Cerebral blood flow, vascular resistance, and oxygen metabolism in acute brain trauma: redefining the role of cerebral perfusion pressure?

OBJECTIVES: To evaluate normal or high cerebral perfusion pressure in relation to cerebral blood flow and oxygen metabolism, as well as other multivariate cerebral hemodynamic and metabolic interrelationships, in acute brain trauma in humans.
DESIGN: Prospective, observational study.
SETTING: Neuroscience intensive care unit of a university hospital. PATIENTS: Adults (n = 66) with severe acute brain trauma (Glasgow Coma Scale scores from 4 to 8), undergoing multivariate physiologic studies involving cerebral perfusion pressure, cerebral blood flow, cerebral metabolic rate of oxygen consumption, total hemoglobin content, arterio-jugular oxygen content difference, and cerebral vascular resistance, along with other routine procedures.
INTERVENTIONS: None.
MEASUREMENTS AND MAIN RESULTS: Statistical analysis did not demonstrate any correlation between cerebral perfusion pressure and cerebral blood flow, between cerebral perfusion pressure and arterio-jugular oxygen content difference, and between cerebral perfusion pressure and cerebral metabolic rate of oxygen consumption, over a broad spectrum of perfusion pressures ranging from 60 to 130 mm Hg. In contrast, a significant negative correlation was found between cerebral vascular resistance and cerebral blood flow, where higher values of cerebral vascular resistance were associated with lower blood flow levels, and vice versa.
CONCLUSIONS: In severe acute brain trauma, cerebral hemodynamic and oxygen metabolic variables are not necessarily correlated with normal or even high levels of cerebral perfusion pressure. Under these circumstances, cerebral vascular resistance (not perfusion pressure) is more closely correlated with different patterns of cerebral blood flow and metabolism.