Janaillac M, et al. - The relationships between cerebral regional tissue oxygen saturation (CrSO₂), perfusion index (PI), echocardiographic, and clinical parameters in extremely preterm infants in their first 72 h of life were determined. The cardiac output markedly increased over the 72 h of the study period. A strong inter-connection existed between CrSO₂ and preductal PI with cardiac output during low cardiac output states.