Cerebral vasomotor reactivity testing in head injury: the link between pressure and flow.

BACKGROUND: It has been suggested that a moving correlation index between mean arterial blood pressure and intracranial pressure, called PRx, can be used to monitor and quantify cerebral vasomotor reactivity in patients with head injury. OBJECTIVES: To validate this index and study its relation with cerebral blood flow velocity and cerebral autoregulation; and to identify variables associated with impairment or preservation of cerebral vasomotor reactivity. METHODS: The PRx was validated in a prospective study of 40 head injured patients. A PRx value of less than 0.3 indicates intact cerebral vasomotor reactivity, and a value of more than 0.3, impaired reactivity. Arterial blood pressure, intracranial pressure, mean cerebral perfusion pressure, and cerebral blood flow velocity, measured bilaterally with transcranial Doppler ultrasound, were recorded. Dynamic cerebrovascular autoregulation was measured using a moving correlation coefficient between arterial blood pressure and cerebral blood flow velocity, the Mx, for each cerebral hemisphere. All variables were compared in patients with intact and impaired cerebral vasomotor reactivity. RESULTS: No correlation between arterial blood pressure or cerebral perfusion pressure and cerebral blood flow velocity was seen in 19 patients with intact cerebral vasomotor reactivity. In contrast, the correlation between these variables was significant in 21 patients with impaired cerebral vasomotor reactivity, whose cerebral autoregulation was reduced. There was no correlation with intracranial pressure, arterial blood pressure, cerebral perfusion pressure, or interhemispheric cerebral autoregulation differences, but the values for these indices were largely within normal limits. CONCLUSIONS: The PRx is valid for monitoring and quantifying cerebral vasomotor reactivity in patients with head injury. This intracranial pressure based index reflects changes in cerebral blood flow and cerebral autoregulatory capacity, suggesting a close link between blood flow and intracranial pressure in head injured patients. This explains why increases in arterial blood pressure and cerebral perfusion pressure may be useful for reducing intracranial pressure in selected head injured patients (those with intact cerebral vasomotor reactivity).

Subarachnoid hemorrhage of unknown origin and the basilar artery configuration.

It is unclear whether the configuration of the basilar artery (BA) in patients with subarachnoid hemorrhage (SAH) of unknown origin is comparable to that in normal subjects or whether there are differences which may help to identify the origin. We studied the BA configuration in 57 patients with SAH of unknown origin (10%), who were identified in a prospectively collected series of 549 SAH patients consecutively admitted to our service over a 9-year period. There were 30 patients (53%) with non-perimesencephalic SAH and 27 with perimesencephalic SAH (47%). According to a standardized algorithm we determined, on straight anteroposterior digital subtraction angiography (DSA), the width of the proximal BA segment at the origin of the anterior inferior cerebellar artery and the width of the most distal BA segment between the superior cerebellar arteries and the posterior cerebral arteries. Based on these measurements we calculated the distal-proximal BA ratios and compared them to the ratios obtained in a control group of 31 patients who had DSA for reasons other than aneurysmal SAH. The mean ratio in patients with non-perimesencephalic SAH of unknown origin was 1.150 (range: 1.080-1.230). In patients with perimesencephalic SAH of unknown origin it was 1.156 (range: 1.120-1.250). In the control group the mean ratio was 1.163 (range: 1.125-1.200). There are no variations in the configurations of the BA which could possibly explain the cause of this type of SAH or clarify the origin of hemorrhage.

Continuous monitoring of cerebrovascular autoregulation: a validation study.

BACKGROUND: Continuous monitoring of dynamic cerebral autoregulation, using a moving correlation index of cerebral perfusion pressure and mean middle cerebral artery flow velocity, may be useful in patients with severe traumatic brain injury to guide treatment, and has been shown to be of prognostic value. OBJECTIVE: To compare an index of dynamic cerebral autoregulation (Mx) with an index of static cerebral autoregulation (sRoR). METHODS: Mx was validated in a prospective comparative study against sRoR, using 83 testing sessions in 17 patients with traumatic brain injury. sRoR and Mx were calculated simultaneously during pharmacologically induced blood pressure variations. RESULTS: Mx was significantly correlated with sRoR (R = -0.78, p < 0.05). Nine patients were found to have failure of cerebral autoregulation, with an sRoR value < 50%. If an Mx value of 0.3 was used as the cut off point for failure of cerebral autoregulation, this index had 100% sensitivity and 90% specificity for demonstrating failure of autoregulation compared with the sRoR. An increase in cerebral blood flow velocity correlated significantly with Mx (R = 0.73, p < 0.05) but not with cerebral perfusion pressure (R = 0.41). CONCLUSIONS: Dynamic and static cerebral autoregulation are significantly correlated in traumatic brain injury. Cerebral autoregulation can be monitored continuously, graded, and reliably assessed using a moving correlation analysis of cerebral perfusion pressure and cerebral blood flow velocity (Mx). The Mx index can be used to monitor cerebral blood flow regulation. It is useful in traumatic brain injury because it does not require any external stimulus.