Noninvasive measurement of intracranial pressure via the pulsatility index on transcranial Doppler sonography: Is improvement possible?

Association between Day-to-Day Pulsatility Index Change and Neurocognitive Outcomes in Pediatric Traumatic Brain Injury

Traumatic brain injury (TBI) remains a significant cause of morbidity and mortality in children despite advances in prevention and mitigation strategies. Transcranial Doppler (TCD) ultrasound measures cerebral arterial circulation and allows for the calculation of pulsatility indices (PIs), which provides an assessment of cerebral blood flow changes. Yet, the use of PIs in children with TBI is not well understood. In this study, we defined the day-to-day (DTD) PI change of the anterior cerebral circulation and describe its relationship with injury characteristics and neurocognitive outcomes in children with TBI. A prospective observational parent study of 42 children, 2 months to 15 years of age, with mild or moderate-severe TBI who had serial TCDs provided data for this analysis. Both the mean and variation of DTD PI change were evaluated in the context of injury severity, injury sidedness, and neurocognitive outcome. In those with a unilateral injury, a larger mean DTD PI change in both the injured and uninjured side was found in those with a worse Glasgow Outcome Scale-Extended Pediatrics score at discharge. A larger variation in PI was associated with a worse neurocognitive outcome, irrespective of injury severity. Therefore, the mean and variation of DTD PI change may serve as a potential cerebral vascular biomarker of ongoing secondary injury. The use of PI measurements in the monitoring of children with TBI may provide clinicians with new diagnostic and prognostic insights to inform therapeutic interventions and recovery strategies. However, a larger prospective study is needed to confirm these findings and elucidate potential mechanistic links between DTD PI and clinical outcome measures. To our knowledge, this study is the first of its kind to evaluate the use of PI changes in cerebral vasculature in pediatric TBI patients admitted to the hospital.

A Review of the Methods of Non-Invasive Assessment of Intracranial Pressure through Ocular Measurement

The monitoring of intracranial pressure (ICP) is essential for the detection and treatment of most craniocerebral diseases. Invasive methods are the most accurate approach to measure ICP; however, these methods are prone to complications and have a limited range of applications. Therefore, non-invasive ICP measurement is preferable in a range of scenarios. The current non-invasive ICP measurement methods comprise fluid dynamics, and ophthalmic, otic, electrophysiological, and other methods. This article reviews eight methods of non-invasive estimation of ICP from ocular measurements, namely optic nerve sheath diameter, flash visual evoked potentials, two-depth transorbital Doppler ultrasonography, central retinal venous pressure, optical coherence tomography, pupillometry, intraocular pressure measurement, and retinal arteriole and venule diameter ratio. We evaluated and presented the indications and main advantages and disadvantages of these methods. Although these methods cannot completely replace invasive measurement, for some specific situations and patients, non-invasive measurement of ICP still has great potential.

Evaluation of cerebral hemodynamics by transcranial Doppler ultrasonography and its correlation with intracranial pressure in an animal model of intracranial hypertension

BACKGROUND

Transcranial Doppler has been tested in the evaluation of cerebral hemodynamics as a non-invasive assessment of intracranial pressure (ICP), but there is controversy in the literature about its actual benefit and usefulness in this situation.

OBJECTIVE

To investigate cerebral blood flow assessed by Doppler technique and correlate with the variations of the ICP in the acute phase of intracranial hypertension in an animal model.

METHODS

An experimental animal model of intracranial hypertension was used. The experiment consisted of two groups of animals in which intracranial balloons were implanted and inflated with 4 mL (A) and 7 mL (B) for controlled simulation of different volumes of hematoma. The values of ICP and Doppler parameters (systolic [FVs], diastolic [FVd], and mean [FVm] cerebral blood flow velocities and pulsatility index [PI]) were collected during the entire procedure (before and during hematoma simulations and venous hypertonic saline infusion intervention). Comparisons between Doppler parameters and ICP monitoring were performed.

RESULTS

Twenty pigs were studied, 10 in group A and 10 in group B. A significant correlation between PI and ICP was obtained, especially shortly after abrupt elevation of ICP. There was no correlation between ICP and FVs, FVd or FVm separately. There was also no significant change in ICP after intravenous infusion of hypertonic saline solution.

CONCLUSIONS

These results demonstrate the potential of PI as a parameter for the evaluation of patients with suspected ICP elevation.

Surgical treatment of post-infectious hydrocephalus in infants

The management of post-infective hydrocephalus in infants remains a challenging task for the pediatric neurosurgeon. The decision-making curve is often complex in that appropriate temporizing measures need to be implemented to properly clear any infection within the CSF before any decision can be made regarding a permanent solution. The etiology differs at varying stages of neonatal development, and the weight of the child, skin fragility, and relevant surgical treatment options are often important limiting factors. Deciding on the optimal treatment option involves assessing the etiology, age, and clinical and radiological features of the individual case and selecting the most appropriate surgical option.

Diagnostic Accuracy of Longitudinal Evaluation of Central Nervous System Sonoelastography in Preterm and Term Neonates

OBJECTIVES

The objective of this study was to evaluate the brain elasticity of the central nervous system in preterm and term neonates.

METHODS

Seventy-seven healthy preterm and term neonates (mean gestational age [GA], 37.5 weeks; range, 32.6-40.5 weeks) were included in the study. Periventricular and subcortical white matter, cortical gray matter, and ventricle and subdural spaces were examined with strain elastography ratios. Each patient underwent sonography evaluation twice. The mean age at the time of sonographic evaluation was 9 days (range, 4-15 days) for the first evaluation and 37 days (range, 31-47 days) for the second evaluation. The ratios were correlated with GA, birth weight.

RESULTS

The caudate nucleus and cortical gray matter strain ratios were significantly higher than the periventricular and subcortical white matter strain ratios (P < 0.001). There was a positive relationship between GA and periventricular white matter elastographic scores on the two measurements (P = 0.022 and 0.018, respectively). The term neonates have higher strain rations compared with the preterm neonates at the first assessment (P < 0.01). At the evaluation of the area under the curve for the sonographic examination for the receiver operating characteristic curve, the periventricular white matter was 0.742 (95% confidence interval, 0.689-0.790), and it was 0.773 (95% confidence interval, 0.722-0.818) for the subcortical white matter.

CONCLUSIONS

Neonatal brain development, maturation, and myelination can be assessed by strain elastography. These findings should be evaluated with further larger cohorts that could help to prevent neonatal brain damages.

Utility of Transcranial Doppler in Moderate and Severe Traumatic Brain Injury: A Narrative Review of Cerebral Physiologic Metrics

Since its creation in the 1980s, transcranial Doppler (TCD) has provided a method of non-invasively monitoring cerebral physiology and has become an invaluable tool in neurocritical care. In this narrative review, we examine the role TCD has in the management of the moderate and severe traumatic brain injury (TBI) patient. We examine the principles of TCD and the ways in which it has been applied to gain insight into cerebral physiology following TBI, as well as explore the clinical evidence supporting these applications. Its usefulness as a tool to non-invasively determine intracranial pressure, detect post-traumatic vasospasm, predict patient outcome, and assess the state of cerebral autoregulation are all explored.

Review: pathophysiology of intracranial hypertension and noninvasive intracranial pressure monitoring

Measurement of intracranial pressure (ICP) is crucial in the management of many neurological conditions. However, due to the invasiveness, high cost, and required expertise of available ICP monitoring techniques, many patients who could benefit from ICP monitoring do not receive it. As a result, there has been a substantial effort to explore and develop novel noninvasive ICP monitoring techniques to improve the overall clinical care of patients who may be suffering from ICP disorders. This review attempts to summarize the general pathophysiology of ICP, discuss the importance and current state of ICP monitoring, and describe the many methods that have been proposed for noninvasive ICP monitoring. These noninvasive methods can be broken down into four major categories: fluid dynamic, otic, ophthalmic, and electrophysiologic. Each category is discussed in detail along with its associated techniques and their advantages, disadvantages, and reported accuracy. A particular emphasis in this review will be dedicated to methods based on the use of transcranial Doppler ultrasound. At present, it appears that the available noninvasive methods are either not sufficiently accurate, reliable, or robust enough for widespread clinical adoption or require additional independent validation. However, several methods appear promising and through additional study and clinical validation, could eventually make their way into clinical practice.

Intra-aortic balloon pump does not influence cerebral hemodynamics and neurological outcomes in high-risk cardiac patients undergoing cardiac surgery: an analysis of the IABCS trial

Background

The intra-aortic balloon pump (IABP) is often used in high-risk patients undergoing cardiac surgery to improve coronary perfusion and decrease afterload. The effects of the IABP on cerebral hemodynamics are unknown. We therefore assessed the effect of the IABP on cerebral hemodynamics and on neurological complications in patients undergoing cardiac surgery who were randomized to receive or not receive preoperative IABP in the ‘Intra-aortic Balloon Counterpulsation in Patients Undergoing Cardiac Surgery’ (IABCS) trial.

Methods

This is a prospectively planned analysis of the previously published IABCS trial. Patients undergoing elective coronary artery bypass surgery with ventricular ejection fraction ≤ 40% or EuroSCORE ≥ 6 received preoperative IABP (n = 90) or no IABP (n = 91). Cerebral blood flow velocity (CBFV) of the middle cerebral artery through transcranial Doppler and blood pressure through Finometer or intra-arterial line were recorded preoperatively (T1) and 24 h (T2) and 7 days after surgery (T3) in patients with preoperative IABP (n = 34) and without IABP (n = 33). Cerebral autoregulation was assessed by the autoregulation index that was estimated from the CBFV response to a step change in blood pressure derived by transfer function analysis. Delirium, stroke and cognitive decline 6 months after surgery were recorded.

Results

There were no differences between the IABP and control patients in the autoregulation index (T1: 5.5 ± 1.9 vs. 5.7 ± 1.7; T2: 4.0 ± 1.9 vs. 4.1 ± 1.6; T3: 5.7 ± 2.0 vs. 5.7 ± 1.6, p = 0.97) or CBFV (T1: 57.3 ± 19.4 vs. 59.3 ± 11.8; T2: 74.0 ± 21.6 vs. 74.7 ± 17.5; T3: 71.1 ± 21.3 vs. 68.1 ± 15.1 cm/s; p = 0.952) at all time points. Groups were not different regarding postoperative rates of delirium (26.5% vs. 24.2%, p = 0.83), stroke (3.0% vs. 2.9%, p = 1.00) or cognitive decline through analysis of the Mini-Mental State Examination (16.7% vs. 40.7%; p = 0.07) and Montreal Cognitive Assessment (79.16% vs. 81.5%; p = 1.00).

Conclusions

The preoperative use of the IABP in high-risk patients undergoing cardiac surgery did not affect cerebral hemodynamics and was not associated with a higher incidence of neurological complications.

Trial registrationhttp://www.clinicaltrials.gov (NCT02143544).

Use of a Doppler-Based Pulsatility Index to Evaluate Cerebral Hemodynamics in Neurocritical Patients After Hemicraniectomy

OBJECTIVES

As a noninvasive method for evaluation of cerebral hemodynamics, the correct interpretation of transcranial Doppler or transcranial imaging (TCI) data remains a major challenge. We explored how to interpret the pulsatility index (PI) derived via TCI during evaluations of cerebral hemodynamics in posthemicraniectomy patients.

METHODS

We included patients who underwent invasive arterial pressure and intracranial pressure (ICP) monitoring and simultaneous TCI examinations after hemicraniectomy. We classified the PI of the middle cerebral artery (MCA) into ipsilateral (craniectomy side) and contralateral (opposite side) and analyzed both data sets. The statistical analysis was performed by the Bland-Altman approach, by calculating intraclass correlation coefficients and Spearman correlations, and by drawing receiver operating characteristic curves. Pulsatility index probability charts were created for ICPs exceeding 20, 25, and 30 mm Hg and cerebral perfusion pressures (CPPs) lower than 70, 60, and 50 mm Hg; we thus explored defined ICP and CPP values.

RESULTS

The ipsilateral and contralateral MCA PI data differed. Only the ipsilateral MCA PI showed a weak correlation with ICP (r = 0.378; P < .001). The receiver operating characteristic curve analysis revealed limited diagnostic utility of bilateral MCA PIs for ICP and CPP assessments. An extremely elevated MCA PI indicated that patients were at high risk of a dangerous ICP elevation or CPP reduction. However, MCA PI values within the normal range did not effectively rule out an ICP of 20 mm Hg or higher but effectively eliminated a CPP lower than 50 mm Hg.

CONCLUSIONS

In posthemicraniectomy patients, the Doppler-based MCA PI value was ineffectively for quantitative ICP and CPP evaluations but a useful index for assessment of cerebral hemodynamics in terms of the probability of an ICP elevation or a CPP reduction.

Ultrasonography Monitoring of Optic Nerve Sheath Diameter and Retinal Vessels in Patients with Cerebral Hemorrhage

BACKGROUND AND PURPOSE

Evaluation of the diagnostic accuracy of optic nerve sheath diameter (ONSD) and Doppler indices of central retinal arteries and veins for the detection of increased intracranial pressure (ICP) in intracerebral hemorrhage (ICH) and of the usefulness of a second assessment of these variables in the monitoring of ICH.

METHODS

A total of 46 acute ICH patients with (group 1, n = 25) and without (group 2, n = 21) clinical and radiological computed tomography signs of raised ICP and 40 healthy controls were recruited. The median binocular ONSD and Doppler indices of retinal vessels including resistive index (RI) and retinal venous pulsation (RVP) were compared among groups, both at admission and later during ICH monitoring.

RESULTS

Median binocular ONSD showed higher accuracy for the detection of increased ICP (sensitivity and specificity 100%), while Doppler indices were less accurate (sensitivity 48% and specificity 95% for RI; 80% and 62% for RVP). In ICH patients, ONSD was significantly elevated in group 1 both at admission (6.40 mm [interquartile range [IQR] = .70] vs. 4.70 [.40]) and at control time (6.00 [.55] vs. 4.55 [.40]; P < .01), as well as RI (.79 [.11] vs. .77 [.03] and .80 [.06] vs. .75 [.35]; P = .01). RVP was significantly increased in group 1 only at admission (3.20 cm/s [1.05] vs. 2.00 [1.55], P = .02).

CONCLUSIONS

Median binocular ONSD evaluation showed higher accuracy for the estimation of elevated ICP compared with Doppler indices of retinal vessels. The ONSD enlargement detected in the early phase of ICH persists at control time.

Relationship Between Brain Pulsatility and Cerebral Perfusion Pressure: Replicated Validation Using Different Drivers of CPP Change

Background

Determination of relationships between transcranial Doppler (TCD)-based spectral pulsatility index (sPI) and pulse amplitude (AMP) of intracranial pressure (ICP) in 2 groups of severe traumatic brain injury (TBI) patients (a) displaying plateau waves and (b) with unstable mean arterial pressure (MAP).

Methods

We retrospectively reviewed patients with severe TBI and continuous TCD monitoring displaying either plateau waves or unstable MAP from 1992 to 1998. We utilized linear and nonlinear regression techniques to describe both cohorts: cerebral perfusion pressure (CPP) versus AMP, CPP versus sPI, mean ICP versus ICP AMP, mean ICP versus sPI, and AMP versus sPI.

Results

Nonlinear regression techniques were employed to analyze the relationships with CPP. In plateau wave and unstable MAP patients, CPP versus sPI displayed an inverse nonlinear relationship (R² = 0.820 vs. R² = 0.610, respectively), with the CPP versus sPI relationship best modeled by the following function in both cases: PI = a + (b/CPP). Similarly, in both groups, CPP versus AMP displayed an inverse nonlinear relationship (R² = 0.610 vs. R² = 0.360, respectively). Positive linear correlations were displayed in both the plateau wave and unstable MAP cohorts between: ICP versus AMP, ICP versus sPI, AMP versus sPI.

Conclusions

There is an inverse relationship through nonlinear regression between CPP versus AMP and CPP versus sPI display. This provides evidence to support a previously-proposed model of TCD pulsatility index. ICP shows a positive linear correlation with AMP and sPI, which is also established between AMP and sPI.

Electronic supplementary material

The online version of this article (doi:10.1007/s12028-017-0404-9) contains supplementary material, which is available to authorized users.