Cerebral Autoregulation Monitoring with Ultrasound-Tagged Near-Infrared Spectroscopy in Cardiac Surgery Patients

Myths and methodologies: Assessment of dynamic cerebral autoregulation by the mean flow index

The mean flow index-usually referred to as Mx-has been used for assessing dynamic cerebral autoregulation (dCA) for almost 30 years. However, concerns have arisen regarding methodological consistency, construct and criterion validity, and test-retest reliability. Methodological nuances, such as choice of input (cerebral perfusion pressure, invasive or non-invasive arterial pressure), pre-processing approach and artefact handling, significantly influence mean flow index values, and previous studies correlating mean flow index with other established dCA metrics are confounded by inherent methodological flaws like heteroscedasticity, while the mean flow index also fails to discriminate individuals with presumed intact versus impaired dCA (discriminatory validity), and its prognostic performance (predictive validity) across various conditions remains inconsistent. The test-retest reliability, both within and between days, is generally poor. At present, no single approach for data collection or pre-processing has proven superior for obtaining the mean flow index, and caution is advised in the further use of mean flow index-based measures for assessing dCA, as current evidence does not support their clinical application.

Perioperative stroke

Ischaemic or haemorrhagic perioperative stroke (that is, stroke occurring during or within 30 days following surgery) can be a devastating complication following surgery. Incidence is reported in the 0.1-0.7% range in adults undergoing non-cardiac and non-neurological surgery, in the 1-5% range in patients undergoing cardiac surgery and in the 1-10% range following neurological surgery. However, higher rates have been reported when patients are actively assessed and in high-risk populations. Prognosis is significantly worse than stroke occurring in the community, with double the 30-day mortality, greater disability and diminished quality of life among survivors. Considering the annual volume of surgeries performed worldwide, perioperative stroke represents a substantial burden. Despite notable differences in aetiology, patient populations and clinical settings, existing clinical recommendations for perioperative stroke are extrapolated mainly from stroke in the community. Perioperative in-hospital stroke is unique with respect to the stroke occurring in other settings, and it is essential to apply evidence from other settings with caution and to identify existing knowledge gaps in order to effectively guide patient care and future research.

Regional disparity in continuously measured time-domain cerebrovascular reactivity indices: a scoping review of human literature

Objective: Cerebral blood vessels maintaining relatively constant cerebral blood flow (CBF) over wide range of systemic arterial blood pressure (ABP) is referred to as cerebral autoregulation (CA). Impairments in CA expose the brain to pressure-passive flow states leading to hypoperfusion and hyperperfusion. Cerebrovascular reactivity (CVR) metrics refer to surrogate metrics of pressure-based CA that evaluate the relationship between slow vasogenic fluctuations in cerebral perfusion pressure/ABP and a surrogate for pulsatile CBF/cerebral blood volume.Approach: We performed a systematically conducted scoping review of all available human literature examining the association between continuous CVR between more than one brain region/channel using the same CVR index.Main Results: In all the included 22 articles, only handful of transcranial doppler (TCD) and near-infrared spectroscopy (NIRS) based metrics were calculated for only two brain regions/channels. These metrics found no difference between left and right sides in healthy volunteer, cardiac surgery, and intracranial hemorrhage patient studies. In contrast, significant differences were reported in endarterectomy, and subarachnoid hemorrhage studies, while varying results were found regarding regional disparity in stroke, traumatic brain injury, and multiple population studies.Significance: Further research is required to evaluate regional disparity using NIRS-based indices and to understand if NIRS-based indices provide better regional disparity information than TCD-based indices.

Cerebral tissue oximeter suitable for real-time regional oxygen saturation monitoring in multiple clinical settings

Maintenance of adequate blood perfusion and oxygen delivery is essential for cerebral metabolism. Cerebral oximeters based on near-infrared spectroscopy (NIRS) have been used for noninvasive, continuous, real-time monitoring of cerebral oxygen saturation and management of cerebral oxygen adequacy perioperatively and intraoperatively in various clinical situations, such as cardiac surgery, anesthesia, and cerebral auto-regulation. In this study, a portable and modular cerebral tissue oximeter (BRS-1) was designed for real-time detection of regional oxygen saturation over the brain, finger, or other targeted body tissues, as well as for wireless cerebral oxygenation monitoring. The compact and lightweight design of the system makes it easy to use during ambulance transport, in an emergency cart, or in an intensive care unit. The system performance of the BRS-1 oximeter was evaluated and compared with two US FDA-cleared cerebral oximeters during a controlled hypoxia experiment. The results showed that the BRS-1 oximeter can be used for real-time detection of cerebral desaturation with an accuracy similar to the two commercial oximeters. More importantly, the BRS-1 oximeter is capable of capturing cerebral oxygen saturation wirelessly. The BRS-1 cerebral oximeter can provide valuable insights for clinicians for real-time monitoring of cerebral/tissue perfusion and management of patients in prehospital and perioperative periods.

Advances in Neuroimaging and Monitoring to Defend Cerebral Perfusion in Noncardiac Surgery

Noncardiac surgery conveys a substantial risk of secondary organ dysfunction and injury. Neurocognitive dysfunction and covert stroke are emerging as major forms of perioperative organ dysfunction, but a better understanding of perioperative neurobiology is required to identify effective treatment strategies. The likelihood and severity of perioperative brain injury may be increased by intraoperative hemodynamic dysfunction, tissue hypoperfusion, and a failure to recognize complications early in their development. Advances in neuroimaging and monitoring techniques, including optical, sonographic, and magnetic resonance, have progressed beyond structural imaging and now enable noninvasive assessment of cerebral perfusion, vascular reserve, metabolism, and neurologic function at the bedside. Translation of these imaging methods into the perioperative setting has highlighted several potential avenues to optimize tissue perfusion and deliver neuroprotection. This review introduces the methods, metrics, and evidence underlying emerging optical and magnetic resonance neuroimaging methods and discusses their potential experimental and clinical utility in the setting of noncardiac surgery.

Reliability and validity of the mean flow index (Mx) for assessing cerebral autoregulation in humans: A systematic review of the methodology

Cerebral autoregulation is a complex mechanism that serves to keep cerebral blood flow relatively constant within a wide range of cerebral perfusion pressures. The mean flow index (Mx) is one of several methods to assess dynamic cerebral autoregulation, but its reliability and validity have never been assessed systematically. The purpose of the present systematic review was to evaluate the methodology, reliability and validity of Mx.Based on 128 studies, we found inconsistency in the pre-processing of the recordings and the methods for calculation of Mx. The reliability in terms of repeatability and reproducibility ranged from poor to excellent, with optimal repeatability when comparing overlapping recordings. The discriminatory ability varied depending on the patient populations; in general, those with acute brain injury exhibited a higher Mx than healthy volunteers. The prognostic ability in terms of functional outcome and mortality ranged from chance result to moderate accuracy.Since the methodology was inconsistent between studies, resulting in varying reliability and validity estimates, the results were difficult to compare. The optimal method for deriving Mx is currently unknown.

Neuromonitoring and Neurocognitive Outcomes in Cardiac Surgery: A Narrative Review

Neurocognitive dysfunction after cardiac surgery can present with diverse clinical phenotypes, which include postoperative delirium, postoperative cognitive dysfunction, and stroke, and it presents a significant healthcare burden for both patients and providers. Neurologic monitoring during cardiac surgery includes several modalities assessing cerebral perfusion and oxygenation (near-infrared spectroscopy, transcranial Doppler and jugular venous bulb saturation monitoring) and those that measure cerebral function (processed and unprocessed electroencephalogram), reflecting an absence of a single, definitive neuromonitor. This narrative review briefly describes the technologic basis of these neuromonitoring modalities, before exploring their use in clinical practice, both as tools to predict neurocognitive dysfunction, and with a bundle of interventions designed to optimize cerebral oxygen supply, with the aim of reducing postoperative delirium and cognitive dysfunction following cardiac surgery.

The response of a standardized fluid challenge during cardiac surgery on cerebral oxygen saturation measured with near-infrared spectroscopy

Near infrared spectroscopy (NIRS) has been used to evaluate regional cerebral tissue oxygen saturation (ScO₂) during the last decades. Perioperative management algorithms advocate to maintain ScO₂, by maintaining or increasing cardiac output (CO), e.g. with fluid infusion. We hypothesized that ScO₂ would increase in responders to a standardized fluid challenge (FC) and that the relative changes in CO and ScO₂ would correlate. This study is a retrospective substudy of the FLuid Responsiveness Prediction Using Extra Systoles (FLEX) trial. In the FLEX trial, patients were administered two standardized FCs (5 mL/kg ideal body weight each) during cardiac surgery. NIRS monitoring was used during the intraoperative period and CO was monitored continuously. Patients were considered responders if stroke volume increased more than 10% following FC. Datasets from 29 non-responders and 27 responders to FC were available for analysis. Relative changes of ScO₂ did not change significantly in non-responders (mean difference - 0.3% ± 2.3%, p = 0.534) or in fluid responders (mean difference 1.6% ± 4.6%, p = 0.088). Relative changes in CO and ScO₂ correlated significantly, p = 0.027. Increasing CO by fluid did not change cerebral oxygenation. Despite this, relative changes in CO correlated to relative changes in ScO₂. However, the clinical impact of the present observations is unclear, and the results must be interpreted with caution.Trial registration:http://ClinicalTrial.gov identifier for main study (FLuid Responsiveness Prediction Using Extra Systoles-FLEX): NCT03002129.

Comparative Study of Novel Noninvasive Cerebral Autoregulation Volumetric Reactivity Indices Reflected by Ultrasonic Speed and Attenuation as Dynamic Measurements in the Human Brain

This is a comparative study of two novel noninvasive cerebrovascular autoregulation (CA) monitoring methods based on intracranial blood volume (IBV) changes in the human brain. We investigated the clinical applicability of the new volumetric reactivity index (VRx2), reflected by intracranial ultrasonic attenuation dynamics for noninvasive CA monitoring. The CA was determined noninvasively on 43 healthy participants by calculating the volumetric reactivity index (VRx1 from time-of-flight of ultrasound, VRx2 from attenuation of ultrasound). The VRx was calculated as a moving correlation coefficient between the arterial blood pressure and noninvasively measured IBV slow waves. Linear regression between VRx1 and VRx2 (averaged per participants) showed a significant correlation (r = 0.731, p < 0.0001, 95% confidence interval [0.501–0.895]) in data filtered by bandpass filtering. On the other hand, FIR filtering demonstrated a slightly better correlation (r = 0.769, p < 0.0001, 95% confidence interval [0.611–0.909]). The standard deviation of the difference by bandpass filtering was 0.1647 and bias −0.3444; and by FIR filtering 0.1382 and bias −0.3669. This comparative study showed a significant coincidence of the VRx2 index compared to that of VRx1. Hence, VRx2 could be used as an alternative, cost-effective noninvasive cerebrovascular autoregulation index in the same way as VRx1 values are used.

Does uncontrolled diabetes mellitus affect cerebral hemodynamics in heart surgery?

Background

In this study, we aimed to investigate the effects of poor blood glucose control on the intraoperative cerebral system in patients undergoing coronary artery bypass grafting using various neuromonitors.

Methods

Between January 2011 and December 2011, a total of 40 adult patients (31 males, 9 females; mean age 58.8±9.2 years; range, 38 to 78 years) who were scheduled for elective coronary artery bypass grafting were included in the study. The patients were divided into four groups according to hemoglobin A1c levels as follows: Group 1 including non-diabetic controls (n=11); Group 2 including those with a hemoglobin A1c value of <7% (n=10); Group 3 including those with a hemoglobin A1c value of 7 to 10% (n=11); and Group 4 including those with a hemoglobin A1c value of ≥10% (n=8). Cerebral monitoring was performed with near-infrared spectroscopy and transcranial Doppler. Measurement periods were defined as follows: Before anesthesia induction (period 1), 10 min after anesthesia induction (period 2), during cannulation (period 3), 10 min after cardiopulmonary bypass (period 4), at 32°C temperature during cardiopulmonary bypass (period 5), at 36°C temperature during cardiopulmonary bypass (period 6), and at the end of the operation (period 7).

Results

There was a significant difference in the near-infrared spectroscopy values in the cannulation period for both right (p<0.001) and left (p=0.002) sides and the mean transcranial Doppler flow velocity (p=0.002) in Group 4, compared to Group 1. The heart rate was found to be significantly lower in Group 4 in the cannulation period. The near-infrared spectroscopy values and transcranial Doppler blood flow velocity decreased in Group 4 in all measurement periods.

Conclusion

The results of our study show that, in patients with severe diabetes undergoing open heart surgery, heart rate decreases in the cannulation period due to possible autonomic neuropathy, and cerebral blood flow and oxygenation decrease. For these patients, particularly in the cannulation period, perfusion of both cerebral and other organs should be closely monitored and necessary interventions should be performed.

Enhancement of diffuse correlation spectroscopy tissue blood flow measurement by acoustic radiation force

The current research on acousto-optic effects focuses on the interactions of acoustic waves with static optical properties rather than dynamic features such as tissue blood flow. Diffuse correlation spectroscopy (DCS) is an emerging technology capable of direct measurements of tissue blood flow by probing the movements of red blood cells (RBCs). In this article, we investigated the relations between the acoustic radiation force (ARF) and ultrasonic patterns by the finite element simulations. Based on the outcomes, we experimentally explored how the ultrasound-generated ARF enhance the DCS data as well as the blood flow measurements. The results yield the optimal pattern to generate ARF and elucidate the relations between the ultrasonic emission and flow elevations. The flow modality combing the DCS with ARF modulations, which was proposed in this study for the first time, would promote disease diagnosis and therapeutic assessment in the situation wherein the blood flow contrast between healthy and pathological tissues is insufficient.

Cerebrovascular autoregulation impairments during cardiac surgery with cardiopulmonary bypass are related to postoperative cognitive deterioration: prospective observational study

BACKGROUND

Postoperative cognitive dysfunction (POCD) occurs in approximately 33-83% of patients after cardiac surgery with cardiopulmonary bypass (CPB). Recent clinical data suggest that real-time, intraoperative monitoring of patient-specific cerebrovascular autoregulation (CA) may help to prevent POCD by detecting individual critical limits for mean arterial pressure (MAP) outside which CA is impaired. Objectives of the study were to detect the episodes of impaired CA during cardiac surgery with CPB, and to investigate the association between CA impairment and POCD.

METHODS

The observational study of non-invasive ultrasonic volumetric CA monitoring included 59 patients undergoing elective coronary artery bypass graft surgery with CPB. All patients underwent series of neuropsychological tests the day before and ten days after the surgery in order to evaluate cognitive function.

RESULTS

Twenty-two patients (37%) experienced POCD, 37 patients (63%) showed no cognitive deterioration. The duration of the single longest CA impairment event was found reliably associated with occurrence of POCD (P<0.05). The critical duration of the single longest CA impairment event was 5.03 minutes (odds ratio 14.5; CI 3.9-51.8) for studied population.

CONCLUSIONS

Prospective clinical study showed that single longest CA impairment may result in post-operative deterioration of mental abilities. The duration of the single longest CA impairment event is the risk factor that is associated with POCD.

Cerebrovascular autoregulation monitoring and patient-centred outcomes after cardiac surgery: a systematic review

BACKGROUND

Impaired cerebrovascular autoregulation (CVAR) is observed in up to 20% of cardiac surgical patients. This systematic review aims to evaluate the association between impaired CVAR, measured by current monitoring techniques, and patient-centred outcomes in adults following cardiac surgery.

METHODS

MEDLINE, EMBASE, PubMed, MEDLINE In-Process and Cochrane Library were systematically searched through 8 December 2017. Studies were included if they assessed associations between CVAR and patient-centred outcomes in the adult cardiac surgical population. The primary outcome of this systematic review was mortality. Secondary outcomes were stroke, delirium and acute kidney injury. Risk of bias was systematically assessed, and the GRADE methodology was used to evaluate the quality of evidence across outcomes.

RESULTS

Eleven observational studies and no randomised controlled trials met the inclusion criteria. Due to methodological heterogeneity, meta-analysis was not possible. There was a high risk of bias within individual studies and low quality of evidence across outcomes. Of the included studies, one assessed mortality, five assessed stroke, four assessed delirium, and three assessed acute kidney injury. No reliable conclusions can be drawn from the one study assessing mortality. Interpretation of studies investigating CVAR and stroke, delirium and acute kidney injury was complicated by the lack of standardisation of monitoring techniques as well as varying definitions of impaired CVAR.

CONCLUSIONS

There is a paucity of high quality evidence for CVAR monitoring and its associations with outcome measures in post-cardiac surgical patients, highlighting the need for future studies.

The patient with hypertension undergoing surgery

PURPOSE OF REVIEW

General recommendations for the perioperative management of patients with hypertensive disease have not evolved much over the past 20 years, yet new pathophysiological concepts have emerged and new monitoring techniques are available today. In this review, we will discuss their significance and potential role in the modern perioperative care of hypertensive patients.

RECENT FINDINGS

For hypertensive patients, total cardiovascular risk rather than blood pressure (BP) alone should determine the preoperative strategy. Except for grade 3 hypertension, surgery should not be deferred on the basis of an elevated BP in the preoperative assessment.New data suggest that even brief hypotensive episodes during surgery may have significant impact on outcome. Isolated systolic hypertension is the predominant phenotype in elderly patients who may be particularly vulnerable to hypoperfusion in the perioperative setting.New monitoring techniques such as echocardiography and near-infrared spectroscopy may provide crucial information to optimize intraoperative control of BP based on an individual patient's pathophysiology.

SUMMARY

Hypertension is highly prevalent in patients presenting for surgery yet its impact on surgical outcome is still debated. Guidelines on risk stratification and perioperative hemodynamic management of patients with hypertensive disease remain sparse and cannot rely much on solid new evidence. Target organ damage associated with hypertensive disease rather than high BP per se appears to determine perioperative risk. In the absence of new data, an individualized and pathophysiology-based approach to control BP may be the best option to guide these patients through the perioperative period.

Blood Flow and Continuous EEG Changes during Symptomatic Plateau Waves

Benign meningiomas uncommonly lead to significant cerebral edema, with only a few cases previously reported in the medical literature. The present study describes the case of a 49-year-old female who had a meningioma resection. She subsequently developed malignant cerebral edema and had episodes that were initially concerning for seizure activity. However, transient blood flow changes concerning for intracranial pressure (ICP) crises, were demonstrated on electroencephalogram (EEG) as well as noninvasive cerebral blood flow monitoring. The present case highlights the importance of close monitoring in patients with post meningioma resection cerebral edema because of the possibility of ICP crises.

Autoregulation in paediatric TBI-current evidence and implications for treatment

BACKGROUND

Children who survive acute traumatic brain injury are at risk of death from subsequent brain swelling and secondary injury. Strict physiologic management in the ICU after traumatic brain injury is believed to be key to survival, and cerebral perfusion pressure is a prominent aspect of post brain injury care. However, optimal cerebral perfusion pressure targets for children are not known. Autoregulation monitoring has been used to delineate individualized optimal perfusion pressures for patients with traumatic brain injury. The methods to do so are diverse, confusing, and not universally validated.

METHODS

In this manuscript, we discuss the history of autoregulation monitoring, outline and categorize the methods used to measure autoregulation, and review the available validation data for methods used to monitor autoregulation.

CONCLUSIONS

Impaired autoregulation after traumatic brain injury is associated with a poor prognosis. Observational data suggests that optimal neurologic outcome and survival are associated with optimal perfusion pressure defined by autoregulation monitoring. No randomized, controlled, interventional data is available to assess autoregulation monitoring after pediatric traumatic brain injury.

Dexmedetomidine reduces the neuronal apoptosis related to cardiopulmonary bypass by inhibiting activation of the JAK2-STAT3 pathway

Cardiopulmonary bypass (CPB) constitutes one of the primary methodologies pertaining to cardiac surgery. However, this form of surgery can cause damage to the body. Many studies have reported that dexmedetomidine confers cerebral protection. In this study, we aimed to investigate the effect and mechanism of dexmedetomidine on neuronal apoptosis caused by CPB. Here, rats were treated with different doses of dexmedetomidine by intravenous infusion 2 hours after CPB. We observed that dexmedetomidine treatment to rats reduces the S100β, NSE levels in plasma, and neuronal apoptosis following CPB in a dose-dependent manner. Furthermore, we observed that the beneficial effect of dexmedetomidine treatment following CPB was associated with a reduction in IL6, an inflammatory cytokine in plasma and cortex. Our results suggest that dexmedetomidine provides neuroprotective effects by inhibiting inflammation and reducing neuronal apoptosis. There was a correlation between the protective effect on the brain and the dose of dexmedetomidine. In addition, dexmedetomidine administration inhibits phosphorylation of JAK2 and STAT3 proteins in the hippocampus of rats 2 hours after CPB. Therefore, we speculate that the JAK2–STAT3 pathway plays an important role in the neuroprotective effects of dexmedetomidine following brain injury induced by CPB.

Cerebral Autoregulation-oriented Therapy at the Bedside

This comprehensive review summarizes the evidence regarding use of cerebral autoregulation-directed therapy at the bedside and provides an evaluation of its impact on optimizing cerebral perfusion and associated functional outcomes. Multiple studies in adults and several in children have shown the feasibility of individualizing mean arterial blood pressure and cerebral perfusion pressure goals by using cerebral autoregulation monitoring to calculate optimal levels. Nine of these studies examined the association between cerebral perfusion pressure or mean arterial blood pressure being above or below their optimal levels and functional outcomes. Six of these nine studies (66%) showed that patients for whom median cerebral perfusion pressure or mean arterial blood pressure differed significantly from the optimum, defined by cerebral autoregulation monitoring, were more likely to have an unfavorable outcome. The evidence indicates that monitoring of continuous cerebral autoregulation at the bedside is feasible and has the potential to be used to direct blood pressure management in acutely ill patients.

Blood pressure deficits in acute kidney injury: not all about the mean arterial pressure?

Acute kidney injury (AKI) is associated with increased morbidity and mortality. Although there are many causes of AKI, it is known that patients undergoing high-risk surgery are known to be at significant risk. Although much effort has centred on the minimum arterial pressure needed to maintain renal perfusion, this tends to be based on relatively crude measures such as the mean arterial pressure (MAP), which is widely used as an index for the optimal blood pressure. The rationale behind maintaining MAP is to provide adequate organ perfusion, although this is difficult to assess other than by applying crude end-points. Recent studies have examined the progression of AKI as defined by the KDIGO criteria in terms of time-weighted average values for premorbid and within-ICU haemodynamic pressure-related parameters. Although principally performed on patients who had undergone cardiovascular surgery and who were on vasopressor support, some interesting results were obtained suggesting that crude MAP may not be an adequate target in AKI. In patients with AKI progression, greater observed deficits in mean perfusion pressure, diastolic arterial perfusion, and diastolic perfusion pressures were observed. This study may highlight potential modifiable risk factors for the prevention of progression of AKI, and hopefully translate into improved outcomes.

Multimodality Neuromonitoring

The monitoring of systemic and central nervous system physiology is central to the management of patients with neurologic disease in the perioperative and critical care settings. There exists a range of invasive and noninvasive and global and regional monitors of cerebral hemodynamics, oxygenation, metabolism, and electrophysiology that can be used to guide treatment decisions after acute brain injury. With mounting evidence that a single neuromonitor cannot comprehensively detect all instances of cerebral compromise, multimodal neuromonitoring allows an individualized approach to patient management based on monitored physiologic variables rather than a generic one-size-fits-all approach targeting predetermined and often empirical thresholds.

Cerebral Autoregulation Real-Time Monitoring

Cerebral autoregulation is a mechanism which maintains constant cerebral blood flow (CBF) despite changes in mean arterial pressure (MAP). Assessing whether this mechanism is intact or impaired and determining its boundaries is important in many clinical settings, where primary or secondary injuries to the brain may occur. Herein we describe the development of a new ultrasound tagged near infra red light monitor which tracks CBF trends, in parallel, it continuously measures blood pressure and correlates them to produce a real time autoregulation index. Its performance is validated in both in-vitro experiment and a pre-clinical case study. Results suggest that using such a tool, autoregulation boundaries as well as its impairment or functioning can be identified and assessed. It may therefore assist in individualized MAP management to ensure adequate organ perfusion and reduce the risk of postoperative complications, and might play an important role in patient care.

Cerebral blood flow and autoregulation: current measurement techniques and prospects for noninvasive optical methods

Cerebral blood flow (CBF) and cerebral autoregulation (CA) are critically important to maintain proper brain perfusion and supply the brain with the necessary oxygen and energy substrates. Adequate brain perfusion is required to support normal brain function, to achieve successful aging, and to navigate acute and chronic medical conditions. We review the general principles of CBF measurements and the current techniques to measure CBF based on direct intravascular measurements, nuclear medicine, X-ray imaging, magnetic resonance imaging, ultrasound techniques, thermal diffusion, and optical methods. We also review techniques for arterial blood pressure measurements as well as theoretical and experimental methods for the assessment of CA, including recent approaches based on optical techniques. The assessment of cerebral perfusion in the clinical practice is also presented. The comprehensive description of principles, methods, and clinical requirements of CBF and CA measurements highlights the potentially important role that noninvasive optical methods can play in the assessment of neurovascular health. In fact, optical techniques have the ability to provide a noninvasive, quantitative, and continuous monitor of CBF and autoregulation.

Noteworthy Literature in 2015

This article is a review of the literature published during the 12 months of 2015, which is of interest to the congenital cardiac anesthesiologist. While the review is not exhaustive, it identifies 7 themes in the literature for 2015 and cites 78 peer-reviewed publications.

Perioperative optimal blood pressure as determined by ultrasound tagged near infrared spectroscopy and its association with postoperative acute kidney injury in cardiac surgery patients

OBJECTIVES

Perioperative blood pressure management by targeting individualized optimal blood pressure, determined by cerebral blood flow autoregulation monitoring, may ensure sufficient renal perfusion. The purpose of this study was to evaluate changes in the optimal blood pressure for individual patients, determined during cardiopulmonary bypass (CPB) and during early postoperative period in intensive care unit (ICU). A secondary aim was to examine if excursions below optimal blood pressure in the ICU are associated with risk of cardiac surgery-associated acute kidney injury (CSA-AKI).

METHODS

One hundred and ten patients undergoing cardiac surgery had cerebral blood flow monitored with a novel technology using ultrasound tagged near infrared spectroscopy (UT-NIRS) during CPB and in the first 3 h after surgery in the ICU. The correlation flow index (CFx) was calculated as a moving, linear correlation coefficient between cerebral flow index measured using UT-NIRS and mean arterial pressure (MAP). Optimal blood pressure was defined as the MAP with the lowest CFx. Changes in optimal blood pressure in the perioperative period were observed and the association of blood pressure excursions (magnitude and duration) below the optimal blood pressure [area under the curve (AUC) < OptMAP mmHgxh] with incidence of CSA-AKI (defined using Kidney Disease: Improving Global Outcomes criteria) was examined.

RESULTS

Optimal blood pressure during early ICU stay and CPB was correlated (r = 0.46, P < 0.0001), but was significantly higher in the ICU compared with during CPB (75 ± 8.7 vs 71 ± 10.3 mmHg, P = 0.0002). Thirty patients (27.3%) developed CSA-AKI within 48 h after the surgery. AUC < OptMAP was associated with CSA-AKI during CPB [median, 13.27 mmHgxh, interquartile range (IQR), 4.63-20.14 vs median, 6.05 mmHgxh, IQR 3.03-12.40, P = 0.008], and in the ICU (13.72 mmHgxh, IQR 5.09-25.54 vs 5.65 mmHgxh, IQR 1.71-13.07, P = 0.022).

CONCLUSIONS

Optimal blood pressure during CPB and in the ICU was correlated. Excursions below optimal blood pressure (AUC < OptMAP mmHgXh) during perioperative period are associated with CSA-AKI. Individualized blood pressure management based on cerebral autoregulation monitoring during the perioperative period may help improve CSA-AKI-related outcomes.

Blood Pressure Deviations From Optimal Mean Arterial Pressure During Cardiac Surgery Measured With a Novel Monitor of Cerebral Blood Flow and Risk for Perioperative Delirium: A Pilot Study

OBJECTIVE

The aim of this study was to evaluate whether excursions of blood pressure from the optimal mean arterial pressure during and after cardiac surgery are associated with postoperative delirium identified using a structured examination.

DESIGN

Prospective, observational study.

SETTING

University hospital.

PARTICIPANTS

The study included 110 patients undergoing cardiac surgery.

INTERVENTIONS

Patients were monitored using ultrasound-tagged near-infrared spectroscopy to assess optimal mean arterial pressure by cerebral blood flow autoregulation monitoring during cardiopulmonary bypass and the first 3 hours in the intensive care unit.

MEASUREMENTS AND MAIN RESULTS

The patients were tested preoperatively and on postoperative days 1 to 3 with the Confusion Assessment Method or Confusion Assessment Method for the Intensive Care Unit, the Delirium Rating Scale-Revised-98, and the Mini Mental State Examination. Summative presence of delirium on postoperative days 1 through 3, as defined by the consensus panel following Diagnostic and Statistical Manual of Mental Disorders-IV-TR criteria, was the primary outcome. Delirium occurred in 47 (42.7%) patients. There were no differences in blood pressure excursions above and below optimal mean arterial pressure between patients with and without summative presence of delirium. Secondary analysis showed blood pressure excursions above the optimal mean arterial pressure to be higher in patients with delirium (mean±SD, 33.2±26.51 mmHgxh v 23.4±16.13 mmHgxh; p = 0.031) and positively correlated with the Delirium Rating Scale score on postoperative day 2 (r = 0.27, p = 0.011).

CONCLUSIONS

Summative presence of delirium was not associated with perioperative blood pressure excursions; but on secondary exploratory analysis, excursions above the optimal mean arterial pressure were associated with the incidence and severity of delirium on postoperative day 2.