Letters to the Editor: Letters & Announcements
We thank Dr. Nordström for his concern about two important issues. First, he questions whether trial manipulations of arterial blood pressure can be helpful in determining optimal perfusion pressure after head injury. In our study we varied arterial pressure across a wide range and measured intracranial pressure, autoregulation capacity, and brain tissue oxygenation. We found that the combined responses of these variables could be interpreted in a consistent way using autoregulation theory. Thus, from these observations we inferred whether cerebral perfusion pressure was within autoregulation limits or whether it was at or below the lower autoregulation threshold. We did not explore the upper threshold. Although we agree that sustained blood pressure interventions are necessary to determine the long-term effects on intracranial pressure, the concern that increased perfusion pressure will aggravate intracranial hypertension may only be warranted if both the blood-brain barrier is disrupted and arteriolar vasomotor responses are abolished after injury. The latter was not observed in our study.
Second, Dr. Nordström suggests the use of microdialysis techniques at the bedside. This is a promising research tool, but it may not be as readily available in a clinical setting as the monitors we used. However, we encourage researchers to study the cerebral physiological responses to induced (not spontaneous) variations in arterial pressure at regular time intervals after head injury using multiple available tools.
O. L. Cremer, MD
Department of Anesthesiology
University Medical Center
Utrecht, The Netherlands.