Neuromonitoring during adult cardiac surgery.

Available online at www.jbr-pub.org Open Access at PubMed Central The Journal of Biomedical Research, 2016, 30(3):171-173 Perspective Neuromonitoring during adult cardiac surgery Anna K. Kowalczyk, Bradlee J. Bachar, Hong Liu  Department of Anesthesiology and Pain Medicine, University of California Davis, Sacramento, CA 95817, USA. Introduction Cerebral oximetry The brain has been considered an index organ for global tissue perfusion because of the physiological processes aimed at flow preservation to vital organs of the body [1] .When cerebral perfusion is compromised, other organs are likely inadequately perfused as well. It would therefore be prudent to monitor cerebral perfu- sion based on the proposition that interventions aimed at its preservation will likely result in adequate tissue perfusion of the whole body and reduced complications related to ischemia of various organs. It is worth emphasizing the difference between tissue perfusion and tissue oxygen supply. It is a consensus that the normal oxygen supply/demand ratio is impor- tant to normal tissue metabolic physiology at the molec- ular level. Because oxygen demand is largely related to perfusion, it is perfusion that remains the main focus of all clinicians in the cardiac operating room [1] . Very brief periods of cerebral hypoperfusion occur fre- quently during cardiac surgery due to a multitude of fac- tors (reduced cardiac output, low pump flow, decreased perfusion pressure, etc.) but are of minute clinical sig- nificance. It is prolonged or cumulative hypoperfusion, particularly in watershed areas of the brain, undetected by standard monitors such as arterial blood pressure or pulse oximetry, that leads to brain tissue injury and adverse outcomes [2] . To date, no device has been devel- oped that can reliably, continuously and non-invasively monitor global cerebral tissue perfusion directly. A num- ber of existing monitors can indirectly assess regional cerebral perfusion and provide information useful in managing cerebral blood flow and oxygen supply. Cerebral tissue oximetry operates via measurement of hemoglobin saturation of the mixed arterial, cap- illary and venous blood in superficial frontal lobe being illuminated by near-infrared light. The number represents the ratio of the oxygenated hemoglob in to total hemoglobin, with the frequently reported range of 50-80 and bilateral (right and left) hemisphere difference of no more than 10 points. Desaturation below 50% or more than 20% below baseline, obtained in an awake, non-sedated patient breathing room air, has been used as the threshold of interven- tion in cardiac patients. Previous evidence shows that interventions aimed at maintaining cerebral sat- uration at baseline correlate with reduced neuropsy- chological complications and decreased length of hospital stay [2-4] . The benefit of the monitor is that it is non-invasive and as such poses virtually no known harm to the patient. It is portable, easy to apply and operate as well as interpret. The cost is moderate and can be jus- tified by the beneficial outcome it associates with. It is now considered by many experts in the field as a standard of monitoring during cardiac surgery [2] . Given that both hemispheres are monitored, it can differen- tiate between global and unilateral causes of hypop- erfusion, such as head position or unilateral vessel occlusion. Because the technology does not require pulsatile flow, it offers an advantage during cardio- pulmonary bypass or in patients with non-pulsatile arterial flow (e.g. patients with left ventricular assist devices). Corresponding author: Hong Liu, MD, Professor of Anesthesiology, Department of Anesthesiology and Pain Medicine,University of California Davis Health System, 4150 V Street, Sacramento, CA 95817, USA, Tel: 1-916-734-2413, email: hualiu@ucdavis.edu. Received 20 November 2015, Revised 08 December 2015, Accepted 03 February 2016, Epub 10 March 2016 CLC number: R614, Document code: B The authors reported no conflict of interests. © 2016 by the Journal of Biomedical Research. All rights reserved. doi: 10.7555/JBR.30.20150159