CEREBRAL OXYGENATION MEASURED BY NEAR-INFRARED SPECTROSCOPY DURING CARDIOPULMONARY BYPASS AND DEEP HYPOTHERMIC CIRCULATORY ARREST IN PIGLETS

Near infrared spectroscopy (NIRS) shows large changes in cerebral oxyh emoglobin (Hbo(2)), deoxyhemoglobin (Hb), and oxidation state of cytoc hrome aa(3) (Cyto(2)) in infants undergoing cardiopulmonary bypass and deep hypothermic circulatory arrest (CPB-DHCA). To evaluate the physi ologic significance of these clinical NIRS measurements, we applied th e technique in a piglet model of CPB-DHCA. After an initial stabilizat ion period on CPB, animals (n = 8) were cooled to 15 degrees C, subjec ted to DHCA for 1 h, then reperfused with rewarming and monitored for 180 min. NIRS measurements were compared with determinations of cerebr al blood flow (CBF). During cooling, Cyto(2) decreased markedly, where as Hbo(2) increased. DHCA was associated with a sharp decrease in Hbo( 2), a corresponding increase in Hb, and smaller, less consistent furth er decrease in Cyto(2). NIRS measurements recovered toward baseline wi th reperfusion. CBF decreased during cooling and recovered to baseline levels with reperfusion. These findings are consistent with existing human data and show that 1) cooling is associated with increased oxyge nation of cerebral hemoglobin despite a reduction in CBF; 2) Cyto(2) b ecomes more reduced during cooling, consistent with a net cellular oxy gen deficit; and 3) DHCA is associated with rapid cerebral hemoglobin deoxygenation and a small further reduction of Cyto(2).