John J. McAuliffe

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.

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.

Race and Unequal Burden of Perioperative Pain and Opioid Related Adverse Effects in Children

BACKGROUND: Interindividual variability in pain perception and analgesic response is a major problem in perioperative practice. Adult studies suggest pain management is influenced by patient’s race. The objective of this study is to evaluate the influence of race on perioperative pain treatment in children. METHODS: Prospective observational study evaluating effect of race on analgesia and opioid related adverse effects after tonsillectomy in African American and Caucasian children. A sample of 194 healthy children between 6 and 15 years of age were included. Race was self-identified by parents. All participants received standard perioperative care with a standard anesthetic and an intraoperative dose of morphine. Analgesia outcomes included maximum postoperative pain scores, postoperative opioid requirement, and analgesic interventions. Safety outcomes included incidences of opioid related adverse effects. RESULTS: African American children experienced significantly more postoperative pain than Caucasian children as measured by postoperative opioid requirement (P = .0011), maximum postoperative pain scores (P < .0001), and analgesic interventions (P < .0001) in the recovery room. Although Caucasian children received relatively less opioids perioperatively, they had significantly higher opioid related adverse effects (P = .039). African American children with obstructive sleep apnea were more likely to have prolonged post anesthesia recovery unit stay due to inadequate pain control. CONCLUSIONS: After similar uses of intraoperative morphine for tonsillectomy, there was an unequal burden of increased pain in African American children and increased opioid adverse effects in Caucasian children in the recovery room. Though Caucasian children received relatively less opioids perioperatively, they had higher incidences of opioid related adverse effects than African American children.

Effect of increasing depth of dexmedetomidine anesthesia on upper airway morphology in children

Objective:  This prospective study examines the dose–response effects of dexmedetomidine on upper airway morphology in children with no obstructive sleep apnea (OSA).

Effect of increasing depth of dexmedetomidine and propofol anesthesia on upper airway morphology in children and adolescents with obstructive sleep apnea

STUDY OBJECTIVE To examine the dose-response effects of dexmedetomidine (DEX) and propofol (PROP) on airway morphology in children and adolescents with a history of obstructive sleep apnea (OSA). DESIGN Prospective, single-blinded, controlled comparative study. SETTING University-affiliated teaching hospital. PATIENTS 60 patients with a history of OSA who presented for a magnetic resonance imaging (MRI) sleep study. INTERVENTIONS Patients were randomized to two equal groups (DEX or PROP). Magnetic resonance images of the airway were obtained during low (1 μg/kg/hr) and high (3 μg/kg/hr) doses of DEX, or low (100 μg/kg/m) and high (200 μg/kg/m) doses of PROP, based on group assignment. MEASUREMENTS The airway anteroposterior (AP) diameter, transverse diameter, and sectional areas were measured at the level of the nasopharyngeal airway and retroglossal airway. The influence of the two drugs and OSA severity, as determined by polysomnography, on airway dimensions was examined using mixed-effects analysis of covariance models. MAIN RESULTS Upper airway morphology was completed in 45 patients. Most airway measurements showed statistically nonsignificant associations with increasing doses of PROP and DEX. As the dosage increased, average airway dimensions were typically unchanged or slightly increased with DEX compared with airway dimensions that were unchanged or slightly decreased with PROP. An airway intervention was required in three children (11%) in the DEX group and 7 children (23%) in the PROP group (P = NS). CONCLUSIONS Both agents provided an acceptable level of anesthesia for MRI sleep studies in patients with OSA, with statistically nonsignificant changes in airway dimensions.

Characterization and quantification of isoflurane-induced developmental apoptotic cell death in mouse cerebral cortex.

BACKGROUND:Accumulating evidence indicates that isoflurane and other, similarly acting anesthetics exert neurotoxic effects in neonatal animals. However, neither the identity of dying cortical cells nor the extent of cortical cell loss has been sufficiently characterized. We conducted the present study to immunohistochemically identify the dying cells and to quantify the fraction of cells undergoing apoptotic death in neonatal mouse cortex, a substantially affected brain region. METHODS:Seven-day-old littermates (n = 36) were randomly assigned to a 6-hour exposure to either 1.5% isoflurane or fasting in room air. Animals were euthanized immediately after exposure and brain sections were double-stained for activated caspase 3 and one of the following cellular markers: Neuronal Nuclei (NeuN) for neurons, glutamic acid decarboxylase (GAD)65 and GAD67 for GABAergic cells, as well as GFAP (glial fibrillary acidic protein) and S100&bgr; for astrocytes. RESULTS:In 7-day-old mice, isoflurane exposure led to widespread increases in apoptotic cell death relative to controls, as measured by activated caspase 3 immunolabeling. Confocal analyses of caspase 3–labeled cells in cortical layers II and III revealed that the overwhelming majority of cells were postmitotic neurons, but some were astrocytes. We then quantified isoflurane-induced neuronal apoptosis in visual cortex, an area of substantial injury. In unanesthetized control animals, 0.08% ± 0.001% of NeuN-positive layer II/III cortical neurons were immunoreactive for caspase 3. By contrast, the rate of apoptotic NeuN-positive neurons increased at least 11-fold (lower end of the 95% confidence interval [CI]) to 2.0% ± 0.004% of neurons immediately after isoflurane exposure (P = 0.0017 isoflurane versus control). In isoflurane-treated animals, 2.9% ± 0.02% of all caspase 3–positive neurons in superficial cortex also coexpressed GAD67, indicating that inhibitory neurons may also be affected. Analysis of GABAergic neurons, however, proved unexpectedly complex. In addition to inducing apoptosis among some GAD67-immunoreactive neurons, anesthesia also coincided with a dramatic decrease in both GAD67 (0.98 vs 1.84 ng/mg protein, P < 0.00001, anesthesia versus control) and GAD65 (2.25 ± 0.74 vs 23.03 ± 8.47 ng/mg protein, P = 0.0008, anesthesia versus control) protein levels. CONCLUSIONS:Prolonged exposure to isoflurane increased neuronal apoptotic cell death in 7-day-old mice, eliminating approximately 2% of cortical neurons, of which some were identified as GABAergic interneurons. Moreover, isoflurane exposure interfered with the inhibitory nervous system by downregulating the central enzymes GAD65 and GAD67. Conversely, at this age, only a minority of degenerating cells were identified as astrocytes. The clinical relevance of these findings in animals remains to be determined.

Isoflurane-delayed preconditioning reduces immediate mortality and improves striatal function in adult mice after neonatal hypoxia-ischemia.

BACKGROUND: Exposure to hypoxia and isoflurane (Iso) before hypoxia–ischemia has been found to be neuroprotective in neonatal rats. We investigated the long-term effects of delayed preconditioning with Iso, hypoxia, or room air on motor and cognitive function in mice that had 65 min of hypoxia–ischemia on postnatal day 10. METHODS: Nine-day-old C57x129T2 F1 mice received either 1.8% Iso, hypoxic (10% O2 in N2), or sham (room air) preconditioning. The following day, the mice were subjected to permanent right common carotid ligation or sham ligation followed by 65 min of hypoxia, or room air. At 70 days of age, learning was tested using a series of Morris water maze tests. Striatal function was assessed by response to apomorphine injection. Histological analysis was performed on adult brain (P120) sections of striatum and dorsal hippocampus. RESULTS: Iso preconditioning 24 h before severe neonatal hypoxia–ischemia reduced preweaning mortality from 20% to 0% (P < 0.04) and improved striatal function in adult mice, as assessed by circling after apomorphine injection (P < 0.028), but no improvements in performance were noted in the spatial-reference memory water maze tests. Hypoxic preconditioning improved learning relative to the sham-preconditioned group on the hidden maze, but not the more difficult reduced maze test of spatial memory. It had no significant effect on preweaning mortality and apomorphine response. Histologic analysis showed the hippocampus of non-preconditioned and Iso-preconditioned animals to be equally injured. CONCLUSION: Iso and hypoxia confer selective functional neuroprotection in a delayed preconditioning paradigm in neonatal mice.

Desflurane, isoflurane, and sevoflurane provide limited neuroprotection against neonatal hypoxia-ischemia in a delayed preconditioning paradigm.

Background:The volatile anesthetics desflurane, isofluorane, and sevoflurane have been found to produce neuroprotection in various paradigms. The authors used these agents in a delayed preconditioning model to test the hypothesis that they could provide neuroprotection against neonatal hypoxia-ischemia as assessed by a battery of behavioral tests. Methods:Institutional Animal Care and Use Committee approval was obtained. A total of 140, C57-129T2 F1 hybrid 9-day-old mice were randomized to 3 h of preconditioning with room air (Group Sham and Group HI), 8.4% desflurane in 40% oxygen (Group D), 1.8% isoflurane (Group I), or 3.1% sevoflurane (Group S). Twenty-four hours later, the Group HI, D, I, and S mice had 60 min of hypoxia-ischemia, and Group Sham had 60 min of sham HI. Surviving animals had behavioral testing, including open field activity, acoustic startle, prepulse inhibition, rotorod, novel object recognition, water mazes, and apomorphine challenge. Histologic analysis was also performed. Results:Mice in Groups D, I, and S performed better than Group HI and similarly to Group Sham on novel object recognition and apomorphine challenge and better than Group HI but not as well as Group Sham on cued maze testing. All mice exposed to hypoxia-ischemia performed worse than Group Sham on the spatially oriented water mazes with no difference among groups. Histologic sections did not show any significant effect of preconditioning on injury scores. Conclusions:Volatile agent preconditioning partially protects perirhinal cortex and striatal dependent functions against moderate to severe neonatal hypoxia-ischemia.

Susceptibility of Transcranial Electric Motor-evoked Potentials to Varying Targeted Blood Levels of Dexmedetomidine during Spine Surgery

Background:Dexmedetomidine has been increasingly used as an adjunct to opioid–propofol total intravenous anesthesia (TIVA). The authors tested the hypothesis and found that clinically relevant blood levels of dexmedetomidine do not produce significant attenuation of the amplitude of transcranial electric motor-evoked potentials either independently or by interaction with propofol in a dose-dependent manner. Methods:The authors planned to recruit 72 patients with idiopathic scoliosis who had posterior spine fusion surgery during propofol and remifentanil TIVA with dexmedetomidine as an adjunct. However, the authors terminated the study after enrolling 44 patients because of change in surgical technique. Before administering dexmedetomidine, baseline transcranial electric motor-evoked potentials were acquired during TIVA with remifentanil and propofol. Patients were randomized to varying targeted blood levels of dexmedetomidine (0.4, 0.6, and 0.8 ng/ml) and propofol (2.5, 3.75, and 5 &mgr;g/ml) using a factorial design. The primary outcome variable was amplitude of transcranial electric motor-evoked potential. The secondary outcome was amplitude of cortical somatosensory-evoked potentials. Results:Of the 44 recruited patients, 40 completed the study, and their data were analyzed. The administration of dexmedetomidine in increasing doses as an adjunct to propofol-based TIVA caused a clinically and statistically significant attenuation of amplitudes of transcranial electric motor-evoked potentials. Conclusion:The authors conclude that under the stimulation conditions used, dexmedetomidine as an anesthetic adjunct to propofol-based TIVA at clinically relevant target plasma concentrations (0.6–0.8 ng/ml) can significantly attenuate the amplitude of transcranial electric motor-evoked potentials.