Background: Cerebral autoregulation is important to maintain a constant perfusion in the face of changes in blood pressure. It is reported to be impaired in pathologic states, including hypertension, cerebral infarction, and head injury. However, it is not clear whether cerebral autoregulation is impaired in resuscitated patients after cardiac arrest.
Methods: Cerebral autoregulation in comatose patients after cardiac arrest was assessed by using an indirect method of cerebral blood flow (CBF). Eight patients who had cardiac arrest outside of the hospital and were successfully resuscitated in the emergency room were included in this study. A catheter was inserted percutaneously into the right internal jugular vein and positioned so that the tip was in the jugular bulb. Mean arterial pressure (MAP) was changed to a value of 30% lower or higher than baseline MAP by infusing trimethaphan or methoxamine, respectively. At each MAP level, arterial and jugular bulb venous blood gases were measured, and arterial-jugular bulb venous oxygen content difference (AVDO2) was calculated.
Results: The 1/AVDO2 (CBFI) and oxygen saturation of jugular bulb venous blood (SjvO2) significantly decreased at the lower MAP level, and significantly increased at the higher MAP level. The ratio of the CBFI at the lower MAP level to the CBFI at baseline (CBFI-L/CBFI-B) inversely correlated with the SjvO2 at baseline.
Conclusions: Assuming that the cerebral metabolic rate of oxygen does not change during the interventions in MAP, the changes of CBFI and SjvO2 seen after the decrease or increase in MAP indicate that cerebral autoregulation was impaired in these resuscitated patients. The degree of the impairment of cerebral autoregulation may be secondary to the degree of brain injury caused by the cerebral ischemia accompanying cardiac arrest.