Middle cerebral artery flow, the critical closing pressure, and the optimal mean arterial pressure in comatose cardiac arrest survivors-An observational study.

AIM: This study estimated the critical closing pressure (CrCP) of the cerebrovascular circulation during the post-cardiac arrest syndrome and determined if CrCP differs between survivors and non-survivors. We also compared patients after cardiac arrest to normal controls.
METHODS: A prospective observational study was performed at the ICU of a tertiary university hospital in Nijmegen, the Netherlands. We studied 11 comatose patients successfully resuscitated from a cardiac arrest and treated with mild therapeutic hypothermia and 10 normal control subjects. Mean flow velocity (MFV) in the middle cerebral artery was measured by transcranial Doppler at several time points after admission to the ICU. CrCP was determined by a cerebrovascular impedance model.
RESULTS: MFV was similar in survivors and non-survivors upon admission to the ICU, but increased stronger in non-survivors compared to survivors throughout the observation period (P<0.001). MFV was significantly lower in survivors immediately after cardiac arrest compared to normal controls (P<0.001), with a gradual restoration toward normal values. CrCP decreased significantly from 61.4[51.0-77.1]mmHg to 41.7[39.9-51.0]mmHg in the first 48h, after which it remained stable (P<0.001). CrCP was significantly higher in survivors compared to non-survivors (P=0.002). CrCP immediately after cardiac arrest was significantly higher compared to the control group (P=0.02).
CONCLUSIONS: CrCP is high after cardiac arrest with high cerebrovascular resistance and low MFV. This suggests that cerebral perfusion pressure should be maintained at a sufficient high level to avoid secondary brain injury. Failure to normalize the cerebrovascular profile may be a parameter of poor outcome.