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Toxic and protective effects of inhaled anaesthetics on the developing animal brain: Systematic review and update of recent experimental work

Liu, Jingjin; Rossaint, Rolf; Sanders, Robert D.; Coburn, Mark

Author Information
European Journal of Anaesthesiology: December 2014 - Volume 31 - Issue 12 - p 669-677
doi: 10.1097/EJA.0000000000000073


The exposure of infants and children to surgery and general anaesthesia has dramatically increased in recent decades. A report from the USA National Center for Health Statistics estimated that 6 million children undergo surgical care each year in the United States.1 The widespread use of general anaesthetics in paediatric anaesthesia makes its well tolerated application an extremely important issue in public health. In 1999, John Olney and colleagues first reported that N-methyl-d-aspartate (NMDA) antagonists, including ketamine, triggered widespread neuroapoptosis in the developing brain.2 Subsequently, researchers could show that many anaesthetics, including nitrous oxide, isoflurane and ketamine, induced apoptotic changes in the brain of neonatal rodents.3 More importantly, several general anaesthetics were proved to induce long-term cognitive impairment in different animal models.4–6 There were, however, some studies displaying potentially protective effects of general anaesthetics on the developing brain.7,8 As a result, a growing number of studies addressed the effects of inhalational anaesthetics on the immature brain in recent years (Supplementary Digital Content Tables 1 and 2, We provide an overview of the available preclinical evidence gained in the past 5 years on both the detrimental effects and the neuroprotective potential in special settings, of inhaled anaesthetics on the developing brain.

Materials and methods

A PubMed search was performed in June 2013 with the following keywords: published in the last 5 years, animals, (inhaled anesthesia OR inhaled anaesthesia OR inhaled anesthetic OR inhaled anaesthetic OR inhaled narcotic OR inhalational anesthesia OR inhalational anaesthesia OR inhalational anesthetic OR inhalational anaesthetic OR inhalational narcotic OR volatile anesthetic OR volatile anaesthetic) AND (neuro* OR brain OR cerebral OR apoptosis OR toxicity OR impairment OR disability OR disorder OR abnormal OR deficit OR injury OR insult OR protect*) AND (pediatric OR child* OR baby OR infant OR newborn OR neonat* OR developing OR immature OR fetus OR fetal OR embryo OR young). The reference lists of relevant articles and recent reviews were also hand-searched for additional studies.


The search strategy revealed 196 relevant titles. An additional 23 titles were discovered by a hand-search of the reference lists of relevant articles and recent reviews. In total, 216 records were identified after duplicates have been removed. Only 81 studies, however, studies were included in this systematic review. One hundred and thirty-five records were excluded due to the following reasons: review articles (26 studies); comments (two studies); studies in which the animals have completed their biological development (16 studies); studies that discussed the effects of agents except for inhaled anaesthetics (17 studies); studies that concerned the changes outside the central nervous system (39 studies); and studies that focused on the issues other than the detrimental or the neuroprotective effects of inhaled anaesthetics (35 studies). The procedures and results of the literature search are summarised in Fig. 1.

Fig. 1
Fig. 1:
Literature search procedures and results.

Sixty-eight articles assessed the structural and/or functional abnormalities induced by inhaled anaesthetics in the developing brain, and the possible protective approaches (Supplementary Digital Content Table 1, Isoflurane was the anaesthetic agent addressed most frequently (in 30 studies), and sevoflurane was the second (16 studies). Three studies dealt with xenon, and one study involved nitrous oxide. Ten studies used anaesthetic cocktails (e.g. isoflurane and nitrous oxide, or a further combination with midazolam) in the experiments. A further eight studies compared the efficiency of two or more anaesthetics. Referring to the animal species, 63 of the studies were carried out in rodents, two were in piglets and three were in primates. Twenty-six of the articles reported long-term neurobehavioural dysfunction in animals. In contrast, 13 articles focused on the protective profile of inhalational anaesthetics on perinatal hypoxic-ischaemic brain injury (Supplementary Digital Content Table 2, Seven of them dealt with the effect of noble gases, and six focused on volatile anaesthetics. Among these studies, 11 were carried out in rodents, and the remaining two were in piglets. Eight of the articles confirmed the protective effect of inhaled anaesthetics with neurobehavioural tests.

Several studies reported developmental neurotoxicity of inhaled anaesthetic agents in rodents, piglets and primates. Apoptotic neuronal death, influence on neurogenesis, impacts on synaptogenesis and axon guidance, glial cell impairment, neuroinflammation, cytosolic Ca2+ increase and mitochondrial dysfunction were identified as possible mechanisms of inhaled anaesthetic-induced toxicity in the immature brain. Administration of xenon, dexmedetomidine, hydrogen, pramipexole (PPX), EUK-134, N-stearoyl-l-tyrosine (NsTyr), bumetanide, recombinant erythropoietin (rEPO) and environmental enrichment exerted therapeutic effect. On the contrary, volatile anaesthetics may be advantageous when used for a defined period in perinatal hypoxic-ischaemic brain injury. In addition, the noble gases such as xenon and argon, were demonstrated to be effective neuroprotectants in models of perinatal hypoxic-ischaemic brain injury.


Our review has highlighted a considerable number of preclinical studies showing that the immature brain is vulnerable to inhaled anaesthetic agents. In contrast, in perinatal hypoxic-ischaemic brain injury models, inhalational anaesthetics exerted neuroprotective effects including both pre- and postconditioning mechanisms.

Detrimental effects of inhaled anaesthetics on the developing brain in rodents, piglets and primates

Both in-vivo and in-vitro exposure of gestational and neonatal rodents to inhaled anaesthetics lead to neurotoxicity in the developing brain. Only a few studies, however, studies could identify cognitive impairment persisting into juvenile or adulthood. In addition, immature piglets and primates seem to be vulnerable to inhalational anaesthesia exposure. However, unlike primates and rodents, cognition has not been assessed in pigs (Supplementary Digital Content Table 1,

There are various theories attempting to explain the mechanism of inhalational anaesthetic-induced toxicity in the immature brain. Inhaled anaesthetic agents displayed neurodegenerative effects by inducing apoptotic neuronal death in specific brain regions.9–14 The cortex, hippocampus, thalamus and basal ganglia appear particularly sensitive to anaesthetics.9,12,13 Some researchers considered the influence of anaesthetics on neurogenesis as another important mechanism.15–17 Neurogenesis occurs during brain development and persists in the subventricular zone and the hippocampal dentate gyrus in the adult brain, in which it is important for certain types of learning and memory.16 It was shown that exposure of neonatal rodents to inhaled anaesthetics resulted in reduction of neurogenesis, and subsequently lead to progressive and persistent cognitive deficits.15,16 In order to maintain the normal function of the brain, the central nervous system requires proper formation of precise neuronal circuits during brain maturation. External factors that affect synaptogenesis and axon guidance may interfere with neuronal network development, thus leading to dysfunction of the brain later in life.18 Inhalational anaesthetic agents impacted upon synaptogenesis by disturbing actin cytoskeletal depolymerisation sculpting and altering dendritic spine architecture.11,18–20 Axon guidance is a process that is vital to circuit formation and normal brain development, as axons are required to navigate over long distances to form synapses with appropriate dendritic targets. A range of severe cognitive defects are features of human developmental disorders that result from disrupted axon guidance.21,22 Mintz et al.22,23 determined that inhaled anaesthetics disturbed axon guidance by acting via γ-aminobutyric acid (GABA)-mediated mechanisms, and thus potentially interfered with circuit formation. Inhalational anaesthetics not only influence the survival and development of neurons but also impact on glial cells. Brambrink et al.24 demonstrated in the rhesus macaque that isoflurane-induced apoptosis involved both white matter and grey matter with selectively vulnerable oligodendrocytes. Lunardi et al.19 showed that exposure to isoflurane impaired the growth of immature astrocytes and morphological development. In addition, neuroinflammation, including microglia activation and increase of proinflammatory cytokines in the brain, may result in cognitive disorder.25,26 It was shown that exposure of neonatal mice to sevoflurane induced neuroinflammation and cognitive impairment; the latter was ameliorated by anti-inflammatory treatment.27 Inhaled anaesthetic agents were thought to increase cytosolic Ca2+ via activation of GABAA receptor, one of the main receptors responsible for the anaesthesia effect of general anaesthetics, thereby influencing neuronal plasticity and exerting a deleterious effect in the developing brain.28,29 Furthermore, Sanchez et al.30 and Boscolo et al.31,32 found in their experiments that inhalational anaesthetics impaired mitochondrial morphogenesis and synaptic transmission, caused mitochondrial dysfunction, extensive reactive oxygen species (ROS) upregulation and lipid peroxidation in neonatal rat subiculum, and induced long-term cognitive impairment later in life.

Exposure time is crucial for subsequent outcomes of anaesthetic-induced neurotoxicity. The brain is especially vulnerable during early development. For example, neither single nor multiple exposures of the adult mice or rats to inhaled anaesthetics lead to detrimental effect on the brain, whereas the same anaesthesia regimens administrated to neonatal rodents resulted in significant histopathology and neurocognitive impairments.15,16,27 Interestingly, the immature brain seems to be less effected by anaesthetic-induced toxicity as animals grow older. In one study, exposure of 1-month-old mice to isoflurane resulted only in a transient decrease of filopodial (small membranous protrusions found primarily on dendritic stretches of developing neurons) elimination, which disappeared within 1 day after the animals awakened.33 It is worth noting, however, that in the experiment carried out by Hofacer et al.,34 anaesthetic-induced neuroapoptosis was shown to extend into adulthood in brain regions with ongoing neurogenesis, such as dentate gyrus and olfactory bulb, although the absolute number of dying cells was much less than in young mice. As the authors pointed out, this finding suggested that anaesthetic vulnerability did not reflect the age of the organism, but the age of the neuron, and therefore may potentially not only be relevant to children but also to adults undergoing anaesthesia.34

As many inhaled anaesthetics have been demonstrated to cause neuroapoptosis and persistent learning deficits when given to young animals, comparison of agent-specific differences in the development of neurotoxicity is of great interest in order to minimise the adverse outcomes after anaesthetic exposure to the immature brain. Some studies compared the neuroapoptotic properties of commonly used inhalational anaesthetics, such as desflurane, sevoflurane and isoflurane, in equivalent doses. One study35 demonstrated that equipotent concentrations of the above mentioned three anaesthetics had similar neurotoxic profiles. Others, however, indicated some anaesthetic agents have a greater neurodegenerative effect.6,27,36,37 For example, Shen et al.27 showed that exposure of neonatal mice to 3% sevoflurane for 2 h daily for 3 days induced cognitive impairment and neuroinflammation, while similar exposure to 9% desflurane did not lead to developing brain toxicity. Liang et al.36 and Ramage et al.37 demonstrated that isoflurane caused greater neurodegeneration and memory deficit than an equivalent exposure to sevoflurane in the immature rodent brain. In addition, Kodama et al.6 reported that neonatal exposure to desflurane induced significantly greater neuroapoptosis than sevoflurane and isoflurane. Mice exposed to desflurane had substantially impaired working memory; however, performance in working memory tasks in mice exposed neonatally to sevoflurane or isoflurane was normal.6 The inconsistent results may be due to the different biologic indicators and behavioural test modules used in the experiments, the anaesthetic regimens and absolute concentrations administrated to animals, and even the strain diversity. Nevertheless, there are some studies indicating that inhaled anaesthetics might exert minor or no neurotoxic effect on the developing brain. Bercker et al.38 demonstrated that use of 3 to 5% sevoflurane for 6 h induced neither neurodegeneration nor learning deficits in neonatal rats. In addition, in an in-vitro study carried out by Berns et al.,39 up to 6 (8%) and 12 h (4%) exposure to sevoflurane, cell viability was the same when compared with untreated controls. Loepke et al.40 showed that isoflurane exposure led to increased immediate brain cell degeneration. However, neither significant reduction in neuronal density nor deficits in spontaneous locomotion, spatial learning or memory function affect neurobehavioural performances in the juvenile period.41

There are inconsistent data regarding the neuroapoptotic effects of xenon. Although some in-vivo and in-vitro studies reported that xenon alone was not neurotoxic,42,43 others indicated a proapoptotic property of xenon.44–46 Brosnan and Bickler46 presented recently that xenon was not neurotoxic at subminimum alveolar concentrations (MAC); however, it caused neurotoxicity at 1 MAC and greater concentrations. This is consistent with our finding that xenon provided maximal neuroprotective effect at 0.5 atm (∼0.53 MAC),47,48 but it reversed at higher pressures and exhibited significant neurotoxicity at 2 atm (∼2.1 MAC).49 Further research is required to identify a toxic/therapeutic ratio for xenon, as well as the mechanisms of xenon protection and toxicity.

Campbell et al.50 demonstrated that clinically relevant anaesthetic concentrations of ketamine, nitrous oxide and isoflurane had no significant neurotoxic effect applied individually or when given as an anaesthetic cocktail in vitro, even with an exposure up to 12 h. The author considered that neurotoxicity previously reported in vivo is not due to direct cytotoxicity of anaesthetic agents but results from other effects of the anaesthetised state during early brain development.50 Shu et al.5 discovered in their experiment that nociceptive stimulation augmented anaesthetic-induced neuroapoptosis and cognitive impairment. Another researcher showed that widespread brain cell death was generated by both isoflurane and carbon dioxide, and the degree and distribution of cell death was similar in isoflurane and carbon dioxide treated groups.51 Hypoglycaemia, however, did not seem to be responsible for the neurodegeneration, as dextrose supplementation failed to prevent neuronal loss in neonatal mice.40 Hence, many factors may exert additional effects on brain development including surgical stimulation, intraoperative pain and hypercapnia.

In summary, the majority of studies have linked inhaled anaesthetics to toxic effects in the brain after gestational or neonatal exposure. A time window of vulnerability exists when the brain grows rapidly during early development. Apoptotic neuronal death, influence on neurogenesis, impacts on synaptogenesis and axon guidance, glial cell impairment, neuroinflammation, cytosolic Ca2+ increase and mitochondrial dysfunction were identified as possible mechanisms of inhaled anaesthetic-induced developmental neurotoxicity. Furthermore, commonly used inhalational anaesthetics, such as desflurane, sevoflurane and isoflurane, were compared for the neuroapoptotic properties in equivalent doses in order to minimise the subsequent adverse outcomes. However, no anaesthetic appears to be superior. In addition to inhaled anaesthetics, the impacts of the anaesthetised state during early brain development, for example surgical stimuli, intraoperative pain as well as hypercapnia, demonstrated neurotoxicity in the immature brain.

Neuroprotective approaches to protect against inhaled anaesthetic-induced neurotoxicity

Considering the inhaled anaesthetic-induced deleterious effects in the central nervous system, attempts to protect the immature brain are of vital interest. The noble gas xenon has very rapid onset and recovery characteristics, as well as haemodynamic stability.52–54 Preconditioning with xenon prevented nitrous oxide and isoflurane-induced neuroapoptosis and cognitive deterioration, while hypoxic pretreatment exacerbated the toxicity of these anaesthetics, and nitrous oxide pretreatment had no effect.55 Early in life, α2 adrenoceptors could activate cellular survival mechanisms via endogenous norepinephrine, thus exerting a trophic role in central nervous system signalling.56,57 Acting as an α2 agonist, dexmedetomidine was shown to attenuate isoflurane-induced neuroapoptosis and provide neurocognitve protection in the immature brain.58,59 Hydrogen has recently received attention because of its ability to easily penetrate the blood–brain barrier as well as its antioxidant potential.60 It was determined in neonatal mice that hydrogen coadministered with sevoflurane reduced oxidative stress, neuronal apoptosis and subsequent neurobehavioural deficits.4 Furthermore, cotreatment with the mitochondrial-targeted antioxidant PPX or synthetic ROS scavenger EUK-134 significantly preserved mitochondrial integrity, downregulated lipid peroxidation, decreased neuronal loss and provided long-lasting protection against cognitive impairment in neonatal rats exposed to inhaled anaesthetics.31,61 The first identified endocannabinoid N-arachidonoylethanolamine (AEA) plays a crucial neuroprotective role in certain neurodegenerative diseases. NsTyr, an AEA analogue, was reported to protect immature brain against developmental sevoflurane neurotoxicity through MEK/extracellular signal-related kinases 1 and 2 (ERK1/2) MAPK signalling pathway.62 In addition, bumetanide, a specific inhibitor of chloride uptake, was shown to alleviate the epileptogenic and neurotoxic effects of sevoflurane in early postnatal rats by suppressing the excitatory output of sevoflurane-potentiated GABAA/glycine systems.63 Recombinant erythropoietin (rEPO) displayed a neuroprotective effect in isoflurane-induced mouse brain damage and learning impairments.64 Moreover, it was demonstrated that sevoflurane-induced long-term cognitive impairment was reversed by environmental enrichment (physical exercise, social interaction and environmental complexity) even when instituted with a 3-week delay after anaesthesia.13,27 In short, these experimental results provide several promising therapeutic strategies to alleviate neurotoxicity caused by inhalational anaesthesia exposure in the developing brain.

The protective profile of noble gases in perinatal hypoxic-ischaemic brain injury

Xenon is an inert gas that has proved to be efficient in clinical anaesthesia and is relatively devoid of clinically significant adverse haemodynamic properties.53,65 Results from various in-vitro and in-vivo animal studies have consistently demonstrated the neuroprotective effect of xenon.49,53,54,66 When administered after hypoxia-ischaemia in neonatal piglets and rats, treatment with xenon appreciably reduced cerebral magnetic resonance spectra (MRS) abnormalities and cell death markers, ameliorated histopathological outcomes and improved short and long-term neurological functions.67–69 Xenon also attenuated brain injury and exerted long-lasting functional neuroprotection when administrated before hypoxia-ischaemia insult.70,71 Zhuang et al.7 compared the protective profile of xenon and two other noble gases, argon and helium, in a rat neonatal asphyxia model. They demonstrated that all three inert gases improved cell survival, brain structural integrity and neurologic function at a juvenile age after moderate hypoxic-ischaemia. Argon improved cell survival to a naive level, whereas xenon and helium did not.7 Given that argon lacks a sedative effect and is highly cost-effective compared with xenon,54 future research should pursue argon neuroprotection. Some researchers have explored the protective efficiency of xenon in combination with other anaesthetic agents or techniques. A xenon/hypothermia regimen proved to have an additive neuroprotective effect after hypoxic-ischaemia than either treatment in isolation.68,69 Coadministration of lower doses of xenon and sevoflurane (20% + 0.75%) achieved a similar protective effect as either anaesthetic alone (75% xenon and 1.5% sevoflurane).70 Combined with the evidence described above concerning the potentially neurotoxic effects of xenon, further information is required to identify xenon's therapeutic window. This should be further identified from animal histologic and behavioural studies. In the meantime, if clinical trials are pursued, then subanaesthetic doses, which appear well tolerated from a neurotoxicity perspective, should be considered.

The protective profile of volatile anaesthetics in perinatal hypoxic-ischaemic brain injury

The volatile anaesthetics, such as desflurane, isoflurane and sevoflurane, have been proven to exert neuroprotection in various paradigms.72 The neuroprotective profile of isoflurane in perinatal hypoxic-ischaemic brain injury and the underlying mechanisms were studied by several researchers. Zhou et al.8 showed that isoflurane post-treatment decreased brain injury and improved long-term neurobehavioural outcomes; the effects were mediated by activating sphingosine-1-phosphate (S1P)/phosphatidylinositol-3-kinase (PI3K)/Akt signalling pathway. In the study by Sasaoka et al.,73 acute preconditioning of isoflurane in neonatal rats subjected to a hypoxic-ischaemic injury resulted in only transient neuroprotection. In in-vitro studies, preconditioning or postconditioning of isoflurane was demonstrated by McMurtrey and Li et al., 74,75 respectively. They showed that rat hippocampal neuronal damage was attenuated by inhibition of Ca2+/calmodulin-dependent protein kinases II (CaMKII) and NMDA receptors, activation of adenosine A2A receptors, upregulating of heme oxygenase-1 (HO-1) and activation of Erk1/2/hypoxia inducible factor (HIF)-1α pathway.74–76 Moreover, Luo et al.,70 Yang et al.71 and McAuliffe et al.72 proved that preconditioning with sevoflurane and desflurane demonstrated neuroprotective properties both in vitro and in vivo.These studies revealed that volatile anaesthetic agents may be advantageous when used for a defined period during the operative procedure.

Future considerations

The preclinical findings concerning the effects of inhaled anaesthetics on the developing brain are mixed. The existing data are not adequate for experts and clinicians to draw final conclusions. Therefore, additional research is needed to further identify this issue. Well designed preclinical research on this topic is particularly important. Several recommendations and guidelines, such as the Stroke Therapy Academic Industry Roundtable (STAIR) recommendations77 and the National Institute of Neurological Disorders and Stroke (NINDS) guidelines (, have been published to improve the quality and utility of preclinical research. These fundamental principles should also apply to animal studies concerning anaesthetic-related effects on the immature brain. First of all, rigorous experimental design and transparent reporting are essential factors for high-quality studies; random allocation to treatment group; concealment of drug assignment and blinded assessment of outcome in order to eliminate randomisation and assessment bias; setting of the control groups should be adequate; a priori inclusion/exclusion criteria should be defined; appropriate power and sample size calculations should be performed and reported; dose–response results should be documented; reasons for excluding animals from the final data analysis should be announced; and all results, including negative and positive results, should be reported. Second, in order to obtain evidence that could guide clinical treatments effectively, animal experiments should be designed to closely mirror the clinical settings. Timing, dosage, duration and frequency of anaesthesia exposure should be carefully considered; both histological and behavioural outcomes should be assessed, and the effects of anaesthetics should be surveyed both acutely and long term; and relevant functional and biomarker endpoints should be included that could be also obtained in human trials. After initial evaluations in healthy male neonates, further studies should be carried out in females, animals with comorbid conditions and concomitant medications, as well as animals undergoing the most common surgical procedures required for young children, such as myringotomy and grommets for chronic ear infection, tonsillectomy, hernia repair and circumcision.78 Third, most of the preclinical studies were initially conducted in rodents. However, higher order species should also be tested. The data, especially the neurobehavioural outcomes in piglets and primates, are of great importance, as their brain development closely parallels humans.79 Fourth, in order to verify the reliability and stability of studies, the observed results should be reproducible in at least two independent laboratories.

The mechanisms of inhaled anaesthetic-induced neurotoxicity remain open to further research. The equivalence of the developmental status and the vulnerable time windows between animals and humans should be carefully assessed. In addition, noninvasive examinations and rapid diagnosis methods need to be developed.


Although robust preclinical results have shown that gestational and neonatal exposure to inhaled anaesthetics are deleterious to the developing brain, other studies indicated that the developmental neurotoxicity of inhalational anaesthetics is mild. Owing to the potential publication bias of the currently available articles, some studies showing no statistical significance might have been excluded. In addition, prospective clinical trials concerning the safety of general anaesthetics used in infants and children are difficult to conduct, as children cannot be ethically randomised to a ‘no anaesthesia’ group. Nonetheless, inhaled anaesthetics, such as desflurane, isoflurane and sevoflurane, are commonly used in paediatric anaesthesia. As a result, more animal studies are urgently needed to further clarify the effects of inhalational anaesthetics on the developing brain. Despite the difficult path to translate experimental results into clinical applications, research must address the mechanisms of injury to identify potential therapeutic targets. However, as suggested by the SmartTots consensus statement (, which considers the safety of anaesthetics and sedative agents administered to infants and young children and is endorsed by several communities including ESA and ASA, the risks and benefits of procedures requiring anaesthetics as well as the known health risks of not treating certain conditions should be judged and weighed carefully. Meanwhile, preclinical data suggest a benefit from noble gas and volatile anaesthetic-induced neuroprotection in perinatal hypoxic-ischaemic brain injury. In addition to some ongoing clinical trials (such as TOBYXe, NCT00934700; CoolXenon2, NCT01545271), more studies are needed to assess the safety and efficacy profiles of these potential therapies.

Acknowledgements relating to this article

Assistance with the review: none.

Financial support and sponsorship: Jingjin Liu is supported by the Overseas Study Program of Guangzhou Elite Project.

Conflicts of interest: none.

Presentation: none.


1. DeFrances CJ, Cullen KA, Kozak LJ. National Hospital Discharge Survey: 2005 annual summary with detailed diagnosis and procedure data. Vital and health statistics Series 13, Data from the National Health Survey. 165ed.Rockville, Md: National Center for Health Statistics; 2007; 1–209.
2. Ikonomidou C, Bosch F, Miksa M, et al. Blockade of NMDA receptors and apoptotic neurodegeneration in the developing brain. Science 1999; 283:70–74.
3. Loepke AW, Soriano SG. An assessment of the effects of general anesthetics on developing brain structure and neurocognitive function. Anesth Analg 2008; 106:1681–1707.
4. Yonamine R, Satoh Y, Kodama M, et al. Coadministration of hydrogen gas as part of the carrier gas mixture suppresses neuronal apoptosis and subsequent behavioral deficits caused by neonatal exposure to sevoflurane in mice. Anesthesiology 2013; 118:105–113.
5. Shu Y, Zhou Z, Wan Y, et al. Nociceptive stimuli enhance anesthetic-induced neuroapoptosis in the rat developing brain. Neurobiol Dis 2012; 45:743–750.
6. Kodama M, Satoh Y, Otsubo Y, et al. Neonatal desflurane exposure induces more robust neuroapoptosis than do isoflurane and sevoflurane and impairs working memory. Anesthesiology 2011; 115:979–991.
7. Zhuang L, Yang T, Zhao H, et al. The protective profile of argon, helium, and xenon in a model of neonatal asphyxia in rats. Crit Care Med 2012; 40:1724–1730.
8. Zhou Y, Lekic T, Fathali N, et al. Isoflurane posttreatment reduces neonatal hypoxic-ischemic brain injury in rats by the sphingosine-1-phosphate/phosphatidylinositol-3-kinase/Akt pathway. Stroke 2010; 41:1521–1527.
9. Brambrink AM, Evers AS, Avidan MS, et al. Isoflurane-induced neuroapoptosis in the neonatal rhesus macaque brain. Anesthesiology 2010; 112:834–841.
10. Jiang H, Huang Y, Xu H, et al. Hypoxia inducible factor-1alpha is involved in the neurodegeneration induced by isoflurane in the brain of neonatal rats. J Neurochem 2012; 120:453–460.
11. Lemkuil BP, Head BP, Pearn ML, et al. Isoflurane neurotoxicity is mediated by p75NTR-RhoA activation and actin depolymerization. Anesthesiology 2011; 114:49–57.
12. Satomoto M, Satoh Y, Terui K, et al. Neonatal exposure to sevoflurane induces abnormal social behaviors and deficits in fear conditioning in mice. Anesthesiology 2009; 110:628–637.
13. Shih J, May LD, Gonzalez HE, et al. Delayed environmental enrichment reverses sevoflurane-induced memory impairment in rats. Anesthesiology 2012; 116:586–602.
14. Istaphanous GK, Ward CG, Nan X, et al. Characterization and quantification of isoflurane-induced developmental apoptotic cell death in mouse cerebral cortex. Anesth Analg 2013; 116:845–854.
15. Zhu C, Gao J, Karlsson N, et al. Isoflurane anesthesia induced persistent, progressive memory impairment, caused a loss of neural stem cells, and reduced neurogenesis in young, but not adult, rodents. J Cereb Blood Flow Metab 2010; 30:1017–1030.
16. Stratmann G, Sall JW, May LD, et al. Isoflurane differentially affects neurogenesis and long-term neurocognitive function in 60-day-old and 7-day-old rats. Anesthesiology 2009; 110:834–848.
17. Sall JW, Stratmann G, Leong J, et al. Isoflurane inhibits growth but does not cause cell death in hippocampal neural precursor cells grown in culture. Anesthesiology 2009; 110:826–833.
18. Briner A, De Roo M, Dayer A, et al. Volatile anesthetics rapidly increase dendritic spine density in the rat medial prefrontal cortex during synaptogenesis. Anesthesiology 2010; 112:546–556.
19. Lunardi N, Hucklenbruch C, Latham JR, et al. Isoflurane impairs immature astroglia development in vitro: the role of actin cytoskeleton. J Neuropath Exp Neur 2011; 70:281–291.
20. Head BP, Patel HH, Niesman IR, et al. Inhibition of p75 neurotrophin receptor attenuates isoflurane-mediated neuronal apoptosis in the neonatal central nervous system. Anesthesiology 2009; 110:813–825.
21. Engle EC. Human genetic disorders of axon guidance. Cold Spring Harbor Perspect Biol 2010; 2:a001784.
22. Mintz CD, Barrett KM, Smith SC, et al. Anesthetics interfere with axon guidance in developing mouse neocortical neurons in vitro via a gamma-aminobutyric acid type A receptor mechanism. Anesthesiology 2013; 118:825–833.
23. Mintz CD, Smith SC, Barrett KM, Benson DL. Anesthetics interfere with the polarization of developing cortical neurons. J Neurosurg Anesthesiol 2012; 24:368–375.
24. Brambrink AM, Back SA, Riddle A, et al. Isoflurane-induced apoptosis of oligodendrocytes in the neonatal primate brain. Ann Neurol 2012; 72:525–535.
25. Wilson CJ, Finch CE, Cohen HJ. Cytokines and cognition: the case for a head-to-toe inflammatory paradigm. J Am Geriatr Soc 2002; 50:2041–2056.
26. Rudolph JL, Ramlawi B, Kuchel GA, et al. Chemokines are associated with delirium after cardiac surgery. J Gerontol A Biol Sci Med Sci 2008; 63:184–189.
27. Shen X, Dong Y, Xu Z, et al. Selective anesthesia-induced neuroinflammation in developing mouse brain and cognitive impairment. Anesthesiology 2013; 118:502–515.
28. Zhao YL, Xiang Q, Shi QY, et al. GABAergic excitotoxicity injury of the immature hippocampal pyramidal neurons’ exposure to isoflurane. Anesth Analg 2011; 113:1152–1160.
29. Zhao Y, Liang G, Chen Q, et al. Anesthetic-induced neurodegeneration mediated via inositol 1,4,5-trisphosphate receptors. J Pharmacol Exp Ther 2010; 333:14–22.
30. Sanchez V, Feinstein SD, Lunardi N, et al. General anesthesia causes long-term impairment of mitochondrial morphogenesis and synaptic transmission in developing rat brain. Anesthesiology 2011; 115:992–1002.
31. Boscolo A, Starr JA, Sanchez V, et al. The abolishment of anesthesia-induced cognitive impairment by timely protection of mitochondria in the developing rat brain: the importance of free oxygen radicals and mitochondrial integrity. Neurobiol Dis 2012; 45:1031–1041.
32. Boscolo A, Milanovic D, Starr JA, et al. Early exposure to general anesthesia disturbs mitochondrial fission and fusion in the developing rat brain. Anesthesiology 2013; 118:1086–1097.
33. Yang G, Chang PC, Bekker A, et al. Transient effects of anesthetics on dendritic spines and filopodia in the living mouse cortex. Anesthesiology 2011; 115:718–726.
34. Hofacer RD, Deng M, Ward CG, et al. Cell age-specific vulnerability of neurons to anesthetic toxicity. Ann Neurol 2013; 73:695–704.
35. Istaphanous GK, Howard J, Nan X, et al. Comparison of the neuroapoptotic properties of equipotent anesthetic concentrations of desflurane, isoflurane, or sevoflurane in neonatal mice. Anesthesiology 2011; 114:578–587.
36. Liang G, Ward C, Peng J, et al. Isoflurane causes greater neurodegeneration than an equivalent exposure of sevoflurane in the developing brain of neonatal mice. Anesthesiology 2010; 112:1325–1334.
37. Ramage TM, Chang FL, Shih J, et al. Distinct long-term neurocognitive outcomes after equipotent sevoflurane or isoflurane anaesthesia in immature rats. Br J Anaesth 2013; 110 (Suppl 1):i39–i46.
38. Bercker S, Bert B, Bittigau P, et al. Neurodegeneration in newborn rats following propofol and sevoflurane anesthesia. Neurotox Res 2009; 16:140–147.
39. Berns M, Zacharias R, Seeberg L, et al. Effects of sevoflurane on primary neuronal cultures of embryonic rats. Eur J Anaesthesiol 2009; 26:597–602.
40. Loepke AW, Istaphanous GK, McAuliffe JJ 3rd, et al. The effects of neonatal isoflurane exposure in mice on brain cell viability, adult behavior, learning, and memory. Anesth Analg 2009; 108:90–104.
41. Feng X, Liu JJ, Zhou X, et al. Single sevoflurane exposure decreases neuronal nitric oxide synthase levels in the hippocampus of developing rats. Br J Anaesth 2012; 109:225–233.
42. Ma D, Williamson P, Januszewski A, et al. Xenon mitigates isoflurane-induced neuronal apoptosis in the developing rodent brain. Anesthesiology 2007; 106:746–753.
43. Sabir H, Bishop S, Cohen N, et al. Neither xenon nor fentanyl induces neuroapoptosis in the newborn pig brain. Anesthesiology 2013; 119:345–357.
44. Cattano D, Williamson P, Fukui K, et al. Potential of xenon to induce or to protect against neuroapoptosis in the developing mouse brain. Can J Anaesth 2008; 55:429–436.
45. Cattano D, Valleggi S, Cavazzana AO, et al. Xenon exposure in the neonatal rat brain: effects on genes that regulate apoptosis. Minerva Anestesiol 2011; 77:571–578.
46. Brosnan H, Bickler PE. Xenon neurotoxicity in rat hippocampal slice cultures is similar to isoflurane and sevoflurane. Anesthesiology 2013; 119:335–344.
47. Koblin DD, Fang Z, Eger EI 2nd, et al. Minimum alveolar concentrations of noble gases, nitrogen, and sulfur hexafluoride in rats: helium and neon as nonimmobilizers (nonanesthetics). Anesth Analg 1998; 87:419–424.
48. Miller KW, Paton WD, Smith EB, Smith RA. Physicochemical approaches to the mode of action of general anesthetics. Anesthesiology 1972; 36:339–351.
49. Coburn M, Maze M, Franks NP. The neuroprotective effects of xenon and helium in an in vitro model of traumatic brain injury. Crit Care Med 2008; 36:588–595.
50. Campbell LL, Tyson JA, Stackpole EE, et al. Assessment of general anaesthetic cytotoxicity in murine cortical neurones in dissociated culture. Toxicology 2011; 283:1–7.
51. Stratmann G, May LD, Sall JW, et al. Effect of hypercarbia and isoflurane on brain cell death and neurocognitive dysfunction in 7-day-old rats. Anesthesiology 2009; 110:849–861.
52. Ma D, Hossain M, Pettet GK, et al. Xenon preconditioning reduces brain damage from neonatal asphyxia in rats. J Cereb Blood Flow Metab 2006; 26:199–208.
53. Derwall M, Coburn M, Rex S, et al. Xenon: recent developments and future perspectives. Minerva Anestesiol 2009; 75:37–45.
54. Coburn M, Rossaint R. Argon in the fast lane: noble gases and their neuroprotective effects. Crit Care Med 2012; 40:1965–1966.
55. Shu Y, Patel SM, Pac-Soo C, et al. Xenon pretreatment attenuates anesthetic-induced apoptosis in the developing brain in comparison with nitrous oxide and hypoxia. Anesthesiology 2010; 113:360–368.
56. Winzer-Serhan UH, Leslie FM. Expression of alpha2A adrenoceptors during rat neocortical development. J Neurobiol 1999; 38:259–269.
57. Song ZM, Abou-Zeid O, Fang YY. alpha2a adrenoceptors regulate phosphorylation of microtubule-associated protein-2 in cultured cortical neurons. Neuroscience 2004; 123:405–418.
58. Sanders RD, Sun P, Patel S, et al. Dexmedetomidine provides cortical neuroprotection: impact on anaesthetic-induced neuroapoptosis in the rat developing brain. Acta Anaesthesiol Scand 2010; 54:710–716.
59. Sanders RD, Xu J, Shu Y, et al. Dexmedetomidine attenuates isoflurane-induced neurocognitive impairment in neonatal rats. Anesthesiology 2009; 110:1077–1085.
60. Ohsawa I, Ishikawa M, Takahashi K, et al. Hydrogen acts as a therapeutic antioxidant by selectively reducing cytotoxic oxygen radicals. Nature Med 2007; 13:688–694.
61. Boscolo A, Ori C, Bennett J, et al. Mitochondrial protectant pramipexole prevents sex-specific long-term cognitive impairment from early anaesthesia exposure in rats. Br J Anaesth 2013; 110 (Suppl 1):i47–i52.
62. Wang WY, Yang R, Hu SF, et al. N-stearoyl-L-tyrosine ameliorates sevoflurane induced neuroapoptosis via MEK/ERK1/2 MAPK signaling pathway in the developing brain. Neurosci Lett 2013; 541:167–172.
63. Edwards DA, Shah HP, Cao W, et al. Bumetanide alleviates epileptogenic and neurotoxic effects of sevoflurane in neonatal rat brain. Anesthesiology 2010; 112:567–575.
64. Tsuchimoto T, Ueki M, Miki T, et al. Erythropoietin attenuates isoflurane-induced neurodegeneration and learning deficits in the developing mouse brain. Paediatr Anaesth 2011; 21:1209–1213.
65. Sanders RD, Ma D, Maze M. Xenon: elemental anaesthesia in clinical practice. Br Med Bull 2004; 71:115–135.
66. Fries M, Nolte KW, Coburn M, et al. Xenon reduces neurohistopathological damage and improves the early neurological deficit after cardiac arrest in pigs. Crit Care Med 2008; 36:2420–2426.
67. Faulkner S, Bainbridge A, Kato T, et al. Xenon augmented hypothermia reduces early lactate/N-acetylaspartate and cell death in perinatal asphyxia. Ann Neurol 2011; 70:133–150.
68. Chakkarapani E, Dingley J, Liu X, et al. Xenon enhances hypothermic neuroprotection in asphyxiated newborn pigs. Ann Neurol 2010; 68:330–341.
69. Hobbs C, Thoresen M, Tucker A, et al. Xenon and hypothermia combine additively, offering long-term functional and histopathologic neuroprotection after neonatal hypoxia/ischemia. Stroke 2008; 39:1307–1313.
70. Luo Y, Ma D, Ieong E, et al. Xenon and sevoflurane protect against brain injury in a neonatal asphyxia model. Anesthesiology 2008; 109:782–789.
71. Yang T, Zhuang L, Rei Fidalgo AM, et al. Xenon and sevoflurane provide analgesia during labor and fetal brain protection in a perinatal rat model of hypoxia-ischemia. PLoS One 2012; 7:e37020.
72. McAuliffe JJ, Loepke AW, Miles L, et al. Desflurane, isoflurane, and sevoflurane provide limited neuroprotection against neonatal hypoxia-ischemia in a delayed preconditioning paradigm. Anesthesiology 2009; 111:533–546.
73. Sasaoka N, Kawaguchi M, Kawaraguchi Y, et al. Isoflurane exerts a short-term but not a long-term preconditioning effect in neonatal rats exposed to a hypoxic-ischaemic neuronal injury. Acta Anaesthesiol Scand 2009; 53:46–54.
74. McMurtrey RJ, Zuo Z. Isoflurane preconditioning and postconditioning in rat hippocampal neurons. Brain Res 2010; 1358:184–190.
75. Li QF, Zhu YS, Jiang H. Isoflurane preconditioning activates HIF-1alpha, iNOS and Erk1/2 and protects against oxygen-glucose deprivation neuronal injury. Brain Res 2008; 1245:26–35.
76. Li Q, Zhu Y, Jiang H, et al. Up-regulation of heme oxygenase-1 by isoflurane preconditioning during tolerance against neuronal injury induced by oxygen glucose deprivation. Acta Biochim Biophys Hung 2008; 40:803–810.
77. Fisher M, Feuerstein G, Howells DW, et al. Update of the stroke therapy academic industry roundtable preclinical recommendations. Stroke 2009; 40:2244–2250.
78. Rabbitts JA, Groenewald CB, Moriarty JP, Flick R. Epidemiology of ambulatory anesthesia for children in the United States: 2006 and 1996. Anesth Analg 2010; 111:1011–1015.
79. Sanders RD, Hassell J, Davidson AJ, et al. Impact of anaesthetics and surgery on neurodevelopment: an update. Br J Anaesth 2013; 110 (Suppl 1):i53–i72.
80. Li Y, Wang F, Liu C, et al. JNK pathway may be involved in isoflurane-induced apoptosis in the hippocampi of neonatal rats. Neurosci Lett 2013; 545:17–22.
    81. Culley DJ, Cotran EK, Karlsson E, et al. Isoflurane affects the cytoskeleton but not survival, proliferation, or synaptogenic properties of rat astrocytes in vitro. Br J Anaesth 2013; 110 (Suppl 1):i19–i28.
      82. Xiang Q, Tan L, Zhao YL, et al. Isoflurane enhances spontaneous Ca(2+) oscillations in developing rat hippocampal neurons in vitro. Acta Anaesthesiol Scand 2009; 53:765–773.
        83. Kong FJ, Ma LL, Hu WW, et al. Fetal exposure to high isoflurane concentration induces postnatal memory and learning deficits in rats. Biochem Pharmacol 2012; 84:558–563.
          84. Kong FJ, Tang YW, Lou AF, et al. Effects of isoflurane exposure during pregnancy on postnatal memory and learning in offspring rats. Mol Biol Rep 2012; 39:4849–4855.
            85. Palanisamy A, Baxter MG, Keel PK, et al. Rats exposed to isoflurane in utero during early gestation are behaviorally abnormal as adults. Anesthesiology 2011; 114:521–528.
              86. Kong F, Xu L, He D, et al. Effects of gestational isoflurane exposure on postnatal memory and learning in rats. Eur J Pharmacol 2011; 670:168–174.
                87. Wang S, Peretich K, Zhao Y, et al. Anesthesia-induced neurodegeneration in fetal rat brains. Pediatr Res 2009; 66:435–440.
                  88. Schubert H, Eiselt M, Walter B, et al. Isoflurane/nitrous oxide anesthesia and stress-induced procedures enhance neuroapoptosis in intrauterine growth-restricted piglets. Intensive Care Med 2012; 38:1205–1214.
                    89. Zou X, Liu F, Zhang X, et al. Inhalation anesthetic-induced neuronal damage in the developing rhesus monkey. Neurotoxicol Teratol 2011; 33:592–597.
                      90. Zhou ZW, Shu Y, Li M, et al. The glutaminergic, GABAergic, dopaminergic but not cholinergic neurons are susceptible to anaesthesia-induced cell death in the rat developing brain. Neuroscience 2011; 174:64–70.
                        91. Medeiros LF, Rozisky JR, de Souza A, et al. Lifetime behavioural changes after exposure to anaesthetics in infant rats. Behav Brain Res 2011; 218:51–56.
                          92. Wang SQ, Fang F, Xue ZG, et al. Neonatal sevoflurane anesthesia induces long-term memory impairment and decreases hippocampal PSD-95 expression without neuronal loss. Eur Rev Med Pharmacol Sci 2013; 17:941–950.
                            93. Li Y, Liu C, Zhao Y, et al. Sevoflurane induces short-term changes in proteins in the cerebral cortices of developing rats. Acta Anaesthesiol Scand 2013; 57:380–390.
                              94. Fang F, Xue Z, Cang J. Sevoflurane exposure in 7-day-old rats affects neurogenesis, neurodegeneration and neurocognitive function. Neurosci Bull 2012; 28:499–508.
                              95. Lu Y, Wu X, Dong Y, et al. Anesthetic sevoflurane causes neurotoxicity differently in neonatal naive and Alzheimer disease transgenic mice. Anesthesiology 2010; 112:1404–1416.
                                96. Zhang X, Xue Z, Sun A. Subclinical concentration of sevoflurane potentiates neuronal apoptosis in the developing C57BL/6 mouse brain. Neurosci Lett 2008; 447:109–114.
                                  97. Zheng H, Dong Y, Xu Z, et al. Sevoflurane anesthesia in pregnant mice induces neurotoxicity in fetal and offspring mice. Anesthesiology 2013; 118:516–526.
                                    98. Piehl E, Foley L, Barron M, et al. The effect of sevoflurane on neuronal degeneration and GABAA subunit composition in a developing rat model of organotypic hippocampal slice cultures. J Neurosurg Anesthesiol 2010; 22:220–229.
                                      99. Wang Y, Cheng Y, Liu G, et al. Chronic exposure of gestation rat to sevoflurane impairs offspring brain development. Neurol Sci 2012; 33:535–544.
                                        100. Seubert CN, Zhu W, Pavlinec C, et al. Developmental effects of neonatal isoflurane and sevoflurane exposure in rats. Anesthesiology 2013; 119:358–364.
                                          101. Cattano D, Valleggi S, Abramo A, et al. Nitrous oxide discretely up-regulates nNOS and p53 in neonatal rat brain. Minerva Anestesiol 2010; 76:420–424.
                                            102. Thoresen M, Hobbs CE, Wood T, et al. Cooling combined with immediate or delayed xenon inhalation provides equivalent long-term neuroprotection after neonatal hypoxia-ischemia. J Cereb Blood Flow Metab 2009; 29:707–714.

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