Poor Regional Cerebral Oxygenation During Critical Illness May Be Associated With Acute and Chronic Neurological Dysfunction
Survivors of critical illness frequently exhibit acute (i.e., delirium) and chronic neurological complications. Intensive care unit prevalence of delirium is as high as 80% and has been associated with increased length of hospital stay, mortality, and long-term cognitive impairment. However, the underlying etiology of delirium, and long-term dysfunction, remains unknown but may be associated with cerebral ischemia. A key element of resuscitation during critical illness is guided at assessing proxies of perfusion to maintain adequate oxygen delivery (e.g., renal perfusion is assessed by measuring urine output and serum creatinine). However, there is currently no well-defined surrogate of cerebral perfusion used in routine clinical practice. Near-infrared spectroscopy (NIRS) is a non-invasive technique to quantify regional cerebral oxygenation (rSO2) that has been used for decades in the cardiac operating theatre and resulted in targeted algorithms to optimize rSO2. However, these algorithms do not exist during critical illness. The primary objective of this thesis was to assess if low levels of rSO2 are associated with delirium. The subsequent chapters herein will demonstrate the feasibility of using NIRS to monitor rSO2 (e.g., did not interfere with patient care), which provided the infrastructure to conduct the CONFOCAL pilot that identified low rSO2 as an independent predictor of delirium. Additionally, the physiologic determinants of the rSO2 signal were assessed. This regression analysis accounted for a significant proportion of variance in the rSO2 signal (R2=.54), which was associated with age, partial pressure of carbon dioxide, hemoglobin, and heart rate. At 3- and 12-months, participants were primarily impaired in visuospatial/executive function, immediate, and delayed memory. Therefore, these findings support the hypothesis that low rSO2 is associated with delirium and suggest that optimizing rSO2 may offer promising avenues for future critical care practices to prevent delirium. However, the determinants of long-term impairment will need to be assessed.