Near-infrared spectroscopy (NIRS) could be a useful continuous, non-invasive technique for monitoring the effect of partial pressure of carbon dioxide (PaCO 2 ) fluctuations in the cerebral circulation during ventilation. The aim of this study was to examine the efficacy of NIRS to detect acute changes in cerebral blood flow following PaCO 2 fluctuations after confirming the autoregulation physiology in piglets. Fourteen piglets (o72 h of life) were studied. Mean arterial blood pressure, oxygen saturation, pH, glycemia, hemoglobin, electrolytes, and temperature were monitored. Eight animals were used to evaluate brain autoregulation, assessing superior cava vein Doppler as a proxy of cerebral blood flow changing mean arterial blood pressure. Another 6 animals were used to assess hypercapnia generated by decreasing ventilatory settings and complementary CO 2 through the ventilator circuit and hypocapnia due to increasing ventilatory settings. Cerebral blood flow was determined by jugular vein blood flow by Doppler and continuously monitored with NIRS. A decrease in PaCO 2 was observed after hyperventilation (47.6±2.4 to 29.0±4.9 mmHg). An increase in PaCO 2 was observed after hypoventilation (48.5±5.5 to 90.4± 25.1 mmHg). A decrease in cerebral blood flow after hyperventilation (21.8 ± 10.4 to 15.1 ± 11.0 mL/min) and an increase after hypoventilation (23.4 ± 8.4 to 38.3 ± 10.5 mL/min) were detected by Doppler ultrasound. A significant correlation was found between cerebral oxygenation and Doppler-derived parameters of blood flow and PaCO 2 . Although cerebral NIRS monitoring is mainly used to detect changes in regional brain oxygenation, modifications in cerebral blood flow following experimental PaCO 2 changes were detected in newborn piglets when no other important variables were modified.