Pressure Reactivity-Based Optimal Cerebral Perfusion Pressure in a Traumatic Brain Injury Cohort.

OBJECTIVES: Retrospective data from patients with severe traumatic brain injury (TBI) indicate that deviation from the continuously calculated pressure reactivity-based "optimal" cerebral perfusion pressure (CPPopt) is associated with worse patient outcome. The objective of this study was to assess the relationship between prospectively collected CPPopt data and patient outcome after TBI. METHODS: We prospectively collected intracranial pressure (ICP) monitoring data from 231 patients with severe TBI at Addenbrooke's Hospital, UK. Uncleaned arterial blood pressure and ICP signals were recording using ICM+® software on dedicated bedside computers. CPPopt was determined using an automatic curve fitting procedure of the relationship between pressure reactivity index (PRx) and CPP using a 4-h window, as previously described. The difference between an instantaneous CPP value and its corresponding CPPopt value was denoted every minute as ΔCPPopt. A negative ΔCPPopt that was associated with impaired PRx (>+0.15) was denoted as being below the lower limit of reactivity (LLR). Glasgow Outcome Scale (GOS) score was assessed at 6 months post-ictus. RESULTS: When ΔCPPopt was plotted against PRx and stratified by GOS groupings, data belonging to patients with a more unfavourable outcome had a U-shaped curve that shifted upwards. More time spent with a ΔCPPopt value below the LLR was positively associated with mortality (area under the receiver operating characteristic curve = 0.76 [0.68-0.84]). CONCLUSIONS: In a recent cohort of patients with severe TBI, the time spent with a CPP below the CPPopt-derived LLR is related to mortality. Despite aggressive CPP- and ICP-oriented therapies, TBI patients with a fatal outcome spend a significant amount of time with a CPP below their individualised CPPopt, indicating a possible therapeutic target.

Effects of pneumoperitoneum and Trendelenburg position on intracranial pressure assessed using different non-invasive methods.

BACKGROUND: The laparoscopic approach is becoming increasingly frequent for many different surgical procedures. However, the combination of pneumoperitoneum and Trendelenburg positioning associated with this approach may increase the patient's risk for elevated intracranial pressure (ICP). Given that the gold standard for the measurement of ICP is invasive, little is known about the effect of these common procedures on ICP. METHODS: We prospectively studied 40 patients without any history of cerebral disease who were undergoing laparoscopic procedures. Three different methods were used for non-invasive estimation of ICP: ultrasonography of the optic nerve sheath diameter (ONSD); transcranial Doppler-based (TCD) pulsatility index (ICPPI); and a method based on the diastolic component of the TCD cerebral blood flow velocity (ICPFVd). The ONSD and TCD were measured immediately after induction of general anaesthesia, after pneumoperitoneum insufflation, after Trendelenburg positioning, and again at the end of the procedure. RESULTS: The ONSD, ICPFVd, and ICPPI increased significantly after the combination of pneumoperitoneum insufflation and Trendelenburg positioning. The ICPFVd showed an area under the curve of 0.80 [95% confidence interval (CI) 0.70-0.90] to distinguish the stage associated with the application of pneumoperitoneum and Trendelenburg position; ONSD and ICPPI showed an area under the curve of 0.75 (95% CI 0.65-0.86) and 0.70 (95% CI 0.58-0.81), respectively. CONCLUSIONS: The concomitance of pneumoperitoneum and the Trendelenburg position can increase ICP as estimated with non-invasive methods. In high-risk patients undergoing laparoscopic procedures, non-invasive ICP monitoring through a combination of ONSD ultrasonography and TCD-derived ICPFVd could be a valid option to assess the risk of increased ICP.

Non-invasive Monitoring of Intracranial Pressure Using Transcranial Doppler Ultrasonography: Is It Possible?

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.

Assessment of non-invasive ICP during CSF infusion test: an approach with transcranial Doppler.

BACKGROUND: This study aimed to compare four non-invasive intracranial pressure (nICP) methods in a prospective cohort of hydrocephalus patients whose cerebrospinal fluid dynamics was investigated using infusion tests involving controllable test-rise of ICP. METHOD: Cerebral blood flow velocity (FV), ICP and non-invasive arterial blood pressure (ABP) were recorded in 53 patients diagnosed for hydrocephalus. Non-invasive ICP methods were based on: (1) interaction between FV and ABP using black-box model (nICP_BB); (2) diastolic FV (nICP_FVd); (3) critical closing pressure (nICP_CrCP); (4) transcranial Doppler-derived pulsatility index (nICP_PI). Correlation between rise in ICP (∆ICP) and ∆nICP and averaged correlations for changes in time between ICP and nICP during infusion test were investigated. RESULTS: From baseline to plateau, all nICP estimators increased significantly. Correlations between ∆ICP and ∆nICP were better represented by nICP_PI and nICP_BB: 0.45 and 0.30 (p < 0.05). nICP_FVd and nICP_CrCP presented non-significant correlations: -0.17 (p = 0.21), 0.21 (p = 0.13). For changes in ICP during individual infusion test nICP_PI, nICP_BB and nICP_FVd presented similar correlations with ICP: 0.39 ± 0.40, 0.39 ± 0.43 and 0.35 ± 0.41 respectively. However, nICP_CrCP presented a weaker correlation (R = 0.29 ± 0.24). CONCLUSIONS: Out of the four methods, nICP_PI was the one with best performance for predicting changes in ∆ICP during infusion test, followed by nICP_BB. Unreliable correlations were shown by nICP_FVd and nICP_CrCP. Changes of ICP observed during the test were expressed by nICP values with only moderate correlations.

Non-extensive entropy and the extraction of BOLD spatial information in event-related functional MRI.

Functional magnetic resonance imaging (fMRI) data analysis has been carried out recently in the framework of information theory, by means of the Shannon entropy. As a natural extension, a method based on the generalized Tsallis entropy was developed to the analysis event-related (ER-fMRI), where a brief stimulus is presented, followed by a long period of rest. The new technique aims for spatial localization neuronal activity due to a specific task. This method does not require a priori hypothesis of the hemodynamic response function (HRF) shape and the linear relation between BOLD responses with the presented task. Numerical simulations were performed so as to determine the optimal values of the Tsallis q parameter and the number of levels, L. In order to avoid undesirable divergences of the Tsallis entropy, only positive q values were studied. Results from simulated data (with L = 3) indicated that, for q = 0.8, the active brain areas are detected with the highest performance. Moreover, the method was tested for an in vivo experiment and demonstrated the ability to discriminate active brain regions that selectively responded to a bilateral motor task.