Estimation of jugular venous O2 saturation from cerebral oximetry or arterial O2 saturation during isocapnic hypoxia

Objective.Near-infrared spectroscopy (NIRS) has the potential forproviding valuable information about oxygen delivery to the brain. However,questions have been raised about the accuracy of these measurements. Thisstudy was undertaken to compare noninvasive cerebral saturation measurementsto jugular venous saturation under conditions of hypoxia and hypercapnia.Methods.Data was obtain on forty-two subjects. Cerebral oxygenationwas measured with a Somanetics INVOS 4100-SSA placed on the forehead of thesubjects. PETCO₂ was controlled to approximately 2 and 7 mmHg aboveresting values and PETO₂ was controlled to 80, 45, 60 and 41 mmHgconsecutively for four of five minutes each. Internal jugular blood gasmeasurements were made via a retrograde catheter. Results.Both thecerebral oximetry measured saturation (rSO₂) and the jugular venoussaturation (Sj O₂) were significantly increasedby increasing the PETCO₂ at all levels of hypoxia. The increase inthe rSO₂ was less than the increase inSj O₂. The rSO₂ had a bias of 5.2%and a precision of 10.7% compared to the measuredSj O₂. Discussion.Cerebral oxygensaturation measured by cerebral oximetry compares well to the measuredSj O₂ in normal subjects, despite multiplephysiological reasons for differences. The closer relationship ofSj O₂ to rSO₂ than SaO₂under the conditions of these experiments indicates that the measurementreflects primarily intracranial saturation. However, outcome studies underclinical conditions are needed to determine the clinical utility of cerebraloximetry. This revised version was published online in July 2006 with corrections to the Cover Date.