Abstract
BackgroundMechanical ventilation to alter and improve respiratory gases is a fundamental feature of critical care and intraoperative anesthesia management. The range of inspired O2 and expired CO2 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) CO2 management influences the incidence of perioperative neurocognitive disorder (POND). The interaction of O2 and CO2 on cerebral blood flow (CBF) and oxygenation with alterations common in the critical care and operating room environments has not been well studied.MethodsWe examine the effects of controlled alterations in both ET O2 and CO2 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 CO2 and O2 in various combinations commonly observed during anesthesia.ResultsDynamic 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.ConclusionsHuman 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 registrationClincialTrials.gov NCT02126215 for some components of the study. First registered April 29, 2014.
Highlights
Mechanical ventilation to alter and improve respiratory gases is a fundamental feature of critical care and intraoperative anesthesia management
We have previously hypothesized that alterations in ET CO2 common during anesthesia could contribute to perioperative neurocognitive disorder (POND) [1] in vulnerable individuals based on observed alterations in blood oxygenation level-dependent (BOLD) magnetic resonance imaging (MRI) during controlled CO2 “stress testing” [2,3,4]
In the present study, using blood oxygenation leveldependent (BOLD) and pseudo-continuous arterial spin labeling MRI, we examine the effects of controlled alterations in ET O2 and CO2 in various combinations commonly observed during anesthesia and surgery on cerebral oxygenation and cerebral blood flow (CBF) in healthy awake adults
Summary
Mechanical ventilation to alter and improve respiratory gases is a fundamental feature of critical care and intraoperative anesthesia management. The use of 100% oxygen during anesthesia induction and emergence and maintenance of anesthesia with inspired O2 concentrations of 50% are typical Periods of both hypocapnia during mechanical ventilation and hypercapnia during the reestablishment of spontaneous ventilation are common. Follow-up work confirms intraoperative hypocapnia as a marker for POND [5] These findings were recently substantiated in a study where anesthesia was stabilized with multiple closedloop controllers, with one controller limiting swings in ET CO2 thereby limiting hypocapnia during mechanical ventilation [6]. Intraoperative hyperoxia has been shown to increase the incidence of postoperative delirium in cardiac surgery patients [11] Alterations in both respiratory ET gases have been implicated in POND. The neurophysiological interactions between commonly observed combined alterations in O2 and CO2 ET gas tensions that occur during intraoperative mechanical ventilation have not been well delineated
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