The influence of xenon on regulation of the autonomic nervous system in patients at high risk of perioperative cardiac complications †

Effects of inhaled low-concentration xenon gas on naltrexone-precipitated withdrawal symptoms in morphine-dependent mice

BACKGROUND

Opioid withdrawal symptoms (OWS) are highly aversive and prompt unprescribed opioid use, which increases morbidity, mortality, and, among individuals being treated for opioid use disorder (OUD), recurrence. OWS are driven by sympathetic nervous system (SNS) hyperactivity that occurs when blood opioid levels wane. We tested whether brief inhalation of xenon gas, which inhibits SNS activity and is used clinically for anesthesia and diagnostic imaging, attenuates naltrexone-precipitated withdrawal-like signs in morphine-dependent mice.

METHODS

Adult CD-1 mice were implanted with morphine sulfate-loaded (60 mg/ml) minipumps and maintained for 6 days to establish morphine dependence. On day 7, mice were given subcutaneous naltrexone (0.3 mg/kg) and placed in a sealed exposure chamber containing either 21% oxygen/balance nitrogen (controls) or 21% oxygen/added xenon peaking at 30%/balance nitrogen. After 10 minutes, mice were transferred to observation chambers and videorecorded for 45 minutes. Videos were scored in a blind manner for morphine withdrawal behaviors. Data were analyzed using 2-way ANOVAs testing for treatment and sex effects.

RESULTS AND CONCLUSIONS

Xenon-exposed mice exhibited fewer jumps (P = 0.010) and jumping suppression was detectible within the first 10-minute video segment, but no sex differences were detected. Brief inhalation of low concentration xenon rapidly and substantially attenuated naltrexone-precipitated jumping in morphine-dependent mice, suggesting that it can inhibit OWS. If xenon effects translate to humans with OUD, xenon inhalation may be effective for reducing OWS, unprescribed opioid use, and for easing OUD treatment initiation, which could help lower excess morbidity and mortality associated with OUD.

Clinical efficacy of xenon versus propofol: A systematic review and meta-analysis

BACKGROUND

Interest in the anesthetic use of xenon, a noble gas, has waxed and waned for decades, and the clinical effects of xenon are still debated. We performed a meta-analysis to compare the clinical efficacy of xenon with that of propofol.

METHODS

Electronic searches were performed through December 2017 using various databases, including PubMed, Embase, and the Cochrane Library. We identified thirteen trials that included a total of 817 patients.

RESULTS

Patients treated with xenon had a lower bispectral index (BIS) (weighted mean difference (WMD): -6.26, 95% confidence interval (CI): -11.33 to -1.18, P = .02), a higher mean arterial blood pressure (MAP) (WMD: 7.00, 95% CI: 2.32-11.68, P = .003) and a lower heart rate (HR) (WMD: -9.45, 95% CI: -12.28 to -6.63, P < 0.00001) than propofol-treated patients. However, there were no significant differences between the 2 treatment groups in the effects of nondepolarizing muscular relaxants, the duration spent in the postanesthesia care unit (PACU) (WMD: -0.94, 95% CI: -8.79-6.91, P = .81), or the incidence of perioperative complications [assessed using the outcomes of postoperative nausea and vomiting (PONV) (relative risk (RR): 2.01, 95% CI: 0.79-5.11, P = .14), hypotension (RR: 0.62, 95% CI: 0.27 to 1.40, P = .25), hypertension (RR: 1.27, 95% CI: 0.73-2.21, P = .39) and bradycardia (RR: 1.00, 95% CI: 0.36-2.74, P = 1.00)].

CONCLUSION

In this meta-analysis of randomized controlled trials, we found that xenon treatment resulted in a higher MAP, a lower HR, and a smaller BIS index than treatment with propofol.

Xenon for the prevention of postoperative delirium in cardiac surgery: study protocol for a randomized controlled clinical trial

Background

Postoperative delirium (POD) is a manifestation of acute postoperative brain dysfunction that is frequently observed after cardiac surgery. POD is associated with short-term complications such as an increase in mortality, morbidity, costs and length of stay, but can also have long-term sequelae, including persistent cognitive deficits, loss of independence, and increased mortality for up to 2 years. The noble gas xenon has been demonstrated in various models of neuronal injury to exhibit remarkable neuroprotective properties. We therefore hypothesize that xenon anesthesia reduces the incidence of POD in elderly patients undergoing cardiac surgery with the use of cardiopulmonary bypass.

Methods/Design

One hundred and ninety patients, older than 65 years, and scheduled for elective cardiac surgery, will be enrolled in this prospective, randomized, controlled trial. Patients will be randomized to receive general anesthesia with either xenon or sevoflurane. Primary outcome parameter will be the incidence of POD in the first 5 postoperative days. The occurrence of POD will be assessed by trained research personnel, blinded to study group, with the validated 3-minute Diagnostic Confusion Assessment Method (3D-CAM) (on the intensive care unit in its version specifically adapted for the ICU), in addition to chart review and the results of delirium screening tools that will be performed by the bedside nurses). Secondary outcome parameters include duration and severity of POD, and postoperative cognitive function as assessed with the Mini-Mental State Examination.

Discussion

Older patients undergoing cardiac surgery are at particular risk to develop POD. Xenon provides remarkable hemodynamic stability and has been suggested in preclinical studies to exhibit neuroprotective properties. The present trial will assess whether the promising profile of xenon can be translated into a better outcome in the geriatric population.

Trial registration

EudraCT Identifier: 2014-005370-11 (13 May 2015).

Anesthetic gases and global warming: Potentials, prevention and future of anesthesia

Global warming refers to an average increase in the earth′s temperature, which in turn causes changes in climate. A warmer earth may lead to changes in rainfall patterns, a rise in sea level, and a wide range of impacts on plants, wildlife, and humans. Greenhouse gases make the earth warmer by trapping energy inside the atmosphere. Greenhouse gases are any gas that absorbs infrared radiation in the atmosphere and include: water vapor, carbon dioxide (CO₂), methane (CH₄), nitrous oxide (N₂O), halogenated fluorocarbons (HCFCs), ozone (O₃), perfluorinated carbons (PFCs), and hydrofluorocarbons (HFCs). Hazardous chemicals enter the air we breathe as a result of dozens of activities carried out during a typical day at a healthcare facility like processing lab samples, burning fossil fuels etc. We sometimes forget that anesthetic agents are also greenhouse gases (GHGs). Anesthetic agents used today are volatile halogenated ethers and the common carrier gas nitrous oxide known to be aggressive GHGs. With less than 5% of the total delivered halogenated anesthetic being metabolized by the patient, the vast majority of the anesthetic is routinely vented to the atmosphere through the operating room scavenging system. The global warming potential (GWP) of a halogenated anesthetic is up to 2,000 times greater than CO₂. Global warming potentials are used to compare the strength of different GHGs to trap heat in the atmosphere relative to that of CO₂. Here we discuss about the GWP of anesthetic gases, preventive measures to decrease the global warming effects of anesthetic gases and Xenon, a newer anesthetic gas for the future of anesthesia.

Safety and feasibility of xenon as an adjuvant to sevoflurane anaesthesia in children undergoing interventional or diagnostic cardiac catheterization: study protocol for a randomised controlled trial

BACKGROUND

Xenon has minimal haemodynamic side effects when compared to volatile or intravenous anaesthetics. Moreover, in in vitro and in animal experiments, xenon has been demonstrated to convey cardio- and neuroprotective effects. Neuroprotection could be advantageous in paediatric anaesthesia as there is growing concern, based on both laboratory studies and retrospective human clinical studies, that anaesthetics may trigger an injury in the developing brain, resulting in long-lasting neurodevelopmental consequences. Furthermore, xenon-mediated neuroprotection could help to prevent emergence delirium/agitation. Altogether, the beneficial haemodynamic profile combined with its putative organ-protective properties could render xenon an attractive option for anaesthesia of children undergoing cardiac catheterization.

METHODS/DESIGN

In a phase-II, mono-centre, prospective, single-blind, randomised, controlled study, we will test the hypothesis that the administration of 50% xenon as an adjuvant to general anaesthesia with sevoflurane in children undergoing elective cardiac catheterization is safe and feasible. Secondary aims include the evaluation of haemodynamic parameters during and after the procedure, emergence characteristics, and the analysis of peri-operative neuro-cognitive function. A total of 40 children ages 4 to 12 years will be recruited and randomised into two study groups, receiving either a combination of sevoflurane and xenon or sevoflurane alone.

DISCUSSION

Children undergoing diagnostic or interventional cardiac catheterization are a vulnerable patient population, one particularly at risk for intra-procedural haemodynamic instability. Xenon provides remarkable haemodynamic stability and potentially has cardio- and neuroprotective properties. Unfortunately, evidence is scarce on the use of xenon in the paediatric population. Our pilot study will therefore deliver important data required for prospective future clinical trials.

TRIAL REGISTRATION

EudraCT: 2014-002510-23 (5 September 2014).

Evaluation of hemodynamic effects of xenon in dogs undergoing hemorrhagic shock

OBJECTIVES

The anesthetic gas xenon is reported to preserve hemodynamic stability during general anesthesia. However, the effects of the gas during shock are unclear. The objective of this study was to evaluate the effect of Xe on hemodynamic stability and tissue perfusion in a canine model of hemorrhagic shock.

METHOD

Twenty-six dogs, mechanically ventilated with a fraction of inspired oxygen of 21% and anesthetized with etomidate and vecuronium, were randomized into Xenon (Xe; n = 13) or Control (C; n = 13) groups. Following hemodynamic monitoring, a pressure-driven shock was induced to reach an arterial pressure of 40 mmHg. Hemodynamic data and blood samples were collected prior to bleeding, immediately after bleeding and 5, 20 and 40 minutes following shock. The Xe group was treated with 79% Xe diluted in ambient air, inhaled for 20 minutes after shock.

RESULT

The mean bleeding volume was 44 mL.kg-1 in the C group and 40 mL.kg-1 in the Xe group. Hemorrhage promoted a decrease in both the cardiac index (p<0.001) and mean arterial pressure (p<0.001). These changes were associated with an increase in lactate levels and worsening of oxygen transport variables in both groups (p<0.05). Inhalation of xenon did not cause further worsening of hemodynamics or tissue perfusion markers.

CONCLUSIONS

Xenon did not alter hemodynamic stability or tissue perfusion in an experimentally controlled hemorrhagic shock model. However, further studies are necessary to validate this drug in other contexts.

[Current developments in xenon research. Importance for anesthesia and intensive care medicine]

The noble gas xenon exerts favorable anesthetic properties along with remarkable hemodynamic stability in healthy patients undergoing elective surgery. It represents the nearly ideal anesthetic and provides safe and well controllable anesthesia although the exact mechanism by which xenon produces anesthesia remains to be elucidated. In addition xenon offers organ protective properties for vital organs including the brain, heart and kidneys which seem to be synergistic when used in combination with therapeutic hypothermia. As the high cost of xenon will probably preclude its wider use as a routine anesthetic, data from extensive tests in large numbers of high risk patients is needed to confirm its possible superiority in this setting.

Haemodynamic changes and heart rate variability during midazolam-propofol co-induction

In a prospective, blind, randomised study, we examined the effects of midazolam-propofol co-induction on haemodynamic (blood pressure, heart rate and stroke volume) and heart rate variability. The latter was measured by spectral analysis using the maximum-entropy method to calculate the following: the low frequency component (LF), which reflects both the cardiac sympathetic and parasympathetic activity, the high frequency component (HF) and entropy, which reflects the cardiac parasympathetic activity, the total power (TP), calculated by the addition of LF and HF, and the LF/HF ratio, which reflects the balance between the cardiac sympathetic and parasympathetic nervous activity. Forty patients were randomly allocated to the propofol group and the midazolam-propofol group, and the parameters described above were calculated at baseline (T1), post induction (T2), after tracheal intubation (T3), and 3 min (T4) and 5 min after intubation (T5). Propofol was administered at 2.5 mg.kg(-1) in the propofol group and midazolam at 0.1 mg.kg(-1) followed by propofol at 1.5 mg.kg(-1) in the midazolam-propofol group for anaesthesia induction. Then, propofol was administered at 4-6 mg.kg(-1)propofol for maintenance in both groups. The midazolam-propofol group showed compensated haemodynamic changes, which were related to significant increases in the LF/HF ratio at T2, T4 and T5 (p = 0.011, 0.038 and 0.034). These results suggest that the midazolam-propofol combination yielded compensated modulatory effects on the cardiovascular system, including preserved baroreflex activity.

Emergence and early cognitive function in the elderly after xenon or desflurane anaesthesia: a double-blinded randomized controlled trial †

BACKGROUND

Postoperative cognitive impairment after general anaesthesia, especially in the elderly, is a well-recognized problem. Xenon, known to be an N-methyl-d-aspartate antagonist, may be advantageous. In this study, the early cognitive function in the elderly after general anaesthesia with xenon was compared with that after desflurane.

METHODS

After approval by the local ethical committee and after obtaining written informed consent, patients were enrolled in this randomized, double-blinded, controlled study. Thirty-eight patients (65-75 yr old, ASA status I-III) undergoing an elective surgery with a planned duration of 60-180 min were allocated to either the xenon (n = 18) or the desflurane (n = 20) anaesthesia group. The primary outcome was the cognitive Test for Attentional Performance (TAP) with its subtests Alertness, Divided Attention, and Working Memory. After baseline assessment 12-24 h before operation, patients were followed-up 6-12 and 66-72 h after operation. Secondary outcomes were emergence times from anaesthesia and the modified Aldrete score.

RESULTS

No difference was found between the groups in the TAP at 6-12 and 66-72 h after operation. In the xenon group, emergence time was significantly faster for the following parameters: time to open eyes (P = 0.001), to react on demand (P = 0.001), to extubation (P = 0.001), and for time and spatial orientation (P = 0.007). The modified Aldrete score was significantly higher after 30, 45 and 60 min in the xenon group.

CONCLUSIONS

There was no difference in the postoperative cognitive testing at 6-12 and 66-72 h. Xenon was associated in the elderly with a faster emergence from general anaesthesia than desflurane.

Autonomic cardiac control with xenon anaesthesia in patients at cardiovascular risk

BACKGROUND

The cardiovascular stability found with xenon anaesthesia may be caused by absence of circulatory depression. Xenon may also act directly on autonomic cardiovascular control.

METHODS

In a prospective, randomized design, 26 patients (ASA class III and IV) with increased cardiac risk were anaesthetized for elective non-cardiac surgery with either xenon (n = 13) or propofol (n = 13), each combined with remifentanil. From intraoperative Holter ECG, 5-min intervals of stable sinus rhythm were analysed at baseline anaesthesia with etomidate/remifentanil, and after 30 and 60 min of propofol or xenon anaesthesia. Target criteria were total power and ratio of low to high frequency power of the heart rate (HR) power spectrum between 0.003 and 0.4 Hz, indicating global activity and sympatho-vagal balance of autonomic modulation of HR.

RESULTS

When compared with baseline, total power decreased with propofol from 8.6 (1.6) to 7.1 (0.5) and to 7.8 (1.1) ms(2) at 30 and 60 min, respectively, [mean (sd) of logarithmic transform] and was unchanged with xenon (P = 0.02; anova). The low/high frequency power ratio changed from 3.0 (3.5) to 4.3 (4.3) and 4.1 (6.2), respectively, with xenon and from 3.9 (3.6) to 1.8 (1.5) and 1.8 (0.8) with propofol (P = 0.04; generalized linear model test). Mean arterial pressure was significantly higher with xenon throughout (P < 0.001; anova).

CONCLUSIONS

Propofol caused a decrease in arterial pressure as well as autonomic HR modulation, but xenon did not. The higher arterial pressure with xenon anaesthesia may be explained by less suppression of sympatho-vagal balance.