The relation between arterial oxygen tension and cerebral blood flow during cardiopulmonary bypass

OBJECTIVES: Neurological impairment occurs in up to 25% of infantsundergoing cardiopulmonary bypass with or without circulatory arrest.Potential causes include alterations in cerebral blood flow, hypoxia andembolisation. During cardiopulmonary bypass, arterial oxygen tension ismaintained at levels which under normal conditions cause cerebralvasoconstriction; this is a potential mechanism for ischaemia. The aim ofthis study was to explore the relation between arterial oxygen tension andcerebral blood flow during cardiopulmonary bypass. METHODS: Near infraredspectroscopy was used to explore the relation between arterial oxygentension and cerebral blood flow in 14 patients (median age 8 months; range1 month to 10 years 11 months). The relations between arterial oxygentension, arterial carbon dioxide tension, temperature, haematocrit, pumpflow rate, mean arterial pressure and cerebral blood flow, were examinedusing multivariate analysis. RESULTS: There was no relation betweencerebral blood flow and arterial oxygen tension, but a highly significantrelation was observed between cerebral blood flow and pump flow rate, withcerebral blood flow decreasing 4.2-fold per L.m-2.min-1 decrease of pumpflow rate. CONCLUSION: There was no relation between arterial oxygentension and cerebral blood flow during cardiopulmonary bypass, but low pumpflow rate may lead to reduced cerebral blood flow.