Background: Therapeutic hypothermia (TH) has become standard treatment for severe and moderate hypoxic-ischemic neonatal encephalopathy (HIE). Our group has developed an optically based, noninvasive concept of assessing the capacity for oxygen delivery from the microcirculation to the cells of a tissue under investigation. The hypothesis was that mechanisms of reduced oxygen delivery due to reduced metabolism in cooled asphyxiated neonates could be characterized with this concept.
Methods: The skin of 28 asphyxiated newborn infants was studied on days 1 and 3 during TH and on day 4 following rewarming with laser Doppler perfusion measurements (LDPM), computer-assisted video microscopy (CAVM), and diffuse reflectance spectroscopy (DRS). Twenty-five healthy neonates served as a control group.
Results: The LDPM decreased during cooling (P < 0.01). Functional capillary density was higher both during and following TH compared with control infants (P < 0.01). Capillary flow velocities were reduced during TH (P < 0.05). The heterogeneity of the flow velocities was larger in the HIE infants than in the control infants. Tissue oxygen extraction was higher during TH (P < 0.01).
Conclusion: This study indicates that assessments of skin microvascular density, capillary flow velocity, and oxygen extraction can be used to characterize reduced oxygen delivery to cells during TH.