Background Intraoperative neuromonitoring (IONM) is often used during cerebral endovascular procedures.

Objective To investigate the relationship between intraoperative vascular complications and IONM signal changes, and the impact of interventions on signal resolution and postoperative outcomes.

Methods A series of 2278 cerebral endovascular procedures conducted under general anesthesia and using electroencephalography and somatosensory evoked potential monitoring were retrospectively reviewed. A subset of 763 procedures also included motor evoked potentials (MEPs). IONM alerts were categorized as either a partial attenuation or complete loss of signal. Vascular complications were subcategorized as due to rupture, emboli, instrumentation, or vasospasm. Odds ratios (ORs) for new postoperative motor deficits were calculated and diagnostic accuracy was measured using sensitivity, specificity, and likelihood ratios.

Results The overall incidence of new postoperative motor deficit was 1.2%; 20.4% in cases with an IONM alert and 0.09% in cases without an alert. Relative to procedures with no alerts, odds of a new deficit increased if there was partial signal attenuation (OR=210.9, 95% CI 44.3 to 1003.5, p<0.0001) and increased further with complete loss of signal (OR=1437.3, 95% CI 297.3 to 6948.2, p<0.0001). Relative to procedures with unresolved alerts, odds of a new deficit decreased if the alert was fully resolved (OR=0.039, 95% CI 0.005 to 0.306, p<0.002). Procedures using MEPs had slightly higher sensitivity (92.3% vs 85.7%) but slightly lower specificity (96.7% vs 98.2%).

Conclusions An IONM alert associated with an arterial complication is associated with a dramatic increase in odds of a new postoperative deficit; however, if there is resolution of the alert prior to closure, odds of a new deficit decrease significantly.