Intracranial pressure and its surrogates

Abstract

Intracranial hypertension [intracranial pressure (ICP) [20 mmHg] is a life-threatening complication seen in a significant proportion of patients following severe traumatic and nontraumatic brain insults [1][2][3]. Sustained elevations in ICP generally signal secondary injury processes such as cerebral edema, hemorrhage, hydrocephalus and ischemia, and as a consequence the management of ICP has become a keystone in neurocritical care. Especially in unresponsive patients when the diagnostic yield of physical examination is limited, temporal trends in ICP can help identify critical changes in intracranial compliance and responses to therapy. Many studies indicate an independent association between the magnitude and duration of ICP elevation and unfavorable outcomes following severe brain injury [2][3][4]. The difference of ICP and mean arterial pressure, cerebral perfusion pressure (CPP), is widely used to infer relationships between systemic circulatory function and cerebral blood flow. Many interventions in brain resuscitation, such as hyperosmolar therapy, sedation, controlled ventilation, and use of vasopressor or inotropic agents, are targeted to ICP and CPP goals. Current guidelines recommend ICP monitoring in patients with severe traumatic brain injury (TBI) who are comatose after resuscitation and who either have abnormalities on cranial computed tomography (CT) scan or meet at least two of the following three criteria: age[40 years; systolic blood pressure \90 mmHg; or motor posturing [5].The gold standard for measuring ICP is via devices placed inside the brain (intraventricular and intraparenchymal monitors). These devices are resource-intensive, carry small but significant risks of infection and hemorrhage, and in the case of intraparenchymal monitors are prone to drift with accuracy declining over time. Alternative methods have been proposed that noninvasively assess ICP through the measurement of a surrogate variable: these include neuroimaging (cranial CT and brain MRI), transcranial Doppler, tympanic membrane displacement, intraocular pressure, venous ophtalmodynanometry, and changes in the optic nerve sheath diameter (ONSD). In this issue of Intensive Care Medicine, Dubourg et al.[6] present a meta-analysis of studies

Ultrasound measurements versus invasive intracranial pressure measurement method in patients with brain injury: a retrospective study

“…The results of the study were consistent with the clinical studies [5, 17] but not consistent with case report [19]. The possible justification is that in physiological parameters may affect pulsatility index [17] while intracranial pressure is independent parameter [20]. Even, intracranial pressure is a dynamic dimension that changes rapidly with time [7] and it is unclear whether or how pulsatility index would change.…”

Ultrasound measurement of optic nerve diameter and optic nerve sheath diameter in healthy Chinese adults

“…Moreover, previous studies demonstrated a good intra- and inter-observer reliability of the measurement of ONSD by ultrasonography [ 12 , 13 ]. It has been suggested as an indicator of intracranial hypertension in recent years [ 10 , 14 – 19 ]. However, there is still no unified standard threshold of enlarged ONSD to determine intracranial hypertension, which varies from 5.0 mm to 5.9 mm [ 20 ].…”

“…Although elevated ICP can be detected by computed tomography or magnetic resonance imaging, these techniques are expensive, time-consuming and requiring patient’s transportation. In recent years, measurement of optic nerve sheath diameter (ONSD) by ultrasonography has been developed and suggested as a possible indicator of intracranial hypertension [ 10 ]. The optic nerve sheath is a membrane covering the optic nerve behind the eye, and is continuous with the dura mater over the brain.…”

Association of optic nerve sheath diameter in ocular ultrasound with prognosis in patients presenting with acute stroke symptoms

“…Thus, prediction and monitoring of ICP are recommended in stroke and in cases suspicious of having intracranial hypertension 7 . Recent studies show that measurement of optic nerve sheath diameter (ONSD) (a membrane continuous with the dura mater) by ultrasound (US), is indirectly an indicator of ICP 8 …”