What Is Therapeutic Hypothermia?
Therapeutic hypothermia has proven effectiveness in minimizing permanent brain damage after hypoxic-ischemic encephalopathy, or HIE. HIE is a type of brain injury caused by a lack of oxygenated blood flow. In infants, it can occur due to complications in late pregnancy, birth, or the neonatal period.
What Do We Already Know About Therapeutic Hypothermia?
Researchers know that administering therapeutic hypothermia very shortly after a baby has experienced hypoxic-ischemic injury (current standard of care dictates that this occur within six hours, although it may be effective up to 24 hours) can dramatically improve their prognosis. However, less is known about the exact effects of therapeutic hypothermia on different regions in the brain, or about the optimal ways of administering this treatment.
Why Are Brain Models Important?
Stephen Blowers and colleagues recently published a paper in Nature, describing their work on a new bioheat model. Blowers et al. note that although the target temperature for therapeutic hypothermia is < 36°C, “even a fraction of a degree Celsius change could be clinically relevant.”
Direct measurements of brain temperature are generally invasive, so researchers have relied on models to predict how neonates will respond to therapeutic hypothermia. A prior model, which concluded that surface cooling only reduced temperature in the outer 102 cm of brain tissue, has been criticized for being too simple. More recent models have included the vasculature, but ignored directional flow and counter-current effects associated with smaller vessels. Blowers et al. set out to build a more complex model that could better predict effects on the brain. They included a 1-D vasculature in a 3-D porous media domain, and called their method the VaPor model.
What Does the VaPor Model Tell Us About Neonatal Cooling Therapy?
Prior models suggested that core cerebral temperatures could only be cooled through full-body therapeutic hypothermia, but the VaPor model indicates that scalp cooling alone can lower core temperatures in neonates. The authors suggest that warming blankets can be used over the rest of the body, and full-body hypothermia can be avoided.
Blowers et al. emphasize that accounting for counter-current effects is very important at all scales of blood flow. There are still certain aspects of the brain’s reaction to hypothermia that this model couldn’t account for; future work may provide more details. However, the authors note that changes in temperature with increased vasculature seemed to plateau, which indicates that adding more detail might not have a major impact.
Finally, Blowers et al. explain that the VaPor model is very flexible due to its vascular nature, and alterations to the model are easy to make. Therefore, it can be applied to studies on a wide variety of topics.
Blowers, Stephen, et al. “How Does Blood Regulate Cerebral Temperatures during Hypothermia?” Scientific Reports, vol. 8, no. 1, 2018, doi:10.1038/s41598-018-26063-7.