The physiological determinants of near-infrared spectroscopy-derived regional cerebral oxygenation in critically ill adults.

Background: To maintain adequate oxygen delivery to tissue, resuscitation of critically ill patients is guided by assessing surrogate markers of perfusion. As there is no direct indicator of cerebral perfusion used in routine critical care, identifying an accurate strategy to monitor brain perfusion is paramount. Near-infrared spectroscopy (NIRS) is a non-invasive technique to quantify regional cerebral oxygenation (rSO ₂ ) that has been used for decades during cardiac surgery which has led to targeted algorithms to optimize rSO ₂ being developed. However, these targeted algorithms do not exist during critical care, as the physiological determinants of rSO ₂ during critical illness remain poorly understood.
Materials and Methods: This prospective observational study was an exploratory analysis of a nested cohort of patients within the CONFOCAL study ( NCT02344043 ) who received high-fidelity vital sign monitoring. Adult patients (≥ 18 years) admitted < 24 h to a medical/surgical intensive care unit were eligible if they had shock and/or required mechanical ventilation. Patients underwent rSO ₂ monitoring with the FORESIGHT oximeter for 24 h, vital signs were concurrently recorded, and clinically ordered arterial blood gas samples and hemoglobin concentration were also documented. Simultaneous multiple linear regression was performed using all available predictors, followed by model selection using the corrected Akaike information criterion (AICc).
Results: Our simultaneous multivariate model included age, heart rate, arterial oxygen saturation, mean arterial pressure, pH, partial pressure of oxygen, partial pressure of carbon dioxide (PaCO ₂ ), and hemoglobin concentration. This model accounted for a significant proportion of variance in rSO ₂ (R ²  = 0.58, p < 0.01) and was significantly associated with PaCO ₂ (p < 0.05) and hemoglobin concentration (p < 0.01). Our selected regression model using AICc accounted for a significant proportion of variance in rSO ₂ (R ²  = 0.54, p < 0.01) and was significantly related to age (p < 0.05), PaCO ₂ (p < 0.01), hemoglobin (p < 0.01), and heart rate (p < 0.05).
Conclusions: Known and established physiological determinants of oxygen delivery accounted for a significant proportion of the rSO ₂ signal, which provides evidence that NIRS is a viable modality to assess cerebral oxygenation in critically ill adults. Further elucidation of the determinants of rSO ₂ has the potential to develop a NIRS-guided resuscitation algorithm during critical illness.
Trial Registration: This trial is registered on clinicaltrials.gov (Identifier: NCT02344043 ), retrospectively registered January 8, 2015.