Cerebral oxygenation during cardiopulmonary bypass measured by near-infrared spectroscopy: effects of hemodilution, temperature, and flow.
OBJECTIVE
To determine the effects of hemodilution, PaCO2, PaO2, arterial pressure, and temperature on cerebral oxygenation during mild hypothermic cardiopulmonary bypass (CPB).


METHODS
Fourteen patients electively scheduled for cardiac surgery.


METHODS
Oxyhemoglobin (HbO2), deoxyhemoglobin (Hb), hemoglobin differential (Hb-diff = HbO2-Hb), and oxidized cytochrome aa3 (CtO2) were measured with near-infrared spectroscopy (NIRS) during CPB.


RESULTS
With onset of CPB, a significant decrease in HbO2 (median, -4.55 micromol/L; 25th to 75th percentile, -5.5 to -3.1; p < 0.05), Hb-diff (median, -3.88 micromol/L; 25th to 75th percentile, -4.7 to -1.9; p < 0.05), and CtO2 (median, -0.05 micromol/L; 25th to 75th percentile, -0.15 to 0; p < 0.001) occurred. The simultaneous decrease in arterial hemoglobin concentration (from 11.7 to 8.5 g/100 mL, p < 0.005) correlated significantly with changes in HbO2 (r2 = 0.71; p < 0.001), Hb-diff (r2 = 0.59; p < 0.005), and CtO2 (r2 = 0.57; p < 0.005). After 24 minutes of CPB, the largest decline in HbO2 (-5.03 micromol/L) and Hb-diff (-5.68 micromol/L) was recorded, whereas CtO2 showed no changes during cooling. During CPB, Hb and Hb-diff significantly correlated with the duration of CPB, PaO2 and PaCO2.


CONCLUSIONS
In early stages of CPB, a diminished cerebral oxygen supply was found, which may be caused by acute hemodilution. Despite an increased extraction of oxygen as demonstrated by the decrease in Hb-diff, cerebral energy balance reflected by CtO2 was maintained within a safe range during cooling. Because NIRS measures regional cerebral oxygenation, it is useful as an adjunct to global measures in the early noninvasive detection of cerebral hypoxia.
Lassnigg
A
A
Department of Cardiothoracic and Vascular Anesthesia, University Clinic of Vienna, Austria.
Hiesmayr
M
M
Keznickl
P
P
Müllner
T
T
Ehrlich
M
M
Grubhofer
G
G
D001794:Blood Pressure; D001831:Body Temperature; D002245:Carbon Dioxide / Q000097:blood; D002315:Cardiopulmonary Bypass; D013504:Cardiovascular Surgical Procedures; D002560:Cerebrovascular Circulation; D003576:Electron Transport Complex IV / Q000378:metabolism; D006438:Hemodilution; D006454:Hemoglobins / Q000032:analysis; D006801:Humans; D007036:Hypothermia, Induced; D008875:Middle Aged; D010084:Oxidation-Reduction; D010100:Oxygen / Q000097:blood*; D010108:Oxyhemoglobins / Q000032:analysis; D019265:Spectroscopy, Near-Infrared
D006454:Hemoglobins; D010108:Oxyhemoglobins; D002245:Carbon Dioxide; C100003:deoxyhemoglobin; D003576:Electron Transport Complex IV; D010100:Oxygen