Determinants of cerebral fractional oxygen extraction using near infrared spectroscopy in preterm neonates

Cerebral fractional oxygen extraction (FOE) represents the balance between cerebral oxygen delivery and consumption. This study aimed to determine cer ebral FOE in preterm infants during hypotension, during moderate anemia, an d with changes in the Paco(2). Three groups of neonates were studied: stabl e control neonates (n = 43), anemic neonates (n = 46), and hypotensive neon ates (n = 19). Cerebral FOE was calculated from the arterial oxygen saturat ion measured by pulse oximetry, and cerebral venous oxygen saturation was m easured using near infrared spectroscopy with partial jugular venous occlus ion. Mean +/- SD cerebral FOE was similar in control (0.292 +/- 0.06), anem ic (0.310 +/- 0.08; P = 0.26). and hypotensive (0.278 +/- 0.06; P = 0.41) n eonates. After anemic neonates were transfused, mean +/- SD cerebral FOE de creased to 0.274 +/- 0.05 (P = 0.02), There was a weak negative correlation with the hemoglobin concentration (n = 89, r = -0.24, P = 0.04) but not wi th the hemoglobin F fraction (n = 56. r = 0.24, P = 0.09). In the hypotensi ve neonates, there was no relationship between cerebral FOE and blood press ure (n = 19, r = 0.34, P = 0.15). There was a significant negative correlat ion between cerebral FOE and Paco(2) within individuals (n = 14, r = -0.63, P = 0.01), but there was no relationship between individuals (n = 14, r = 0, P = 1). Cerebral FOE was not significantly altered in neonates with eith er mild anemia or hypotension. There were, however, changes in cerebral FOE when physiological changes occurred over a relatively short period: Cerebr al FOE decreased after blood transfusion and increased with decreasing Paco (2). AS no change in cerebral FOE was seen during hypotension, it was specu lated that cerebral oxygen delivery may have been maintained by cerebral bl ood now autoregulation.