Cerebral vasoconstriction in comatose patients resuscitated from a cardiac arrest?

Objective: To determine the role of cerebral vasoconstriction in the delayed hypoperfusion phase in comatose patients after cardiac arrest. Design: Prospective study. Setting: Medical intensive care unit in a university hospital. Patients: 10 comatose patients (Glasgow Coma Score less than or equal to 6) successfully resuscitated from a cardiac arrest occurring outside the hospital. Measurements: We measured the pulsatility index (PI) and mean blood flow velocity (MFV) of the middle cerebral artery, the cerebral oxygen extraction ratio and jugular bulb levels of endothelin, nitrate, and cGMP during the first 24 h after cardiac arrest. Results: The PI decreased significantly from 1.86+/-1.02 to 1.05+/-0.22 (p=0.03). The MFV increased significantly from 29+/-10 to 62+/-25 cm/s (p=0.003). Cerebral oxygen extraction ratio decreased also from 0.39+/-0.13 to 0.24+/-0.11 (p=0.015). Endothelin levels were high but did not change during the study period. Nitrate levels varied widely and showed a slight but significant decrease from 37.1 mu mol/l (median; 25th-75th percentiles: 26.8-61.6) to 31.3 mu mol/l (22.1-39.6) (p=0.04). Cyclic guanosine monophosphate levels increased significantly from 2.95 nmol/l (median; 25th-75th percentiles: 2.48-5.43) to 7.5 nmol/l (6.2-14.0) (p=0.02). Conclusions: We found evidence of increased cerebrovascular resistance during the first 24 h after cardiac arrest with persistent high endothelin levels, gradually decreasing nitrate levels, and gradually increasing cGMP levels. This suggests that active cerebral vasoconstriction due to an imbalance between local vasodilators and vasoconstrictors plays a role in the delayed hypoperfusion phase.