Arterial and venous contributions to near-infrared cerebral oximetry.
BACKGROUND
Cerebral oximetry is a noninvasive bedside technology using near-infrared light to monitor cerebral oxygen saturation (Sco2) in an uncertain mixture of arteries, capillaries, and veins. The present study used frequency domain near-infrared spectroscopy to determine the ratio of arterial and venous blood monitored by cerebral oximetry during normoxia, hypoxia, and hypocapnia.


METHODS
Twenty anesthetized children aged < 8 yr with congenital heart disease of varying arterial oxygen saturation (Sao2) were studied during cardiac catheterization. Sco2, Sao2, and jugular bulb oxygen saturation (Sjo2) were measured by frequency domain near-infrared spectroscopy and blood oximetry at normocapnia room air, normocapnia 100% inspired O2, and hypocapnia room air.


RESULTS
Among subject conditions, Sao2 ranged from 68% to 100%, Sjo2 from 27% to 96%, and Sco2 from 29% to 92%. Sco2 was significantly related to Sao2 (y = 0. 85 x -17, r = 0.47), Sjo2 (y = 0.77 x +13, r = 0.70), and the combination (Sco2 = 0.46 Sao2 + 0.56 Sjo2 - 17, R = 0.71). The arterial and venous contribution to cerebral oximetry was 16 +/- 21% and 84 +/- 21%, respectively (where Sco2 = alpha Sao2 + beta Sjo2 with alpha and beta being arterial and venous contributions). The contribution was similar among conditions but differed significantly among subjects (range, approximately 40:60 to approximately 0:100, arterial:venous).


CONCLUSIONS
Cerebral oximetry monitors an arterial/venous ratio of 16:84, similar in normoxia, hypoxia, and hypocapnia. Because of biologic variation in cerebral arterial/venous ratios, use of a fixed ratio is not a good method to validate the technology.
Watzman
H M
HM
Brain Research Laboratory, Departments of Anesthesiology and Critical Care Medicine, The Children's Hospital of Philadelphia, Philadelphia, Pennsylvania, USA.
Kurth
C D
CD
Montenegro
L M
LM
Rome
J
J
Steven
J M
JM
Nicolson
S C
SC
D001921:Brain / Q000098:blood supply*; D002245:Carbon Dioxide / Q000097:blood; D006328:Cardiac Catheterization; D002536:Cerebral Arteries; D002550:Cerebral Veins; D002560:Cerebrovascular Circulation; D002648:Child; D002675:Child, Preschool; D005260:Female; D006330:Heart Defects, Congenital / Q000097:blood; D006801:Humans; D016857:Hypocapnia / Q000097:blood; D000860:Hypoxia / Q000097:blood; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D008991:Monitoring, Physiologic / Q000379:methods; D010092:Oximetry / Q000379:methods*; D010100:Oxygen / Q000097:blood*; D019265:Spectroscopy, Near-Infrared / Q000379:methods*
D002245:Carbon Dioxide; D010100:Oxygen