Protecting the Brain With Xenon Anesthesia for Neurosurgical Procedures

Neuroprotection by the noble gases argon and xenon as treatments for acquired brain injury: a preclinical systematic review and meta-analysis

BACKGROUND

The noble gases argon and xenon are potential novel neuroprotective treatments for acquired brain injuries. Xenon has already undergone early-stage clinical trials in the treatment of ischaemic brain injuries, with mixed results. Argon has yet to progress to clinical trials as a treatment for brain injury. Here, we aim to synthesise the results of preclinical studies evaluating argon and xenon as neuroprotective therapies for brain injuries.

METHODS

After a systematic review of the MEDLINE and Embase databases, we carried out a pairwise and stratified meta-analysis. Heterogeneity was examined by subgroup analysis, funnel plot asymmetry, and Egger's regression.

RESULTS

A total of 32 studies were identified, 14 for argon and 18 for xenon, involving measurements from 1384 animals, including murine, rat, and porcine models. Brain injury models included ischaemic brain injury after cardiac arrest (CA), neurological injury after cardiopulmonary bypass (CPB), traumatic brain injury (TBI), and ischaemic stroke. Both argon and xenon had significant (P<0.001), positive neuroprotective effect sizes. The overall effect size for argon (CA, TBI, stroke) was 18.1% (95% confidence interval [CI], 8.1-28.1%), and for xenon (CA, TBI, stroke) was 34.1% (95% CI, 24.7-43.6%). Including the CPB model, only present for xenon, the xenon effect size (CPB, CA, TBI, stroke) was 27.4% (95% CI, 11.5-43.3%). Xenon, both with and without the CPB model, was significantly (P<0.001) more protective than argon.

CONCLUSIONS

These findings provide evidence to support the use of xenon and argon as neuroprotective treatments for acquired brain injuries. Current evidence suggests that xenon is more efficacious than argon overall.

Review: Potential alternatives to high-concentration carbon dioxide stunning of pigs at slaughter

Using carbon dioxide (CO₂) for stunning pigs at slaughter is common in Europe. The use of group stunning is a major advantage with CO₂, which is done without restraining the pigs and with minimized human contact. However, high concentrations of CO₂ have been known for decades to cause pain, fear and distress in pigs before loss of consciousness, and the stunning method is clearly associated with animal welfare concerns. This study reviewed the scientific literature to find recent developments or evaluations of alternative methods that could lead to the replacement of CO₂ for stunning pigs at slaughter. Potential alternative methods found in the literature were described and then assessed to identify specific research and development needs for their further development. Only 15 empirical studies were found in the search of peer-reviewed literature since 2004, which is less than one per year. Furthermore, half of the studies focused on evaluating methods to improve high-concentration CO₂ stunning rather than an alternative to CO₂. Since no clear alternative has emerged, nor a method to improve CO₂ stunning, there is obviously a strong need to focus research and development to find solutions for improving animal welfare when stunning pigs at slaughter.

Efficacy of xenon anesthesia in preventing postoperative cognitive dysfunction after cardiac and major non-cardiac surgeries in elderly patients: a topical review

Elderly patients undergoing major cardiac and non-cardiac surgeries have a high propensity (up to 40–60%) of developing postoperative cognitive dysfunction, which are caused by patient’s factors, type of surgery, intraoperative and postoperative factors. All these pose a challenge to the clinicians. The noble gas xenon does not undergo metabolism or any kind of biotransformation in the body owing to its inert nature. Xenon confers excellent hemodynamic stability and provides excellent recovery at the end of surgery. This topical review discusses advantages of xenon anesthesia in elderly patients undergoing major cardiac and non-cardiac surgeries and whether it is worth using a costly anesthetic in elderly patients for preventing postoperative cognitive dysfunction.

Anesthetic considerations for awake craniotomy

Awake craniotomy is a gold standard of care for resection of brain tumors located within or close to the eloquent areas. Both asleep-awake-asleep technique and monitored anesthesia care have been used effectively for awake craniotomy and the choice of optimal anesthetic approach is primarily based on the preferences of the anesthesiologist and surgical team. Propofol, remifentanil, dexmedetomidine, and scalp nerve block provide the reliable conditions for intraoperative brain mapping. Appropriate patient selection, adequate perioperative psychological support, and proper anesthetic management for individual patients in each stage of surgery are crucial for procedural safety, success, and patient satisfaction.

Anesthesia and Cognitive Outcome in Elderly Patients: A Narrative Viewpoint

Better ways to manage preoperative, intraoperative and postoperative care of surgical patients is the bailiwick of anesthesiologists. Although we care for patients of all ages, protecting the cognitive capacity of elderly patients more frequently requires procedures and practices that go beyond routine care for nonelderly adults. This narrative review will consider current understanding of the reasons that elderly patients need enhanced care, and recommendations for that care based on established and recent empirical research. In that latter regard, unless and until we are able to classify anesthetic neurotoxicity as a rare complication, the first-do-no-harm approach should: (1) add anesthesia to surgical intervention on the physiological cost side of the cost/benefit ratio when making decisions about whether and when to proceed with surgery; (2) minimize anesthetic depth and periods of electroencephalographic suppression; (3) limit the duration of continuous anesthesia whenever possible; (4) consider the possibility that regional anesthesia with deep sedation may be as neurotoxic as general anesthesia; and (5) when feasible, use regional anesthesia with light or no sedation.

Effects of Xenon-Based Anesthetic Exposure on the Expression Levels of Polysialic Acid Neural Cell Adhesion Molecule (PSA-NCAM) on Human Neural Stem Cell-Derived Neurons

Numerous studies suggest a long duration of anesthesia during the late gestation period and infancy is associated with an increased risk of neuronal damage and neurocognitive impairment. The noble gas xenon is an anesthetic that is reported to have neuroprotective effects in some circumstances at certain concentrations. Currently, the effects of xenon on the brain and its potential neuroprotective properties, and/or the effects of xenon used in combination with other anesthetics, are not clearly understood and some reported data appear contradictory. In the present study, human neural stem cells were employed as a human-relevant model to evaluate the effects of xenon when it was co-administered with propofol, a frequently used anesthetic in pediatric anesthesia, and to understand the mechanism(s). The expression of polysialic acid (PSA) neural cell adhesion molecule (NCAM) on human neural stem cell-differentiated neurons was investigated as a key target molecule. PSA is a specific marker of developing neurons. It is essential for neuronal viability and plasticity. Human neural stem cells were maintained in neural differentiation medium and directed to differentiate into neuronal and glial lineages, and were exposed to propofol (50 μM) for 16 h in the presence or absence of xenon (33%). The neural stem cell-derived neurons were characterized by labelling cells with PSA-NCAM, after 5 days of differentiation. Propofol- and/or xenon-induced neurotoxicities were determined by measuring PSA immunoreactivity. A time course study showed that neuronal cell surface PSA was clearly cleaved off from NCAM by endoneuraminidase N (Endo-N), and eliminated PSA immunostaining was not re-expressed 4, 8, or 16 h after Endo-N washout. However, in the presence of 33% xenon, intense PSA staining on neuronal cell surface and processes was evident 16 h after Endo-N washout. In addition, prolonged (16 h) propofol exposure significantly decreased the positive rate of PSA-labeled neurons. When combined with xenon, propofol's adverse effects on neurons were attenuated. This work, conducted on the human neural stem cell-derived models, has provided evidence of the beneficiary effects of xenon on neurons and helps develop xenon-based anesthesia regimens in the pediatric population.

The Role of Heme Oxygenase-1 in Remote Ischemic and Anesthetic Organ Conditioning

The cytoprotective effects of the heme oxygenase (HO) pathway are widely acknowledged. These effects are mainly mediated by degradation of free, pro-oxidant heme and the generation of carbon monoxide (CO) and biliverdin. The underlying mechanisms of protection include anti-oxidant, anti-apoptotic, anti-inflammatory and vasodilatory properties. Upregulation of the inducible isoform HO-1 under stress conditions plays a crucial role in preventing or reducing cell damage. Therefore, modulation of the HO-1 system might provide an efficient strategy for organ protection. Pharmacological agents investigated in the context of organ conditioning include clinically used anesthetics and sedatives. A review from Hoetzel and Schmidt from 2010 nicely summarized the effects of anesthetics on HO-1 expression and their role in disease models. They concluded that HO-1 upregulation by anesthetics might prevent or at least reduce organ injury due to harmful stimuli. Due to its clinical safety, anesthetic conditioning might represent an attractive pharmacological tool for HO-1 modulation in patients. Remote ischemic conditioning (RIC), first described in 1993, represents a similar secure option to induce organ protection, especially in its non-invasive form. The efficacy of RIC has been intensively studied herein, including on patients. Studies on the role of RIC in influencing HO-1 expression to induce organ protection are emerging. In the first part of this review, recently published pre-clinical and clinical studies investigating the effects of anesthetics on HO-1 expression patterns, the underlying signaling pathways mediating modulation and its causative role in organ protection are summarized. The second part of this review sums up the effects of RIC.

Is xenon a suitable euthanasia agent for mice?

OBJECTIVE

To compare behavioural and electrophysiological variables of mice undergoing gas euthanasia with either xenon (Xe) or carbon dioxide (CO₂).

STUDY DESIGN

Single animals chronically instrumented for electroencephalography (EEG) recording were randomized to undergo euthanasia with either CO₂ or Xe (n = 6 animals per group).

ANIMALS

Twelve adult (>6 weeks old) male C57Bl6/n mice.

METHODS

Mice were surgically instrumented with EEG and electromyogram electrodes. Following a 7-day recovery period, animals were placed individually in a sealed chamber and a 5-minute baseline recorded in 21% O₂. Gas [100% Xe (n = 6) or 100% CO₂ (n = 6)] was then added to the chamber at 30% chamber volume minute^-1 (2.8 L minute^-1) until cessation of breathing. EEG, behaviour (jumping and freezing) and locomotion speed were recorded throughout.

RESULTS

Mice undergoing single gas euthanasia with Xe did not show jumping or freezing behaviours and had reduced locomotion speed compared to baseline, in contrast to CO₂, which resulted in increases in these variables. EEG recordings revealed sedative effects from Xe but heightened arousal from CO₂.

CONCLUSIONS

Our data suggest that Xe may be less aversive than CO₂ when using a 30% chamber volume minute^-1 fill rate and could improve the welfare of mice undergoing gas euthanasia.