Cerebral autoregulation is impaired during deep hypothermia – a porcine multimodal neuromonitoring study

Aim of the study:

Cerebrovascular autoregulation (AR) maintains stable cerebral blood flow over a wide range of cerebral perfusion pressure (CPP) levels. The effect of a decrease in core temperature on AR is unclear; however, it may play an important role during the intensive care of post cardiac arrest patients or during and after the rescue of accidental hypothermic patients. We therefore aimed to investigate the change of the dynamic AR indices during induction of deep hypothermia (HT) in a porcine model mimicking the clinical scenario of accidental hypothermia.

Methods:

Thirteen pigs were surface-cooled to a core temperature of 28 °C. High-frequency monitoring included arterial blood pressure (MAP), intracranial pressure (ICP), brain tissue oxygen tension (PbtO2), cerebral regional oxygen saturation (rSO2) and cerebral autoregulation indices (pressure reactivity index (PRx), oxygen reactivity index (ORx) and cerebral oximetry index (COx)).

Results:

Targeted temperature was reached after 160 minutes (IQR, 146 – 191 min) reflecting a rapid induction of deep HT (-4 °C/h). MAP and CPP remained stable until a core temperature of 35 °C was reached (69 ± 8 and 53 ± 7 mmHg respectively) and significantly decreased to 58 ± 17 and 40 ± 17 mmHg at 28 °C (p = 0.031 and p = 0.015, respectively). Despite the decrease observed in MAP and CPP brain oxygenation significantly increased (PbtO2 by 5 mmHg and rSO2 by 7%, p = 0.037 and p = 0.029, respectively). There was no change in ICP during HT induction. Baseline AR indices reflected normal cerebral AR in all pigs and did not change until a temperature of 34 °C (ORx), 33 °C (PRx) and 30 °C (COx) was reached. At lower temperature AR-indices significantly increased (PRx: p < 0.001, ORx: p = 0.02, COx: p = 0.03), reflecting impaired cerebral AR.

Conclusions:

Cerebrovascular AR is impaired during accidental moderate to deep hypothermia. Despite the decrease in MAP and CPP, brain oxygenation was not deranged most likely due to decreased consumption during hypothermia. Further studies are needed to define the optimal blood pressure target during deep hypothermia.