Update of cerebral oximetry in critically ill patients

Study objectives: Invasive and time-consuming methods of evaluating cerebral functioning, including jugular bulb venous saturation and electroencephalograms (EEG), have been used in non–emergency department (ED) settings to monitor cerebral function and predict the neurologic outcome of patients. Real-time regional cerebral oximetry compares favorably to invasive methods in predicting neurologic outcomes in certain patient groups and actually detects oximetric changes faster than EEG or jugular bulb saturation. Cerebral oximetry, using near-infrared spectroscopy, is able to provide a continuous, noninvasive method to monitor cerebral oxygen supply and demand. The technology is approved by the US Food and Drug Administration for use in coronary bypass grafting and carotid endarterectomies, during which it correlated well with short-term neurologic outcome. There is no practical means to monitor brain function in critically ill ED patients, which almost certainly affects their overall neurologic outcome. Cerebral oximetry used in critically ill ED patients may be predictive of neurologic outcome at hospital discharge and adequacy of resuscitation. Methods: We performed a prospective observational study on a convenience sample of critically ill patients presenting to the EDs of 2 teaching institutions. Patients were enrolled if they presented with an acute alteration of their mental status or were critically ill as defined by a need for emergency resuscitation or intubation. Patients were excluded if they were younger than 18 years, had severe trauma that precluded placement of the cerebral oximetry, or presented with do-not-resuscitate papers. The cerebral oximeter was attached to the patient only during their stay in the ED. Initial and final regional cerebral oxygenation (rSO2) saturation values, patient demographics, vital signs, and laboratory results were recorded. Neurologic outcome was defined by the Glasgow Outcome Scale (GOS) score at hospital discharge. The GOS consists of 5 categories: dead, vegetative, severe disability, mild to moderate disability, and return to baseline. For statistical analysis, neurologic outcome was converted from an ordinal (1 through 5) to a dichotomous variable (good 4 to 5/poor 1 to 3). Data analysis was performed using descriptive statistics. This study was reviewed and approved by our institutional review board. Results: A total of 71 patients have been enrolled to date, representing the largest cohort of patients evaluated by cerebral oximetry in an ED setting. Neurologic outcomes were available for 65 (91.5%) of the enrolled patients. Normal rSO2 values based on previous literature are between 47% and 83%; therefore, patientsʹ rSO2 values were also divided into 2 groups (ie, those with normal and abnormal rSO2values). Sixty-four percent of enrolled patients had a poor outcome. The positive predictive value (PPV) of an abnormal rSO2at either the initial or final recording and a poor neurologic outcome was 78.8%, whereas the negative predictive value (NPV) of an abnormal rSO2 on either recording was 38% for a good outcome. The PPV and NPV of an abnormal final rSO2level to predict poor neurologic outcome were 90.0% and 51.1%, respectively. Sixteen patients had abnormal initial and final rSO2values; 15 of these patients (93.8% [15/16]) had a poor neurologic outcome. Finally, 13 patients with abnormal initial and final rSO2values and who had recorded parameters of resuscitation (ie, base deficits) had abnormal base deficits or an abnormal anion gap acidosis. Conclusion: Abnormal cerebral oximetry is a good predictor of poor neurologic outcome.