A Narrative Review Illustrating the Clinical Utility of Electroencephalogram-Guided Anesthesia Care in Children

The major therapeutic end points of general anesthesia include hypnosis, amnesia, and immobility. There is a complex relationship between general anesthesia, responsiveness, hemodynamic stability, and reaction to noxious stimuli. This complexity is compounded in pediatric anesthesia, where clinicians manage children from a wide range of ages, developmental stages, and body sizes, with their concomitant differences in physiology and pharmacology. This renders anesthetic requirements difficult to predict based solely on a child's age, body weight, and vital signs. Electroencephalogram (EEG) monitoring provides a window into children's brain states and may be useful in guiding clinical anesthesia management. However, many clinicians are unfamiliar with EEG monitoring in children. Young children's EEGs differ substantially from those of older children and adults, and there is a lack of evidence-based guidance on how and when to use the EEG for anesthesia care in children. This narrative review begins by summarizing what is known about EEG monitoring in pediatric anesthesia care. A key knowledge gap in the literature relates to a lack of practical information illustrating the utility of the EEG in clinical management. To address this gap, this narrative review illustrates how the EEG spectrogram can be used to visualize, in real time, brain responses to anesthetic drugs in relation to hemodynamic stability, surgical stimulation, and other interventions such as cardiopulmonary bypass. This review discusses anesthetic management principles in a variety of clinical scenarios, including infants, children with altered conscious levels, children with atypical neurodevelopment, children with hemodynamic instability, children undergoing total intravenous anesthesia, and those undergoing cardiopulmonary bypass. Each scenario is accompanied by practical illustrations of how the EEG can be visualized to help titrate anesthetic dosage to avoid undersedation or oversedation when patients experience hypotension or other physiological challenges, when surgical stimulation increases, and when a child's anesthetic requirements are otherwise less predictable. Overall, this review illustrates how well-established clinical management principles in children can be significantly complemented by the addition of EEG monitoring, thus enabling personalized anesthesia care to enhance patient safety and experience.

Safe sedation management using volatile anesthetics during cardiopulmonary bypass

Several pieces of evidence suggest that volatile anesthetics (VAs), which were originally used as sedatives, have myocardial protective effects against cardiac ischemia-reperfusion injury. In Europe and the United States, the use of VAs during cardiopulmonary bypass (CPB) is widespread, as 2019 European Association for Cardio-Thoracic Surgery (EACTS)/European Association of Cardiothoracic Anaesthesiology/European Board of Cardiovascular Perfusion, 2011 American College of Cardiology/American Heart Association, and 2017 EACTS guidelines recommend their use in cardiovascular surgery, based on their potential myocardial protective effects. In other countries, including Japan, the use of VAs is gradually increasing. Therefore, it is important to be aware of the risks and possible adverse events associated with VA use during CPB to ensure safe sedation management. Herein, we describe in detail issues such as intraoperative awareness, air pollution, and damage to oxygenators due to VA use and propose precautions.

Inhalational or total intravenous anesthetic for cardiac surgery: does the debate even exist?

PURPOSE OF REVIEW

Perioperative myocardial injury related to cardiac surgery is associated with organ dysfunction and increased mortality. Volatile anesthetics (VA) have been used during cardiac surgery for decades because of their direct and indirect preconditioning and protection against ischemia-reperfusion injury. The current review provides a summary of the latest literature comparing pharmacological preconditioning and the potential benefits of using VA versus total intravenous anesthesia (TIVA) for general anesthesia to improve outcomes after cardiac surgery.

RECENT FINDINGS

Recent literature reports lower mortality and better outcomes when VA is used alone or in combination with remote ischemic preconditioning compared with groups receiving TIVA. However, inconsistent research findings over the years have led to continued debate regarding the anesthetic technique considered more favorable for cardiac surgery.

SUMMARY

Research findings regarding the use of volatile anesthetic versus TIVA for better outcomes after cardiac surgery are inconsistent. Variability in timing, duration, dosing, and type of VA as well as surgical and patient-related factors may have influenced these results. Therefore, either technique can reasonably be adopted depending on provider and institutional preference and used safely in patients undergoing cardiac surgery.

Volatile Versus Intravenous Anesthetics in Cardiac Anesthesia: a Narrative Review

Purpose of the Review

The present review addresses clinicians and gives an overview about the experimental rationale for pharmacological conditioning associated with volatile anesthetics, opioids, and propofol; the current clinical data; and the technical considerations regarding the clinical routine in cardiac anesthesia.

Recent Findings

Volatile anesthetics have been standard of care for general anesthesia for cardiac surgery, especially while using cardiopulmonary bypass. The 2019 published MYRIAD trial was not able to show a difference in mortality or cardiac biomarkers for volatile anesthetics compared to total intravenous anesthesia (TIVA), raising the question of equivalence with respect to patient outcome.

Summary

Reviewing the literature, the scientific foundation for the belief of clinically relevant conditioning by uninterrupted administration of a volatile anesthetic is weak. TIVA can also be performed safely in patients undergoing cardiac surgery.

Desflurane and sevoflurane concentrations in blood passing through the oxygenator during cardiopulmonary bypass: a randomized prospective pilot study

Purpose

Volatile anesthetics (VAs) protect myocardial cells in cardiovascular surgery. A recent clinical trial of cardiopulmonary bypass (CPB) surgery reported no significant difference in mortality rates between the use of VAs and total intravenous anesthetics at 1 year postoperatively. However, oxygenator function may affect the VA pharmacokinetics. Thus, we measured the VA blood concentrations during CPB in patients managed with four different microporous polypropylene hollow fiber membrane oxygenators.

Methods

Twenty-four patients scheduled for elective CPB were randomly allocated to one of the two VA groups (desflurane and sevoflurane groups) and, then, randomly divided into one of four oxygenator groups: Terumo, LivaNova, Medtronic, and Senko (n = 3). Additionally, in each VA group, three patients were randomly selected and redundantly allocated to the human lung group (for control blood VA concentration without oxygenator). Blood samples collected 20 min after starting 6.0 vol% desflurane or 1.7 vol% sevoflurane were analyzed using gas chromatography. Oxygenator-related complications and structural changes in the membrane surface of each oxygenator after surgery were evaluated.

Results

The mean (standard deviation) concentrations of desflurane and sevoflurane in the human lung were 182.4 (23.2) and 54.0 (9.6) μg/ml, respectively; not significantly different from those in the four oxygenator groups. No oxygenator-related complications occurred. Structural changes in membrane fibers did not occur after clinical use, except for difficulty in image acquisition with Senko products.

Conclusion

Our results demonstrated that the blood concentrations of desflurane and sevoflurane passing through oxygenators used during CPB were similar to those in the human lung control.

Electronic supplementary material

The online version of this article (10.1007/s00540-020-02844-1) contains supplementary material, which is available to authorized users.

Volatile Anesthesia Versus Total Intravenous Anesthesia During Cardiopulmonary Bypass: A Narrative Review on the Technical Challenges and Considerations

The Mortality in Cardiac Surgery Randomized Controlled Trial of Volatile Anesthetics (MYRIAD) demonstrated that cardiac surgery with either volatile anesthesia or intravenous anesthesia techniques can be comparable with respect to morbidity and mortality. Maintaining anesthesia during cardiopulmonary bypass (CPB) with either approach requires appreciation of the nuances that are unique to each. This narrative review addresses these technical challenges and other considerations.

Depth of anesthesia by Narcotrend® and postoperative characteristics in children undergoing cardiac surgery under extracorporeal circulation: a retrospective comparison of two anesthetic regimens

BACKGROUND

Depth of anesthesia may be insufficient in pediatric cardiac anesthesia if a total intravenous anesthetic regimen with opioids and midazolam is used during cardiopulmonary bypass. The advantages of sevoflurane-based balanced anesthesia may be (1) a more graduated regulation of the depth of anesthesia during cardiopulmonary bypass and (2) a reduction in postoperative ventilation time for children in comparison with total intravenous anesthesia.

AIM

To evaluate a possibly positive effect of sevoflurane-based balanced anesthesia in children undergoing cardiac surgery we analyzed whether this anesthetic regimen had a significant effect related to (1) depth of anesthesia, (2) the need for opioids during cardiopulmonary bypass as well as on postoperative characteristics such as (3) time of postoperative ventilation, and (4) duration of stay in the intensive care unit in comparison with total intravenous anesthesia.

METHODS

In a retrospective analysis, data from heart-lung machine protocols from 2013 to 2016 were compared according to anesthetic regimen (sevoflurane-balanced anesthesia, n = 70 vs. total intravenous anesthesia, n = 65). Children (age: 8 weeks to 14 years) undergoing cardiac surgery with cardiopulmonary bypass were included. As a primary outcome measure, we compared Narcotrend^® system-extracted data to detect insufficient phases of anesthetic depth during extracorporeal circulation under moderate hypothermia. Postoperatively, we measured the postoperative ventilation time and the number of days in the intensive care unit. Furthermore, we analyzed patients' specific characteristics such as opioid consumption during cardiopulmonary bypass. Regression analysis relating primary objectives was done using the following variables: anesthetic regimen, age, severity of illness/surgery, and cumulative dosage of opiates during cardiopulmonary bypass.

RESULTS

No significant differences were observed in descriptive patient characteristics (age, body weight, height, and body temperature) between the two groups. Further, no significant differences were found in depth of anesthesia by analyzing phases of superficial B1-C2-electroencephalography Narcotrend^® data. No marked difference between the groups was observed for the duration of postoperative intensive care unit stay. However, the postoperative ventilation time (median (95% CI, hours)) was significantly lower in the sevoflurane-based balanced anesthesia group (6.0 (2.0-15.0)) than in the total intravenous anesthesia group (13.5 (7.0-25)). A higher dosage of opioids and midazolam was required in the total intravenous anesthesia group to maintain adequate anesthesia during cardiopulmonary bypass. Regression analysis showed an additional, significant impact of the following factors: severity of illness and severity grade of cardiac surgery (according to Aristotle) on the primary endpoint.

CONCLUSION

In children undergoing cardiac surgery in our department, the use of sevoflurane-balanced anesthesia during cardiopulmonary bypass showed no superiority of inhalational agents over total intravenous anesthesia with opioids and benzodiazepines preventing phases of superficial anesthesia, but a marked advantage for the postoperative ventilation time compared with total intravenous anesthesia.

A Comparison of the Arterial Blood Concentration of Isoflurane During Cardiopulmonary Bypass Between 2 Polypropylene Oxygenators

OBJECTIVE

The primary objective was to compare arterial blood concentration of isoflurane during cardiopulmonary bypass (CPB) between 2 polypropylene oxygenators of different designs. Secondary objectives were to compare levels of Bispectral Index Score (BIS) during CPB between the 2 oxygenators and to examine the relationships between oxygenator exhaust and arterial blood concentrations of isoflurane and BIS.

DESIGN

Single, blinded, randomized control trial.

SETTING

Teaching hospital.

PARTICIPANTS

Twenty-five patients undergoing cardiac surgery with CPB.

INTERVENTIONS

Subjects were randomly assigned (1:1) to Inspire 8F (Sorin) or Affinity Fusion (Medtronic) oxygenators.

MEASUREMENTS AND MAIN RESULTS

The mean arterial blood concentration in the Inspire 8F (Sorin) group was 59 (standard deviation [SD] 23) µg/mL, compared with 53 (SD 17) µg/mL in the Affinity Fusion (Medtronic) group with a nonsignificant mean difference of 6 (95% confidence interval = -11, 22) µg/mL (t[23] = 0.676, p = 0.50). No significant difference in BIS was found between the groups (p = 0.896). Moderate and strong, negative correlations respectively, were found between arterial and oxygenator exhaust correlations and BIS (r = -0.472, p < 0.05; r = -0.812, p < 0.001). A strong, positive correlation was found between arterial and exhaust isoflurane concentration (r = 0.810, p < 0.0005).

CONCLUSIONS

No significant difference in arterial blood concentration of isoflurane or BIS was found between the Inspire 8F (Sorin) and Affinity Fusion (Medtronic) oxygenators. A significant positive correlation was found between arterial blood and oxygenator exhaust concentrations of isoflurane, as well as significant negative correlations between both arterial and oxygenator exhaust concentrations of isoflurane and BIS.

The depth of anaesthesia associated with the administration of isoflurane 2.5% during cardiopulmonary bypass

BACKGROUND

Administering isoflurane 2.5% into the oxygenator during cardiopulmonary bypass results in no patient movement. However, doing so may result in an excessive depth of anaesthesia particularly, when hypothermia is induced. Bispectral index and arterial blood and oxygenator exhaust concentrations of volatile anaesthetics should be related to depth of anaesthesia. The primary aim of this study was to measure the depth of anaesthesia using bispectral index, resulting from administering isoflurane 2.5% into the oxygenator during cardiopulmonary bypass, and secondary aims were to examine the relationships between blood and oxygenator exhaust isoflurane concentrations and bispectral index.

METHODS

Arterial and mixed-venous blood samples were aspirated at three time points during cardiopulmonary bypass and measured for isoflurane concentration using mass spectrometry. Simultaneously, oxygenator exhaust isoflurane concentration, nasopharyngeal temperature and bispectral index were recorded.

RESULTS

When averaged across the three time points, all patients had a bispectral index score below 40 (binomial test, p < 0.001). There were no significant correlations between bispectral index score and arterial or mixed-venous blood isoflurane concentrations (r = -0.082, p = 0.715; r = -0.036, p = 0.874) and oxygenator exhaust gas concentration of isoflurane (r = -0.369, p = 0.091).

CONCLUSION

When 2.5% isoflurane was administered into the sweep gas supply to the oxygenator during cardiopulmonary bypass, all patients experienced a bispectral index score less than 40 and no significant relationship was found between either arterial or mixed-venous blood or oxygenator exhaust concentrations of isoflurane and bispectral index.

Effect of cardiopulmonary bypass on cytochrome P450 enzyme activity: implications for pharmacotherapy

For patients undergoing cardiopulmonary bypass (CPB) during cardiac surgery, there are well-documented changes in the pharmacokinetics (PK) of commonly administered drugs. Although multiple factors potentially underpin these changes, there has been scant research attention on the impact of CPB to alter the activities of cytochrome P450 (CYP) isoenzymes. PK changes during cardiac surgery with CPB have the potential to adversely affect the safety and efficacy of pharmacotherapy and increase the risk of drug-drug interactions. Clinically significant changes in drug PK during CPB are likely to be prominent for drugs where CYP metabolism is a major clearance (CL) mechanism. However, clinical data from patients undergoing CPB surgery in support of this hypothesis are lacking, leaving a significant knowledge gap. In this review, we address the effects of CPB on the release of pro-inflammatory cytokines, in surgeries with and without CPB, both pre and post initiation of surgery. We reviewed literature to explore the relationship between the release of pro-inflammatory cytokines, and the expression and activities of CYP enzymes. Through this approach, we provide new insight on the effects of CPB on the PK of drugs administered to patients in the clinical setting. Future research to address this knowledge gap will have considerable impact to assist clinicians with optimizing pharmacotherapy in this patient population.

Impact of temperature on the Narcotrend Index during hypothermic cardiopulmonary bypass in children with sevoflurane anesthesia

Background:

During cardiopulmonary bypass (CPB) in children, anesthesia maintained by sevoflurane administered via the oxygenator is increasingly common. Anesthetic uptake and requirement may be influenced by the non-physiological conditions during hypothermic CPB. Narcotrend-processed EEG monitoring may, therefore, be useful to guide the administration of sevoflurane during this phase.

Objective:

The objective of this prospective, clinical, observational study was to assess the correlation between body temperature, Narcotrend Index (NI) and administered sevoflurane in children during CPB.

Methods:

Forty-four children aged 0 to 10 years undergoing hypothermic cardiac surgery were studied. On bypass, anesthesia was maintained with sevoflurane administered via the oxygenator of the heart-lung machine. Nasopharyngeal temperature, NI and minimum alveolar concentration (MAC) of sevoflurane were recorded in intervals of 10 minutes. Expiratory gas was sampled from the oxygenator’s sole expiratory port via a separate connecting line and the MAC was measured by the agent analyzer of the anesthesia machine.

Results:

Raw (r = 0.74) and corrected (r = 0.73) r-values show that narcosis depth (as indicated by NI) can primarily be explained by the interaction of MAC and temperature. The analysis of variance (without the interaction term) confirms the significant and independent association of both factors, MAC (p<0.004, 95%CI: 0.19 to 0.46) and temperature (p<0.0001, 95%CI: 0.68 to 0.78), with the NI. During hypothermia, sevoflurane had been reduced significantly (r = 0.41, p<0.0001, 95%CI: 0.33 to 0.48).

Conclusion:

Perfusionists and anesthetists should be aware of the results of processed electroencephalograph (EEG) monitoring during CPB. Sevoflurane requirements differ inter-individually; they may decrease during cooling and increase during rewarming. Therefore, it seems reasonable to include the results of processed EEG monitoring when administering sevoflurane during CPB in children, but further studies are necessary to confirm this thesis.

Assessing the depth of isoflurane anaesthesia during cardiopulmonary bypass

INTRODUCTION

Bispectral index (BIS) and monitoring of end-tidal concentration may be associated with a reduction in the incidence of awareness during volatile-based general anaesthesia. An analogue of end-tidal concentration during cardiopulmonary bypass (CPB) is measuring exhausted isoflurane concentration from the oxygenator as an estimate to blood and, so, brain concentration. The aim of this study was to determine the relationships between oxygenator exhaust and blood concentrations of isoflurane and the BIS score during CPB when administering isoflurane into the sweep gas supply to the oxygenator.

METHODS

Seventeen patients undergoing elective cardiac surgery using CPB and isoflurane with BIS monitoring were recruited in a single-centre university hospital. Isoflurane gas was delivered via a calibrated vaporiser at the beginning of anaesthetic induction. Radial arterial blood samples were collected after the initiation of CPB and before aortic cross-clamping, which were analysed for isoflurane by gas chromatography and mass spectrometry. The BIS score and the concentration of exhausted isoflurane from the oxygenator membrane, as measured by an anaesthetic gas analyser, were recorded at the time of blood sampling.

RESULTS

The mean duration of anaesthetic induction to arterial blood sampling was 90 min (95%CI: 80,100). On CPB, the median BIS was 39 (range, 7-43) and the mean oxygenator exhaust isoflurane concentration was 1.24 ± 0.21%. No significant correlation was demonstrated between BIS with arterial isoflurane concentration (r=-0.19, p=0.47) or oxygenator exhaust isoflurane concentration (r=0.07, p=0.80). Mixed-venous blood temperature was moderately correlated to BIS (r=0.50, p=0.04). Oxygenator exhaust isoflurane concentration was moderately, positively correlated with its arterial concentration (r=0.64, p<0.01).

DISCUSSION

In conclusion, in patients undergoing heart surgery with CPB, the findings of this study indicate that, whilst oxygenator exhaust concentrations were significantly associated with arterial concentrations of isoflurane, neither had any association with the BIS scores, whereas body temperature has moderate positive correlation.

Volatile anaesthetics added to cardiopulmonary bypass are associated with reduced cardiac troponin

Background:

Every year, over 1 million cardiac surgical procedures are performed all over the world. Reducing myocardial necrosis could have strong implications in postoperative clinical outcomes. Volatile anaesthetics have cardiac protective properties in the perioperative period of cardiac surgery. However, little data exists on the administration of volatile agents during cardiopulmonary bypass. The aim of this study was to assess if volatile anaesthetics administration during cardiopulmonary bypass reduces cardiac troponin release after cardiac surgery.

Materials and methods:

We retrospectively analysed data from 942 patients who underwent cardiac surgery in a teaching hospital. The only difference between the groups was the management of anaesthesia during CPB. The volatile group received sevoflurane or desflurane while the control group received a combination of propofol infusion and fentanyl boluses. Patients who received volatile anaesthetics during cardiopulmonary bypass (n=314) were propensity-matched 1:2 with patients who did not receive volatile anaesthetics during CPB (n=628).

Results:

We found a reduction in peak postoperative troponin I, from 7.8 ng/ml (4.8-13.1) in the non-volatile group to 6.8 ng/ml (3.7-11.8) in the volatile group (p=0.013), with no differences in mortality [2 (0.6%) in the volatile group and 2 (0.3%) in the non-volatile group (p=0.6)].

Conclusions:

Adding volatile anaesthetics during cardiopulmonary bypass was associated with reduced peak postoperative troponin levels. Larger studies are required to confirm our data and to assess the effect of volatile agents on survival.

Coronary Sinus Isoflurane Concentration in Cardiac Surgery

OBJECTIVE

Volatile anesthetic agents such as isoflurane may be associated with fewer adverse myocardial events compared with total intravenous anesthesia in cardiac surgery. The authors aimed to determine whether reasonable isoflurane concentrations at tissue level were being achieved to protect the myocardium using this agent. The isoflurane concentration in myocardium has never been measured. The primary aim was to sample coronary sinus (CS) blood and measure its isoflurane concentration. Secondary aims were to determine whether the CS blood concentration would equilibrate with the arterial blood concentration and the relationship of CS blood concentration with oxygenator exhaust isoflurane concentrations during cardiopulmonary bypass (CPB).

DESIGN

Prospective, observational study.

SETTING

Single-center university hospital.

PARTICIPANTS

The study comprised 23 patients undergoing cardiac surgery using CPB and isoflurane.

MEASUREMENTS AND MAIN RESULTS

Shortly after initiation of CPB and insertion of a CS retrograde cardioplegia catheter but before aortic cross-clamping, CS blood was aspirated, followed by radial artery blood, which then were analyzed for isoflurane with gas chromatography and mass spectrometry. The oxygenator exhaust isoflurane level was measured with an anesthetic gas analyzer. The mean arterial and CS isoflurane concentrations were 87.7 ± 50.1 and 73.0 ± 42.9 μg/mL, respectively. There was a significant mean difference of 14.7 μg/mL (95% confidence interval 6.7-22.8) between CS and arterial isoflurane concentrations. Oxygenator exhaust isoflurane levels were correlated positively with those in the CS blood (r = 0.68, p < 0.001) and arterial blood (r = 0.72, p < 0.001).

CONCLUSIONS

This was the first study in which CS blood was sampled and measured for isoflurane concentration. The CS isoflurane concentration could be estimated from the isoflurane concentration in the oxygenator exhaust gas. However, the value of this relationship is limited because the CS isoflurane concentration does not accurately represent its myocardial levels during CPB.

Tricks, tips, and literature review on the adapted vaporize system to deliver volatile agents during cardiopulmonary bypass

Background:

Recently, evidence of cardio-protection and reduction in mortality due to the use of volatile agents during cardiac surgery led to an increase in their use during cardiopulmonary bypass (CPB). These findings seem to be enhanced when the volatile agents are used during all the surgical procedure, including the CPB period.

Aims:

Since the administration of volatile agents through CPB can be beneficial to the patients, we decided to review the use of volatile agents vaporized in the CPB circuit and to summarize some tricks and tips of this technique using our 10-year experience of Brazilian and Italian centers with a large volume of cardiac surgeries.

Study Setting:

Hospital.

Methods:

A literature review.

Results:

During the use of the volatile agents in CPB, it is very important to analyze all gases that come in and go out of the membrane oxygenators. The proper monitoring of inhaled and exhaled fraction of the gas allows not only monitoring of anesthesia level, but also the detection of possible leakage in the circuit. Any volatile agent in the membrane oxygenator is supposed to pollute the operating theater. This is the major reason why proper scavenging systems are always necessary when this technique is used.

Conclusion:

While waiting for industry upgrades, we recommend that volatile agents should be used during CPB only by skilled perfusionists and physicians with the aim to reduce postoperative morbidity and mortality.

Feasibility of Anesthesia Maintenance With Sevoflurane During Cardiopulmonary Bypass: A Pilot Pharmacokinetics Study

OBJECTIVE

Adequate maintenance of hypnosis during anesthesia throughout surgery using sevoflurane alone was investigated. In addition, sevoflurane pharmacokinetics during cardiopulmonary bypass were analyzed.

DESIGN

This was a pilot pharmacokinetic study.

SETTING

Tertiary care university hospital.

PARTICIPANTS

The study comprised 10 patients aged between 18 and 75 years who underwent elective mitral valve surgery.

INTERVENTIONS

The end-tidal and sevoflurane plasma concentrations were measured throughout cardiac surgery procedures involving cardiopulmonary bypass. The sevoflurane plasma concentration was measured using gas chromatography. In addition, the ratio between sevoflurane alveolar concentration and inspired concentration over time (F_A/F_I) was analyzed to describe wash-in and wash-out curves.

MEASUREMENTS AND MAIN RESULTS

Hypnosis was maintained adequately throughout surgery using sevoflurane alone. The bispectral index was maintained between 40 and 60 during cardiopulmonary bypass. The end-tidal sevoflurane was significantly different before and during cardiopulmonary bypass (1.86%±0.54% v 1.30%±0.58%, respectively; p<0.001). However, the sevoflurane plasma concentration was not significantly different before and after cardiopulmonary bypass start-up (40.55 µg/mL [76.62-125.33] before cardiopulmonary bypass and 36.24 µg/mL [56.49-81-42] during cardiopulmonary bypass). This mismatch possibly can be explained by changes that occured after cardiopulmonary bypass start-up, such as reductions of body temperature (36.33°C±0.46°C v 32.98°C±2.38°C, respectively; p<0.001) and hematocrit (35.62%±3.98% v 25.5%±3.08%, respectively; p<0.001). The sevoflurane alveolar concentration varied according to sevoflurane plasma concentration and bispectral index values. No adverse events regarding sevoflurane administration during cardiopulmonary bypass were observed.

CONCLUSIONS

Sevoflurane end-tidal values were reliable indicators of adequate anesthesia during all cardiac surgery procedures involving cardiopulmonary bypass.

Evaluation of the potential toxicity of unmodified and modified cyclodextrins on murine blood-brain barrier endothelial cells

In this study, we investigated the cytotoxic effects of unmodified α-cyclodextrin (α-CD) and modified cyclodextrins, including trimethyl-β-cyclodextrin (TRIMEB) and hydroxypropyl-β-cyclodextrin (HPβCD), on immortalized murine microvascular endothelial (cEND) cells of the blood-brain barrier (BBB). A CellTiter-Glo viability test, performed on the cEND cells showed significant differences among the different cyclodextrins. After 24 hr of incubation, TRIMEB was the most cytotoxic, and HPβCD was non-toxic. α-CD and TRIMEB exhibited greater cytotoxicity in the Dulbecco's modified Eagle's medium than in heat-inactivated human serum indicating protective properties of the human serum. The predicted dynamic toxicity profiles (Td) for α-CD and TRIMEB indicated higher cytotoxicity for these cyclodextrins compared to the reference compound (dimethylsulfoxide). Molecular dynamics simulation of cholesterol binding to the CDs suggested that not just cholesterol but phospholipids extraction might be involved in the cytotoxicity. Overall, the results demonstrate that HPβCD has the potential to be used as a candidate for drug delivery vector development and signify a correlation between the in vitro cytotoxic effect and cholesterol binding of cyclodextrins.

Fluid filtration and vascular compliance during cardiopulmonary bypass: effects of two volatile anesthetics

BACKGROUND

As intraoperative fluid accumulation may negatively impact post-operative organ function, strategies minimizing edema generation should be sought for. During general anesthesia, isoflurane in contrast to sevoflurane has been associated with increased fluid extravasation and edema generation. In this study, we tested sevoflurane against isoflurane with focus on vascular compliance and fluid shifts in an experimental cardiopulmonary bypass (CPB) model.

METHODS

Sixteen pigs underwent 120 min of cardiopulmonary bypass with isoflurane or sevoflurane anesthesia. Net fluid balance, plasma volume, serum-electrolytes, serum-albumin, serum-protein, colloid osmotic pressures in plasma and interstitial fluid, hematocrit levels, and total tissue water content were recorded. Intra-abdominal and intracranial pressures were measured directly, and fluid extravasation rates were calculated.

RESULTS

Fluid extravasation rate increased dramatically in both groups during initiation of cardiopulmonary bypass, with no group differences. The animals of the sevoflurane group needed significantly more fluid supplementation to maintain a constant reservoir volume in the CPB circuit during bypass. Plasma volumes prior to bypass were 56.5 ± 7.9 ml/kg (mean ± SD) and 58.7 ± 3.8 ml/kg in the isoflurane group and sevoflurane group, respectively. During bypass, plasma volumes in the isoflurane group decreased about 25%, and remained significantly lowered when compared to the sevoflurane group, where the values remained stable.

CONCLUSIONS

No differences in fluid extravasation rates were observed between sevoflurane and isoflurane. The increased net fluid balance in the sevoflurane group during cardiopulmonary bypass was not associated with edema generation. Plasma volume was retained in the sevoflurane group, in contrast to the isoflurane group.

Relationship between Sevoflurane Plasma Concentration, Clinical Variables and Bispectral Index Values during Cardiopulmonary Bypass

Background

Anesthetic administration is increasingly guided by electroencephalography (EEG)-based monitoring, such as the bispectral index (BIS). However, during cardiopulmonary bypass (CPB), factors other than the administered hypnotic agents may influence EEG signals, and their effects on BIS values are unknown.

Methods

This report is a secondary analysis of data from a prospective, controlled interventional study comparing the effect of sevoflurane administration guided by BIS monitoring (group Sevo_BIS) and constant administration of sevoflurane (group Sevo_1.8Vol%) during CPB. Sevoflurane plasma concentration (SPC) was measured using gas chromatography. The relationships of BIS to SPC, CPB pump flow, arterial pressure, hematocrit, temperature, time on CPB, and patient characteristics were analysed.

Results

No association was observed between BIS values and SPC in group Sevo_BIS. In group Sevo_1.8Vol%, a 40 μg ml^-1 increase in SPC, which encompassed the entire range of observed values of the SPC in this analysis, was associated with a decrease of 3.6 (95% confidence interval (CI): 1.1–6.1) in BIS values (p = 0.005). Each increase in CPB time of 10 minutes was associated with an increase in BIS values of 0.25 (95%CI: 0.11–0.39, p<0.001). Path analysis revealed that the BIS values of Sevo_BIS patients were 5.3 (95%CI: 3.2–7.5) units higher than those of Sevo_1.8Vol% patients (p<0.001), which was the strongest effect on BIS values. Path analysis revealed a slope of 0.5 (95%CI: 0.3–0.7) BIS units per 1°C body temperature (p<0.001).

Conclusion

BIS monitoring is insensitive to clinically relevant changes in SPC in individual patients during CPB.

Sevoflurane-Sulfobutylether-β-Cyclodextrin Complex: Preparation, Characterization, Cellular Toxicity, Molecular Modeling and Blood-Brain Barrier Transport Studies

The objective of the present investigation was to study the ability of sulfobutylether-β-cyclodextrin (SBEβCD) to form an inclusion complex with sevoflurane (SEV), a volatile anesthetic with poor water solubility. The inclusion complex was prepared, characterized and its cellular toxicity and blood-brain barrier (BBB) permeation potential of the formulated SEV have also been examined for the purpose of controlled drug delivery. The SEV-SBEβCD complex was nontoxic to the primary brain microvascular endothelial (pEND) cells at a clinically relevant concentration of sevoflurane. The inclusion complex exhibited significantly higher BBB permeation profiles as compared with the reference substance (propranolol) concerning calculated apparent permeability values (P_app). In addition, SEV binding affinity to SBEβCD was confirmed by a minimal Gibbs free energy of binding (ΔG_bind) value of −1.727 ± 0.042 kcal·mol⁻¹ and an average binding constant (K_b) of 53.66 ± 9.24 mM indicating rapid drug liberation from the cyclodextrin amphiphilic cavity.

Bispectral index guided titration of sevoflurane in on-pump cardiac surgery reduces plasma sevoflurane concentration and vasopressor requirements: a prospective, controlled, sequential two-arm clinical study

BACKGROUND

Electroencephalographic-based monitoring systems such as the bispectral index (BIS) may reduce anaesthetic overdose rates.

OBJECTIVE

We hypothesised that goal-directed sevoflurane administration (guided by BIS monitoring) could reduce the sevoflurane plasma concentration (SPC) and intraoperative vasopressor doses during on-pump cardiac surgery.

DESIGN

A prospective, controlled, sequential two-arm clinical study.

SETTING

German university medical centre with more than 2500 cardiac surgery interventions per year.

PATIENTS

Sixty elective on-pump cardiac surgery patients.

INTERVENTION

In group Sevo1.8% (n = 29), the sedation depth was maintained with a sustained inspired concentration of sevoflurane 1.8% before and during cardiopulmonary bypass (CPB). In group SevoBIS (n = 31), the inspired sevoflurane concentration was titrated to maintain a BIS target between 40 and 60.

OUTCOME MEASURES

SPC during CPB and the intraoperative administration of noradrenaline. Additional analyses were performed on intraoperative awareness, postoperative blood lactate concentration, duration of mechanical ventilation, intensive care unit length of stay and kidney injury.

RESULTS

Mean inspired sevoflurane concentration was 0.8% in group SevoBIS, representing a 57.1% reduction (P < 0.001) compared with group Sevo1.8%. The mean SPC was 42.3 μg ml(-1) [95% confidence interval (CI) 40.0 to 44.6] in group Sevo1.8% and 21.0 μg ml(-1) (95% CI 18.8 to 23.3) in group SevoBIS, representing a 50.2% reduction (P < 0.001). During CPB, the mean cumulative dose of noradrenaline administered was 13.48 μg kg(-1) (95% CI 10.52 to 17.19) in group Sevo1.8% and 4.06 μg kg(-1) (95% CI 2.67 to 5.97) in group SevoBIS (P < 0.001). Pearson's correlation coefficient (between the cumulative applied dosage of sevoflurane calculated from the area under the curve of the SPC over time and the administered cumulative noradrenaline dose) was 0.607 (P < 0.001). No intraoperative awareness signs were detected.

CONCLUSION

BIS-guided titration of sevoflurane reduces the SPC and decreases noradrenaline administration compared with routine care during on-pump cardiac surgery.