**7.5 Transcranial Doppler in systemic conditions**

*Advancement and New Understanding in Brain Injury*

**7.4 Intracranial hypertension**

diastolic phase of the cardiac cycle [66].

to improve cerebral perfusion in the presence of ICH.

the acute stage of the ischemic cerebrovascular event.

of brain blood flow in response to the treatments instituted.

measures to prevent brain infarctions; 4) to verify relative changes in the dynamics

TCD is important for assessing the effects of ICH on brain circulation. It is especially useful in patients where invasive ICP monitoring is absent because it allows the estimation of cerebral perfusion pressure (eCPP) (Section 1.1.2). In addition, changes in intracranial pressure may be associated with alterations in intracranial flow waveform. Thus, the increase in ICP can lead to PI elevation with progressive reduction of mean and diastolic blood flow velocities. In general, PI modifications occur when CPP is less than 70 mmHg2. At the moment when ICP is equal to diastolic systemic blood pressure, the blood velocity of diastolic flow reaches zero, characterizing the momentary absence of cerebral blood perfusion during the

In other situations, even with invasive ICP monitoring, TCD also plays a key role as a real-time evaluator of the efficacy of therapeutic measures used for the treatment of ICH; TCD can also be used as an alternative method to detect erroneous measurements of ICP monitors. Furthermore, TCD may reveal that increased ICP may be associated with hyperdynamic brain circulation due to impaired cerebrovascular autoregulation. In this condition, CPP formula cannot be used as a parameter

TCD also allows the evaluation of intracranial compliance by means of simultaneous compression maneuvers of the internal jugular veins and the increase of MAP. Under normal conditions, this maneuver causes a slight increase in brain blood volume and ICP augmentation. In patients with reduced intracranial compliance, venous compression would cause PI elevation and reduction of mean brain blood flow velocities [67] leptomeningeal arteries during acute arterial occlusion. Still in the acute phase, the detection of emboli by TCD in the region of the occluded artery may be indicative of recanalization of this arterial

In the subacute stage of ischemic cerebrovascular disease, TCD assesses the hemodynamic repercussion of extracranial carotid disease through CO2 reactivity tests and the presence and hemodynamic repercussion of intracranial stenosis. Embolic activity in a single intracranial arterial system may suggest an embolic source that originates from the ipsilateral carotid artery (arterial embolism) and this finding is suggestive of an increased risk of recurrence of the ischemic event when embolic activity is detected in multiple intracranial arterial systems such as bilateral carotids and vertebrobasilar, it may be suspected that the emboli have cardiac, aorta and/or paradoxical origin. With the infusion of saline solution with microbubbles (small particles of gas) in peripheral vein, TCD can detect the passage of microbubbles in brain circulation, allowing diagnosis of communication between arterial and venous circulations, such as the oval foramen persistence or pulmonary

In summary, TCD in ischemic cerebrovascular disease allows: 1) to detect intracranial arterial stenosis and occlusions; 2) to study the hemodynamic brain effects resulting from extracranial occlusive carotid diseases; 3) to evaluate the pattern and effectiveness of brain collateral circulation; 4) quantify vascular reserve by means of reactivity tests to carbon dioxide; 5) detect the passage of microemboli, in real time, through intracranial circulation; 6) to monitor the reopening of obstructed intracranial arteries, either spontaneous or consequent to thrombolytic therapy, in

**110**

segment.

fistula [68].
