BackgroundThe invasive nature of the current methods for monitoring of intracranial pressure (ICP) has prevented their use in many clinical situations. Several attempts have been made to develop methods to monitor ICP non-invasively. The aim of this study is to assess the relationship between ultrasound-based non-invasive ICP (nICP) and invasive ICP measurement in neurocritical care patients.Methods and findingsThis was a prospective, single-cohort observational study of patients admitted to a tertiary neurocritical care unit. Patients with brain injury requiring invasive ICP monitoring were considered for inclusion. nICP was assessed using optic nerve sheath diameter (ONSD), venous transcranial Doppler (vTCD) of straight sinus systolic flow velocity (FVsv), and methods derived from arterial transcranial Doppler (aTCD) on the middle cerebral artery (MCA): MCA pulsatility index (PIa) and an estimator based on diastolic flow velocity (FVd). A total of 445 ultrasound examinations from 64 patients performed from 1 January to 1 November 2016 were included. The median age of the patients was 53 years (range 37–64). Median Glasgow Coma Scale at admission was 7 (range 3–14), and median Glasgow Outcome Scale was 3 (range 1–5). The mortality rate was 20%. ONSD and FVsv demonstrated the strongest correlation with ICP (R = 0.76 for ONSD versus ICP; R = 0.72 for FVsv versus ICP), whereas PIa and the estimator based on FVd did not correlate with ICP significantly. Combining the 2 strongest nICP predictors (ONSD and FVsv) resulted in an even stronger correlation with ICP (R = 0.80). The ability to detect intracranial hypertension (ICP ≥ 20 mm Hg) was highest for ONSD (area under the curve [AUC] 0.91, 95% CI 0.88–0.95). The combination of ONSD and FVsv methods showed a statistically significant improvement of AUC values compared with the ONSD method alone (0.93, 95% CI 0.90–0.97, p = 0.01). Major limitations are the heterogeneity and small number of patients included in this study, the need for specialised training to perform and interpret the ultrasound tests, and the variability in performance among different ultrasound operators.ConclusionsOf the studied ultrasound nICP methods, ONSD is the best estimator of ICP. The novel combination of ONSD ultrasonography and vTCD of the straight sinus is a promising and easily available technique for identifying critically ill patients with intracranial hypertension.

Although intracranial pressure (ICP) is essential to guide management of patients suffering from acute brain diseases, this signal is often neglected outside the neurocritical care environment. This is mainly attributed to the intrinsic risks of the available invasive techniques, which have prevented ICP monitoring in many conditions affecting the intracranial homeostasis, from mild traumatic brain injury to liver encephalopathy. In such scenario, methods for non-invasive monitoring of ICP (nICP) could improve clinical management of these conditions. A review of the literature was performed on PUBMED using the search keywords ‘Transcranial Doppler non-invasive intracranial pressure.’ Transcranial Doppler (TCD) is a technique primarily aimed at assessing the cerebrovascular dynamics through the cerebral blood flow velocity (FV). Its applicability for nICP assessment emerged from observation that some TCD-derived parameters change during increase of ICP, such as the shape of FV pulse waveform or pulsatility index. Methods were grouped as: based on TCD pulsatility index; aimed at non-invasive estimation of cerebral perfusion pressure and model-based methods. Published studies present with different accuracies, with prediction abilities (AUCs) for detection of ICP ≥20 mmHg ranging from 0.62 to 0.92. This discrepancy could result from inconsistent assessment measures and application in different conditions, from traumatic brain injury to hydrocephalus and stroke. Most of the reports stress a potential advantage of TCD as it provides the possibility to monitor changes of ICP in time. Overall accuracy for TCD-based methods ranges around ±12 mmHg, with a great potential of tracing dynamical changes of ICP in time, particularly those of vasogenic nature.

Objectives: In patients at risk of hypoxic ischemic brain injury following cardiac arrest, we sought to (i) characterize brain oxygenation and determine the prevalence of brain hypoxia, (ii) characterize autoregulation using the pressure reactivity index (PRx) and identify the optimal mean arterial pressure (MAPOPT), and (iii) assess the relationship between MAPOPT and brain tissue oxygenation (PbtO2). Design: Prospective interventional study. Setting: Quaternary intensive care unit. Patients: Adult patients with return to spontaneous circulation (ROSC) greater than 10 minutes and a post-resuscitation Glasgow Coma Score under 9 within 72 hours of cardiac arrest. Interventions: All patients underwent multimodal neuromonitoring which included: (i) PbtO2, (ii) intracranial pressure; (iii) jugular venous continuous oximetry (SjvO2); (iv) regional saturation of oxygen (rSO2) using near-infrared spectroscopy, and (iv) PRx based determination of MAPOPT, lower and upper limit of autoregulation. We additionally collected MAP, end tidal carbon dioxide (ETCO2) and temperature. All data were captured at 300 Hz using ICM+® brain monitoring software. Measurements and Main Results: Ten patients (7 males) were included with a median age 47 (range 20-71) and ROSC 22 minutes (12-36). The median duration of monitoring was 47 hours (15-88) and median duration from cardiac arrest to inclusion was 15 hours (6-44). The mean PbtO2 was 23 mmHg (SD 8) and the mean percentage of time with a PbtO2 below 20 mmHg was 38% (6-100). The mean PRx was 0.23 (0.27) and the percentage of time with a PRx greater than 0.3 was 50% (12-91). The mean MAPOPT, lower and upper of autoregulation were 89 mmHg (11), 82mmHg (8) and 96 mmHg (9), respectively. There was marked betweenpatient variability in the relationship between MAP and indices of brain oxygenation. As the patients' actual MAP approached MAPOPT, PbtO2 increased (p<0.001). This positive relationship did not persist when the actual MAP was above MAPOPT. Conclusions: Episodes of brain hypoxia in HIBI are frequent and perfusion within proximity of MAPOPT is associated with increased PbtO2. PRx can yield MAPOPT, lower and upper limit of autoregulation in patients following cardiac arrest.