Investigators aim to assess sensitivity and specificity of transcranial doppler in ruling out intracranial hypertension in all patients admitted to intensive care unit for brain injury and needing Intracranial Pressure (ICP) monitoring (according to international guidelines). Non invasive ICP measurement through the use of transcranial doppler will be carried out before and after standard invasive ICP monitoring placement.

As part of intensive treatment of brain injury, intracranial pressure (ICP) should be controlled when the cerebral perfusion pressure (CPP) falls below 60-70 millimeters of mercury (mmHg) (depending on the cause of injury) and/or the ICP is greater than 20 mmHg. Intracranial hypertension (ICHP) occurs in approximately 30-40% of all patients with severe traumatic brain injury and it is not infrequent in patients with non traumatic brain injury, such as subarachnoid hemorrhage (SAH), spontaneous intracerebral hemorrhage (SICH), and ischemic stroke (IS), and the presence of ICHP and inadequate CPP has been correlated to poor outcome. Therefore, measures to monitor ICP and CPP should be instituted as soon as possible in patients with severe brain injury. Currently, available methods for ICP monitoring include epidural, subdural, subarachnoid, parenchymal, and ventricular locations. Historically, ventricular ICP catheter has been used as the reference standard and the preferred technique when possible. It is the most accurate, and reliable method of monitoring ICP. Subarachnoid, subdural, and epidural monitors are less accurate. Unfortunately, all of the described methods are invasive, associated with a complication rate and are not inexpensive. For this reason, new methods have been developed in order to measure ICP non invasively. Transcranial Doppler (TCD) allows insonation of the basal cerebral arteries and the measurement of blood flow velocities in such vessels in by using a low-frequency-pulsed Doppler of 2 Mega Hertz (MHz) over the acoustic window regions. Many authors have analysed the doppler wave shape and the relation among diastolic, systolic and mean velocities in order to find a correlation with ICP and CPP. Few formulas have been described, in our study, the method introduced and tested by Schmidt et Al. in 2000 was adopted. Those authors observed a relationship among mean arterial blood pressure (ABP) diastolic flow velocity (FVd) and mean flow velocity (FVm) in the middle cerebral artery (MCA) that led them to find a formula able to yield CPP (estimated CPP: ABP x FVd / FVm + 14); once CPP is estimated, ICPtcd is easily calculated (ICP= ABP- CPP). The first aim of our study is to evaluate the sensitivity and specificity of ICPtcd, compared to invasive ICP measurement, in order to exclude elevated ICP in patients with acute brain injury such as epidural hematomas (EDH), subdural hematomas (SDH), subarachnoid hemorrhage (SAH), intraparenchymal hemorrhage (IPH), ischaemic strokes (IS), traumatic brain injury (TBI). Inclusion criteria are:

• acute brain injury requiring invasive ICP monitoring
• Age > 18 yrs.

Exclusion criteria are:

• inaccessible or poor acoustic ultrasound window;
• a cardiovascular disease causing hemodynamic variations affecting the TCD reading (severe arrhythmia, severe cardiac valvular stenosis, moderate or severe vasospasm);
• patients receiving craniotomy or had craniectomy before first time frame 1°,
• any treatment for intracranial hypertension or manipulation of arterial blood pressure between the non-invasive ICPtcd measurements and the invasive ICP (ICPi) measurement. (This is most likely to happen during time frame 1°).

All patients included will have evaluation of non-invasive ICP monitoring through use of TCD (ICPtcd), and at least three TCD Measurements will be performed and correlated with non-invasive ICP. The timing for the TCD measurements and correlations will be as follows:

• 1° measurement: will be performed before, and as close as possible, to ICP monitoring probe placement.
• 2° measurement. Immediately following ICP monitoring probe placement;
• 3° measurement: after ICP management optimization (2-3 hours after the second measurement).

The first brain CT will be performed before invasive ICP placement (this CT scan is normally performed for diagnostic purposes) and whenever it is appropriate to perform the second scan, either for a change in clinical status, or according to guidelines and clinical judgment. If possible from 8 - 12 hrs following the first scan.

Inclusion Criteria:

• Brain injury (All patients with brain injury, at risk of developing intracranial hypertension, requiring invasive intracranial pressure monitoring. );
• Patients requiring invasive ICP monitoring;
• Age > 18 yrs.

Exclusion Criteria:

• inaccessible ultrasound window;
• a cardiovascular disease causing hemodynamic variations affecting the TCD reading (severe arrhythmia, severe cardiac valvular stenosis, moderate or severe vasospasm),
• Patient already with craniotomy or craniectomy before first time frame 1°,
• any treatment for intracranial hypertension or manipulation of arterial blood pressure intervening between the non-invasive ICPtcd measurements and the invasive ICP (ICPi) measurement.

All patients with brain injury, at risk of developing intracranial hypertension, requiring invasive intracranial pressure monitoring.