Monitoring of cerebral blood flow autoregulation in adults undergoing sevoflurane anesthesia: a prospective cohort study of two age groups

Postoperative cognitive dysfunction after beach chair positioning compared to supine position in orthopaedic surgery in the elderly

INTRODUCTION

Postoperative cognitive dysfunction (POCD) occurs in up to 26% of patients older than 60 years 1 week after non-cardiac surgery. Intraoperative beach chair positioning (BCP) is advantageous for some types of shoulder surgery. However, this kind of positioning leads to a downward bound redistribution of blood volume, with possible hypoperfusion of the brain. We hypothesized that patients > 60 years undergoing orthopaedic shoulder surgery in a BCP might experience more POCD than patients operated in the supine position (SP).

MATERIAL AND METHODS

A single-centre, prospective observational trial of 114 orthopaedic patients was performed. Study groups were established according to the type of intraoperative positioning. Anaesthesiological management was carried out similarly in both groups, including types of anaesthetics and blood pressure levels. POCD was evaluated using the Trail Making Test, the Letter-Number Span and the Regensburger Word Fluency Test. The frequency of POCD 1 week after surgery was considered primary outcome.

RESULTS

Baseline characteristics, including duration of surgery, were comparable in both groups. POCD after 1 week occurred in 10.5% of SP patients and in 21.1% of BCP patients (p = 0.123; hazard ratio 2.0 (CI 95% 0.794-5.038)). After 4 weeks, the incidence of POCD decreased (SP: 8.8% vs. BCP: 5.3%; p = 0.463). 12/18 patients with POCD showed changes in their Word Fluency Tests. Near-infrared spectroscopy (NIRS) values were not lower in patients with POCD compared to those without POCD (54% (50/61) vs. 57% (51/61); p = 0.671).

CONCLUSION

POCD at 1 week after surgery tended to occur more often in patients operated in beach chair position compared to patients in supine position without being statistically significant.

Impact of Intraoperative Fluctuations of Cardiac Output on Cerebrovascular Autoregulation: An Integrative Secondary Analysis of Individual-level Data

BACKGROUND

Intraoperative impairment of cerebral autoregulation (CA) has been associated with perioperative neurocognitive disorders. We investigated whether intraoperative fluctuations in cardiac index are associated with changes in CA.

METHODS

We conducted an integrative explorative secondary analysis of individual-level data from 2 prospective observational studies including patients scheduled for radical prostatectomy. We assessed cardiac index by pulse contour analysis and CA as the cerebral oxygenation index (COx) based on near-infrared spectroscopy. We analyzed (1) the cross-correlation between cardiac index and COx, (2) the correlation between the time-weighted average (TWA) of the cardiac index below 2.5 L min-1 m-2, and the TWA of COx above 0.3, and (3) the difference in areas between the cardiac index curve and the COx curve among various subgroups.

RESULTS

The final analysis included 155 patients. The median cardiac index was 3.16 [IQR: 2.65, 3.72] L min-1 m-2. Median COx was 0.23 [IQR: 0.12, 0.34]. (1) The median cross-correlation between cardiac index and COx was 0.230 [IQR: 0.186, 0.287]. (2) The correlation (Spearman ρ) between TWA of cardiac index below 2.5 L min-1 m-2 and TWA of COx above 0.3 was 0.095 (P=0.239). (3) Areas between the cardiac index curve and the COx curve did not differ significantly among subgroups (<65 vs. ≥65 y, P=0.903; 0 vs. ≥1 cardiovascular risk factors, P=0.518; arterial hypertension vs. none, P=0.822; open vs. robot-assisted radical prostatectomy, P=0.699).

CONCLUSIONS

We found no meaningful association between intraoperative fluctuations in cardiac index and CA. However, it is possible that a potential association was masked by the influence of anesthesia on CA.

Tonic down-rolling and eccentric down-positioning of eyes under sevoflurane anesthesia without non-depolarizing muscle relaxant and its relationship with depth of anesthesia

Purpose

To analyze the relationship between eccentric downward eye movement/eccentric downward eye-positioning (EDEM/EDEP) encountered in patients undergoing ophthalmic surgeries and its return to a centralized position under general anesthesia (GA) with the depth of anesthesia (DOA).

Methods

Patients undergoing ophthalmic surgeries (6 months-12 years) under sevoflurane anesthesia without non-depolarizing muscle relaxant (NDMR) who witnessed a sudden tonic EDEM/EDEP were both retrospectively (R-group) and prospectively (P-group) enrolled (ambispective study). R-group included data-points after induction (AI) till the time surgery lasted while P-group compiled data both during induction (DI) and AI. DOA in terms of MAC (minimum alveolar concentration) at the time of EDEM/EDEP and centralization of eyeball and their timings were noted and compared for both AI and DI data-points. Also, vertical eccentric eye positions were scored and correlated with MAC.

Results

AI data included 22 (14R+8P) events and their mean MAC of EDEM/EDEP and centralization were 1.60 ± 0.25 and 1.18 ± 0.17 respectively (p = 0.000). DI data included 62 (P) cases and its mean MAC of EDEM/EDEP and centralization was 2.19 ± 0.43 and 1.39 ± 0.26 respectively (p = 0.000). Median (IQR) eye positions during down-positioning in 84 events was -3 (-3.9 to -2.5). It was preceded by an eccentric upward drift of eyes in 10/22 (6R+4P) AI cases. A strong negative correlation was seen between DOA and eccentric eye positions (r = -0.77, p = 0.000).

Conclusions

Tonic down-rolling of eyes is not uncommon in children seen without NDMR with higher depths of sevoflurane anesthesia compared to point of centralization and fluctuations in DOA should be avoided to circumvent inadvertent complications during ocular surgery.

A retrospect and outlook on the neuroprotective effects of anesthetics in the era of endovascular therapy

Studies on the neuroprotective effects of anesthetics were carried out more than half a century ago. Subsequently, many cell and animal experiments attempted to verify the findings. However, in clinical trials, the neuroprotective effects of anesthetics were not observed. These contradictory results suggest a mismatch between basic research and clinical trials. The Stroke Therapy Academic Industry Roundtable X (STAIR) proposed that the emergence of endovascular thrombectomy (EVT) would provide a proper platform to verify the neuroprotective effects of anesthetics because the haemodynamics of patients undergoing EVT is very close to the ischaemia–reperfusion model in basic research. With the widespread use of EVT, it is necessary for us to re-examine the neuroprotective effects of anesthetics to guide the use of anesthetics during EVT because the choice of anesthesia is still based on team experience without definite guidelines. In this paper, we describe the research status of anesthesia in EVT and summarize the neuroprotective mechanisms of some anesthetics. Then, we focus on the contradictory results between clinical trials and basic research and discuss the causes. Finally, we provide an outlook on the neuroprotective effects of anesthetics in the era of endovascular therapy.

Traumatic Brain Injury: Intraoperative Management and Intensive Care Unit Multimodality Monitoring

Traumatic brain injury is a devastating event associated with substantial morbidity. Pathophysiology involves the initial trauma, subsequent inflammatory response, and secondary insults, which worsen brain injury severity. Management entails cardiopulmonary stabilization and diagnostic imaging with targeted interventions, such as decompressive hemicraniectomy, intracranial monitors or drains, and pharmacological agents to reduce intracranial pressure. Anesthesia and intensive care requires control of multiple physiologic variables and evidence-based practices to reduce secondary brain injury. Advances in biomedical engineering have enhanced assessments of cerebral oxygenation, pressure, metabolism, blood flow, and autoregulation. Many centers employ multimodality neuromonitoring for targeted therapies with the hope to improve recovery.

Vascular and neuronal effects of general anesthesia on the brain: An fMRI study

BACKGROUND AND PURPOSE

A number of functional magnetic resonance imaging (fMRI) studies rely on application of anesthetic agents during scanning that can modulate and complicate interpretation of the measured hemodynamic blood oxygenation level-dependent (BOLD) response. The purpose of the present study was to investigate the effect of general anesthesia on two main components of BOLD signal including neuronal activity and vascular response.

METHODS

Breath-holding (BH) fMRI was conducted in wakefulness and under anesthesia states in 9 patients with drug-resistant epilepsy who needed to get scanned under anesthesia during laser interstitial thermal therapy. BOLD and BOLD cerebrovascular reactivity (BOLD-CVR) maps were compared using t-test between two states to assess the effect of anesthesia on neuronal activity and vascular factors (p < .05).

RESULTS

Overall, our findings revealed an increase in BOLD-CVR and decrease in BOLD response under anesthesia in several brain regions. The results proposed that the modulatory mechanism of anesthetics on neuronal and vascular components of BOLD signal may work in different ways.

CONCLUSION

This experiment for the first human study showed that anesthesia may play an important role in dissociation between neuronal and vascular responses contributed to hemodynamic BOLD signal using BH fMRI imaging that may assist the implication of general anesthesia and interpretation of outcomes in clinical setting.

Risk of perioperative stroke and cerebral autoregulation monitoring: a systematic review

BACKGROUND

Perioperative stroke, delirium, and cognitive impairment could be related to management and to variations in blood pressure control, cerebral hypoperfusion and raised blood volume. Cerebral autoregulation (CAR) is a mechanism to maintain cerebral perfusion through the control of the vascular tone and hemodynamic reactions in the circulation.

OBJECTIVE

The present systematic review addresses the relationship between impaired CAR and perioperative stroke by evaluating the rate of neurological complications after surgery in studies in which perioperative CAR was tested or monitored.

METHODS

We included randomized clinical trials and prospective observational studies. All studies had adjusted the relative risk, hazard ratio or 95% confidence interval (95%CI) values. These estimation effects were tested using random-effects models. Heterogeneity among the selected studies was assessed using the Higgins and Thompson I² statistics.

RESULTS

The Web of Science, PubMed and EMBASE electronic databases were searched to retrieve articles. A total of 4,476 studies published between 1983 and 2019 were analyzed, but only 5 qualified for the data extraction and were included in the final analysis. The combined study cohort comprised 941 patients who underwent CAR monitoring during surgical procedures. All studies provided information about perioperative stroke, which equated to 16% (158 of 941) of the overall patient population.

CONCLUSION

The present meta-analysis showed evidence of the impact of CAR impairment in the risk of perioperative stroke. On the pooled analysis, blood fluctuations or other brain insults large enough to compromise CAR were associated with the outcome of stroke (odds ratio [OR]: 2.26; 95%CI: 1.54-2.98; p < 0.0001).

Cerebral Autoregulation in Non-Brain Injured Patients: A Systematic Review

Introduction: Cerebral autoregulation (CA) plays a fundamental role in the maintenance of adequate cerebral blood flow (CBF). CA monitoring, through direct and indirect techniques, may guide an appropriate therapeutic approach aimed at improving CBF and reducing neurological complications; so far, the role of CA has been investigated mainly in brain-injured patients. The aim of this study is to investigate the role of CA in non-brain injured patients.

Methods: A systematic consultation of literature was carried out. Search terms included: “CA and sepsis,” “CA and surgery,” and “CA and non-brain injury.”

Results: Our research individualized 294 studies and after screening, 22 studies were analyzed in this study. Studies were divided in three groups: CA in sepsis and septic shock, CA during surgery, and CA in the pediatric population. Studies in sepsis and intraoperative setting highlighted a relationship between the incidence of sepsis-associated delirium and impaired CA. The most investigated setting in the pediatric population is cardiac surgery, but the role and measurement of CA need to be further elucidated.

Conclusion: In non-brain injured patients, impaired CA may result in cognitive dysfunction, neurological damage, worst outcome, and increased mortality. Monitoring CA might be a useful tool for the bedside optimization and individualization of the clinical management in this group of patients.

Intraoperative impaired cerebrovascular autoregulation and delayed neurocognitive recovery after major oncologic surgery: a secondary analysis of pooled data

Cerebral blood flow is tightly regulated by cerebrovascular autoregulation (CVA), and intraoperative impairment of CVA has been linked with perioperative neurocognitive disorders. We aim to assess whether impairment of CVA during major oncologic surgery is associated with delayed neurocognitive recovery (DNCR) postoperatively. We performed a secondary analysis of prospectively collected data. Patients were included if they had undergone complete pre- and postoperative neuropsychological assessments, continuous intraoperative measurement of CVA, and major oncologic surgery for visceral, urological, or gynecological cancer. Intraoperative CVA was measured using the time-correlation method based on near-infrared-spectroscopy, and DNCR was assessed with a neuropsychological test battery. A decline in cognitive function before hospital discharge compared with a preoperative baseline assessment was defined as DNCR. One hundred ninety-five patients were included in the analysis. The median age of the study population was 65 years (IQR: 60–68); 11 patients (5.6%) were female. Forty-one patients (21.0%) fulfilled the criteria for DNCR in the early postoperative period. We found a significant association between impaired intraoperative CVA and DNCR before hospital discharge (OR = 1.042 [95% CI: 1.005; 1.080], p = 0.028). The type of surgery (radical prostatectomy vs. other major oncologic surgery; OR = 0.269 [95% CI: 0.099; 0.728], p = 0.010) and premedication with midazolam (OR = 3.360 [95% CI: 1.039; 10.870], p = 0.043) were significantly associated with the occurrence of DNCR in the early postoperative period. Intraoperative impairment of CVA is associated with postoperative neurocognitive function early after oncologic surgery. Therefore, intraoperative monitoring of CVA may be a target for neuroprotective interventions. The initial studies were retrospectively registered with primary clinical trial registries recognized by the World Health Organization (ClinicalTrials.gov Identifiers: DRKS00010014, 21.03.2016 and NCT04101006, 24.07.2019).

Mechanism underlying sevoflurane-induced protection in cerebral ischemia–reperfusion injury

Cerebral ischemia is an extremely complex disease that can be caused by a variety of factors. Cerebral ischemia can cause great harm to human body. Sevoflurane is a volatile anesthetic that is frequently used in clinic, and has a lot of advantages, such as quick induction of general anesthesia, quick anesthesia recovery, no respiratory tract irritation, muscle relaxation, and small cycle effect. The mechanism of sevoflurane preconditioning or post-treatment induction is poorly understood. The purpose of this study was to illustrate the mechanism underlying sevoflurane-induced protection in cerebral ischemia–reperfusion injury and also provide theoretical guidance for future research.

Laser speckle contrast imaging of forehead cutaneous blood flow during carotid endarterectomy as a potential non-invasive method for surrogate monitoring of cerebral perfusion

Monitoring cerebral perfusion is important for goal-directed anesthesia. Taking advantage of the supply of the supraorbital region and Glabella from the internal carotid artery (ICA), we evaluated changes in cutaneous blood flow using laser speckle contrast imagining (LSCI) as a potential method for indirect real-time monitoring of cerebral perfusion. Nine patients (8 men, mean age 70 years) underwent eversion carotid endarterectomy under local anesthesia. Cutaneous blood flow of the forehead was monitored using LSCI. During clamping of the common carotid artery (CCA), ipsilateral supraorbital region and Glabellas cutaneous blood flow dropped from 334 ± 135 to 221 ± 109 AU (p = 0.023) (AU: arbitrary flux units) and from 384 ± 151 to 276 ± 107 AU (p = 0.023), respectively, whilst the contralateral supraorbital region cutaneous blood flow remained unchanged. The supraorbital cutaneous blood flow did not change significantly following reperfusion of the external carotid artery (ECA) (221 ± 109 to 281 ± 154 AU; p = 0.175) and ICA (281 ± 154 to 310 ± 184 AU; p = 01). A comparable trend for Glabella followed ECA (276 ± 107 to 342 ± 170 AU; p = 0.404) and ICA (342 ± 170 to 352 ± 191 AU; p = 01) reperfusion. In patients undergoing carotid endarterectomy under local anesthesia, LSCI of the supraorbital and Glabella regions reflected clamping of the CCA but did not distinguish reperfusion of the ICA from that of the ECA.

Comparing the effect of positioning on cerebral autoregulation during radical prostatectomy: a prospective observational study

Purpose

Surgery in the prolonged extreme Trendelenburg position may lead to elevated intracranial pressure and compromise cerebral hemodynamic regulation. We hypothesized that robot-assisted radical prostatectomy with head-down tilt causes impairment of cerebral autoregulation compared with open retropubic radical prostatectomy in the supine position.

Methods

Patients scheduled for elective radical prostatectomy were included at a tertiary care prostate cancer clinic. Continuous monitoring of the cerebral autoregulation was performed using the correlation method. Based on measurements of cerebral oxygenation with near-infrared spectroscopy and invasive mean arterial blood pressure (MAP), a moving correlation coefficient was calculated to obtain the cerebral oxygenation index as an indicator of cerebral autoregulation. Cerebral autoregulation was measured continuously from induction until recovery from anesthesia.

Results

There was no significant difference in cerebral autoregulation between robot-assisted and open retropubic radical prostatectomy during induction (p = 0.089), intraoperatively (p = 0.162), and during recovery from anesthesia (p = 0.620). Age (B = 0.311 [95% CI 0.039; 0.583], p = 0.025) and a higher difference between baseline MAP and intraoperative MAP (B = 0.200 [95% CI 0.073; 0.327], p = 0.002) were associated with impaired cerebral autoregulation, whereas surgical technique was not (B = 3.339 [95% CI  1.275; 7.952], p = 0.155).

Conclusion

Compared with open radical prostatectomy in the supine position, robot-assisted surgery in the extreme Trendelenburg position with capnoperitoneum did not lead to an impairment of cerebral autoregulation during the perioperative period in our study population.

Trial registration number: DRKS00010014, date of registration: 21.03.2016, retrospectively registered.

Electronic supplementary material

The online version of this article (10.1007/s10877-020-00549-0) contains supplementary material, which is available to authorized users.

Effect of sevoflurane on systemic and cerebral circulation, cerebral autoregulation and CO2 reactivity

Background

Sevoflurane is one of the most frequently used inhaled anesthetics for general anesthesia. Previously it has been reported that at clinically used doses of sevoflurane, cerebral vasoreactivity is maintained. However, there are no data how sevoflurane influences systemic and cerebral circulation in parallel. The aim of our study was to assess systemic and cerebral hemodynamic changes as well as cerebral CO₂-reactivity during sevoflurane anesthesia.

Methods

Twenty nine patients undergoing general anesthesia were enrolled. Anesthesia was maintained with 1 MAC sevoflurane in 40% oxygen. Ventilatory settings (respiratory rate and tidal volume) were adjusted to reach and maintain 40, 35 and 30 mmHg EtCO₂ for 5 min respectively. At the end of each period, transcranial Doppler and hemodynamic parameters using applanation tonometry were recorded.

Results

Systemic mean arterial pressure significantly decreased during anesthetic induction and remained unchanged during the entire study period. Central aortic and peripherial pulse pressure and augmentation index as markers of arterial stiffness significantly increased during the anesthetic induction and remained stable at the time points when target CO₂ levels were reached. Both cerebral autoregulation and cerebral CO₂-reactivity was maintained at 1 MAC sevoflurane.

Discussion

Cerebral autoregulation and CO₂-reactivity is preserved at 1 MAC sevoflurane. Cerebrovascular effects of anesthetic compounds have to be assessed together with systemic circulatory effects.

Trial registration

The study was registered at http://www.clinicaltrials.gov, identifier: NCT02054143, retrospectively registered. Date of registration: February 4, 2014.

Entropy Measures as Descriptors to Identify Apneas in Rheoencephalographic Signals

Rheoencephalography (REG) is a simple and inexpensive technique that intends to monitor cerebral blood flow (CBF), but its ability to reflect CBF changes has not been extensively proved. Based on the hypothesis that alterations in CBF during apnea should be reflected in REG signals under the form of increased complexity, several entropy metrics were assessed for REG analysis during apnea and resting periods in 16 healthy subjects: approximate entropy (ApEn), sample entropy (SampEn), fuzzy entropy (FuzzyEn), corrected conditional entropy (CCE) and Shannon entropy (SE). To compute these entropy metrics, a set of parameters must be defined a priori, such as, for example, the embedding dimension m, and the tolerance threshold r. A thorough analysis of the effects of parameter selection in the entropy metrics was performed, looking for the values optimizing differences between apnea and baseline signals. All entropy metrics, except SE, provided higher values for apnea periods (p-values < 0.025). FuzzyEn outperformed all other metrics, providing the lowest p-value (p = 0.0001), allowing to conclude that REG signals during apnea have higher complexity than in resting periods. Those findings suggest that REG signals reflect CBF changes provoked by apneas, even though further studies are needed to confirm this hypothesis.

Novel method for intraoperative assessment of cerebral autoregulation by paced breathing

Background

Cerebral autoregulation (CA) is the mechanism that maintains constancy of cerebral blood flow (CBF) despite variations in blood pressure (BP). Patients with attenuated CA have been shown to have an increased incidence of peri-operative stroke. Studies of CA in anaesthetized subjects are rare, because a simple and non-invasive method to quantify the integrity of CA is not available. In this study, we set out to improve non-invasive quantification of CA during surgery. For this purpose, we introduce a novel method to amplify spontaneous BP fluctuations during surgery by imposing mechanical positive pressure ventilation at three different frequencies and quantify CA from the resulting BP oscillations.

Methods

Fourteen patients undergoing sevoflurane anaesthesia were included in the study. Continuous non-invasive BP and transcranial Doppler-derived CBF velocity (CBF V ) were obtained before surgery during 3 min of paced breathing at 6, 10, and 15 bpm and during surgery from mechanical positive pressure ventilation at identical frequencies. Data were analysed using frequency domain analysis to obtain CBF V -to-BP phase lead as a continuous measure of CA efficacy. Group averages were calculated. Values are means ( sd ), and P <0.05 was used to indicate statistical significance.

Results

Preoperative vs intraoperative CBF V -to-BP phase lead was 43 (9) vs 45 (8)°, 25 (8) vs 24 (10)°, and 4 (6) vs -2 (12)° during 6, 10, and 15 bpm, respectively (all P =NS).

Conclusions

During surgery, cerebral autoregulation indices were similar to values determined before surgery. This indicates that CA can be quantified reliably and non-invasively using this novel method and confirms earlier evidence that CA is unaffected by sevoflurane anaesthesia.

Clinical trial registration

NCT03071432.

Vasoactive agents to improve brain perfusion: pathophysiology and clinical utilization

PURPOSE OF REVIEW

This review highlights the aspects of pathophysiology that make it difficult to predict the effects of any attempt to improve brain perfusion and reviews the options to improve brain perfusion according to the needs of an individual patient, focusing on the choice of a suitable threshold for cerebral perfusion pressure.

RECENT FINDINGS

Typically, vasopressors or vasodilators that do not directly influence the cerebral vascular bed are used to improve cerebral perfusion. Positive inotropic substances are rarely used, as the relationship between cardiac output and cerebral blood flow is complex and difficult to measure. Combining perfusion pressure monitoring with monitoring of brain metabolism or oxygenation to adapt cerebral perfusion to the needs of an individual patient has been disappointing. Recently, attempts to individualize perfusion pressure based on measurements of cerebrovascular autoregulation have shown promising results in the management of traumatic brain injury and during cardiac surgery. Currently, only preliminary data are available linking optimized cerebral perfusion to improved outcome.

SUMMARY

Optimizing cerebral perfusion remains a difficult goal. All our attempts to manipulate brain perfusion are influenced in an unpredictable manner by underlying diseases. Autoregulation-based strategies to individualize cerebral perfusion management warrant further investigation.

Effects of anesthesia on cerebral blood flow, metabolism, and neuroprotection

Administration of anesthetic agents fundamentally shifts the responsibility for maintenance of homeostasis from the patient and their intrinsic physiological regulatory mechanisms to the anesthesiologist. Continuous delivery of oxygen and nutrients to the brain is necessary to prevent irreversible injury and arises from a complex series of regulatory mechanisms that ensure uninterrupted cerebral blood flow. Our understanding of these regulatory mechanisms and the effects of anesthetics on them has been driven by the tireless work of pioneers in the field. It is of paramount importance that the anesthesiologist shares this understanding. Herein, we will review the physiological determinants of cerebral blood flow and how delivery of anesthesia impacts these processes.

Preemptive volume therapy to prevent hemodynamic changes caused by the beach chair position: hydroxyethyl starch 130/0.4 versus Ringer's acetate-a controlled randomized trial

BACKGROUND

Hemodynamic instability frequently occurs in beach chair positioning for surgery, putting patients at risk for cerebral adverse events. This study examined whether preoperative volume loading with crystalloids alone or with a crystalloid-colloid combination can prevent hemodynamic changes that may be causative for unfavorable neurologic outcomes.

METHODS

The study randomly assigned 43 adult patients undergoing shoulder surgery to 3 study groups. Each group received an infusion of 500 mL of Ringer's acetate between induction of anesthesia and being placed in the beach chair position. The crystalloid group received an additional bolus of 1000 mL Ringer's acetate. The hydroxyethyl starch group was administered an additional bolus of 500 mL of 6% hydroxyethyl starch 130/0.4. Hemodynamic monitoring was accomplished via an esophageal Doppler probe. Cerebral oxygen saturation was examined with near-infrared spectroscopy. Changes in stroke volume variation between the prone and beach chair positions were defined as the primary outcome parameter. Secondary outcomes were changes in cardiac output and cerebral oxygen saturation.

RESULTS

The control group was prematurely stopped after enrollment of 4 patients because of adverse events. In the hydroxyethyl starch group, stroke volume variation remained constant during positioning maneuvers (P = .35), whereas a significant increase was observed in the Ringer's acetate group (P < .01; P = .014 for intergroup comparison). This was also valid for changes in cardiac output. Cerebral oxygen saturation significantly decreased in both groups.

CONCLUSIONS

Preprocedural boluses of 500 mL of 6% hydroxyethyl starch 130/0.4 as well as 1000 mL of Ringer's acetate were efficient in preserving hemodynamic conditions during beach chair position.

Sevoflurane based anaesthesia does not affect already impaired cerebral autoregulation in patients with type 2 diabetes mellitus

BACKGROUND

The baroreflex regulates arterial blood pressure (BP). During periods when blood pressure changes, cerebral blood flow (CBF) is kept constant by cerebral autoregulation (CA). In patients with diabetes mellitus (DM), low baroreflex sensitivity (BRS) is associated with impaired CA. As sevoflurane-based anaesthesia obliterates BRS, we hypothesised that this could aggravate the already impaired CA in patients with DM resulting in a 'double-hit' on cerebral perfusion leading to increased fluctuations in blood pressure and cerebral perfusion.

METHODS

On the day before surgery, we measured CBF velocity (CBFV), heart rate, and BP to determine BRS and CA efficacy (CBFV_mean-to-BP_mean-phase lead) in 25 patients with DM and in 14 controls. During the operation, BRS and CA efficacy were determined during sevoflurane-based anaesthesia. Patients with DM were divided into a group with high BRS (DM_BRS↑) and a group with low BRS (DM_BRS↓). Values presented are median (inter-quartile range).

RESULTS

Preoperative vs intraoperative BRS was 6.2 (4.5-8.5) vs 1.9 (1.1-2.5, P<0.001) ms mm Hg^-1 for controls, 5.8 (4.9-7.6) vs 2.7 (1.5-3.9, P<0.001) ms mm Hg^-1 for patients with DM_BRS↑, and 1.9 (1.5-2.8) vs 1.1 (0.6-2.5, P=0.31) ms mm Hg^-1 for patients with DM_BRS↓. Preoperative vs intraoperative CA efficacy was 43° (38-46) vs 43° (38-51, P=0.30), 44° (36-49) vs 41° (32-49, P=0.52), and 34° (28-40) vs 30° (27-38, P=0.64) for controls, DM_BRS↑, and DM_BRS↓ patients, respectively.

CONCLUSIONS

In diabetic patients with low preoperative BRS, preoperative CA efficacy was also impaired. In controls and diabetic patients, CA was unaffected by sevoflurane-based anaesthesia. We therefore conclude that sevoflurane-based anaesthesia does not contribute to a 'double-hit' phenomenon on cerebral perfusion.

CLINICAL TRIAL REGISTRATION

NCT 03071432.

Perioperative neurocognition in elderly patients

PURPOSE OF REVIEW

The extrinsic risk factors for postoperative cognitive disturbance have been a source of concern during the perioperative period, and these risk factors remain the subject of controversy. This review of recent studies focuses on the effect of these factors on postoperative cognitive disturbance during the perioperative period.

RECENT FINDINGS

Impairment of cerebral autoregulation may predispose patients to intraoperative cerebral malperfusion, which may subsequently induce postoperative cognitive disturbance. The neurotoxicity of several volatile anesthetics may contribute to cognitive functional decline, and the impact of intravenous anesthesia on cognitive function requires further exploration. Multimodal analgesia may not outperform traditional postoperative analgesia in preventing postoperative delirium. Furthermore, acute pain and chronic pain may exacerbate the cognitive functional decline of patients with preexisting cognitive impairment. The nuclear factor-kappa beta pathway is an important node in the neuroinflammatory network.

SUMMARY

Several intraoperative factors are associated with postoperative cognitive disturbance. However, if these factors are optimized in perioperative management, postoperative cognitive disturbance will improve.

Recent advances in cerebral oximetry. Assessment of cerebral autoregulation with near-infrared spectroscopy: myth or reality?

In recent years, the feasibility of near-infrared spectroscopy to continuously assess cerebral autoregulation has gained increasing interest. By plotting cerebral oxygen saturation over blood pressure, clinicians can generate an index of autoregulation: the cerebral oximetry index (COx). Successful integration of this monitoring ability in daily critical care may allow clinicians to tailor blood pressure management to the individual patient's need and might prove to be a major step forward in terms of patient outcome.

Associations Between Impaired Cerebral Blood Flow Autoregulation, Cerebral Oxygenation, and Biomarkers of Brain Injury and Postoperative Cognitive Dysfunction in Elderly Patients After Major Noncardiac Surgery

BACKGROUND

Increasing evidence links postoperative cognitive dysfunction (POCD) to surgery and anesthesia. POCD is recognized as an important neuropsychological adverse outcome in surgical patients, particularly the elderly. This prospective cohort study aimed to investigate whether POCD is associated with impaired intraoperative cerebral autoregulation and oxygenation, and increased levels of biomarkers of brain injury.

METHODS

Study subjects were patients ≥65 years of age scheduled for major noncardiac surgery. Cognitive function was assessed before and 1 week after surgery. POCD was diagnosed if a decline of >1 standard deviation of z-scores was present in ≥2 variables of the test battery. The incidence of POCD 1 week after surgery was modeled as a multivariable function of the index of autoregulation (MxA) and tissue oxygenation index (TOI), adjusting for baseline neuropsychological assessment battery (Consortium to Establish a Registry for Alzheimer's Disease-Neuropsychological Assessment Battery [CERAD-NAB]) total score and the maximum C-reactive protein (CRP) concentration. The biomarkers of brain injury neuron-specific enolase and S100β protein, age, and level of education were included in secondary multivariable logistic regression analyses.

RESULTS

Of the 82 patients who completed the study, 38 (46%) presented with POCD 1 week after surgery. In the multivariable regression analysis, higher intraoperative MxA (odds ratio [OR; 95% confidence interval (CI)], 1.39 [1.01-1.90] for an increase of 0.1 units, P = .08 after Bonferroni adjustment), signifying less effective autoregulation, was not associated with higher odds of POCD. The univariable logistic regression model for MxA yielded an association with POCD (OR [95% CI], 1.44 [1.06-1.95], P = .020). Tissue oxygenation index (1.12 [0.41-3.01] for an increase of 10%, P = 1.0 after Bonferroni adjustment) and baseline CERAD-NAB total score (0.80 [0.45-1.42] for an increase of 10 points, P = .45) did not affect the odds of POCD. POCD was associated with elevated CRP on postoperative day 2 (median [interquartile range]; 175 [81-294] vs 112 [62-142] mg/L, P = .033); however, the maximum CRP value (OR [95% CI], 1.35 [0.97-1.87] for a 2-fold increase, P = .07) had no distinct effect on POCD.

CONCLUSIONS

Impairment of intraoperative cerebral blood flow autoregulation is not predictive of early POCD in elderly patients, although secondary analyses indicate that an association probably exists.

A clinical review of inhalation anesthesia with sevoflurane: from early research to emerging topics

A large number of studies during the past two decades have demonstrated the efficacy and safety of sevoflurane across patient populations. Clinical researchers have also investigated the effects of sevoflurane, its hemodynamic characteristics, its potential protective effects on several organ systems, and the incidence of delirium and cognitive deficiency. This review examines the clinical profiles of sevoflurane and other anesthetic agents, and focuses upon emerging topics such as organ protection, postoperative cognitive deficiency and delirium, and novel ways to improve postanesthesia outcomes.

Journal of clinical monitoring and computing 2016 end of year summary: monitoring cerebral oxygenation and autoregulation

In the perioperative and critical care setting, monitoring of cerebral oxygenation (ScO₂) and cerebral autoregulation enjoy increasing popularity in recent years, particularly in patients undergoing cardiac surgery. Monitoring ScO₂ is based on near infrared spectroscopy, and attempts to early detect cerebral hypoperfusion and thereby prevent cerebral dysfunction and postoperative neurologic complications. Autoregulation of cerebral blood flow provides a steady flow of blood towards the brain despite variations in mean arterial blood pressure (MAP) and cerebral perfusion pressure, and is effective in a MAP range between approximately 50–150 mmHg. This range of intact autoregulation may, however, vary considerably between individuals, and shifts to higher thresholds have been observed in elderly and hypertensive patients. As a consequence, intraoperative hypotension will be poorly tolerated, and might cause ischemic events and postoperative neurological complications. This article summarizes research investigating technologies for the assessment of ScO₂ and cerebral autoregulation published in the Journal of Clinical Monitoring and Computing in 2016.

Anesthesia in Experimental Stroke Research

Anesthetics have enabled major advances in development of experimental models of human stroke. Yet, their profound pharmacologic effects on neural function can confound the interpretation of experimental stroke research. Anesthetics have species-, drug-, and dose-specific effects on cerebral blood flow and metabolism, neurovascular coupling, autoregulation, ischemic depolarizations, excitotoxicity, inflammation, neural networks, and numerous molecular pathways relevant for stroke outcome. Both preconditioning and postconditioning properties have been described. Anesthetics also modulate systemic arterial blood pressure, lung ventilation, and thermoregulation, all of which may interact with the ischemic insult as well as the therapeutic interventions. These confounds present a dilemma. Here, we provide an overview of the anesthetic mechanisms of action and molecular and physiologic effects on factors relevant to stroke outcomes that can guide the choice and optimization of the anesthetic regimen in experimental stroke.