Ultrasound-based non invasive intracranial pressure

Intracranial pressure (ICP) is an important monitoring modality in the clinical management of several neurological diseases carrying the intrinsic risk of potentially lethal intracranial hypertension (ICH). Considering that the brain is in an enclosed compartment, ICH leads to brain hypoperfusion and eventually ischaemia followed by irreversible neuronal damage. Traumatic brain injury (TBI), for instance, is a condition in which ICH is strongly associated with unfavourable outcome and death. Although ICP can guide patient management in neurocritical care settings, this parameter is not commonly monitored in many clinical conditions outside this environment. The invasive character of the standard methods for ICP assessment and their associated risks to the patient (like infections, brain tissue lesions, haemorrhage) contribute to this scenario. Such risks have prevented ICP assessment in a broad range of diseases like in patients with risk of coagulopathy, as well as in other conditions in which invasive assessment is not considered or outweighed by the risks of the procedure. Provided that knowledge of ICP can be crucial for the successful management of patients in many sub-critical conditions, non-invasive estimation of ICP (nICP) may be helpful when indications for invasive ICP assessment are not met and when it is not immediately available or even contraindicated. Several methods for non-invasive assessment of ICP (nICP) have been described so far. Transcranial Doppler (TCD), for instance, is primarily a technique for diagnosing various intracranial vascular disorders such as emboli, stenosis, or vasospasm, but has been broadly utilised for non-invasive ICP monitoring due to its ability to detect changes in cerebral blood flow velocity derived from ICP variations. Moreover, TCD allows monitoring of these parameters as they may change in time. Optic nerve sheath diameter ultrasonography (ONSD) is another non-invasive tool which gained interest in the last years. The optic nerve sheath is in continuous with the subarachnoid space, and when ICP increased, the diameter of ONSD enlarges proportionally to ICP. The focus of this thesis is on the assessment, applications and development of ultrasoundbased for nICP assessment in different clinical conditions where this parameter is relevant but in many circumstances not considered, including TBI and other neurological diseases ULTRASOUND BASED NON-INVASIVE INTRACRANIAL PRESSURE 17 associated with impairment of cerebral blood flow circulation. As main results, ONSD and TCD-based non-invasive methods could replicate changes in direct ICP across time confidently, and could provide reasonable accuracy in comparison to the standard invasive techniques. These findings support the use of ultrasound based non-invasive ICP methods in a variety of clinical conditions requiring management of intracranial pressure and brain perfusion. More importantly, the low costs associated with nICP methods, ultrasound machines are widely available medical devices, could contribute to its widespread use as a reliable alternative for ICP monitoring in everyday clinical practice.