Andreas W. Loepke

An assessment of the effects of general anesthetics on developing brain structure and neurocognitive function.

BACKGROUND:Neuronal cell death after general anesthesia has recently been documented in several immature animal models. Worldwide, volatile anesthetics are used in millions of young children every year during surgical procedures and imaging studies. The possibility of anesthesia-induced neurotoxicity during an uneventful anesthetic in neonates or infants has led to serious questions about the safety of pediatric anesthesia. However, the applicability of animal data to clinical anesthesia practice remains uncertain. In the present review, we assess the evidence for the effects of commonly used anesthetics on neuronal structure and neurocognitive function in newborn humans and animals. METHODS:Medical databases, including Medline, Cinahl, and Pubmed, abstract listings of the American Society of Anesthesiologists, International Anesthesia Research Society, Society for Pediatric Anesthesia, and Society for Neuroscience Annual Meetings, and personal files were queried regarding anesthesia-induced neurotoxicity. RESULTS:A growing number of studies in immature animal models demonstrate degenerative effects of several anesthetics on neuronal structure. A few studies reveal cognitive impairment in adult animals after neonatal anesthesia. There are no prospective studies evaluating neurocognitive function in children after neonatal exposure to anesthetics. However, several retrospective reviews demonstrate temporary neurological sequelae after prolonged anesthetic exposure in young children and larger studies identify long-term neurodevelopmental impairment after neonatal surgery and anesthesia. CONCLUSIONS:The evidence for anesthesia-induced neurodegeneration in animal models is compelling. Although this phenomenon has not been prospectively studied in young children, anecdotal data point toward the possibility for neurological impairment after surgery and anesthesia early in life. Given the serious implications for public health, further investigations of this phenomenon are imperative, both in laboratory animals and in young children.

Comparison of the Neuroapoptotic Properties of Equipotent Anesthetic Concentrations of Desflurane, Isoflurane, or Sevoflurane in Neonatal Mice

Background:Volatile anesthetics facilitate surgical procedures and imaging studies in millions of children every year. Neuronal cell death after prolonged exposure to isoflurane in developing animals has raised serious concerns regarding its safe use in children. Although sevoflurane and desflurane are becoming more popular for pediatric anesthesia, their cytotoxic effects have not been compared with those of isoflurane. Accordingly, using newborn mice, the current study established the respective potencies of desflurane, isoflurane, and sevoflurane and then compared equipotent doses of these anesthetics regarding their effects on cortical neuroapoptosis. Methods:Minimum alveolar concentrations were determined in littermates (aged 7–8 days, n = 42) using tail-clamp stimulation in a bracketing study design. By using equipotent doses of approximately 0.6 minimum alveolar concentration, another group of littermates was randomly assigned to receive desflurane, isoflurane, or sevoflurane or to fast in room air for 6 h. After exposure, animals (n = 47) were euthanized, neocortical apoptotic neuronal cell death was quantified, and caspase 3 activity was compared between the four groups. Results:The minimum alveolar concentration was determined to be 12.2% for desflurane, 2.7% for isoflurane, and 5.4% for sevoflurane. After a 6-h exposure to approximately 0.6 minimum alveolar concentration of desflurane, isoflurane, or sevoflurane, neuronal cell death and apoptotic activity were significantly increased, irrespective of the specific anesthetic used. Conclusions:In neonatal mice, equipotent doses of the three commonly used inhaled anesthetics demonstrated similar neurotoxic profiles, suggesting that developmental neurotoxicity is a common feature of all three drugs and cannot be avoided by switching to newer agents.

The effects of neonatal isoflurane exposure in mice on brain cell viability, adult behavior, learning, and memory.

BACKGROUND: Volatile anesthetics, such as isoflurane, are widely used in infants and neonates. Neurodegeneration and neurocognitive impairment after exposure to isoflurane, midazolam, and nitrous oxide in neonatal rats have raised concerns regarding the safety of pediatric anesthesia. In neonatal mice, prolonged isoflurane exposure triggers hypoglycemia, which could be responsible for the neurocognitive impairment. We examined the effects of neonatal isoflurane exposure and blood glucose on brain cell viability, spontaneous locomotor activity, as well as spatial learning and memory in mice. METHODS: Seven-day-old mice were randomly assigned to 6 h of 1.5% isoflurane with or without injections of dextrose or normal saline, or to 6 h of room air without injections (no anesthesia). Arterial blood gases and glucose were measured. After 2 h, 18 h, or 11 wk postexposure, cellular viability was assessed in brain sections stained with Fluoro-Jade B, caspase 3, or NeuN. Nine weeks postexposure, spontaneous locomotor activity was assessed, and spatial learning and memory were evaluated in the Morris water maze using hidden and reduced platform trials. RESULTS: Apoptotic cellular degeneration increased in several brain regions early after isoflurane exposure, compared with no anesthesia. Despite neonatal cell loss, however, adult neuronal density was unaltered in two brain regions significantly affected by the neonatal degeneration. In adulthood, spontaneous locomotor activity and spatial learning and memory performance were similar in all groups, regardless of neonatal isoflurane exposure. Neonatal isoflurane exposure led to an 18% mortality, and transiently increased Paco2, lactate, and base deficit, and decreased blood glucose levels. However, hypoglycemia did not seem responsible for the neurodegeneration, as dextrose supplementation failed to prevent neuronal loss. CONCLUSIONS: Prolonged isoflurane exposure in neonatal mice led to increased immediate brain cell degeneration, however, no significant reductions in adult neuronal density or deficits in spontaneous locomotion, spatial learning, or memory function were observed.

Anaesthetic neurotoxicity and neuroplasticity: an expert group report and statement based on the BJA Salzburg Seminar

Although previously considered entirely reversible, general anaesthesia is now being viewed as a potentially significant risk to cognitive performance at both extremes of age. A large body of preclinical as well as some retrospective clinical evidence suggest that exposure to general anaesthesia could be detrimental to cognitive development in young subjects, and might also contribute to accelerated cognitive decline in the elderly. A group of experts in anaesthetic neuropharmacology and neurotoxicity convened in Salzburg, Austria for the BJA Salzburg Seminar on Anaesthetic Neurotoxicity and Neuroplasticity. This focused workshop was sponsored by the British Journal of Anaesthesia to review and critically assess currently available evidence from animal and human studies, and to consider the direction of future research. It was concluded that mounting evidence from preclinical studies reveals general anaesthetics to be powerful modulators of neuronal development and function, which could contribute to detrimental behavioural outcomes. However, definitive clinical data remain elusive. Since general anaesthesia often cannot be avoided regardless of patient age, it is important to understand the complex mechanisms and effects involved in anaesthesia-induced neurotoxicity, and to develop strategies for avoiding or limiting potential brain injury through evidence-based approaches.

Cognition and Brain Structure Following Early Childhood Surgery With Anesthesia.

BACKGROUND: Anesthetics induce widespread cell death, permanent neuronal deletion, and neurocognitive impairment in immature animals, raising substantial concerns about similar effects occurring in young children. Epidemiologic studies have been unable to sufficiently address this concern, in part due to reliance on group-administered achievement tests, inability to assess brain structure, and limited control for confounders. METHODS: We compared healthy participants of a language development study at age 5 to 18 years who had undergone surgery with anesthesia before 4 years of age (n = 53) with unexposed peers (n = 53) who were matched for age, gender, handedness, and socioeconomic status. Neurocognitive assessments included the Oral and Written Language Scales and the Wechsler Intelligence Scales (WAIS) or WISC, as appropriate for age. Brain structural comparisons were conducted by using T1-weighted MRI scans. RESULTS: Average test scores were within population norms, regardless of surgical history. However, compared with control subjects, previously exposed children scored significantly lower in listening comprehension and performance IQ. Exposure did not lead to gross elimination of gray matter in regions previously identified as vulnerable in animals. Decreased performance IQ and language comprehension, however, were associated with lower gray matter density in the occipital cortex and cerebellum. CONCLUSIONS: The present findings suggest that general anesthesia for a surgical procedure in early childhood may be associated with long-term diminution of language abilities and cognition, as well as regional volumetric alterations in brain structure. Although causation remains unresolved, these findings nonetheless warrant additional research into the phenomenon’s mechanism and mitigating strategies.

The physiologic effects of isoflurane anesthesia in neonatal mice

In neonatal rodents, isoflurane has been shown to confer neurological protection during hypoxia-ischemia and to precipitate neurodegeneration after prolonged exposure. Whether neuroprotection or neurotoxicity result from a direct effect of isoflurane on the brain or an indirect effect through hemodynamic or metabolic changes remains unknown. We recorded arterial blood pressure, heart rate, blood gases, and glucose in 10-day-old mice during 60 min of isoflurane anesthesia with spontaneous or mechanical ventilation, as well as during 60 min of hypoxia-ischemia with isoflurane anesthesia or without anesthesia. During isoflurane anesthesia, hypoglycemia and metabolic acidosis occurred with spontaneous and mechanical ventilation. During hypoxia-ischemia, isoflurane was fatal with spontaneous breathing but survivable with mechanical ventilation, with arterial blood pressure and heart rate being similar to that observed in unanesthetized animals. Minimum alveolar concentration (MAC) was 2.3% in 10-day-old mice. In summary, isoflurane anesthesia precipitated hypoglycemia, which may have contributed to the neurodegeneration observed in neonatal rodents. Use of 0.8 MAC isoflurane for evaluation of neuroprotection during hypoxia-ischemia requires mechanical ventilation and glucose supplementation in this model.

CON : The Toxic Effects of Anesthetics in the Developing Brain: The Clinical Perspective

Sulpicio G. Soriano, MD, FAAP‡ “All models are wrong, some models are useful” This quote by the statistician George E. P. Box seems to have relevance for the current preeminent controversy in pediatric anesthesiology, namely, developmental neuroapoptotic cell death after an anesthetic exposure in the immature brain. Worldwide, general anesthetics and sedatives are used in hundreds of thousands of neonates and infants every year during surgical operations, invasive procedures, and imaging studies. The possibility of anesthesiainduced neuronal cell loss, as suggested by animal models, during an otherwise uneventful procedure has sparked vigorous discussions among anesthesiologists about the safety of anesthesia in human newborns and infants. These concerns were recently addressed at the March 29, 2007, public hearing of the Anesthesia and Life Support Drugs Advisory Committee of the Food and Drug Administration (transcript available at http://www. fda.gov/ohrms/dockets/ac/07/transcripts/2007-4285t1.pdf). Although the exact mechanism of general anesthesia is not entirely understood, alterations of synaptic transmission involving -aminobutyric acid type A (GABAA) and N-methyl-d-aspartate (NMDA) glutamate receptors, to varying degrees, seem to play an important role. Because GABA and NMDA-mediated neuronal activity is essential for normal mammalian brain development, exposure to anesthetics could potentially interfere with brain maturation, learning, and neurocognitive function. Concerns about the effects of general anesthetics on neuronal structure and neurocognitive function were first raised more than two decades ago. In a series of studies, chronic subanesthetic exposure of pregnant rats to halothane led to delayed synaptogenesis and behavioral abnormalities in their pups. More recently, the potential for ketamine to cause increased neuronal cell death was documented in rat pups. However, although ketamine is rarely used for pediatric anesthesia, general anesthetics routinely used in pediatric practice have subsequently also been implicated not only in producing widespread neuronal cell death, but also in leading to long-term cognitive impairment in adult animals exposed to neonatal anesthesia. A 6-h exposure to a combination of isoflurane, nitrous oxide, and midazolam led to widespread apoptotic brain cell death in 7-day-old rats. When animals were examined in adulthood, many tests of behavior and attention remained normal. However, several tests of spatial learning and memory demonstrated impairment in adult animals that were exposed to the anesthetic cocktail as neonates, compared with their unanesthetized littermates. Several groups of investigators have now confirmed the neurotoxic effects of various anesthetics in a variety of in vivo and in vitro developing animal models. From the *Departments of Anesthesia and Pediatrics, Cincinnati Children’s Hospital Medical Center and University of Cincinnati College of Medicine; and †Institute of Pediatric Anesthesia, Cincinnati Children’s Research Foundation, Cincinnati, Ohio; and ‡Department of Anaesthesia, Children’s Hospital Boston and Harvard Medical School, Boston, Massachusetts. Accepted for publication March 5, 2008. Address correspondence and reprint requests to Dr. Andreas Loepke, Department of Anesthesia, Cincinnati Children’s Hospital Medical Center, ML2001, 3333 Burnet Ave., Cincinnati, OH 45229. Address e-mail to Andreas.Loepke@cchmc.org. Copyright

Heterogeneous integration of adult-generated granule cells into the epileptic brain

The functional impact of adult-generated granule cells in the epileptic brain is unclear, with data supporting both protective and maladaptive roles. These conflicting findings could be explained if new granule cells integrate heterogeneously, with some cells taking neutral or adaptive roles and others contributing to recurrent circuitry supporting seizures. Here, we tested this hypothesis by completing detailed morphological characterizations of age- and experience-defined cohorts of adult-generated granule cells from transgenic mice. The majority of newborn cells exposed to an epileptogenic insult exhibited reductions in dendritic spine number, suggesting reduced excitatory input to these cells. A significant subset, however, exhibited higher spine numbers. These latter cells tended to have enlarged cell bodies, long basal dendrites, or both. Moreover, cells with basal dendrites received significantly more recurrent mossy fiber input through their apical dendrites, indicating that these cells are robustly integrated into the pathological circuitry of the epileptic brain. These data imply that newborn cells play complex—and potentially conflicting—roles in epilepsy.

Cerebral oxygen saturation-time threshold for hypoxic-ischemic injury in piglets.

BACKGROUND: Detection of cerebral hypoxia-ischemia (H-I) and prevention of brain injury remains problematic in critically ill neonates. Near-infrared spectroscopy (NIRS), a noninvasive bedside technology could fill this role, although NIRS cerebral O2 saturation (ScO2) viability-time thresholds for brain injury have not been determined. We investigated the relationship between H-I duration at ScO2 35%, a viability threshold which causes neurophysiological impairment, to neurological outcome. METHODS: Forty-six fentanyl-midazolam anesthetized piglets were equipped with NIRS and cerebral function monitor (CFM) to record ScO2 and electrocortical activity (ECA). After carotid occlusion, inspired O2 was adjusted to produce H-I (ScO2 35% with decreased ECA) for 1, 2, 3, 4, 6 or 8 h in different groups, followed by survival to assess neurological outcome by behavioral and histological examination. RESULTS: For H-I lasting 1 or 2 h, ECA and ScO2 during reperfusion rapidly returned to normal and neurological outcomes were normal. For H-I more than 2–3 h, ECA was significantly decreased and ScO2 was significantly increased during reperfusion, suggesting continued depression of tissue O2 metabolism. As H-I increased beyond 2 h, the incidence of neurological injury increased linearly, approximately 15% per h. CONCLUSION: A viability-time threshold for H-I injury is ScO2 of 35% for 2–3 h, heralded by abnormalities in NIRS and CFM during reperfusion. These findings suggest that NIRS and CFM might be used together to predict neurological outcome, and illustrate that there is a several hour window of opportunity during H-I to prevent neurological injury.

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 phenomenons 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.