Brain BOLD MRI O2and CO2stress testing: Implications for perioperative neurocognitive disorder following surgery

Respiratory end-tidal (ET) gas control is fundamental to anaesthetic management. The range of ET O 2 and CO 2 during the conduct of anaesthesia can significantly deviate from values in the awake state. Recent work shows ET CO 2 influences the incidence of perioperative neurocognitive disorder (POND). We examine the effects of controlled alterations in both ET O 2 and CO 2 on cerebral blood flow (CBF) in awake adults using BOLD MRI. Twelve healthy adults had BOLD and CBF responses measured to alterations in ET CO 2 and O 2 in various combinations commonly observed under anaesthesia. Dynamic alterations in regional BOLD and CBF were seen in all subjects with expected and inverse 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. Here we show that human brain CBF responds dramatically to alterations in ET respiratory gas tensions commonly seen during anaesthesia. Such alterations may impact the observed incidence of POND following surgery and intensive care, and is an important area for further investigation.