HOW EVOKED POTENTIALS BEHAVE , WHEN BRAIN SUFFERS FROM ISCHEMIA ❓

🕶Cerebral ischemia slows neurotransmission and neuronal energy metabolism, resulting in decreased amplitude and increased latency of specific peaks. 

🕶For SSEPs, a 50% reduction in amplitude and/or a 10% increase in latency [changes in the central conduction times, namely, the interpeak latencies between the N14 and N20 peaks] of SSEP signals from the baseline are generally accepted to be a significant change 

🕶A 50% reduction on SEP amplitude has been shown to occur when cerebral blood flow decreases below 14 mL/100 g/min 

🕶MEP have less well-defined warning criteria as compared to SSEPs; however, increased stimulus thresholds and/or decreased MEP amplitudes in relation to dramatic events (i.e., clip application) are indicative of pending neurologic insult. 

🕶For BAEP, an increase in latency of more than 1 msec, particularly in wave V, is considered to be clinically significant. 

🕶Unlike EEG monitoring the evoked potential tests can detect subcortical functional status by way of perforating branches such as the anterior choroidal and medial striate arteries 

Reference: Anesthesiology Research and Practice Volume 2014, Article ID 595837, Controversies in the Anesthetic Management of Intraoperative Rupture of Intracranial Aneurysm, Tumul Chowdhury, Andrea Petropolis,Marshall Wilkinson, Bernhard Schaller  Nora Sandu and Ronald B. Cappellani