitude and latency in 10 subjects with neuromuscular blockade (NMB) and 10 without NMB in the operating room under general anesthesia. As the stimulation repetition rate increased, the amplitude of upper and lower extremity cortical responses decreased equally in both groups. The ulnar nerve N20 cortical response amplitude decreased 27.9% at 2.79 Hz, 48.8% at 5.69 Hz, and 53.8% at 8.44 Hz. The tibial nerve P37 cortical response amplitude decreased 30.3% at 2.79 Hz, 53.8% at 5.69 Hz, and 56.8% at 8.44 Hz. Neither upper or lower extremity peripheral or subcortical amplitudes nor upper and lower extremity subcortical or peripheral latencies were affected by increasing repetition rate in either group. Low SSEP stimulation repetition rates ensure the highest quality cortical responses.