Individual Patient Data Meta-Analysis of Dynamic Cerebral Autoregulation and Functional Outcome After Ischemic Stroke.

BACKGROUND: The relationship between dynamic cerebral autoregulation (dCA) and functional outcome after acute ischemic stroke (AIS) is unclear. Previous studies are limited by small sample sizes and heterogeneity. METHODS: We performed a 1-stage individual patient data meta-analysis to investigate associations between dCA and functional outcome after AIS. Participating centers were identified through a systematic search of the literature and direct invitation. We included centers with dCA data within 1 year of AIS in adults aged over 18 years, excluding intracerebral or subarachnoid hemorrhage. Data were obtained on phase, gain, coherence, and autoregulation index derived from transfer function analysis at low-frequency and very low-frequency bands. Cerebral blood velocity, arterial pressure, end-tidal carbon dioxide, heart rate, stroke severity and sub-type, and comorbidities were collected where available. Data were grouped into 4 time points after AIS: <24 hours, 24 to 72 hours, 4 to 7 days, and >3 months. The modified Rankin Scale assessed functional outcome at 3 months. Modified Rankin Scale was analyzed as both dichotomized (0 to 2 versus 3 to 6) and ordinal (modified Rankin Scale scores, 0-6) outcomes. Univariable and multivariable analyses were conducted to identify significant relationships between dCA parameters, comorbidities, and outcomes, for each time point using generalized linear (dichotomized outcome), or cumulative link (ordinal outcome) mixed models. The participating center was modeled as a random intercept to generate odds ratios with 95% CIs. RESULTS: The sample included 384 individuals (35% women) from 7 centers, aged 66.3±13.7 years, with predominantly nonlacunar stroke (n=348, 69%). In the affected hemisphere, higher phase at very low-frequency predicted better outcome (dichotomized modified Rankin Scale) at <24 (crude odds ratios, 2.17 [95% CI, 1.47-3.19]; P<0.001) hours, 24-72 (crude odds ratios, 1.95 [95% CI, 1.21-3.13]; P=0.006) hours, and phase at low-frequency predicted outcome at 3 (crude odds ratios, 3.03 [95% CI, 1.10-8.33]; P=0.032) months. These results remained after covariate adjustment. CONCLUSIONS: Greater transfer function analysis-derived phase was associated with improved functional outcome at 3 months after AIS. dCA parameters in the early phase of AIS may help to predict functional outcome.

Dynamics of critical closing pressure explain cerebral autoregulation impairment in acute cerebrovascular disease.

INTRODUCTION: Cerebral autoregulation (CA) is impaired in acute ischemic stroke (AIS) and is associated with worse patient outcomes, but the underlying physiological cause is unclear. This study tests whether depressed CA in AIS can be linked to the dynamic responses of critical closing pressure (CrCP) and resistance area product (RAP). METHODS: Continuous recordings of middle cerebral blood velocity (MCAv, transcranial Doppler), arterial blood pressure (BP), end-tidal CO2 and electrocardiography allowed dynamic analysis of the instantaneous MCAv-BP relationship to obtain estimates of CrCP and RAP. The dynamic response of CrCP and RAP to a sudden change in mean BP was obtained by transfer function analysis. Comparisons were made between younger controls (≤50 years), older controls (>50 years), and AIS patients. RESULTS: Data from 24 younger controls (36.4 ± 10.9 years, 9 male), 38 older controls (64.7 ± 8.2 years, 20 male), and 20 AIS patients (63.4 ± 13.8 years, 9 male) were included. Dynamic CA was impaired in AIS, with lower autoregulation index (affected hemisphere: 4.0 ± 2.3, unaffected: 4.5 ± 1.8) compared to younger (right: 5.8 ± 1.4, left: 5.8 ± 1.4) and older (right: 4.9 ± 1.6, left: 5.1 ± 1.5) controls. AIS patients also demonstrated an early (0-3 second) peak in CrCP dynamic response, that was not influenced by age. CONCLUSION: These early transient differences in the CrCP dynamic response are a novel finding in stroke and occur too early to reflect underlying regulatory mechanisms. Instead, these may be caused by structural changes to cerebral vasculature. .

Mortality in a Multiethnic Population Attending a One-Stop TIA Clinic.

INTRODUCTION: Studies indicate a 13-27% mortality rate following a transient ischaemic attack (TIA). However, outcomes following TIA/minor stroke since the introduction of rapid-access TIA clinics and prompt vascular risk factor intervention are not known. Specifically, there is paucity of data comparing outcomes between people who are diagnosed with an "acute cerebrovascular" (CV) event or an alternative non-cardiovascular diagnosis (non-CV) in a rapid-access TIA clinic. We aimed to assess the mortality in such a setting. METHODS: A retrospective observational study was undertaken at the Leicester rapid-access secondary care TIA clinic. Data included information collected at the first clinic visit (including comorbidities, and primary diagnosis, categorized as CV and non-CV) and the date of death for people dying during follow-up. RESULTS: 11,524 subjects were included with 33,164 years of follow-up data; 4,746 (41.2%) received a CV diagnosis. The median follow-up time was 2.75 years (interquartile range 1.36-4.32). The crude mortality rate was 37.3 (95% CI: 35.3-39.5) per 1,000 person-years (PTPY). The mortality rate was higher following a CV diagnosis (50.8 [47.2-54.7] PTPY) compared to a non-CV diagnosis (27.9 [25.7-30.4] PTPY), and for males, older people, those of white ethnicity, and people with orthostatic hypotension (OH). DISCUSSION: This study identified possible risk factors associated with a higher mortality in TIA clinic attendees, who may benefit from specific intervention. Future research should explore the underlying causes and the effect of specific targeted management strategies.

Blood Pressure Management After Intracerebral and Subarachnoid Hemorrhage: The Knowns and Known Unknowns.

Blood pressure (BP) elevations often complicate the management of intracerebral hemorrhage and aneurysmal subarachnoid hemorrhage, the most serious forms of acute stroke. Despite consensus on potential benefits of BP lowering in the acute phase of intracerebral hemorrhage, controversies persist over the timing, mechanisms, and approaches to treatment. BP control is even more complex for subarachnoid hemorrhage, where there are rationales for both BP lowering and elevation in reducing the risks of rebleeding and delayed cerebral ischemia, respectively. Efforts to disentangle the evidence has involved detailed exploration of individual patient data from clinical trials through meta-analysis to determine strength and direction of BP change in relation to key outcomes in intracerebral hemorrhage, and which likely also apply to subarachnoid hemorrhage. A wealth of hemodynamic data provides insights into pathophysiological interrelationships of BP and cerebral blood flow. This focused update provides an overview of current evidence, knowledge gaps, and emerging concepts on systemic hemodynamics, cerebral autoregulation and perfusion, to facilitate clinical practice recommendations and future research.

Associations of Early Systolic Blood Pressure Control and Outcome After Thrombolysis-Eligible Acute Ischemic Stroke: Results From the ENCHANTED Study.

BACKGROUND AND PURPOSE: In thrombolysis-eligible patients with acute ischemic stroke, there is uncertainty over the most appropriate systolic blood pressure (SBP) lowering profile that provides an optimal balance of potential benefit (functional recovery) and harm (intracranial hemorrhage). We aimed to determine relationships of SBP parameters and outcomes in thrombolyzed acute ischemic stroke patients. METHODS: Post hoc analyzes of the ENCHANTED (Enhanced Control of Hypertension and Thrombolysis Stroke Study), a partial-factorial trial of thrombolysis-eligible and treated acute ischemic stroke patients with high SBP (150-180 mm Hg) assigned to low-dose (0.6 mg/kg) or standard-dose (0.9 mg/kg) alteplase and intensive (target SBP, 130-140 mm Hg) or guideline-recommended (target SBP <180 mm Hg) treatment. All patients were followed up for functional status and serious adverse events to 90 days. Logistic regression models were used to analyze 3 SBP summary measures postrandomization: attained (mean), variability (SD) in 1-24 hours, and magnitude of reduction in 1 hour. The primary outcome was a favorable shift on the modified Rankin Scale. The key safety outcome was any intracranial hemorrhage. RESULTS: Among 4511 included participants (mean age 67 years, 38% female, 65% Asian) lower attained SBP and smaller SBP variability were associated with favorable shift on the modified Rankin Scale (per 10 mm Hg increase: odds ratio, 0.76 [95% CI, 0.71-0.82]; P<0.001 and 0.86 [95% CI, 0.76-0.98]; P=0.025) respectively, but not for magnitude of SBP reduction (0.98, [0.93-1.04]; P=0.564). Odds of intracranial hemorrhage was associated with higher attained SBP and greater SBP variability (1.18 [1.06-1.31]; P=0.002 and 1.34 [1.11-1.62]; P=0.002) but not with magnitude of SBP reduction (1.05 [0.98-1.14]; P=0.184). CONCLUSIONS: Attaining early and consistent low levels in SBP <140 mm Hg, even as low as 110 to 120 mm Hg, over 24 hours is associated with better outcomes in thrombolyzed acute ischemic stroke patients. Registration: URL: https://www.clinicaltrials.gov; Unique identifier: NCT01422616.

Oral antiplatelet therapy for acute ischaemic stroke.

BACKGROUND: In people with acute ischaemic stroke, platelets become activated and can cause blood clots to form and block an artery in the brain, resulting in damage to part of the brain. Such damage gives rise to the symptoms of stroke. Antiplatelet therapy might reduce the volume of brain damaged by ischaemia and also reduce the risk of early recurrent ischaemic stroke, thereby reducing the risk of early death and improving long-term outcomes in survivors. However, antiplatelet therapy might also increase the risk of fatal or disabling intracranial haemorrhage. OBJECTIVES: To assess the efficacy and safety of immediate oral antiplatelet therapy (i.e. started as soon as possible and no later than two weeks after stroke onset) in people with acute presumed ischaemic stroke. SEARCH METHODS: We searched the Cochrane Stroke Group Trials Register, CENTRAL, MEDLINE Ovid, Embase Ovid, and two trials registers, and performed forward reference/cited reference searching in August 2020. SELECTION CRITERIA: Randomised controlled trials (RCTs) comparing oral antiplatelet therapy (started within 14 days of the stroke) with control in people with definite or presumed ischaemic stroke. DATA COLLECTION AND ANALYSIS: Two review authors independently applied the inclusion criteria and assessed trial quality. For the included trials, they extracted and cross-checked the data. They assessed risk of bias of each study using the Risk of Bias 1 (RoB1) tool and overall certainty of the evidence for each outcome using the GRADE approach. MAIN RESULTS: We included 11 studies involving 42,226 participants. Three new trials have been added since the last update (743 participants). As per the previous version of this review, two trials testing aspirin 160 mg to 300 mg once daily, started within 48 hours of onset, contributed 96% of the data. The risk of bias was low. The maximum follow-up was six months. With treatment, there was a decrease in death or dependency at the end of follow-up (odds ratio (OR) 0.95, 95% confidence interval (CI) 0.91 to 0.99; 7 RCTs, 42,034 participants; moderate-certainty evidence). For every 1000 people treated with aspirin, 13 people would avoid death or dependency (number needed to treat for an additional beneficial outcome 79). AUTHORS' CONCLUSIONS: Antiplatelet therapy with aspirin 160 mg to 300 mg daily, given orally (or by nasogastric tube or per rectum in people who cannot swallow) and started within 48 hours of onset of presumed ischaemic stroke, significantly decreased death and dependency, and reduced the risk of early recurrent ischaemic stroke without a major risk of early haemorrhagic complications; long-term outcomes were improved.

Acid-base balance and cerebrovascular regulation.

The regulation and defence of intracellular pH is essential for homeostasis. Indeed, alterations in cerebrovascular acid-base balance directly affect cerebral blood flow (CBF) which has implications for human health and disease. For example, changes in CBF regulation during acid-base disturbances are evident in conditions such as chronic obstructive pulmonary disease and diabetic ketoacidosis. The classic experimental studies from the past 75+ years are utilized to describe the integrative relationships between CBF, carbon dioxide tension (PCO2 ), bicarbonate (HCO3- ) and pH. These factors interact to influence (1) the time course of acid-base compensatory changes and the respective cerebrovascular responses (due to rapid exchange kinetics between arterial blood, extracellular fluid and intracellular brain tissue). We propose that alterations in arterial [HCO3- ] during acute respiratory acidosis/alkalosis contribute to cerebrovascular acid-base regulation; and (2) the regulation of CBF by direct changes in arterial vs. extravascular/interstitial PCO2 and pH - the latter recognized as the proximal compartment which alters vascular smooth muscle cell regulation of CBF. Taken together, these results substantiate two key ideas: first, that the regulation of CBF is affected by the severity of metabolic/respiratory disturbances, including the extent of partial/full acid-base compensation; and second, that the regulation of CBF is independent of arterial pH and that diffusion of CO2 across the blood-brain barrier is integral to altering perivascular extracellular pH. Overall, by realizing the integrative relationships between CBF, PCO2 , HCO3- and pH, experimental studies may provide insights to improve CBF regulation in clinical practice with treatment of systemic acid-base disorders.

Arterial carbon dioxide and bicarbonate rather than pH regulate cerebral blood flow in the setting of acute experimental metabolic alkalosis.

KEY POINTS: We investigated the influence of arterial PCO2 ( PaCO2 ) with and without acutely elevated arterial pH and bicarbonate ([HCO3- ]) on cerebral blood flow (CBF) regulation in the internal carotid artery and vertebral artery. We assessed stepwise iso-oxic alterations in PaCO2 (i.e. cerebrovascular CO2 reactivity) prior to and following i.v. sodium bicarbonate infusion (NaHCO3- ) to acutely elevate arterial pH and [HCO3- ]. Total CBF was unchanged irrespective of a higher arterial pH at each matched stage of PaCO2 , indicating that CBF is acutely regulated by PaCO2 rather than arterial pH. The cerebrovascular responses to changes in arterial H+ /pH were altered in keeping with the altered relationship between PaCO2 and H+ /pH following NaHCO3- infusion (i.e. changes in buffering capacity). Total CBF was ∼7% higher following NaHCO3- infusion during isocapnic breathing providing initial evidence for a direct vasodilatory influence of HCO3- independent of PaCO2 levels. ABSTRACT: Cerebral blood flow (CBF) regulation is dependent on the integrative relationship between arterial PCO2 ( PaCO2 ), pH and cerebrovascular tone; however, pre-clinical studies indicate that intrinsic sensitivity to pH, independent of changes in PaCO2 or intravascular bicarbonate ([HCO3- ]), principally influences cerebrovascular tone. Eleven healthy males completed a standardized cerebrovascular CO2 reactivity (CVR) test utilizing radial artery catheterization and Duplex ultrasound (CBF); consisting of matched stepwise iso-oxic alterations in PaCO2 (hypocapnia: -5, -10 mmHg; hypercapnia: +5, +10 mmHg) prior to and following i.v. sodium bicarbonate (NaHCO3- ; 8.4%, 50 mEq 50 mL-1 ) to elevate pH (7.408 ± 0.020 vs. 7.461 ± 0.030; P < 0.001) and [HCO3- ] (26.1 ± 1.4 vs. 29.3 ± 0.9 mEq L-1 ; P < 0.001). Absolute CBF was not different at each stage of CO2 reactivity (P = 0.629) following NaHCO3- , irrespective of a higher pH (P < 0.001) at each matched stage of PaCO2 (P = 0.927). Neither hypocapnic (3.44 ± 0.92 vs. 3.44 ± 1.05% per mmHg PaCO2 ; P = 0.499), nor hypercapnic (7.45 ± 1.85 vs. 6.37 ± 2.23% per mmHg PaCO2 ; P = 0.151) reactivity to PaCO2 were altered pre- to post-NaHCO3- . When indexed against arterial [H+ ], the relative hypocapnic CVR was higher (P = 0.019) and hypercapnic CVR was lower (P = 0.025) following NaHCO3- , respectively. These changes in reactivity to [H+ ] were, however, explained by alterations in buffering between PaCO2 and arterial H+ /pH consequent to NaHCO3- . Lastly, CBF was higher (688 ± 105 vs. 732 ± 89 mL min-1 , 7% ± 12%; P = 0.047) following NaHCO3- during isocapnic breathing providing support for a direct influence of HCO3- on cerebrovascular tone independent of PaCO2 . These data indicate that in the setting of acute metabolic alkalosis, CBF is regulated by PaCO2 rather than arterial pH.

Alterations in arterial CO2 rather than pH affect the kinetics of neurovascular coupling in humans.

KEY POINTS: We investigated the influence of arterial PCO2 ( PaCO2 ) with and without acute experimental metabolic alkalosis on neurovascular coupling (NVC). We assessed stepwise iso-oxic alterations in PaCO2 prior to and following intravenous NaHCO3 to acutely elevate arterial pH and [HCO3- ]. The NVC response was not altered following NaHCO3 between stepwise PaCO2 stages; therefore, NVC is acutely mediated by PaCO2 rather than the prevailing arterial [H+ ]/pH. The NVC response was attenuated by 27-38% with -10 mmHg PaCO2 and the absolute peak change was reduced by -19% with +10 mmHg PaCO2 irrespective of acutely elevated arterial pH/[HCO3- ]. The NVC kinetics (i.e. time to peak) were markedly slower with hypercapnia versus hypocapnia (24 ± 5 vs. 7 ± 5 s, respectively) likely indicating an influence of resting cerebrovascular tone on NVC responsiveness. ABSTRACT: Elevations in cerebral metabolism necessitate appropriate coordinated and localized increases in cerebral blood flow (i.e. neurovascular coupling; NVC). Recent pre-clinical work indicates that arterial PCO2 ( PaCO2 ) mediates NVC independently of arterial/extracellular pH; this has yet to be experimentally tested in humans. The goal of this study was to investigate the hypotheses that: (1) the NVC response would be unaffected by acute experimentally elevated arterial pH; rather, PaCO2 would regulate any changes in NVC; and (2) stepwise respiratory alkalosis and acidosis would each progressively reduce the NVC response. Ten healthy males completed a standardized visual stimulus-evoked NVC test during matched stepwise iso-oxic alterations in PaCO2 (hypocapnia: -5, -10 mmHg; hypercapnia: +5, +10 mmHg) prior to and following intravenous NaHCO3 (8.4%, 50 mEq/50 ml) that elevated arterial pH (7.406 ± 0.019 vs. 7.457 ± 0.029; P < 0.001) and [HCO3- ] (26.2 ± 1.5 vs. 29.3 ± 0.9 mEq/l; P < 0.001). Although the NVC response was collectively attenuated by 27-38% with -10 mmHg PaCO2 (stage post hoc: all P < 0.05), this response was unaltered following NaHCO3 (all P > 0.05) irrespective of the higher pH (P = 0.002) at each matched stage of PaCO2 (P = 0.417). The absolute peak change was reduced by -19 ± 41% with +10 mmHg PaCO2 irrespective of acutely elevated arterial pH/[HCO3- ] (stage post hoc: P = 0.022). The NVC kinetics (i.e. time to peak) were markedly slower with hypercapnia versus hypocapnia (24 ± 5 vs. 7 ± 5 s, respectively; stage effect: P < 0.001). Overall, these findings indicate that temporal patterns in NVC are acutely regulated by PaCO2 rather than arterial pH per se in the setting of acute metabolic alkalosis in humans.

Vascular and haemodynamic issues of brain ageing.

The population is ageing worldwide, thus increasing the burden of common age-related disorders to the individual, society and economy. Cerebrovascular diseases (stroke, dementia) contribute a significant proportion of this burden and are associated with high morbidity and mortality. Thus, understanding and promoting healthy vascular brain ageing are becoming an increasing priority for healthcare systems. In this review, we consider the effects of normal ageing on two major physiological processes responsible for vascular brain function: Cerebral autoregulation (CA) and neurovascular coupling (NVC). CA is the process by which the brain regulates cerebral blood flow (CBF) and protects against falls and surges in cerebral perfusion pressure, which risk hypoxic brain injury and pressure damage, respectively. In contrast, NVC is the process by which CBF is matched to cerebral metabolic activity, ensuring adequate local oxygenation and nutrient delivery for increased neuronal activity. Healthy ageing is associated with a number of key physiological adaptations in these processes to mitigate age-related functional and structural declines. Through multiple different paradigms assessing CA in healthy younger and older humans, generating conflicting findings, carbon dioxide studies in CA have provided the greatest understanding of intrinsic vascular anatomical factors that may mediate healthy ageing responses. In NVC, studies have found mixed results, with reduced, equivalent and increased activation of vascular responses to cognitive stimulation. In summary, vascular and haemodynamic changes occur in response to ageing and are important in distinguishing "normal" ageing from disease states and may help to develop effective therapeutic strategies to promote healthy brain ageing.

Appropriate deprescribing in older people: a challenging necessityCommentary to accompany themed collection on deprescribing.

Older people are often taking several medications for a number of different medical conditions. Although physicians prescribe medications to treat diseases and symptoms, there may be also harmful side effects, especially so in older people taking several medications. Unfortunately, regular review of the benefits or risks of prescribed medications is as of yet not part of standard care. Also, data on how and in whom to stop medications in older people are scarce. The reason this is an important area of work is that medication related issues in older people are a common cause of harm, including both expected and unexpected effects of medications. Research to date tells us that to ensure successful implementation of structured and appropriate deprescribing, careful planning within hospital systems is needed. This includes involving different members of the team to ensure the patients truly benefit. The themed collection published on the Age and Ageing journal website offers key articles providing tools to assist decision-making, implementation strategies and multidisciplinary interventions-all with the aim of improving patient outcome and sustainability of deprescribing approaches.

The need for improved discharge criteria for hospitalised patients with COVID-19-implications for patients in long-term care facilities.

In the COVID-19 pandemic, patients who are older and residents of long-term care facilities (LTCF) are at greatest risk of worse clinical outcomes. We reviewed discharge criteria for hospitalised COVID-19 patients from 10 countries with the highest incidence of COVID-19 cases as of 26 July 2020. Five countries (Brazil, Mexico, Peru, Chile and Iran) had no discharge criteria; the remaining five (USA, India, Russia, South Africa and the UK) had discharge guidelines with large inter-country variability. India and Russia recommend discharge for a clinically recovered patient with two negative reverse transcription polymerase chain reaction (RT-PCR) tests 24 h apart; the USA offers either a symptom based strategy-clinical recovery and 10 days after symptom onset, or the same test-based strategy. The UK suggests that patients can be discharged when patients have clinically recovered; South Africa recommends discharge 14 days after symptom onset if clinically stable. We recommend a unified, simpler discharge criteria, based on current studies which suggest that most SARS-CoV-2 loses its infectivity by 10 days post-symptom onset. In asymptomatic cases, this can be taken as 10 days after the first positive PCR result. Additional days of isolation beyond this should be left to the discretion of individual clinician. This represents a practical compromise between unnecessarily prolonged admissions and returning highly infectious patients back to their care facilities, and is of particular importance in older patients discharged to LTCFs, residents of which may be at greatest risk of transmission and worse clinical outcomes.

The critical closing pressure contribution to dynamic cerebral autoregulation in humans: influence of arterial partial pressure of CO2.

KEY POINTS: Dynamic cerebral autoregulation (CA) is often expressed by the mean arterial blood pressure (MAP)-cerebral blood flow (CBF) relationship, with little attention given to the dynamic relationship between MAP and cerebrovascular resistance (CVR). In CBF velocity (CBFV) recordings with transcranial Doppler, evidence demonstrates that CVR should be replaced by a combination of a resistance-area product (RAP) with a critical closing pressure (CrCP) parameter, the blood pressure value where CBFV reaches zero due to vessels collapsing. Transfer function analysis of the MAP-CBFV relationship can be extended to the MAP-RAP and MAP-CrCP relationships, to assess their contribution to the dynamic CA response. During normocapnia, both RAP and CrCP make a significant contribution to explaining the MAP-CBFV relationship. Hypercapnia, a surrogate state of depressed CA, leads to marked changes in dynamic CA, that are entirely explained by the CrCP response, without further contribution from RAP in comparison with normocapnia. ABSTRACT: Dynamic cerebral autoregulation (CA) is manifested by changes in the diameter of intra-cerebral vessels, which control cerebrovascular resistance (CVR). We investigated the contribution of critical closing pressure (CrCP), an important determinant of CVR, to explain the cerebral blood flow (CBF) response to a sudden change in mean arterial blood pressure (MAP). In 76 healthy subjects (age range 21-70 years, 36 women), recordings of MAP (Finometer), CBF velocity (CBFV; transcranial Doppler ultrasound), end-tidal CO2 (capnography) and heart rate (ECG) were performed for 5 min at rest (normocapnia) and during hypercapnia induced by breathing 5% CO2 in air. CrCP and the resistance-area product (RAP) were obtained for each cardiac cycle and their dynamic response to a step change in MAP was calculated by means of transfer function analysis. The recovery of the CBFV response, following a step change in MAP, was mainly due to the contribution of RAP during both breathing conditions. However, CrCP made a highly significant contribution during normocapnia (P < 0.0001) and was the sole determinant of changes in the CBFV response, resulting from hypercapnia, which led to a reduction in the autoregulation index from 5.70 ± 1.58 (normocapnia) to 4.14 ± 2.05 (hypercapnia; P < 0.0001). In conclusion, CrCP makes a very significant contribution to the dynamic CBFV response to changes in MAP and plays a major role in explaining the deterioration of dynamic CA induced by hypercapnia. Further studies are needed to assess the relevance of CrCP contribution in physiological and clinical studies.

Pathophysiological and clinical considerations in the perioperative care of patients with a previous ischaemic stroke: a multidisciplinary narrative review.

With an ageing population and increasing incidence of cerebrovascular disease, an increasing number of patients presenting for routine and emergency surgery have a prior history of stroke. This presents a challenge for pre-, intra-, and postoperative management as the neurological risk is considerably higher. Evidence is lacking around anaesthetic practice for patients with vascular neurological vulnerability. Through understanding the pathophysiological changes that occur after stroke, insight into the susceptibilities of the cerebral vasculature to intrinsic and extrinsic factors can be developed. Increasing understanding of post-stroke systemic and cerebral haemodynamics has provided improved outcomes from stroke and more robust secondary prevention, although this knowledge has yet to be applied to our delivery of anaesthesia in those with prior stroke. This review describes the key pathophysiological and clinical considerations that inform clinicians providing perioperative care for patients with a prior diagnosis of stroke.

The upper frequency limit of dynamic cerebral autoregulation.

KEY POINTS: Dynamic cerebral autoregulation (CA) is expressed by the temporal pattern of cerebral blood flow (CBF) recovery following a sudden change in arterial blood pressure (BP). Transfer function analysis of BP as input and CBF velocity as output can express dynamic CA through its amplitude (or gain) and phase frequency responses. The upper frequency limit (FupLim ) at which dynamic CA can operate is of considerable physiological interest and can also provide additional information about worsening CA due to disease processes. In healthy subjects FupLim was strongly dependent on arterial PCO2 changes induced by four different breathing manoeuvres. The considerable intersubject variability in FupLim suggests that fixed frequency bands should not be adopted for averaging values of gain and phase in studies of dynamic CA. ABSTRACT: Dynamic cerebral autoregulation (CA) can be expressed in the frequency domain by the amplitude and phase frequency responses calculated by transfer function analysis of arterial blood pressure (BP) and cerebral blood flow velocity (CBFV). We studied the effects of arterial PCO2 ( PaCO2 ) on the upper frequency limit (FupLim ) of these responses and its intersubject variability. Twenty-four healthy subjects (11 female, age 36.0 ± 13.4 years) were recruited. Recordings of CBFV (transcranial Doppler ultrasound), BP (Finometer) and end-tidal CO2 ( PETCO2 , capnography) were performed during 5 min at rest (normocapnia) and during four breathing manoeuvres: 5% and 8% CO2 in air and hyperventilation targeting reductions of 5 and 10 mmHg compared to normocapnia. FupLim was determined by the break point of the autoregulation index (ARI) curve as a function of frequency when the phase response was gradually set to zero. The five breathing conditions led to highly significant differences in PETCO2 (p < 0.0001), CBFV (P < 0.0001), ARI (p < 0.0001) and FupLim (p < 0.0001). FupLim ranged from 0.167 ± 0.036 Hz at the lowest values of hypocapnia (28.1 ± 1.9 mmHg) to 0.094 ± 0.040 Hz at the highest level of hypercapnia (41.7 ± 5.4 mmHg), showing a correlation of r = -0.53 (p < 0.001) with PETCO2 . These findings reinforce the key role of PaCO2 in CBF regulation. The considerable intersubject variability of FupLim suggests that fixed frequency bands should not be adopted for averaging values of gain and phase in dynamic CA studies, and that the higher frequency band (0.20-0.40 Hz), in particular, does not contain relevant information about dynamic CA. Further investigations are needed to assess the information value of FupLim as a marker of dynamic CA efficiency in physiological and clinical studies.

Determining differences between critical closing pressure and resistance-area product: responses of the healthy young and old to hypocapnia.

Healthy ageing has been associated with lower cerebral blood flow velocities (CBFVs); however, the behaviour of hemodynamic parameters associated with cerebrovascular tone (critical closing pressure, CrCP) and cerebrovascular resistance (resistance-area product, RAP) remains unclear. Specifically, evidence supports ageing being associated with greater cerebrovascular tone and resistance during exercise with elevated CrCP and RAP in older individuals at rest and during exercise. Comprehensive hemodynamic assessment of CrCP and RAP during hyperventilation-induced hypocapnia in two distinct age groups (young ≤ 49 and old > 50) has not been described. CBFV in the middle cerebral artery (CBFV, transcranial Doppler), blood pressure (BP, Finometer) and end-tidal CO2 (EtCO2, capnography) were recorded in 104 healthy individuals (43 young [age 33.8 (9.3) years], 61 old [age 64.1 (8.5) years]) during a minimum of 60 s of metronome-driven hyperventilation-induced hypocapnia. Autoregulation index was calculated as a function of time, using a moving window autoregressive-moving average model. CBFV was reduced in response to age (p < 0.0001) and hypocapnia (p = 0.023) (young 57.3 (14.4) vs. 44.9 cm s-1 (11.1), old 51.7 (12.9) vs. 37.8 cm s-1 (9.6)). Critical closing pressure (CrCP) increased significantly in response to hypocapnia (young 37.6 (18.5) vs. 39.7 mmHg (16.0), old 33.9 (13.5) vs. 39.3 mmHg (11.4); p < 0.0001). Resistance-area product was increased in response to age (p = 0.001) and hypocapnia (p = 0.004) (young 1.02 (0.40) vs. 1.09 mmHg cm s-1 (11.07), old 1.16 (0.34) vs. 1.34 mmHg cm s-1 (0.39)). RAP and not CrCP mediates differences in cerebrovascular resistance responses to hypocapnia between the healthy young and old individuals.

Interaction of Blood Pressure Lowering and Alteplase Dose in Acute Ischemic Stroke: Results of the Enhanced Control of Hypertension and Thrombolysis Stroke Study.

OBJECTIVE: To determine the extent to which the effects of intensive blood pressure (BP) lowering are modified by doses of alteplase in thrombolysis-eligible acute ischemic stroke (AIS) patients. METHODS: Prespecified analyses of the Enhanced Control of Hypertension and Thrombolysis Stroke Study for patients enrolled in both arms: (i) low-dose (0.6 mg/kg body weight) or standard-dose (0.9 mg/kg) alteplase and (ii) intensive (target systolic BP [SBP] 130-140 mm Hg) or guideline-recommended (target SBP <180 mm Hg) BP management. The primary outcome was functional recovery, measured by a shift in scores on modified Rankin scale at 90 days. The safety outcome was any intracranial hemorrhage (ICH). RESULTS: There were 925 participants (mean age 67 years, 39% female, 77% Asian) randomized to both arms: 242 randomly assigned to guideline/standard-dose (GS); 234 to guideline/low-dose (GL); 227 to intensive/standard-dose (IS); and 222 to intensive/low-dose (IL). Overall, average SBP levels within 24 h were lower in the low-dose compared to standard-dose alteplase group (146 and 144 vs. 151 and 150 mm Hg, for GS and GL vs. IS and IL, respectively, p < 0.0001). There was no heterogeneity of the effects of BP lowering (intensive vs. guideline) on functional recovery between standard-dose (OR 0.81, 95% CI 0.59-1.12) and low-dose alteplase (1.06, 0.77-1.47; p = 0.25 for interaction). Similar results were observed for ICH (p = 0.50 for interaction). CONCLUSIONS: In thrombolysis-treated patients with predominantly mild-to-moderate severity AIS, intensive BP lowering neither improve functional recovery, either with low- or standard-dose intravenous alteplase, nor beneficially interact with low-dose alteplase in reducing ICH. TRIAL REGISTRATION: The trial is registered with ClinicalTrials.gov (NCT01422616).

Cerebral autoregulation in hemorrhagic stroke: A systematic review and meta-analysis of transcranial Doppler ultrasonography studies.

PURPOSE: International guidelines advocate intensive blood pressure (BP) lowering within 6 hours of acute intracerebral hemorrhage (ICH) to a target systolic BP of 130-140 mm Hg, though more intensive lowering may be associated with adverse outcome. Observational studies suggest impaired cerebral autoregulation (CA) following ICH. Transcranial Doppler ultrasonography (TCD), alongside continuous BP monitoring, provides a noninvasive bedside investigation that offers detailed perspectives on physiological perturbations post-acute ICH. This systematic review and meta-analysis focuses on all TCD studies of CA in ICH. METHODS: MEDLINE, EMBASE, and CENTRAL were searched for studies of hemorrhagic stroke and blood flow measurement. RESULTS: Eight studies met inclusion criteria (293 ICH patients); CA was impaired up to 12-days post-acute ICH. Impaired CA was evidenced by reduced transfer function analysis phase and higher mean flow correlation values: these were associated with worsened clinical parameters including ICH-volume and Glasgow Coma Scale. Meta-analysis of CBV demonstrated that, compared to controls, mean CBV was significantly lower in the ipsilateral (49.7 vs 64.8 cm s-1 , Z = 4.26, P < .0001) and contralateral hemispheres following ICH (51.5 vs 64.8 cm s-1 , Z = 3.44, P = .0006). CONCLUSION: Lower mean CBV in combination with impaired CA may have implications for more intensive BP lowering and warrants further studies examining such strategies on cerebral blood flow and its regulatory mechanisms.

Managing high blood pressure during acute ischemic stroke and intracerebral hemorrhage.

PURPOSE OF REVIEW: Blood pressure (BP) elevations above premorbid levels are observed in at least 60% of acute ischemic and hemorrhagic stroke patients, within the first 24 h of symptom onset. A number of potential causes have been hypothesized, and high BP may be associated with poor stroke outcome. This review discusses management strategies of high BP in acute stroke, in the context of current guidelines. RECENT FINDINGS: Excessive BP elevation can impact acute stroke therapeutic strategies, particularly in modifying intervention safety and efficacy. Currently, guidance on BP management in acute ischemic stroke and intracerebral hemorrhage (ICH) exists in a limited number of specific clinical presentations, including spontaneous ICH and continuing versus stopping preexisting antihypertensive therapy. However, ongoing clinical trials will further investigate the safety and efficacy of urgent BP-lowering therapy for other indications. SUMMARY: There are clear national and international guidelines on BP lowering for specific indications, as well as ongoing clinical trials aiming to address common clinical scenarios in which the evidence-base is lacking and uncertain. This is specifically in important stroke subgroups previously excluded from trials, patients requiring mechanical thrombectomy and nonvitamin K antagonist-associated ICH reversal.

Lipid-Lowering Pretreatment and Outcome Following Intravenous Thrombolysis for Acute Ischaemic Stroke: A Post Hoc Analysis of the Enhanced Control of Hypertension and Thrombolysis Stroke Study Trial.

BACKGROUND: Debate exists as to whether statin pretreatment confers an increased risk of 90-day mortality and symptomatic intracranial haemorrhage (sICH) in acute ischaemic stroke (AIS) patients treated with intravenous thrombolysis. We assessed the effects of undifferentiated lipid-lowering pretreatment on outcomes and interaction with low-dose versus standard-dose alteplase in a post hoc subgroup -analysis of the Enhanced Control of Hypertension and Thrombolysis Stroke Study. METHODS: In all, 3,284 thrombolysis-eligible AIS patients (mean age 66.6 years; 38% women), with information on lipid-lowering pretreatment, were randomly assigned to low-dose (0.6 mg/kg) or standard-dose (0.9 mg/kg) intravenous alteplase within 4.5 h of symptom onset. Of the total number of patients, 615 (19%) received statin or other lipid-lowering pretreatment. The primary clinical outcome was combined endpoint of death or disability (modified Rankin Scale scores 2-6) at 90 days. RESULTS: Compared with patients with no lipid-lowering pretreatment, those with lipid-lowering pretreatment were significantly older, more likely to be non-Asian and more likely to have a medical history including vascular co-morbidity. After propensity analysis assessment and adjustment for important baseline variables at the time of randomisation, as well as imbalances in management during the first 7 days of hospital admission, there were no significant differences in mortality (OR 0.85; 95% CI 0.58-1.25, p = 0.42), or in overall -90-day death and disability (OR 0.85, 95% CI 0.67-1.09, p = 0.19), despite a significant decrease in sICH among those with -lipid-lowering pretreatment according to the European Co-operative Acute Stroke Study 2 definition (OR 0.49, 95% CI 0.28-0.83, p = 0.009). No differences in key efficacy or safety outcomes were seen in patients with and without lipid-lowering pretreatment between low- and standard-dose alteplase arms. CONCLUSIONS: Lipid-lowering pretreatment is not associated with adverse outcome in AIS patients treated with intravenous alteplase, whether assessed by 90-day death and disability or death alone.