Apparent cerebral cytochrome aa3 reduction during cardiopulmonary bypass in hypoxaemic children with congenital heart disease. A critical analysis of in vivo near-infrared spectrophotometric data.
The purpose of this analysis was critically to examine the changes of cerebral cytochrome oxidase as detected by near-infrared spectrophotometry (NIRS) during induction of cardiopulmonary bypass (CPB) in fourteen children undergoing open heart surgery. Five children were hypoxaemic (arterial oxygen saturation 49%-84%) before the switch to CPB and nine children were not. In the hypoxaemic children, the total cerebral hemoglobin concentration [tHb] decreased rapidly and markedly, reaching a plateau after 2 min. Surprisingly, cytochrome aa3 concentration in its oxygenated form [CytO2] decreased in parallel while the cerebral haemoglobin oxygenation index [HbO2]-[Hb] increased gradually. In the eight normoxaemic children, changes in the NIRS signals were insignificant. When a standard NIRS algorithm was used, the magnitude of the change in [CytO2] was closely associated with the magnitude of the change in [tHb] (p < 0.0001), the time courses of the [CytO2] and [tHb] signals were parallel in 11 of the 14 children and the error of fit in the NIRS multicomponent analysis increased 10- to 100-fold over system noise. A new NIRS algorithm, using wavelength specific optical pathlengths, did not improve the error of fit but produced smaller estimates of [CytO2] changes, which were unrelated to the [tHb] changes. In our opinion the interesting possibility of monitoring cytochrome oxidation by NIRS requires further validation.
Skov
L
L
Department of Neonatology, Rigshospitalet, Copenhagen, Denmark.
Greisen
G
G
D000465:Algorithms; D001794:Blood Pressure / Q000502:physiology; D001831:Body Temperature; D001921:Brain / Q000201:enzymology*; D002245:Carbon Dioxide / Q000097:blood; D002315:Cardiopulmonary Bypass; D002675:Child, Preschool; D003576:Electron Transport Complex IV / Q000378:metabolism*; D006330:Heart Defects, Congenital / Q000201:enzymology* / Q000601:surgery; D006400:Hematocrit; D006452:Hemoglobinometry / Q000295:instrumentation; D006801:Humans; D000860:Hypoxia / Q000201:enzymology*; D007223:Infant; D007231:Infant, Newborn; D010100:Oxygen / Q000097:blood; D013053:Spectrophotometry
D002245:Carbon Dioxide; D003576:Electron Transport Complex IV; D010100:Oxygen