Later cooling within 6 h and temperatures outside 33-34 °C are not associated with dysfunctional autoregulation...

Cooling delays, temperature outside 33-34 °C, and blood pressure below the mean arterial blood pressure with optimal cerebral autoregulation (MAP_OPT) might diminish neuroprotection from therapeutic hypothermia in neonates with hypoxic-ischemic encephalopathy (HIE). We hypothesized that longer time to reach temperature <34 °C and having temperature outside 33-34 °C would be associated with worse autoregulation and greater brain injury.

Neonates with HIE had rectal temperature and near-infrared spectroscopy autoregulation monitoring during hypothermia (n = 63) and rewarming (n = 58). All underwent brain MRI, and a subset received diffusion tensor imaging MRI before day 10 (n = 41).

Most neonates reached <34 °C at 3-6 h of life. MAP_OPT was identified in 54/63 (86%) during hypothermia and in 53/58 (91%) during rewarming. Cooling time was not related to blood pressure deviation from MAP_OPT. Later cooling was associated with lower ADC scalar in unilateral posterior centrum semiovale but not in other regions. Temperatures >34 °C were associated with blood pressure above MAP_OPT but not with brain injury.

In neonates who were predominantly cooled after 3 h, cooling time was not associated with autoregulation or overall brain injury. Blood pressure deviation above MAP_OPT was associated with temperature >34 °C. Additional studies are needed in a more heterogeneous population.

Cooling time to reach target hypothermia temperature within 6 h of birth did not affect cerebral autoregulation measured by NIRS in neonates with hypoxic-ischemic encephalopathy (HIE). Temperature fluctuations >33-34 °C were associated with blood pressures that exceeded the range of optimal autoregulatory vasoreactivity. Cooling time within 6 h of birth and temperatures >33-34 °C were not associated with qualitative brain injury on MRI. Regional apparent diffusion coefficient scalars on diffusion tensor imaging MRI were not appreciably affected by cooling time or temperature >33-34 °C. Additional research in a larger and more heterogeneous population is needed to determine how delayed cooling and temperatures beyond the target hypothermia range affect autoregulation and brain injury.