Monitoring of cerebral blood flow autoregulation: physiologic basis, measurement, and clinical implications

Impaired Cerebral Autoregulation in Children

Managing acute brain injury involves protecting the brain from secondary injury by addressing the mismatch between metabolic demand and cerebral perfusion. Observational studies have associated impaired cerebral autoregulation, a physiological process governing the regulation of cerebral blood flow, with unfavorable neurological outcomes in both pediatric and adult populations. We review the pathophysiology of cerebral autoregulation and discuss methods for assessing and monitoring it in children after acquired brain injury. We also examine the current research investigating the relationship between impaired cerebral autoregulation and outcomes following traumatic brain injury, cardiac arrest, cardiopulmonary bypass, and extracorporeal membrane oxygenation. Furthermore, we outline potential areas for future research in cerebral autoregulation and its clinical implications for pediatric patients with brain injuries.

Intra-operative haemodynamic monitoring and management of adults having noncardiac surgery: A statement from the European Society of Anaesthesiology and Intensive Care

This article was developed by a diverse group of 25 international experts from the European Society of Anaesthesiology and Intensive Care (ESAIC), who formulated recommendations on intra-operative haemodynamic monitoring and management of adults having noncardiac surgery based on a review of the current evidence. We recommend basing intra-operative arterial pressure management on mean arterial pressure and keeping intra-operative mean arterial pressure above 60 mmHg. We further recommend identifying the underlying causes of intra-operative hypotension and addressing them appropriately. We suggest pragmatically treating bradycardia or tachycardia when it leads to profound hypotension or likely results in reduced cardiac output, oxygen delivery or organ perfusion. We suggest monitoring stroke volume or cardiac output in patients with high baseline risk for complications or in patients having high-risk surgery to assess the haemodynamic status and the haemodynamic response to therapeutic interventions. However, we recommend not routinely maximising stroke volume or cardiac output in patients having noncardiac surgery. Instead, we suggest defining stroke volume and cardiac output targets individually for each patient considering the clinical situation and clinical and metabolic signs of tissue perfusion and oxygenation. We recommend not giving fluids simply because a patient is fluid responsive but only if there are clinical or metabolic signs of hypovolaemia or tissue hypoperfusion. We suggest monitoring and optimising the depth of anaesthesia to titrate doses of anaesthetic drugs and reduce their side effects.

Regional Hypoperfusion Predicts White Matter Tract Degeneration in Recent Single Subcortical Infarcts

BACKGROUND

The association between baseline cerebral perfusion status and perilesional white matter degeneration in recent single subcortical infarcts (RSSIs) is still not well understood. We aimed to investigate the clinical relevance and possible predictors of long-term morphological changes of RSSIs.

METHODS

Patients with RSSI who had baseline computed tomography perfusion and at least 1 follow-up magnetic resonance imaging were retrospectively enrolled from the stroke registry databases. Computed tomography perfusion measurements, infarct size and location, small vessel disease burden, and clinical and radiological outcomes were evaluated. We assessed the association between perfusion status and neuroimaging evolution.

RESULTS

Among the eligible 104 patients with RSSI, the majority (80.8%) had cavitated lesion evolution, and nearly half (46.2%) developed white matter tract degeneration. Patients with secondary white matter injury showed worse functional outcomes. The computed tomography perfusion parameter ratios were defined as the measurements in the regions of interest (infarct lesion or mirrored region) divided by those in the hemisphere of the same side with regions of interest. Lower cerebral blood flow ratio and cerebral blood volume ratio on either lesion side and opposite side were independently associated with white matter tract degeneration after adjusting for hypertension, National Institutes of Health Stroke Scale score, lesion volume, corticospinal tract infarction and follow-up time. We also found a mediation effect of the contralateral cerebral blood flow ratio between corticospinal tract infarction and white matter injury.

CONCLUSIONS

White matter tract degeneration has potential clinical value for indicating worse functional outcomes in RSSIs. Baseline regional hypoperfusion, especially with a lower contralateral cerebral blood flow ratio, independently predicts secondary white matter injury.

Effect of prone position on cerebral hemodynamics and noninvasive intracranial pressure assessed using transcranial Doppler in patients undergoing spine surgeries: a prospective observational study

BACKGROUND

The prone position, frequently used in spine surgeries for optimal surgical access, induces physiological changes in cardiovascular and respiratory parameters. Increased intraabdominal and intrathoracic pressures lead to elevated central venous pressure (CVP). Along with raised intrathoracic pressure, positive end-expiratory pressure (PEEP) results in elevated CVP, impeding venous blood flow from the brain and potentially affecting intracranial pressure (ICP).1 Transcranial Doppler (TCD) ultrasound is a non-invasive method commonly used to measure cerebral hemodynamic parameters, including peak systolic velocity (PSV/ MCAvpeak), mean flow velocity (MFV/MCAvmean), pulsatility index (PI) and resistivity index (RI), which are associated with cerebral vascular resistance, intracranial pressure, and cerebral perfusion pressure (CPP).

METHOD

Thirty-three patients undergoing spine surgery were assessed. The vital and TCD parameters PSV/MCAvpeak, MFV/MCAvmean, PI, and RI were noted in the supine position. (Ta). General anaesthesia was administered, and TCD measurements were repeated after induction. (Ts). Patients were then positioned prone, and TCD measurements were repeated at intervals Tp0 - immediately after the prone position, Tp15 -15 min of the prone position, Tp30 -30 min, Tp45 -45 min and Tp60 - 60 min. Vital parameters were noted at the above-mentioned time points. Non-invasive ICP (nICP) was calculated.

RESULTS

There was a statistically significant decrease in the heart rate (HR) compared to the supine position at Tp45 and Tp45 as compared to Tp0. There was a statistically significant decrease in systolic blood pressure (SBP) as compared to Ta at Tp0 (p < 0.001), Tp15 (p < 0.001), Tp30 (p = 0.003), Tp45 (p = 0.001), and Tp60 (p = 0.018). The study found no statistically significant changes in cerebral hemodynamic parameters (PSV/MCAvpeak, MFV/MCAvmean, PI and RI) and nICP at various time points.

CONCLUSION

Our findings suggest that the prone position does not cause significant changes in cerebral hemodynamics and nICP.

TRIAL REGISTRATION

CTRI/2023/06/053677 dated 08/06/2023.

Comparison of Optic Nerve Sheath Diameter Measurements in Coronary Artery Bypass Grafting Surgery with Pulsatile and Non-Pulsatile Flow

Background and Objectives: In coronary artery bypass grafting (CABG) surgeries, monitoring intracranial pressure (ICP) is crucial due to neurological risks. Although pulsatile flow (PF) during cardiopulmonary bypass (CPB) is considered more physiological than non-pulsatile flow (NPF), its impact on ICP remains unclear. This study aimed to compare preoperative and postoperative optic nerve sheath diameter (ONSD) measurements between PF and NPF techniques to evaluate their effect on ICP changes. Materials and Methods: Sixty patients undergoing elective CABG (aged 45-75 years, ASA II-III-IV) were enrolled and divided into two groups depending on the cardiopulmonary bypass technique determined by the surgeon: PF (Group P, n = 30) and NPF (Group NP, n = 30). ONSD measurements were performed with ultrasound before surgery (Tpreop) and after surgery (Tpostop). Hemodynamic parameters and jugular and carotid vessel diameters were also recorded. Statistical analysis included t-tests, Mann-Whitney U-tests, chi-square tests, and Pearson correlation. Results: Both groups demonstrated significant increases in ONSD postoperatively compared to preoperative values (p < 0.001). However, no statistically significant difference in the magnitude of ONSD change was observed between the PF and NPF groups (p > 0.05). Group P showed lower ejection fractions and higher total inotrope requirements compared to Group NP (p < 0.01), but these factors did not translate into differences in postoperative ICP dynamics. Conclusions: ONSD measurements increased significantly after CABG surgery, regardless of perfusion type. PF and NPF strategies were comparable in terms of their effects on ICP as reflected by ONSD changes. ONSD ultrasonography appears to be a simple, rapid, and non-invasive tool for perioperative ICP monitoring in cardiac surgery. Further studies are needed to confirm these findings with dynamic intraoperative monitoring and neurocognitive assessments.

The intersection of delirium and long-term cognition in older adults: the critical role of delirium prevention

Delirium, a neuropsychiatric syndrome characterized by an acute and usually reversible state of confusion, while dementia is a chronic, acquired cognitive impairment that significantly reduces a patient's ability to perform daily tasks, learn, work, and engage in social interactions. Previous studies indicates that individuals with dementia are more susceptible to delirium than the general population, and that delirium serves as an independent risk factor for the subsequent onset of dementia. However, a major controversy in this field concerns whether delirium is merely a marker of vulnerability to dementia, or whether delirium-induced adverse outcomes such as falls and functional decline contribute to dementia, or whether delirium directly causes permanent neuronal damage and lead to dementia. It is possible that all these hypotheses hold some truth. In this review, we examine the shared and distinct mechanisms of delirium and dementia by reviewing their clinical features, epidemiology, clinicopathological, biomarkers, neuroimaging, and recent experimental studies, and we discuss the importance of targeting delirium to explore new preventive and therapeutic strategies for reducing long-term cognitive impairment.

Sex differences in sleep apnea and Alzheimer's Disease: role of cerebrovascular dysfunction

Obstructive sleep apnea (OSA) significantly impacts cardiovascular health in post-menopausal females. Given that cardiovascular and cerebrovascular diseases are tightly linked, OSA-mediated impacts on cerebrovascular function and Alzheimer's Disease (AD) risk are also likely more manifest in females. This review will: summarize sex differences in cerebrovascular function, review the vascular hypothesis of AD, characterize sex differences in the OSA phenotype and implications for cerebrovascular control, and highlight OSA-mediated AD risk.

Continuous monitoring of intracranial pressure and end tidal carbon dioxide variations in traumatic brain injury: introducing the carbon dioxide reactivity index (CO2Rx)

PURPOSE

The continuous monitoring of cerebral metabolic autoregulation in patients with severe traumatic brain injury (TBI) is poorly documented in the literature and largely absent from clinical practice. This study aimed to assess whether variations in intracranial pressure (ICP) and end-tidal carbon dioxide (ETCO2) can form the basis of an index for cerebrovascular autoregulation reactivity, and whether this index can improve the prediction of clinical outcomes in both adult and pediatric TBI patients.

METHODS

Data from adult and pediatric patients with severe TBI were retrospectively analyzed. The Carbon Dioxide Reactivity Index (CO2Rx) was introduced as a novel tool to assess cerebrovascular reactivity in response to variations in CO2 and ICP. CO2Rx was calculated by analyzing the relationship between ICP and ETCO2, sampled at approximately 5-minute intervals, using linear correlation within moving time windows ranging from 40 to 180 min in 10-minute increments. The discriminatory power of CO2Rx in predicting clinical outcomes was evaluated through Receiver Operating Characteristic (ROC) curve analysis. The primary outcome measures included in-hospital mortality and the 12-month Glasgow Outcome Scale-Extended (GOSE) score.

RESULTS

The study included 218 TBI patients (40 pediatric and 178 adult). CO2Rx values showed a significant correlation with outcomes, with a CO2Rx threshold of 0.28 effectively distinguishing between favorable and unfavorable outcomes. For the fatal/non-fatal outcome, the CO2Rx crude model alone had an Area Under the Curve (AUC) of 0.737. When combined with other predictors (Impact Core + ICP + CO2Rx), this model achieved the highest AUC of 0.929.

CONCLUSION

CO2Rx demonstrated significant predictive value for mortality and unfavorable outcomes in TBI patients, serving as a continuous index of cerebrovascular reactivity to CO2. It holds potential to improve severe TBI management by optimizing the interaction between ventilation and metabolic autoregulation.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT NCT05043545.

Systematic review and meta-analysis of transcranial doppler biomarkers for the prediction of delayed cerebral ischemia following subarachnoid hemorrhage

Delayed cerebral ischemia (DCI) following an aneurysmal subarachnoid hemorrhage (aSAH) significantly impacts mortality, morbidity, and healthcare costs. This study assessed the diagnostic accuracy of Transcranial Doppler (TCD)-derived biomarkers for predicting DCI via a systematic review and meta-analysis. Included studies had to correctly define DCI and report data on sensitivity, specificity, positive predictive value, and negative predictive value. Univariate or bivariate analyses with a random effects model were used, and risk of bias was evaluated with the Quality Assessment of Diagnostic Accuracy Studies. From 23 eligible articles (n = 2371 patients), three biomarker categories were identified: cerebral blood flow velocities (CBFV), cerebral autoregulation, and microembolic signals (MES). The highest sensitivity (0.86, 95% CI 0.71-0.94) and specificity (0.75, 95% CI 0.52-0.94) for DCI prediction were achieved with a mean CBFV of 120 cm/s combined with a Lindegaard ratio. The transient hyperemic response test showed the best performance among autoregulatory biomarkers with a sensitivity of 0.88, (95% CI 0.54-0.98) and specificity of 0.82 (95% CI 0.52-0.94). MES were less effective predictors. Combining CBFV with autoregulatory biomarkers enhanced TCD's predictive value. High heterogeneity and risk of bias were noted, indicating the need for a standardized TCD approach for improved DCI evaluation.

Impact of mild hypo- and hyperventilation on cerebral oxygen supply during general anesthesia

OBJECTIVE

Cerebral blood flow autoregulation is affected by several physiologic and medical factors. Especially arterial carbon dioxide pressures (PaCO2) impact cerebral blood flow. Only extensive changes in end-tidal CO2 have been studied so far. The aim of this study was to evaluate the impact of mild hypo- and hyperventilation on cerebral blood flow as assessed by regional cerebral red blood cell oxygen saturation (rSO2) in two age groups.

METHODS

Two groups of patients were compared under general anesthesia before the surgical procedure was started: A younger patient group (age < 40 years; YP) and older patients aged > 60 years (OP). Anesthetic management was standardized. In both groups, end-tidal CO2 was adjusted either to a low-normal value of 35-37 mmHg or a high-normal value of 43-45 mmHg for 15 min each. The sequence of these interventions was randomized. rSO2 was estimated by near-infrared spectroscopy (NIRS). The primary outcome was defined as the difference in rSO2 between hypo- and hyperventilation between the two age groups.

RESULTS

A total of 78 patients were included. In both groups, there was a statistically significant difference in rSO2 values after 15 min of hypo- versus hyperventilation. In the YP-group, rSO2 was 74 ± 4% after 15 min of hypoventilation and decreased to 68 ± 6% during hyperventilation (p < 0.001). In the OP-group, rSO2 was 71 ± 5% and 65 ± 6%, respectively (p < 0.001). There was no difference concerning changes in comparison of younger and elder patient groups (in both groups, Δ rSO2 = 6 ± 3%; p = 0.732).

CONCLUSION

Even mild hypoventilation increased rSO2 compared to mild hyperventilation and this difference occurred independent of age.

Individualized autoregulation-guided arterial blood pressure management in neurocritical care

Cerebral autoregulation (CA) is the physiological process by which cerebral blood flow is maintained during fluctuations in arterial blood pressure (ABP). There are various validated methods to measure CA, either invasively, with intracranial pressure or brain tissue oxygenation monitors, or noninvasively, with transcranial Doppler ultrasound or near-infrared spectroscopy. Utilizing these monitors, researchers have been able to discern CA patterns in several pathological states, such as but not limited to acute ischemic stroke, spontaneous intracranial hemorrhage, aneurysmal subarachnoid hemorrhage, sepsis, and post-cardiac arrest, and they have found CA to be altered in these patients. CA disturbances predispose patients suffering from these ailments to worse outcomes. Much focus has been placed on CA monitoring in these populations, with an emphasis on arterial blood pressure optimization. Many guidelines recommend universal static ABP targets; however, in patients with altered CA, these targets may make them susceptible to hypoperfusion and further neurological injury. Based on this observation, there has been much investigation on individualized ABP goals and their effect on clinical outcomes. The scope of this review includes (1) a summary of the physiology of CA in healthy adults; (2) a review of the evidence on CA monitoring in healthy individuals; (3) a summary of CA changes and its effect on outcomes in various diseased states including acute ischemic stroke, spontaneous intracranial hemorrhage, aneurysmal subarachnoid hemorrhage, sepsis and meningitis, post-cardiac arrest, hypoxic-ischemic encephalopathy, surgery, and moyamoya disease; and (4) a review of the current evidence on individualized ABP changes in various patient populations.

Evaluation of the effect of fluid management on intracranial pressure in patients undergoing laparoscopic gynaecological surgery based on the ratio of the optic nerve sheath diameter to the eyeball transverse diameter as measured by ultrasound: a randomised controlled trial

BACKGROUND

During gynecological laparoscopic surgery, pneumoperitoneum and the Trendelenburg position (TP) can lead to increased intracranial pressure (ICP). However, it remains unclear whether perioperative fluid therapy impacts ICP. The purpose of this research was to evaluate the impact of restrictive fluid (RF) therapy versus conventional fluid (CF) therapy on ICP in gynecological laparoscopic surgery patients by measuring the ratio of the optic nerve sheath diameter (ONSD) to the eyeball transverse diameter (ETD) using ultrasound.

METHODS

Sixty-four patients who were scheduled for laparoscopic gynecological surgery were randomly assigned to the CF group or the RF group. The main outcomes were differences in the ONSD/ETD ratios between the groups at predetermined time points. The secondary outcomes were intraoperative circulatory parameters (including mean arterial pressure, heart rate, and urine volume changes) and postoperative recovery indicators (including extubation time, length of post-anaesthesia care unit stay, postoperative complications, and length of hospital stay).

RESULTS

There were no statistically significant differences in the ONSD/ETD ratio and the ONSD over time between the two groups (all p > 0.05). From T2 to T4, the ONSD/ETD ratio and the ONSD in both groups were higher than T1 (all p < 0.001). From T1 to T2, the ONSD/ETD ratio in both groups increased by 14.3%. However, the extubation time in the RF group was shorter than in the CF group [median difference (95% CI) -11(-21 to -2) min, p = 0.027]. There were no differences in the other secondary outcomes.

CONCLUSION

In patients undergoing laparoscopic gynecological surgery, RF did not significantly lower the ONSD/ETD ratio but did shorten the tracheal extubation time, when compared to CF.

TRIAL REGISTRATION

ChiCTR2300079284. Registered on December 29, 2023.