Brain BOLD MRI O2 and CO2 stress testing: implications for perioperative neurocognitive disorder following surgery

Background Mechanical ventilation to alter and improve respiratory gases is a fundamental feature of critical care and intraoperative anesthesia management. The range of inspired O.sub.2 and expired CO.sub.2 during patient management can significantly deviate from values in the healthy awake state. It has long been appreciated that hyperoxia can have deleterious effects on organs, especially the lung and retina. Recent work shows intraoperative end-tidal (ET) CO.sub.2 management influences the incidence of perioperative neurocognitive disorder (POND). The interaction of O.sub.2 and CO.sub.2 on cerebral blood flow (CBF) and oxygenation with alterations common in the critical care and operating room environments has not been well studied. Methods We examine the effects of controlled alterations in both ET O.sub.2 and CO.sub.2 on cerebral blood flow (CBF) in awake adults using blood oxygenation level-dependent (BOLD) and pseudo-continuous arterial spin labeling (pCASL) MRI. Twelve healthy adults had BOLD and CBF responses measured to alterations in ET CO.sub.2 and O.sub.2 in various combinations commonly observed during anesthesia. Results Dynamic alterations in regional BOLD and CBF were seen in all subjects with expected and inverse brain voxel responses to both stimuli. These effects were incremental and rapid (within seconds). The most dramatic effects were seen with combined hyperoxia and hypocapnia. Inverse responses increased with age suggesting greater risk. Conclusions Human CBF responds dramatically to alterations in ET gas tensions commonly seen during anesthesia and in critical care. Such alterations may contribute to delirium following surgery and under certain circumstances in the critical care environment. Trial registration ClincialTrials.gov NCT02126215 for some components of the study. First registered April 29, 2014. Keywords: Anesthesia, CO.sub.2, O.sub.2, BOLD, MRI, Cognitive dysfunction, Critical care, Delirium, Mechanical ventilation