Let's Not Throw the Baby Out With the Bath Water

Alternative technique or mitigating strategy for sevoflurane-induced neurodegeneration: a randomized controlled dose-escalation study of dexmedetomidine in neonatal rats

Background

Brain injury in newborn animals from prolonged anaesthetic exposure has raised concerns for millions of children undergoing anaesthesia every yr. Alternative anaesthetic techniques or mitigating strategies are urgently needed to ameliorate potentially harmful effects. We tested dexmedetomidine, both as a single agent alternative technique and as a mitigating adjuvant for sevoflurane anaesthesia.

Methods

Neonatal rats were randomized to three injections of dexmedetomidine (5, 25, 50, or 100 µg kg -1 every 2 h), or 6 h of 2.5% sevoflurane as a single agent without or with dexmedetomidine (1, 5, 10, or 20 µg kg -1 every 2 h). Heart rate, oxygen saturation, level of consciousness, and response to pain were assessed. Cell death was quantified in several brain regions.

Results

Dexmedetomidine provided lower levels of sedation and pain control than sevoflurane. Exposure to either sevoflurane or dexmedetomidine alone did not cause mortality, but the combination of 2.5% sevoflurane and dexmedetomidine in doses exceeding 1 µg kg -1 did. Sevoflurane increased apoptosis in all brain regions; supplementation with dexmedetomidine exacerbated neuronal injury, potentially as a result of ventilatory or haemodynamic compromise. Dexmedetomidine by itself increased apoptosis only in CA2/3 and the ventral posterior nucleus, but not in prefrontal cortex, retrosplenial cortex, somatosensory cortex, subiculum, lateral dorsal thalamic nucleaus, or hippocampal CA1.

Conclusions

We confirm previous findings of sevoflurane-induced neuronal injury. Dexmedetomidine, even in the highest dose, did not cause similar injury, but provided lesser degrees of anaesthesia and pain control. No mitigation of sevoflurane-induced injury was observed with dexmedetomidine supplementation, suggesting that future studies should focus on anaesthetic-sparing effects of dexmedetomidine, rather than injury-preventing effects.

Does pediatric anesthesia cause brain damage? - Addressing parental and provider concerns in light of compelling animal studies and seemingly ambivalent human data

Anesthesia facilitates surgery in millions of young children every year. Structural brain abnormalities and functional impairment observed in animals have created substantial concerns among clinicians, parents, and government regulators. Clinical studies seemed ambivalent; it remains unclear whether differential species effects exist towards anesthetic exposure. The current literature search and analysis attempts to unify the available clinical and animal studies, which currently comprise of > 530 in vivo animal studies and > 30 clinical studies. The prevalence of abnormalities was lowest for exposures < 1 hour, in both animals and humans, while studies with injurious findings increased in frequency with exposure time. Importantly, no exposure time, anesthetic technique, or age during exposure was clearly identifiable to be entirely devoid of any adverse outcomes. Moreover, the age dependence of maximum injury clearly identified in animal studies, combined with the heterogeneity in age in most human studies, may impede the discovery of a specific human neurological phenotype. In summary, animal and human research studies identify a growing prevalence of injurious findings with increasing exposure times. However, the existing lack of definitive data regarding safe exposure durations, unaffected ages, and non-injurious anesthetic techniques precludes any evidence-based recommendations for drastically changing current clinical anesthesia management. Animal studies focusing on brain maturational states more applicable to clinical practice, as well as clinical studies focusing on prolonged exposures during distinct developmental windows of vulnerability, are urgently needed to improve the safety of perioperative care for thousands of young children requiring life-saving and quality of life-improving procedures daily.

Neurotoxicity of Inhalation Anesthetics in the Neonatal Rat Brain: Effects on Behavior and Neurodegeneration in the Piriform Cortex

There is concern that clinical use of anesthetic drugs may cause neurotoxicity in the developing brain and subsequent abnormal neurobehavior. We therefore evaluated neurotoxic effects of inhalation anesthetics in the neonatal rat brain, using in vivo histological and neurobehavioral outcomes. Wistar rats (n=79, postnatal day 15) were subjected to a clinically relevant single exposure of urethane, isoflurane, sevoflurane, or placebo, without surgery. At 48 h and 96 h, behavioral parameters were recorded and the animals were sacrificed. In cryosectioned brains, total cells and dying cells in layer II of the piriform cortex were counted using unbiased stereology. At 48 h, cell numbers in layer II of the piriform cortex of all drug-treated animals were reduced versus controls (p=0.01). The effect persisted at 96 h in isoflurane- and urethane-exposed animals. Piriform cortical layer II neurons undergoing degeneration, detected histologically by pyknotic nuclei and eosinophilic cytoplasm, were increased in the animals treated with isoflurane (1.9 ± 0.7 at 96 h) and urethane (2.4 ± 0.8 at 96 h) versus sevoflurane (0.8 ± 0.3 at 96 h) and controls (0.9 ± 0.2 at 96 h). Sevoflurane- and isoflurane-treated animals exhibited increased activity and decreased suckling compared with controls, and sevoflurane-exposed animals also displayed increased rearing behavior at both timepoints.

Do anesthetics harm the developing human brain? An integrative analysis of animal and human studies

Anesthetics that permit surgical procedures and stressful interventions have been found to cause structural brain abnormalities and functional impairment in immature animals, generating extensive concerns among clinicians, parents, and government regulators regarding the safe use of these drugs in young children. Critically important questions remain, such as the exact age at which the developing brain is most vulnerable to the effects of anesthetic exposure, whether a particular age exists beyond which anesthetics are devoid of long-term effects on the brain, and whether any specific exposure duration exists that does not lead to deleterious effects. Accordingly, the present analysis attempts to put the growing body of animal studies, which we identified to include >440 laboratory studies to date, into a translational context, by integrating the preclinical data on brain structure and function with clinical results attained from human neurocognitive studies, which currently exceed 30 studies. Our analysis demonstrated no clear exposure duration threshold below which no structural injury or subsequent cognitive abnormalities occurred. Animal data did not clearly identify a specific age beyond which anesthetic exposure did not cause any structural or functional abnormalities. Several potential mitigating strategies were found, however, no general anesthetic was identified that consistently lacked neurodegenerative properties and could be recommended over other anesthetics. It therefore is imperative, to expand efforts to devise safer anesthetic techniques and mitigating strategies, even before long-term alterations in brain development are unequivocally confirmed to occur in millions of young children undergoing anesthesia every year.

From Drug-Induced Developmental Neuroapoptosis to Pediatric Anesthetic Neurotoxicity-Where Are We Now?

The fetal and neonatal periods are critical and sensitive periods for neurodevelopment, and involve rapid brain growth in addition to natural programmed cell death (i.e., apoptosis) and synaptic pruning. Apoptosis is an important process for neurodevelopment, preventing redundant, faulty, or unused neurons from cluttering the developing brain. However, animal studies have shown massive neuronal cell death by apoptosis can also be caused by exposure to several classes of drugs, namely gamma-aminobutyric acid (GABA) agonists and N-methyl-d-aspartate (NMDA) antagonists that are commonly used in pediatric anesthesia. This form of neurotoxic insult could cause a major disruption in brain development with the potential to permanently shape behavior and cognitive ability. Evidence does suggest that psychoactive drugs alter neurodevelopment and synaptic plasticity in the animal brain, which, in the human brain, may translate to permanent neurodevelopmental changes associated with long-term intellectual disability. This paper reviews the seminal animal research on drug-induced developmental apoptosis and the subsequent clinical studies that have been conducted thus far. In humans, there is growing evidence that suggests anesthetics have the potential to harm the developing brain, but the long-term outcome is not definitive and causality has not been determined. The consensus is that there is more work to be done using both animal models and human clinical studies.

Brain regional vulnerability to anaesthesia-induced neuroapoptosis shifts with age at exposure and extends into adulthood for some regions

BACKGROUND

General anaesthesia facilitates surgical operations and painful interventions in millions of patients every year. Recent observations of anaesthetic-induced neuronal cell death in newborn animals have raised substantial concerns for young children undergoing anaesthesia. However, it remains unclear why some brain regions are more affected than others, why certain neurones are eliminated while neighbouring cells are seemingly unaffected, and what renders the developing brain exquisitely vulnerable, while the adult brain apparently remains resistant to the phenomenon.

METHODS

Neonatal (P7), juvenile (P21), and young adult mice (P49) were anaesthetized with 1.5% isoflurane. At the conclusion of anaesthesia, activated cleaved caspase 3 (AC3), a marker of apoptotic cell death, was quantified in the neocortex (RSA), caudoputamen (CPu), hippocampal CA1 and dentate gyrus (DG), cerebellum (Cb), and olfactory bulb (GrO) and compared with that found in unanaesthetized littermates.

RESULTS

After anaesthetic exposure, increased AC3 was detected in neonatal mice in RSA (11-fold, compared with controls), CPu (10-fold), CA1 (three-fold), Cb (four-fold), and GrO (four-fold). Surprisingly, AC3 continued to be elevated in the DG and GrO of juvenile (15- and 12-fold, respectively) and young adult mice (two- and four-fold, respectively).

CONCLUSIONS

The present study confirms the findings of previous studies showing peak vulnerability to anaesthesia-induced neuronal cell death in the newborn forebrain. It also shows sustained susceptibility into adulthood in areas of continued neurogenesis, substantially expanding the previously observed age of vulnerability. The differential windows of vulnerability among brain regions, which closely follow regional peaks in neurogenesis, may explain the heightened vulnerability of the developing brain because of its increased number of immature neurones.

Neither Xenon nor Fentanyl Induces Neuroapoptosis in the Newborn Pig Brain

Background:

Some inhalation anesthetics increase apoptotic cell death in the developing brain. Xenon, an inhalation anesthetic, increases neuroprotection when combined with therapeutic hypothermia after hypoxic-ischemic brain injury in newborn animals. The authors, therefore, examined whether there was any neuroapoptotic effect of breathing 50% xenon with continuous fentanyl sedation for 24 h at normothermia or hypothermia on newborn pigs.

Methods:

Twenty-six healthy pigs (&lt;24-h old) were randomized into four groups: (1) 24 h of 50% inhaled xenon with fentanyl at hypothermia (Trec = 33.5°C), (2) 24 h of 50% inhaled xenon with fentanyl at normothermia (Trec = 38.5°C), (3) 24 h of fentanyl at normothermia, or (4) nonventilated juvenile controls at normothermia. Five additional nonrandomized pigs inhaled 2% isoflurane at normothermia for 24 h to verify any proapoptotic effect of inhalation anesthetics in our model. Pathological cells were morphologically assessed in cortex, putamen, hippocampus, thalamus, and white matter. To quantify the findings, immunostained cells (caspase-3 and terminal deoxynucleotidyl transferase–mediated deoxyuridine-triphosphate nick-end labeling) were counted in the same brain regions.

Results:

For groups (1) to (4), the total number of apoptotic cells was less than 5 per brain region, representing normal developmental neuroapoptosis. After immunostaining and cell counting, regression analysis showed that neither 50% xenon with fentanyl nor fentanyl alone increased neuroapoptosis. Isoflurane caused on average a 5- to 10-fold increase of immunostained cells.

Conclusion:

At normothermia or hypothermia, neither 24 h of inhaled 50% xenon with fentanyl sedation nor fentanyl alone induces neuroapoptosis in the neonatal pig brain. Breathing 2% isoflurane increases neuroapoptosis in neonatal pigs.

Nitrous oxide: are we still in equipoise? A qualitative review of current controversies

This review considers the current position of nitrous oxide in anaesthetic practice and balances potential beneficial and disadvantageous effects. The classic adverse characteristics of nitrous oxide, such as diffusion hypoxia, expansion of gas-filled spaces, and postoperative nausea and vomiting, are often cited as reasons to avoid this old drug. Recent concerns regarding neurotoxicity, adverse cardiovascular outcomes, and wound complications have further hardened many practitioners against nitrous oxide. New evidence and underpinning mechanistic data, however, suggest potential beneficial effects on the central nervous system, cardiovascular system, and acute and chronic pain. While we await the outcome of large studies including ENIGMA-II, many clinicians have already decided against this agent. The authors argue that this abandonment may be premature. Clinical Trial Registration None required.

Alcohol-induced apoptosis of oligodendrocytes in the fetal macaque brain

Background

In utero exposure of the fetal non-human primate (NHP) brain to alcohol on a single occasion during early or late third-trimester gestation triggers widespread acute apoptotic death of cells in both gray and white matter (WM) regions of the fetal brain. In a prior publication, we documented that the dying gray matter cells are neurons, and described the regional distribution and magnitude of this cell death response. Here, we present new findings regarding the magnitude, identity and maturational status of the dying WM cells in these alcohol-exposed fetal NHP brains.

Results

Our findings document that the dying WM cells belong to the oligodendrocyte (OL) lineage. OLs become vulnerable when they are just beginning to generate myelin basic protein in preparation for myelinating axons, and they remain vulnerable throughout later stages of myelination. We found no evidence linking astrocytes, microglia or OL progenitors to this WM cell death response. The mean density (profiles per mm³) of dying WM cells in alcohol-exposed brains was 12.7 times higher than the mean density of WM cells dying by natural apoptosis in drug-naive control brains.

Conclusions

In utero exposure of the fetal NHP brain to alcohol on a single occasion triggers widespread acute apoptotic death of neurons (previous study) and of OLs (present study) throughout WM regions of the developing brain. The rate of OL apoptosis in alcohol-exposed brains was 12.7 times higher than the natural OL apoptosis rate. OLs become sensitive to the apoptogenic action of alcohol when they are just beginning to generate constituents of myelin in their cytoplasm, and they remain vulnerable throughout later stages of myelination. There is growing evidence for a similar apoptotic response of both neurons and OLs following exposure of the developing brain to anesthetic and anticonvulsant drugs. Collectively, this body of evidence raises important questions regarding the role that neuro and oligo apoptosis may play in the human condition known as fetal alcohol spectrum disorder (FASD), and also poses a question whether other apoptogenic drugs, although long considered safe for pediatric/obstetric use, may have the potential to cause iatrogenic FASD-like developmental disability syndromes.

Newly postulated neurodevelopmental risks of pediatric anesthesia: theories that could rock our world

PURPOSE

General anesthetics can induce apoptotic neurodegeneration and subsequent maladaptive behaviors in animals. Retrospective human studies suggest associations between early anesthetic exposure and subsequent adverse neurodevelopmental outcomes. The relevance of animal data to clinical practice is unclear and to our knowledge the causality underlying observed associations in humans is unknown. We reviewed newly postulated neurodevelopmental risks of pediatric anesthesia and discuss implications for the surgical care of children.

MATERIALS AND METHODS

We queried the MEDLINE®/PubMed® and EMBASE® databases for citations in English on pediatric anesthetic neurotoxicity with the focus on references from the last decade.

RESULTS

Animal studies in rodents and primates demonstrate apoptotic neuropathology and subsequent maladaptive behaviors after exposure to all currently available general anesthetics with the possible exception of α2-adrenergic agonists. Similar adverse pathological and clinical effects occur after untreated pain. Anesthetic neurotoxicity in animals develops only after exposure above threshold doses and durations during a critical neurodevelopmental window of maximal synaptogenesis in the absence of concomitant painful stimuli. Anesthetic exposure outside this window or below threshold doses and durations shows no apparent neurotoxicity, while exposure in the context of concomitant painful stimuli is neuroprotective. Retrospective human studies suggest associations between early anesthetic exposure and subsequent adverse neurodevelopmental outcomes, particularly after multiple exposures. The causality underlying the associations is unknown. Ongoing investigations may clarify the risks associated with current practice.

CONCLUSIONS

Surgical care of all patients mandates appropriate anesthesia. Neurotoxic doses and the duration of anesthetic exposure in animals may have little relevance to clinical practice, particularly surgical anesthesia for perioperative pain. The causality underlying the observed associations between early anesthetic exposure and subsequent adverse neurodevelopmental outcomes is unknown. Anesthetic exposure may be a marker of increased risk. Especially in young children, procedures requiring general anesthesia should be performed only as necessary and general anesthesia duration should be minimized. Alternatives to general anesthesia and the deferral of elective procedures beyond the first few years of life should be considered, as appropriate. Participation in ongoing efforts should be encouraged to generate further data.

Anesthetic neurotoxicity

Concerns for toxic effects of anesthesia to the brains of the young and the elderly are mounting. While experimental evidence for such effects in the developing brain is strong, the underlying mechanisms are less well understood and debate continues as to whether young humans are at risk for anesthetic neurotoxicity. The phenomenon of postoperative cognitive deterioration in the elderly remains controversial. Time course, severity, and whether or not it persists long term are under debate. For both patient groups, today's evidence is not sufficient to guide change in clinical practice. Well-designed research is therefore imperative to tackle this critical issue.

Assessment of general anaesthetic cytotoxicity in murine cortical neurones in dissociated culture

General anaesthetics are proposed to cause unconsciousness by modulating neuronal excitability in the mammalian brain through mechanisms that include enhancement of inhibitory GABA(A) receptor currents and suppression of excitatory glutamate receptor responses. Both intravenous and volatile agents may produce neurotoxic effects during early postnatal rodent brain development through similar mechanisms. In the following study, we investigated anaesthetic cytotoxicity in primary cortical neurones and glia from postnatal day 2-8 mice. Cultures at 4-20 days in vitro were exposed to combinations of ketamine (100 μM to 3 mM), nitrous oxide (75%, v/v) and/or isoflurane (1.5-5%, v/v) for 6-12 h. Neuronal survival and cell death were measured via microtubule associated protein 2 immunoassay and lactate dehydrogenase release assays, respectively. Clinically relevant anaesthetic concentrations of ketamine, nitrous oxide and isoflurane had no significant neurotoxic effects individually or when given as anaesthetic cocktails, even with up to 12 h exposure. This lack of neurotoxicity was observed regardless of whether cultures were prepared from postnatal day 0-2 or day 8 mice, and was also unaffected by number of days in vitro (DIV 4-20). Significant neurotoxic effects were only observed at supraclinical concentrations (e.g. 1-3 mM ketamine). Our study suggests that neurotoxicity previously reported in vivo is not due to direct cytotoxicity of anaesthetic agents, but results from other impacts of the anaesthetised state during early brain development.

Is age-dependent, ketamine-induced apoptosis in the rat somatosensory cortex influenced by temperature?

General anesthetics have long been thought to be relatively safe but recent clinical studies have revealed that exposure of very young children (4 years or less) to agents that act by blocking the N-methyl-D-aspartate receptor (NMDAR) can lead to cognitive deficits as they mature. In rodent and non-human primate studies, blockade of this receptor during the perinatal period leads to a number of molecular, cellular and behavioral pathologies. Despite the overwhelming evidence from such studies, doubt remains as to their clinical relevance. A key issue is whether the primary injury (apoptotic cell death) is specific to receptor blockade or due to non-specific, patho-physiological changes. Principal to this argument is that loss of core body temperature following NMDAR blockade could explain why injury is observed hours later. We therefore examined the neurotoxicity of the general anesthetic ketamine in P7, P14 and P21 rats while monitoring core body temperature. We found that, at P7, ketamine induced the pro-apoptotic enzyme activated caspase-3 in a dose-dependent manner. As expected, injury was greatly diminished by P14 and absent by P21. However, contrary to expectations, we found that core body temperature was not a factor in determining injury. Our data imply that injury is directly related to receptor blockade and is unlikely to be overcome by artificially changing core body temperature.

Developmental neurotoxicity of sedatives and anesthetics: a concern for neonatal and pediatric critical care medicine?

OBJECTIVE

To evaluate the currently available evidence for the deleterious effects of sedatives and anesthetics on developing brain structure and neurocognitive function.

DESIGN

A computerized, bibliographic search of the literature regarding neurodegenerative effects of sedatives and anesthetics in the developing brain.

MEASUREMENTS AND MAIN RESULTS

A growing number of animal studies demonstrate widespread structural damage of the developing brain and long-lasting neurocognitive abnormalities after exposure to sedatives commonly used in neonatal and pediatric critical care medicine. These studies reveal a dose and exposure time dependence of neuronal cell death, characterize its molecular pathways, and suggest a potential early window of susceptibility in humans. Several clinical studies document neurologic abnormalities in neonatal intensive care unit graduates, usually attributed to comorbidities. Emerging human epidemiologic data, however, do not exclude prolonged or repetitive exposure to sedatives and anesthetics in early childhood as contributing factors to some of these abnormalities.

CONCLUSIONS

Neuronal cell death after neonatal exposure to sedatives and anesthetics has been clearly demonstrated in developing animal models. Although the relevance for human medicine remains speculative, the phenomenon's serious implications for public health necessitate further preclinical and clinical studies. Intensivists using sedatives and anesthetics in neonates and infants need to stay informed about this rapidly emerging field of research.

The young: neuroapoptosis induced by anesthetics and what to do about it

Millions of human fetuses, infants, and children are exposed to anesthetic drugs every year in the United States and throughout the world. Anesthesia administered during critical stages of neurodevelopment has been considered safe and without adverse long-term consequences. However, recent reports provide mounting evidence that exposure of the immature animal brain to anesthetics during the period of rapid synaptogenesis, also known as the brain growth spurt period, triggers widespread apoptotic neurodegeneration, inhibits neurogenesis, and causes significant long-term neurocognitive impairment. Herein, we summarize currently available evidence for anesthesia-induced pathological changes in the brain and associated long-term neurocognitive deficits and discuss promising strategies for protecting the developing brain from the potentially injurious effects of anesthetic drugs while allowing the beneficial actions of these drugs to be realized.

General anesthetics and the developing brain

PURPOSE OF REVIEW

General anesthetics and sedatives are used in millions of children every year to facilitate surgical procedures, imaging studies, and sedation in operating rooms, radiology suites, emergency departments, and ICUs. Mounting evidence from animal studies suggests that prolonged exposure to these compounds may induce widespread neuronal cell death and neurological sequelae, seriously questioning the safety of pediatric anesthesia. This review presents recent developments in this rapidly emerging field.

RECENT FINDINGS

In animals, all currently available anesthetics and sedatives that have been studied, such as ketamine, midazolam, diazepam, clonazepam, propofol, pentobarbital, chloral hydrate, halothane, isoflurane, sevoflurane, enflurane, nitrous oxide, and xenon, have been demonstrated to trigger widespread neurodegeneration in the immature brain. In humans, recent preliminary findings from epidemiological studies suggest an association between surgery and anesthesia early in life and subsequent learning abnormalities.

SUMMARY

Neurodegeneration following exposure to anesthetics and sedatives has been clearly established in developing animals. However, while some of the biochemical pathways have been revealed, the phenomenon's particular molecular mechanisms remain unclear. As the phenomenon is difficult to study in humans, clinical evidence is still scarce and amounts to associative and not causal relationships. Owing to the lack of alternative anesthetics, further animal studies into the mechanism as well as clinical studies defining human susceptibility are both urgently needed.

Neonatal repair of cleft lip: a decision-making protocol

PURPOSE

Treatment of clefts lip during the neonatal period remains a controversial subject. Those who are in favor of delayed closure argue a higher-risk general anesthesia when it was performed in neonatal period. The purpose of this study was to evaluate the complications and the feasibility of this surgery during the neonatal period.

METHODS

This was a retrospective study of 61 children with labial, labioalveolar, labio-alveolo-palatine, and labiopalatine clefts between May 2000 and November 2006. Each patient's medical file and particularly his or her anesthesia file was used to record the principal demographic data, the results of the malformation workup, and preoperative complications.

RESULTS

Sixty-one newborns, 20 girls and 41 boys, aged 7.5 +/- 6.7 days were operated on. The mean weight on the day of surgery was 3190 +/- 454 g. Fifty-four children had a malformation workup (abdominal ultrasonography, spinal bone workup, transfontanelle ultrasonography, and cardiac ultrasonography). Thirteen associated malformations (21%) were thereby detected. There were no surgical complications. The anesthesiologists did not have any real intubation problems. In 4 cases, however, intubation was only possible after several laryngoscopies and changing the type of intubation shaft. There were no major complications. However, one child did present a preoperative complication. It was an episode of desaturation with bradycardia that was quickly resolved without further consequences in a child with a ventricular septal defect and an auricular septal defect.

CONCLUSIONS

We think that neonatal lip closure should continue to be performed. It is essential for the psychological status of the parents. We have not found any studies in the literature that reported an anesthesia risk that was greater in the neonatal period than at 3 months in patients without risk of complications.

Isoflurane-induced neuroapoptosis in the developing brain of nonhypoglycemic mice

Drugs that suppress neuronal activity, including general anesthetics used in pediatric and obstetric medicine, trigger neuroapoptosis in the developing rodent brain. Exposure of infant rats for 6 hours to a combination of anesthetic drugs (midazolam, nitrous oxide, isoflurane) reportedly causes widespread apoptotic neurodegeneration, followed by lifelong cognitive deficits. Isoflurane, the dominant ingredient in this triple cocktail, has not been evaluated individually for apoptogenic potential. It was recently reported that (1) the minimum alveolar concentration (MAC) for anesthetizing infant mice with isoflurane is 2.26%, and; (2) that infant mice, without assisted respiration, maintain normal arterial oxygen values but become hypoglycemic when exposed to isoflurane 3% for 30 minutes, then 1.8% for 1 hour (1.46 MAC-hours). In the present experiments, infant mice were exposed to isoflurane at various sub-MAC concentrations and durations, and the brains were evaluated quantitatively 5 hours after initiation of anesthesia exposure to determine the number of neuronal profiles undergoing apoptosis. Blood glucose values were also determined under each of these conditions. All conditions tested (isoflurane at 0.75% for 4 h, 1.5% for 2 h, 2.0% for 1 h) triggered a statistically significant increase in neuroapoptosis compared with the rate of spontaneous apoptosis in littermate controls. Blood glucose determinations ruled out hypoglycemia as a potential cause of the brain damage. It is concluded that exposure to sub-MAC concentrations of isoflurane for one or more hours triggers neuroapoptosis in the infant mouse brain. These findings are consistent with other recent evidence demonstrating that brief exposure to ethanol, ketamine, or midazolam triggers neuroapoptosis in the developing mouse brain.