Dynamic cerebral autoregulation is transiently impaired for one week after large-vessel acute ischemic stroke

Aerobic Training and Mobilization Early Post-stroke: Cautions and Considerations

Knowledge gaps exist in how we implement aerobic exercise programs during the early phases post-stroke. Therefore, the objective of this review was to provide evidence-based guidelines for pre-participation screening, mobilization, and aerobic exercise training in the hyper-acute and acute phases post-stroke. In reviewing the literature to determine safe timelines of when to initiate exercise and mobilization we considered the following factors: arterial blood pressure dysregulation, cardiac complications, blood-brain barrier disruption, hemorrhagic stroke transformation, and ischemic penumbra viability. These stroke-related impairments could intensify with inappropriate mobilization/aerobic exercise, hence we deemed the integrity of cerebral autoregulation to be an essential physiological consideration to protect the brain when progressing exercise intensity. Pre-participation screening criteria are proposed and countermeasures to protect the brain from potentially adverse circulatory effects before, during, and following mobilization/exercise sessions are introduced. For example, prolonged periods of standing and static postures before and after mobilization/aerobic exercise may elicit blood pooling and/or trigger coagulation cascades and/or cerebral hypoperfusion. Countermeasures such as avoiding prolonged standing or incorporating periodic lower limb movement to activate the venous muscle pump could counteract blood pooling after an exercise session, minimize activation of the coagulation cascade, and mitigate potential cerebral hypoperfusion. We discuss patient safety in light of the complex nature of stroke presentations (i.e., type, severity, and etiology), medical history, comorbidities such as diabetes, cardiac manifestations, medications, and complications such as anemia and dehydration. The guidelines are easily incorporated into the care model, are low-risk, and use minimal resources. These and other strategies represent opportunities for improving the safety of the activity regimen offered to those in the early phases post-stroke. The timeline for initiating and progressing exercise/mobilization parameters are contingent on recovery stages both from neurobiological and cardiovascular perspectives, which to this point have not been specifically considered in practice. This review includes tailored exercise and mobilization prescription strategies and precautions that are not resource intensive and prioritize safety in stroke recovery.

Impaired cerebral autoregulation and neurovascular coupling in middle cerebral artery stroke: Influence of severity?

We aimed to assess cerebral autoregulation (CA) and neurovascular coupling (NVC) in stroke patients of differing severity comparing responses to healthy controls and explore the association between CA and NVC with functional outcome. Patients admitted with middle cerebral artery (MCA) stroke and healthy controls were recruited. Stroke severity was defined by the National Institutes of Health Stroke Scale (NIHSS) scores: ≤4 mild, 5-15 moderate and ≥16 severe. Transcranial Doppler ultrasound and Finometer recorded MCA cerebral blood flow velocity (CBFv) and blood pressure, respectively, over 5 min baseline and 1 min passive movement of the elbow to calculate the autoregulation index (ARI) and CBFv amplitude responses to movement. All participants were followed up for three months. A total of 87 participants enrolled in the study, including 15 mild, 27 moderate and 13 severe stroke patients, and 32 control subjects. ARI was lower in the affected hemisphere (AH) of moderate and severe stroke groups. Decreased NVC was seen bilaterally in all stroke groups. CA and NVC correlated with stroke severity and functional outcome. CBFv regulation is significantly impaired in acute stroke, and further compromised with increasing stroke severity. Preserved CA and NVC in the acute period were associated with improved three-month functional outcome.

Assessment of cerebral autoregulation in stroke: A systematic review and meta-analysis of studies at rest

Dynamic cerebral autoregulation (dCA) has been shown to be impaired in cerebrovascular diseases, but there is a lack of consistency across different studies and the different metrics that have been proposed for assessment. We performed a systematic review and meta-analyses involving assessment of dCA in ischemic and hemorrhagic stroke. Thirty-three articles describing assessment of dCA with transfer function analysis (TFA) were included, with meta-analyses performed for derived parameters of gain, phase and autoregulation index (ARI). A total of 1233 patients were pooled from 12 studies on acute ischemic stroke (AIS) and two studies on intracerebral hemorrhage (ICH). In comparison with controls, TFA phase of AIS was significantly reduced (nine studies), in both hemispheres (P < 0.0001). TFA gain provided inconsistent results, with reduced values in relation to controls, for both hemispheres. The ARI (six studies) was reduced compared to controls, in both hemispheres (P < 0.005). In ICH, gain showed higher values compared to controls for the unaffected (P = 0.01), but not for the affected hemisphere. Meta-analyses in AIS have demonstrated that phase and the ARI index can show highly significant differences in comparison with healthy controls, while ICH have been limited by the scarcity of studies and the diversity of units adopted for gain.

Transient Laterality of Cerebral Oxygenation Changes in Response to Head-of-Bed Manipulation in Acute Ischemic Stroke

Background: Cerebral oxygenation monitoring provides important information for optimizing individualized management in patients with acute ischemic stroke (AIS). Although changes in cerebral oxygenation are known to occur in response to head-of-bed (HOB) elevation within 72 h after onset, changes in cerebral oxygenation during stroke recovery are unclear. We compared changes in total- (tHb), oxygenated- (HbO2), and deoxygenated-hemoglobin (deoxyHb) concentrations in response to HOB manipulation between the timeframes within 72 h and 7–10 days after AIS onset. Methods: We measured forehead ΔtHb, ΔHbO2, and ΔdeoxyHb in response to HOB elevation (30°) within 72 h (first measurement) and 7–10 days (second measurement) after AIS onset using time-resolved near-infrared spectroscopy. Results: We enrolled 30 participants (mean age 72.8 ± 11.3 years; 13 women) with a first AIS. There were no significant differences in ΔtHb, ΔHbO2, or ΔdeoxyHb measurements on the infarct or contra-infarct side. At the first measurement, ΔtHb, ΔHbO2, and ΔdeoxyHb measured on the contra-infarct side did not correlate with those measured on the infarct side: ΔtHb (r = 0.114, p = 0.539); ΔHbO2 (r = 0.143, p = 0.440); ΔdeoxyHb (r = 0.227, p = 0.221). Notably, at the second measurement, correlation coefficients of ΔtHb and ΔHbO2 between the contra-infarct and infarct sides were statistically significant: ΔtHb (r = 0.491, p = 0.008); ΔHbO2 (r = 0.479, p = 0.010); ΔdeoxyHb (r = 0.358, p = 0.054). Conclusion: Although changes in cerebral oxygenation in response to HOB elevation had a laterality difference between hemispheres within 72 h of AIS onset, the difference had decreased, at least partially, 7–10 days after AIS onset.

Management of Stroke in the Neurocritical Care Unit

PURPOSE OF REVIEW

This article provides updated information regarding the diagnosis and treatment (specifically critical care management) of acute ischemic stroke. This article also discusses the increased use of thrombolysis and thrombectomy in clinical practice.

RECENT FINDINGS

Stroke is the leading cause of disability in the United States. A significant proportion of patients with acute ischemic stroke require critical care management. Much has changed in the early evaluation and treatment of patients presenting with acute ischemic stroke. The introduction of embolectomy in large vessel occlusions for up to 24 hours post-symptom onset has resulted in one in every three eligible patients with acute ischemic stroke with the potential to lead an independent lifestyle. These patients increasingly require recognition of complications and initiation of appropriate interventions as well as earlier admission to dedicated neurocritical care units to ensure better outcomes.

SUMMARY

This article emphasizes issues related to the management of patients with acute ischemic stroke undergoing mechanical thrombectomy and thrombolysis and addresses the complex physiologic changes affecting neurologic and other organ systems.

Decreases in Blood Pressure During Thrombectomy Are Associated With Larger Infarct Volumes and Worse Functional Outcome

Background and Purpose- After large-vessel intracranial occlusion, the fate of the ischemic penumbra, and ultimately final infarct volume, largely depends on tissue perfusion. In this study, we evaluated whether blood pressure reduction and sustained relative hypotension during endovascular thrombectomy are associated with infarct progression and functional outcome. Methods- We identified consecutive patients with large-vessel intracranial occlusion ischemic stroke who underwent mechanical thrombectomy at 2 comprehensive stroke centers. Intraprocedural mean arterial pressure (MAP) was monitored throughout the procedure. ΔMAP was calculated as the difference between admission MAP and lowest MAP during endovascular thrombectomy until recanalization. Sustained hypotension was measured as the area between admission MAP and continuous measurements of intraprocedural MAP (aMAP). Final infarct volume was measured using magnetic resonance imaging at 24 hours, and functional outcome was assessed using the modified Rankin Scale at discharge and 90 days. Associations with outcome were analyzed using linear and ordinal multivariable logistic regression. Results- Three hundred ninety patients (mean age 71±14 years, mean National Institutes of Health Stroke Scale score of 17) were included in the study; of these, 280 (72%) achieved Thrombolysis in Cerebral Infarction 2B/3 reperfusion. Eighty-seven percent of patients experienced MAP reductions during endovascular thrombectomy (mean 31±20 mm Hg). ΔMAP was associated with greater infarct growth ( P=0.036) and final infarct volume ( P=0.035). Mean ΔMAP among patients with favorable outcomes (modified Rankin Scale score, 0-2) was 20±21 mm Hg compared with 30±24 mm Hg among patients with poor outcome ( P=0.002). In the multivariable analysis, ΔMAP was independently associated with higher (worse) modified Rankin Scale scores at discharge (adjusted odds ratio per 10 mm Hg, 1.17; 95% CI, 1.04-1.32; P=0.009) and at 90 days (adjusted odds ratio per 10 mm Hg, 1.22; 95% CI, 1.07-1.38; P=0.003). The association between aMAP and outcome was also significant at discharge ( P=0.002) and 90 days ( P=0.001). Conclusions- Blood pressure reduction before recanalization is associated with larger infarct volumes and worse functional outcomes for patients affected by large-vessel intracranial occlusion stroke. These results underscore the importance of BP management during endovascular thrombectomy and highlight the need for further investigation of blood pressure management after large-vessel intracranial occlusion stroke.

Dynamic cerebral autoregulation measurement using rapid changes in head positioning: experiences in acute ischemic stroke and healthy control populations

The ideal technique for dynamic cerebral autoregulation (dCA) assessment in critically ill patients should provide considerable variability in blood pressure (BP) but without the need for patient cooperation. We proposed using rapid head positioning (RHP) over spontaneous BP fluctuations for dCA assessment in patients with acute ischemic stroke (AIS). Cerebral blood velocity (transcranial Doppler), beat-to-beat BP (Finometer), and end-tidal CO2 (capnography) were recorded during 5-min baseline and RHP in 16 controls (8 women and 8 men, mean age: 57 ± 16 yr) and 15 patients with AIS (7 women and 8 men, mean age: 69 ± 8 yr) at two (12 ± 8 days) and three visits (13.3 ± 6.9 h, 4.8 ± 3.2 days, and 93.9 ± 11.5 days from the symptom onset), respectively. All participants were able to complete the RHP protocol without difficulty. Compared with controls, patients with AIS were hypocapnic (all visits, P < 0.0024) and hypertensive ( visit 1, P = 0.011), although BP gradually reduced after the acute phase. RHP demonstrated greater beat-to-beat BP variability (BPV) in controls ( visits 1 and 2, P < 0.001) but not in patients with AIS at any visit. Compared with controls, a reduced autoregulation index (ARI) was demonstrated in patients with AIS, at visit 2 for the baseline recording but not at other visits or during RHP. The area under the receiver-operating curve was 0.53 and 0.54 for baseline and RHP, respectively. The RHP paradigm required minimal patient cooperation and could be considered a feasible alternative for assessing dCA, mainly in conditions leading to increased BPV. The lack of BPV increase in AIS with RHP deserves further investigation.

NEW & NOTEWORTHY This study used rapid head positioning (RHP) to enhance blood pressure (BP) variability (BPV) to improve BP signal-to-noise ratio and reliability of dynamic cerebral autoregulation (dCA). RHP was well accepted by controls and acute ischemic stroke (AIS); the increased BPV induced in controls was not observed in AIS, suggesting BPV at rest was already elevated. RHP did not improve detection of impaired CA in AIS; further work is needed to understand the different responses observed.

Systolic Blood Pressure Trajectories in the Acute Phase and Clinical Outcomes in 2-Year Follow-up Among Patients With Ischemic Stroke

BACKGROUND

Optimal blood pressure (BP) levels during acute ischemic stroke have not been established. We studied associations between systolic BP trajectories during acute phase and subsequent clinical outcomes among patients with ischemic stroke.

METHODS

A total of 4,036 patients with acute ischemic stroke and elevated BP from the China Antihypertensive Trial in Acute Ischemic Stroke trial were included in this analysis. Three BPs were measured every 2 hours in day 1, every 4 hours during days 2 and 3, and every 8 hours thereafter until hospital discharge or death. Clinical outcomes were assessed at 3, 12, and 24 months. Latent variable mixture modeling was used to identify subgroups that share a similar underlying trajectory of systolic BP during the first 7 days after stroke onset. Logistic regression and Cox proportional hazards models were used to examine the associations between systolic BP trajectories and clinical outcomes during follow-up.

RESULTS

We identified 5 systolic BP trajectories of high, high-to-moderate-low, moderate-high, moderate-low, and low. Compared to participants in high trajectory, multiple-adjusted odds ratios (95% confidence interval) of all-cause mortality at 3 months for individuals in high-to-moderate-low, moderate-high, moderate-low, and low were 0.34 (0.15-0.77), 0.58 (0.32-1.04), 0.29 (0.15-0.56), and 0.56 (0.26-1.19), respectively. Likewise, the corresponding hazard ratios for all-cause mortality in 24 months were 0.66 (0.44-1.00), 0.74 (0.53-1.05), 0.45 (0.32-0.66), and 0.61 (0.40-0.93), respectively. Similar associations were observed for recurrent stroke and cardiovascular disease, and in both the intervention and control groups.

CONCLUSIONS

Patients with moderate-low systolic BP during acute ischemic stroke had a lower risk of adverse clinical outcomes.

Late failure of cerebral autoregulation in hypoxic-ischemic encephalopathy is associated with brain injury: a pilot study

BACKGROUND

Post-resuscitation reperfusion following hypoxic-ischemia (HIE) is associated with secondary brain injury in neonates.

OBJECTIVE

To quantify the association between perfusion exceeding autoregulatory limits and brain injury.

APPROACH

Continuous mean arterial blood pressure (MABP) and cerebral near-infrared spectroscopy (NIRS) data were prospectively collected from infants with HIE. Cerebral oximetry index (COx) was calculated as a moving correlation coefficient between MABP and NIRS. Upper and lower limits of autoregulation were identified by transition from negative to positive correlation. The proportion of time MABP above (hyperperfusion) and below (hypoperfusion) autoregulatory limits was calculated during therapeutic hypothermia (days 1-3).

MAIN RESULTS

Sixteen infants were included; injury was noted in 7/16. There was no significance in hyperperfusion burden between injured and uninjured infants during day one (7% versus 10%, p  =  0.88) or two (4% versus 2%, p  =  0.88), but there was a marked increase for injured infants on day three (54% versus 14%, p  =  0.02). There was a corollary decrease in hypoperfusion for injured versus uninjured infants on day 3 (6% versus 24%, p  =  0.05).

SIGNIFICANCE

HIE infants with brain injury have a late failure of cerebral autoregulation, manifested as a hyperperfusion burden, suggesting pathologic events are active on day 3 of hypothermia. This finding may help to identify infants which might need additional neuroprotection.

Preliminary Study of Dynamic Cerebral Autoregulation in Acute Ischemic Stroke: Association With Clinical Factors

Background and Purpose: Dynamic cerebral autoregulation (dCA) is probably impaired in the acute and even subacute phases after acute ischemic stroke (AIS); however, the relationship between relevant clinical factors and dCA after AIS has not been investigated. The identification of possible determinants may therefore provide potential therapeutic targets to improve dCA in AIS.

Methods: This study enrolled 67 consecutive patients diagnosed with AIS within 3 days from symptom onset. Serial measurements were performed 1–3 days (measurement 1) and 7–10 days (measurement 2) after the onset. Middle cerebral artery blood flow velocities and simultaneous arterial blood pressure (ABP) were recorded continuously with transcranial Doppler combined with a servo-controlled finger plethysmograph. Transfer function analysis was used to derive dCA parameters, phase difference (PD), and coherence in low-frequency range (0.06–0.12 Hz). Univariate and multivariate linear regression analyses were conducted to determine the relationship between clinical factors and PD within the two time points of measurements. Multivariate logistic regression was performed to reveal the relationship between PD and clinical outcomes.

Results: Bilateral PD was significantly lower (indicating impaired dCA) in AIS patients, both in measurement 1 and measurement 2 when compared with those of healthy controls (all P < 0.001). After controlling for relevant clinical factors, in measurement 1, age (β = −0.29, P = 0.01), recombinant tissue plasminogen activator (rt-PA) intravenous thrombolysis (β = 0.25, P = 0.034), subtype of large-artery atherosclerosis (LAA) (β = −0.31, P = 0.007), and uric acid level (β = −0.32, P = 0.009) were significant independent predictors of ipsilateral PD. In measurement 2, subtype of LAA (β = −0.28, P = 0.049) and uric acid level (β = −0.43, P = 0.005) were still significant predictive values for ipsilateral PD. After adjusting for age and National Institutes of Health Stroke Scale at admission, ipsilateral PD >35.37° in measurement 2 was independent predictor of good clinical outcomes (adjusted OR = 6.97, 95% CI: 1.27–38.14, P = 0.03).

Conclusion: DCA was sustained to be bilaterally impaired in the acute and even subacute phase after AIS. Patients who receiving rt-PA thrombolysis tended to have a better dCA in the acute phase. Increasing age, subtype of LAA, and higher uric acid level had prognostic value for disturbed autoregulation. A relatively preserved dCA may predict good clinical outcomes.

Cerebral Autoregulation in Stroke

PURPOSE OF REVIEW

Cerebral autoregulation (CA) is a mechanism that maintains cerebral blood flow constant despite fluctuations in systemic arterial blood pressure. This review will focus on recent studies that measured CA non-invasively in acute cerebrovascular events, a feature unique to the transcranial Doppler ultrasound. We will summarize the rationale for CA assessment in acute cerebrovascular disorders and specifically evaluate the existing data on the value of CA measures in relation to clinical severity, guiding management decisions, and prognostication.

RECENT FINDINGS

Existing data suggest that CA is generally impaired in various cerebrovascular disorders. In patients with small vessel ischemic stroke, CA has been shown to be impaired in both hemispheres, whereas in large territorial strokes, CA impairment has been limited to the affected hemisphere. In these latter patients, impaired CA is also predictive of secondary complications such as hemorrhagic transformation and cerebral edema, hence worse functional outcome. In patients with carotid stenosis, impaired CA may also be associated with a higher ipsilateral hemispheric stroke risk. CA is also strongly linked to outcome in patients with intracranial hemorrhage. In patients with intraparenchymal hemorrhage, CA impairment correlated with clinical and imaging severity, whereas in those with subarachnoid hemorrhage, CA measures have a predictive value for development of delayed cerebral ischemia and radiographic vasospasm. Assessment of CA is increasingly more accessible in acute cerebrovascular disorders and promises to be a valuable measure in guiding hemodynamic management and predicting secondary complication, thus enhancing the care of these patients in the acute setting.

Autoregulation in the Neuro ICU

PURPOSE OF REVIEW

The purpose of this review is to briefly describe the concept of cerebral autoregulation, to detail several bedside techniques for measuring and assessing autoregulation, and to outline the impact of impaired autoregulation on clinical and functional outcomes in acute brain injury. Furthermore, we will review several autoregulation studies in select forms of acute brain injuries, discuss the potential for its use in patient management in the ICU, and suggest further avenues for research.

RECENT FINDINGS

Cerebral autoregulation plays a critical role in regulating cerebral blood flow, and impaired autoregulation has been associated with worse functional and clinical outcomes in various acute brain injuries. There exists a multitude of methods to assess the autoregulatory state in patients using both invasive and non-invasive modalities. Continuous monitoring of patients in the ICU has yielded autoregulatory-derived optimal perfusion pressures that may prevent secondary injury and improve outcomes. Measuring autoregulation continuously at the bedside is now a feasible option for clinicians working in the ICU, although there exists a great need to standardize autoregulatory measurement. While the clinical benefits await prospective and randomized trials, autoregulation-derived parameters show enormous potential for creating an optimal physiological environment for the injured brain.

Comparing Different Recording Lengths of Dynamic Cerebral Autoregulation: 5 versus 10 Minutes

We compared the dynamic cerebral autoregulation (dCA) indices between 5- and 10-minute data lengths by analyzing 37 patients with ischemic stroke and 51 controls in this study. Correlation coefficient (Mx) and transfer function analysis were applied for dCA analysis. Mx and phase shift in all frequency bands were not significantly different between 5- and 10-minute recordings [mean difference: Mx = 0.02; phase shift of very low frequency (0.02–0.07 Hz) = 0.3°, low frequency (0.07–0.20 Hz) = 0.6°, and high frequency (0.20–0.50 Hz) = 0.1°]. However, the gains in all frequency bands of a 5-minute recording were slightly but significantly higher than those of a 10-minute recording (mean difference of gain: very low frequency = 0.05 cm/s/mmHg, low frequency = 0.11 cm/s/mmHg, and high frequency = 0.14 cm/s/mmHg). The intraclass correlation coefficients between all dCA indices of 5- and 10-minute recordings were favorable, especially in Mx (0.93), phase shift in very low frequency (0.87), and gain in very low frequency (0.94). The areas under the receiver operating characteristic curve for stroke diagnosis between 5- and 10-minute recordings were not different. We concluded that dCA assessed by using a 5-minute recording is not significantly different from that using a 10-minute recording in the clinical application.

Paradigm Change? Cardiac Output Better Associates with Cerebral Perfusion than Blood Pressure in Ischemic Stroke

Introduction

In patients with acute ischemic stroke, penumbral perfusion is maintained by collateral flow and so far is maintained by normal mean arterial pressure (MAP) levels. Since MAP is dependent on cardiac function, optimization of cardiac output might be a valuable hemodynamic goal in order to optimize cerebral perfusion (CP).

Methods

Cerebral perfusion was assessed by transcranial color-coded duplex and transcranial perfusion sonography in 10 patients with acute large hemispheric stroke. Time-to-peak (TTP) values of defined regions of interest (ROI) within the middle cerebral artery (MCA) territory were assessed bilaterally in addition to mean flow velocities of the MCA. Via semi-invasive advanced hemodynamic monitoring systemic hemodynamic parameters were assessed, including MAP and cardiac index (CI). Patients received sonographic follow-up after optimizing CI.

Results

TTP values of the deeply located ROIs of the non-affected as well as the affected hemisphere correlated highly significantly with CI (in affected side r = −0.827, p = 0.002; and in non-affected side r = −0.908, p < 0.0001). This demonstrates dependence of CP on CI, while correlation with MAP was not detected. Neither CI nor MAP revealed significant correlation with MCA velocity.

Predictive Value of Dynamic Cerebral Autoregulation Assessment in Surgical Management of Patients with High-Grade Carotid Artery Stenosis

Dynamic cerebral autoregulation (DCA) capacity along with the degree of internal carotid artery (ICA) stenosis and characteristics of the plaque can also play an important role in selection of appropriate treatment strategy. This study aims to classify the patients with severe ICA stenosis according to preoperative state of DCA and to assess its dynamics after surgery. Thirty-five patients with severe ICA stenosis having different clinical type of disease underwent reconstructive surgery. DCA was assessed with transfer function analysis (TFA) by calculating phase shift (PS) between Mayer waves of blood flow velocity (BFV) and blood pressure (BP) before and after operation. In 18 cases, regardless of clinical type, preoperative PS on ipsilateral side was within the normal range and did not change considerably after surgery. In other 17 cases preoperative PS was reliably lower both in patients with symptomatic and asymptomatic stenosis. Surgical reconstruction led to restoration of impaired DCA evidenced by significant increase of PS in postoperative period. Our data suggest that regardless clinical type of disease various state of DCA may be present in patients with severe ICA stenosis. This finding can contribute to establishing the optimal treatment strategy, and first of all for asymptomatic patients. Patients with compromised DCA should be considered as ones with higher risk of stroke and first candidates for reconstructive surgery.

Cerebral blood flow autoregulation is impaired in schizophrenia: A pilot study

Patients with schizophrenia have a higher risk of cardiovascular diseases and higher mortality from them than does the general population; however, the underlying mechanism remains unclear. Impaired cerebral autoregulation is associated with cerebrovascular diseases and their mortality. Increased or decreased cerebral blood flow in different brain regions has been reported in patients with schizophrenia, which implies impaired cerebral autoregulation. This study investigated the cerebral autoregulation in 21 patients with schizophrenia and 23 age- and sex-matched healthy controls. None of the participants had a history of cardiovascular diseases, hypertension, or diabetes. All participants underwent 10-min blood pressure and cerebral blood flow recording through finger plethysmography and Doppler ultrasonography, respectively. Cerebral autoregulation was assessed by analyzing two autoregulation indices: the mean blood pressure and cerebral blood flow correlation coefficient (Mx), and the phase shift between the waveforms of blood pressure and cerebral blood flow determined using transfer function analysis. Compared with the controls, the patients had a significantly higher Mx (0.257 vs. 0.399, p=0.036) and lower phase shift (44.3° vs. 38.7° in the 0.07-0.20Hz frequency band, p=0.019), which indicated impaired maintenance of constant cerebral blood flow and a delayed cerebrovascular autoregulatory response. Impaired cerebral autoregulation may be caused by schizophrenia and may not be an artifact of coexisting medical conditions. The mechanism underlying impaired cerebral autoregulation in schizophrenia and its probable role in the development of cerebrovascular diseases require further investigation.

Risks of Cardiovascular Adverse Events and Death in Patients with Previous Stroke Undergoing Emergency Noncardiac, Nonintracranial Surgery

Background

The outcomes of emergent noncardiac, nonintracranial surgery in patients with previous stroke remain unknown.

Methods

All emergency surgeries performed in Denmark (2005 to 2011) were analyzed according to time elapsed between previous ischemic stroke and surgery. The risks of 30-day mortality and major adverse cardiovascular events were estimated as odds ratios (ORs) and 95% CIs using adjusted logistic regression models in a priori defined groups (reference was no previous stroke). In patients undergoing surgery immediately (within 1 to 3 days) or early after stroke (within 4 to 14 days), propensity-score matching was performed.

Results

Of 146,694 nonvascular surgeries (composing 98% of all emergency surgeries), 5.3% had previous stroke (mean age, 75 yr [SD = 13]; 53% women, 50% major orthopedic surgery). Antithrombotic treatment and atrial fibrillation were more frequent and general anesthesia less frequent in patients with previous stroke (all P &lt; 0.001). Risks of major adverse cardiovascular events and mortality were high for patients with stroke less than 3 months (20.7 and 16.4% events; OR = 4.71 [95% CI, 4.18 to 5.32] and 1.65 [95% CI, 1.45 to 1.88]), and remained increased for stroke within 3 to 9 months (10.3 and 12.3%; OR = 1.93 [95% CI, 1.55 to 2.40] and 1.20 [95% CI, 0.98 to 1.47]) and stroke more than 9 months (8.8 and 11.7%; OR = 1.62 [95% CI, 1.43 to 1.84] and 1.20 [95% CI, 1.08 to 1.34]) compared with no previous stroke (2.3 and 4.8% events). Major adverse cardiovascular events were significantly lower in 323 patients undergoing immediate surgery (21%) compared with 323 successfully propensity-matched early surgery patients (29%; P = 0.029).

Conclusions

Adverse cardiovascular outcomes and mortality were greatly increased among patients with recent stroke. However, events were higher 4 to 14 days after stroke compared with 1 to 3 days after stroke.

Dynamic Cerebral Autoregulation Assessment Using Extracranial Internal Carotid Artery Doppler Ultrasonography

Transcranial Doppler ultrasonography of the middle cerebral artery (MCA) is frequently used to assess dynamic cerebral autoregulation (dCA); however, this is difficult in patients with poor temporal bone windows. In the study described here, we investigated the agreement and sensitivity of dCA indices determined from the extracranial internal carotid artery (ICA) and those determined from the MCA. Measurements for 32 stroke patients and 59 controls were analyzed. Measurement of the mean flow correlation index (Mx) and transfer function analysis based on spontaneous blood pressure fluctuation were simultaneously performed for the extracranial ICA and MCA. The mean values of Mx and phase shift did not significantly differ between the ICA and MCA (mean difference: Mx = 0.01; phase shift of very low frequency [VLF] = 0.7°, low frequency [LF] = 3.3° and high frequency = 4.5°), but the gains in VLF and LF in the ICA were significantly lower than those in the MCA (mean difference: gain of VLF = -0.13, gain of LF = -0.10). The intra-class correlation coefficient between the dCA indices of the ICA and MCA was favorable in Mx (0.76) and the phase shift of VLF (0.72). The area under the receiver operating characteristic curve for stroke diagnosis did not differ among the dCA indices. We conclude that dCA assessed from the ICA is as effective as that from the MCA, but the results are not interchangeable.

Impaired cerebral autoregulation: measurement and application to stroke

Cerebral autoregulation (CA) is a protective mechanism that maintains cerebral blood flow at a relatively constant level despite fluctuations of cerebral perfusion pressure or arterial blood pressure. It is a universal physiological mechanism that may involve myogenic, neural control as well as metabolic regulations of cerebral vasculature in response to changes in pressure or cerebral blood flow. Traditionally, CA has been represented by a sigmoid curve with a wide plateau between about 50 mm Hg and 170 mm Hg of steady-state changes in mean arterial pressure, defined as static CA. With the advent of transcranial Doppler, measurement of cerebral blood flow in response to transient changes in arterial pressure has been used to assess dynamic CA. However, a gold standard for measuring CA is not currently available. Stroke has been the leading cause of long-term adult disability throughout the world. A better understanding of CA and its response to pathological derangements can help assess the severity of stroke, guide management decisions, assess response to interventions and provide prognostic information. The objective of this review is to provide a comprehensive insight about physiology of autoregulation, measurement methodologies and clinical applications in stroke to help build a consensus for what should be included in an internationally agreed protocol for CA testing and monitoring, and to promote its translation into clinical bedside practice for stroke management.

Informatics in neurocritical care: new ideas for Big Data

PURPOSE OF REVIEW

Big data is the new hype in business and healthcare. Data storage and processing has become cheap, fast, and easy. Business analysts and scientists are trying to design methods to mine these data for hidden knowledge. Neurocritical care is a field that typically produces large amounts of patient-related data, and these data are increasingly being digitized and stored. This review will try to look beyond the hype, and focus on possible applications in neurointensive care amenable to Big Data research that can potentially improve patient care.

RECENT FINDINGS

The first challenge in Big Data research will be the development of large, multicenter, and high-quality databases. These databases could be used to further investigate recent findings from mathematical models, developed in smaller datasets. Randomized clinical trials and Big Data research are complementary. Big Data research might be used to identify subgroups of patients that could benefit most from a certain intervention, or can be an alternative in areas where randomized clinical trials are not possible.

SUMMARY

The processing and the analysis of the large amount of patient-related information stored in clinical databases is beyond normal human cognitive ability. Big Data research applications have the potential to discover new medical knowledge, and improve care in the neurointensive care unit.

The Effect of Pulsatility Index on Infarct Volume in Acute Lacunar Stroke

PURPOSE

Lacunar stroke, in the context of small vessel disease, is a type of cerebral infarction caused by occlusion of a penetrating artery. Pulsatility index (PI) is an easily measurable parameter in Transcranial Doppler ultrasound (TCD) study. PI reflects distal cerebral vascular resistance and has been interpreted as a surrogate marker of small vessel disease. We hypothesized that an increased PI, a marker of small vessel disease, might be associated with a larger infarct volume in acute lacunar stroke.

MATERIALS AND METHODS

This study included 64 patients with acute lacunar stroke who underwent TCD and brain MRI. We evaluated the association between the mean PI value of bilateral middle cerebral arteries and infarct volume on diffusion-weighted MRI using univariate and multivariate linear regression.

RESULTS

The mean infarct volume and PI were 482.18±406.40 mm³ and 0.86±0.18, respectively. On univariate linear regression, there was a significant positive association between PI and infarct volume (p=0.001). In the multivariate model, a single standard deviation increase of PI (per 0.18) was associated with an increase of 139.05 mm³ in infarct volume (95% confidence interval, 21.25 to 256.85; p=0.022).

CONCLUSION

We demonstrated that PI was an independent determinant of infarct volume in acute lacunar stroke. The PI value measured in acute stroke may be a surrogate marker of the extent of ischemic injury.

Dissociation among hemodynamic measures in asymptomatic high grade carotid artery stenosis

BACKGROUND

Cerebral blood flow (CBF) regulation is a critical element in cerebrovascular pathophysiology, particularly in large vessel disease, but the best method to use for hemodynamic assessment is not clear. We examined 4 different blood-flow related measures in patients with unilateral high-grade carotid artery disease, assessing asymmetry between the occluded vs non-occluded side, and the correlations among the measures.

METHODS

Thirty-three patients (age 50-93, 19 M) with unilateral 80-100% ICA occlusion but no stroke underwent: 1) mean flow velocity (MFV) in both middle cerebral arteries by transcranial Doppler (TCD), 2) quantitative resting CBF using pseudo-continuous arterial spin labeling (pCASL) MRI, 3) vasomotor reactivity (VMR) in response to 5% CO2 inhalation, and 4) dynamic cerebral autoregulation (DCA) assessing the counter-regulation of blood flow to spontaneous changes in blood pressure using TCD monitoring and finger photoplethysmography. Paired t-tests and Pearson correlations assessed side-to-side differences within each measure, and correlations between measures.

RESULTS

CBF (p=0.001), MFV (p<0.001), VMR (p=0.008), and DCA (p=0.047) all showed significantly lower values on the occluded side. The 4 measures were independent of each other on correlation analysis, even when controlling for age and anterior circle of Willis collateral (all partial correlations <0.233 and p-values >0.468).

CONCLUSIONS

These 4 measures showed high sensitivity to the occluded carotid artery, but their dissociation suggests that any given measure only partially characterizes the hemodynamic state. Additional research is needed to explore the multifaceted biology of cerebral blood flow regulation.

Recanalization Modulates Association Between Blood Pressure and Functional Outcome in Acute Ischemic Stroke

BACKGROUND AND PURPOSE

Historical stroke cohorts reported a U- or J-shaped relationship between blood pressure (BP) and clinical outcome. However, these studies predated current revascularization strategies, disregarding the recanalization state of the affected arterial territory. We aimed to investigate the relationship between BP in the first 24 hours after ischemic stroke and clinical outcome in patients submitted to intravenous or intra-arterial recanalization treatments.

METHODS

Consecutive patients with acute stroke treated with intravenous thrombolysis or intra-arterial therapies were enrolled in a retrospective cohort study. BP was measured on regular intervals throughout day and night during the first 24 hours after stroke onset. The mean systolic BP and diastolic BP during the first 24 hours post stroke were calculated. Recanalization was assessed at 6 hours by transcranial color-coded Doppler, angiography, or angio-computed tomography. Functional outcome was assessed at 3 months by modified Rankin Scale. Linear and quadratic multivariate regression models were performed to determine associations between BP and functional outcome for the whole population and recanalyzed and nonrecanalyzed patients.

RESULTS

We included 674 patients; mean age was 73.28 (SD, 11.50) years. Arterial recanalization was documented in 355 (52.70%) patients. In multivariate analyses, systolic BP and diastolic BP in the first 24 hours post stroke show a J-shaped relationship with functional outcome in the total population and in the nonrecanalyzed patients. Recanalyzed patients show a linear association with functional outcome (systolic BP: odds ratio, 1.015; 95% confidence interval, 1.007-1.024; P=0.001; R(2) change=0.001; P=0.412 and diastolic BP: odds ratio, 1.019; 95% confidence interval, 1.004-1.033; P=0.012; R(2) change<0.001; P=0.635).

CONCLUSIONS

Systemic BP in the first 24 hours after ischemic stroke influences 3-month clinical outcome. This association is dependent on the revascularization status.

Early Blood Pressure Reduction in Acute Ischemic Stroke with Various Severities: A Subgroup Analysis of the CATIS Trial

BACKGROUND

Clinical trials have generally showed a neutral effect of blood pressure (BP) reduction on clinical outcomes among acute ischemic stroke patients. We conducted a prespecified subgroup analysis to assess whether disease severity modifies the effect of early antihypertensive treatment on death and disability among patients with acute ischemic stroke.

METHODS

In the China Antihypertensive Trial in Acute Ischemic Stroke, 4,071 patients with acute ischemic stroke and elevated BP were randomly assigned to receive antihypertensive treatment or to discontinue all hypertension medications within 48 h of symptom onset. The primary outcome was a combination of death and major disability at 14 days or hospital discharge. In this subgroup analysis, participants were categorized into 3 groups according to their baseline NIH Stroke Scale (NIHSS) scores (0-4, 5-15, or ≥16).

RESULTS

At 24 h after randomization, mean systolic BP differences (95% CIs) were -8.5 (-10.0 to -7.1), -9.8 (-11.4 to -8.3), and -9.1 (-14.4 to -3.8) mm Hg between the treatment and control groups (all p values <0.001) for patients with a baseline NIHSS score of 0-4, 5-15, and ≥16, respectively. At day 7 after randomization, the corresponding mean systolic BP differences were -9.3 (-10.5 to -8.2), -9.1 (-10.3 to -7.8), and -10.1 (-15.1 to -5.1) mm Hg between the treatment and control groups (all p values <0.001). The primary outcome was not significantly different between the treatment and control groups at day 14 or hospital discharge among all NIHSS subgroups (p value for homogeneity = 0.66). ORs (95% CI) associated with treatment were 1.14 (0.87-1.49, p = 0.33), 1.04 (0.86-1.25, p = 0.70), and 0.67 (0.18-2.44, p = 0.54) for patients with a baseline NIHSS score of 0-4, 5-15, and ≥16, respectively. The composite outcome of death and major disability at 3-month follow-up did not differ between the 2 comparison groups for all NIHSS subgroups. In addition, vascular events and recurrent stroke were not significantly different between the 2 comparison groups at the 3-month follow-up visit among all NIHSS subgroups except that there was a suggestive risk reduction for recurrent stroke among those with an NIHSS score of 5-15 (OR 0.45, 95% CI 0.20-0.99, p = 0.05).

CONCLUSION

Early BP reduction with antihypertensive medications did not reduce or increase the risk of death, major disabilities, recurrent instances of stroke, and vascular events in acute ischemic stroke patients with a variety of disease severities.

Temporal Course of Dynamic Cerebral Autoregulation in Patients With Intracerebral Hemorrhage

BACKGROUND AND PURPOSE

Cerebral autoregulation is crucial in patients with intracerebral hemorrhage. Dynamic cerebral autoregulation is probably altered in acute intracerebral hemorrhage; however, the temporal course of dynamic cerebral autoregulation and its correlation with clinical factors and outcomes are poorly understood.

METHODS

Forty-three acute supratentorial intracerebral hemorrhage patients (53.7±10.0 years old, 30 men) were enrolled for serial measurements performed on days 1 to 2, 4 to 6, 10 to 12, and 30 days after ictus. Noninvasive continuous cerebral blood flow velocity and arterial blood pressure were recorded simultaneously using transcranial Doppler and a servo-controlled plethysmograph, respectively. Transfer function analysis was used to derive the autoregulatory parameters, including phase difference (PD), gain, and the rate of recovery of cerebral blood flow velocity. Results were compared with healthy controls and correlated with clinical factors and the 90-day outcome.

RESULTS

PD did not differ between affected and unaffected hemispheres over time. A significant lower PD (indicating dynamic cerebral autoregulation impaired) was found in bilateral hemispheres on days 1 to 2, 4 to 6, and 10 to 12, followed by later recovery on day 30. Lower bilateral PD on days 1 to 2 was associated with poorer Glasgow Coma Scale score at that time. Lower affected-side PD on days 4 to 6 was an independent predictive value for a poorer modified Rankin Scale at 90 days.

CONCLUSIONS

In patients with supratentorial intracerebral hemorrhage, dynamic cerebral autoregulation is bilaterally impaired lasting at least 10 to 12 days and recovers within a month. Individual PD value is associated with clinical status at acute stage and affected-side PD on days 4 to 6 can be an independent predictor for clinical outcome.