Author:
Henson Lindsey C.,Calalang Carolyn,Temp John A.,Ward Denham S.
Abstract
Background
A cerebral oximeter measures oxygen saturation of brain tissue noninvasively by near infrared spectroscopy. The accuracy of a commercially available oximeter was tested in healthy volunteers by precisely controlling end-tidal oxygen (P[ET]O2) and carbon dioxide (P[ET]CO2) tensions to alter global cerebral oxygen saturation.
Methods
In 30 healthy volunteers, dynamic end-tidal forcing was used to produce step changes in P[ET]O2 resulting in arterial saturation ranging from approximately 70% to 100% under conditions of controlled normocapnia (each person's resting P[ET]CO2) or hypercapnia (resting plus 7-10 mmHg). Blood arterial (SaO2) and jugular bulb venous (S[jv]O2) saturations during each P(ET)O2 interval were determined by co-oximetry. The cerebral oximeter reading (rSO2) and an estimated jugular venous saturation (S[jv]O2), derived from a combination of SaO2 and rSO2, were compared with the measured S(jv)O2.
Results
The S(jv)O2 was significantly higher with hypercapnia than with normocapnia for the same SaO2. The rSO2 and S(jv)O2 were both highly correlated with S(jv)O2 for individual volunteers (mean r2 = 0.91 for each relation); however, the slopes and intercepts varied widely among volunteers. In three of them, the cerebral oximeter substantially underestimated the measured S(jv)O2.
Conclusions
During isocapnic hypoxia in healthy persons, cerebral oxygenation as estimated by near infrared spectroscopy precisely tracks changes in measured S(jv)O2 within individuals, but the relation exhibits a wide range of slopes and intercepts. Therefore the clinical utility of the device is limited to situations in which tracking trends in cerebral oxygenation would be acceptable.
Publisher
Ovid Technologies (Wolters Kluwer Health)
Subject
Anesthesiology and Pain Medicine