Cerebral circulation and ischemia: How to monitor it during surgery?

Cerebral circulation and ischemia: How to monitor it during surgery?The anesthesiologists from both the United States and China had an open and engaging discussion on intraoperative monitoring of cerebral perfusion and ischemia at the social media -WeChat International Chinese Academy of Anesthesiology (ICAA, www.icaahq.org) group.This discussion is presented here to showcase the role the modern social media plays in enhancing the academic exchange and learning experience on the international stage.Some minor edits were performed for clarity purposes.Kun Liu (University of Sounth China): I have a question and would like to have your opinion.Is anesthesia depth monitoring clinically meaningful in patients undergoing neurological surgeries such as traumatic brain injury, intracranial hemorrhage, brain tumor, etc.?Lingzhong Meng (University of California San Francisco, USA): Dr. Liu, whether deep anesthesia such as burst-suppression is neuroprotective is still unclear.We routinely use Electroencephalography (EEG) monitoring during aneurysm clipping.The surgeon normally request burst suppression.For brain tumor cases, we do not normally monitor bispectral index (BIS), etc.However, the surgeon may perform cortical and subcortical mapping if the tumor is adjacent to eloquent brain in order to maximize the extent of resection.For brain trauma, I personally do not think anesthesia depth monitoring is useful.What matters in traumatic injury cases is to decrease intracranial pressure (ICP) and maintain cerebral perfusion and oxygenation. Yongqing Guo (ShanxiProvincial Hospital, China): Dr. Meng, what types of anesthesia monitoring are used during neurosurgical procedures in the United States?Lingzhong Meng: Dr. Guo, how to monitor neurosurgical patients is institution and surgeon dependent.Now, as anesthesiologists, we would like to monitor intravascular volume status, tissue perfusion, etc.This is important because mannitol that is almost routinely given to patients causes large urine output and volume depletion as a consequence.Also, hyperventilation if adopted can causes vasoconstric-tion, especially the brain, i.e., cerebral vasoconstriction.Wenqi Huang (Sun Yat-Sun University, China): I have a different school of thought.EEG monitoring is very valuable in anesthetized patients.The target of general anesthesia is the brain.The electrophysiological activity of the brain is what the anesthesiologists can rely on, especially when the clinical picture is confusing.The patient complains dizziness when the blood pressure is decreased by epidural or spinal anesthesia.The awake elderly patient will complain dizziness and sickness if the systolic blood pressure is less than 100 mmHg.The patient who is under general anesthesia is unable to tell his/her feeling.The individualized index of cerebral perfusion is the percentage of the Delta wave on EEG tracing that can tell when the blood pressure cannot be further lowered.Cerebral perfusion pressure (CPP) equals mean arterial pressure minus ICP.CPP needs to be maintained above 70 mmHg.It cannot be less than 55 mmHg in patients with traumatic brain injury.Therefore, we should be able to tell how the mean arterial pressure should be maintained under various scenarios.As anesthesiologists, we did not pay the needed attention to hypotension.Therefore, I recommend EEG monitoring for blood pressure care.