New measurements for assessment of impaired cerebral autoregulation using near-infrared spectroscopy.

Some preterm infants have poor cerebral autoregulation. The concordance between cerebral intravascular oxygenation (HbD), computed as the difference between oxygenated (HbO2) and deoxygenated (Hb) haemoglobin, and mean arterial blood pressure (MABP) reflects impaired autoregulation. As HbD is not an absolute value, we developed mathematics to prove that the cerebral tissue oxygenation (TOI), an absolute signal computed as the ratio of HbO2 to total haemoglobin (Hb+HbO2), may replace HbD. In the meantime, we attempt to theoretically predict the true level of autoregulation of a patient by defining a critical percentage of the signal recording time (CPRT). 20 preterm infants with need for intensive care were studied in the first days of life. HbD and TOI were obtained with the NIRO-300 (Hamamatsu, Japan). Invasive MABP was measured continuously. All mathematics showed a strong similarity between HbD and TOI.