Background: Hypoxic gas ventilation therapy has recently been performed to prevent post-birth increased pulmonary blood flow in cases of congenital heart diseases with increased pulmonary blood flow. However, how the oxygen supply to the tissues changes during breathing a hypoxic gas mixture, remains unknown. The changes in cerebral oxygen saturation and blood supply during hypoxic gas ventilation therapy using a nitrogen gas mixture were studied.
Methods and results: Cerebral regional oxygen saturation (cerebral rSO(2)) was measured by near-infrared spectroscopy, and changes in middle cerebral artery (MCA) blood flow and an index of vascular resistance (RI) were assessed in 8 consecutive patients having congenital heart diseases with increased pulmonary blood flow. In all patients, urinary volume increased significantly, and the respiratory rate showed a clear decrease. Percutaneous oxygen saturation showed no significant change. The average of cerebral rSO(2) was 67.3% before hypoxic gas ventilation, but increased to 69.4%, 69.1%, and 70.7% within 1, 12, and 24 h after initiation of treatment, respectively. MCA blood flow significantly increased in the diastolic phase, and RI significantly improved from 0.80 to 0.68 within 12 h after initiation of therapy.
Conclusions: These results indicate that hypoxic gas ventilation therapy does not decrease cerebral oxygen saturation, but safely improves the cerebral blood supply in cases of congenital heart diseases with increased pulmonary blood flow.