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The effects of xenon on sevoflurane anesthesia‐induced acidosis and brain cell apoptosis in immature rats

2020; Wiley; Volume: 31; Issue: 3 Linguagem: Inglês

10.1111/pan.14076

1460-9592

Hannah Gill, Anthony E. Pickering,

Anesthesia and Sedative Agents

Anesthesia-induced neurodegeneration (AIN) occurs in newborn large animal models where physiological homeostasis is maintained. However, most immature rodent models of AIN report mortality rates, and hypercarbia alone, mimicking that produced by anesthesia, increases neuro-apoptosis.1 The potential influence of physiological derangement is one reason why rodent models of AIN are not ideal for predicting clinical effect. However, they remain necessary for the initial pre-clinical investigation of toxicity or treatment. Xenon, a cardio-stable sedative with analgesic properties and shown to reduce isoflurane-AIN in an immature rodent model,2 was recently administered to critically ill babies in UK research trials and was shown to reduce the requirement for sevoflurane during anesthesia in another European trial. Co-administration during anesthesia for babies and young children potentially offers improved hemodynamics and neuroprotection. We aimed to compare the effect of co-administering Xenon with sevoflurane on neuroapoptosis and acid–base homeostasis in immature rats. These experiments were carried out under Home Office License, with University ethical approval. Mixed sex, Wistar rats were randomly assigned on postnatal day 8 to 6-hour exposures to equipotent mixtures of sevoflurane ± xenon in 30% oxygen (equivalent to thrice the effective inhaled concentration of sevoflurane or xenon preventing cold-stimulated vocalization in 95% [EiC95 CSV]3): 2.7% sevoflurane alone (Sevo), 1.8% sevoflurane in 35% xenon (SevoXe35) or 0.9% sevoflurane in 70% xenon (SevoXe70) (n = 9 per group). Two control groups were used (Naïve: anesthetized and culled on removal from the home cage, and Sham: expose to 30% oxygen alone [n = 6 per group]). Gasses were delivered using calibrated, low flow, rotameters and monitoring ensured that CO2 rebreathing was limited to 2%. Immediate decapitation allowed collection of mixed arterio-venous blood for analysis. Brains were harvested, drop fixed, cryoprotected, and coronal blocks were frozen. 25 µm section were cut on a cryostat (Leica 3050), mounted on slides, and stained for cleaved caspase-3 (CC3) immunofluorescence. CC3-positive cells were counted by a researcher blinded to group allocation in four brain areas: Pre-frontal cortex (comprising Sensory Cortex [S1], Motor cortex [M1] and Cingulate Gyrus [Cg]), Caudate Putamen [Cpu], Somatosensory 1 Barrel Field [S1BF] and hippocampus comprising CornuAmmonis 1 and 3 [CA1, CA3] and Dentate Gyrus [DG]). Sample size was calculated using a conservative interpretation of data from Ma et al.2 A two-way ANOVA was used to compare apoptotic cell count by brain area and control group (Naive or Sham). There was no effect of control group (P = .645), therefore, differences in apoptotic cell count between Control, Sevo, SevoXe35, and SevoXe70 were tested using Kruskal–Wallis with Bonferroni correction for multiple comparisons. The relationships between RR and PCO2, and pH and induced apoptosis were estimated using Spearman's Rank correlation coefficient (values between 0.4 and 0.59, 0.6 and 0.79 or 0.8 and 1.0 indicate moderate, strong or very strong correlation). No animals died during the six-hour exposures. The results are shown in the Figure 1. Sevoflurane induced severe acidosis and significant apoptosis in the Sensory Cortex, Pre-frontal Cortex, and Hippocampus. Co-administration of Xenon, reducing the exposure to sevoflurane, significantly lessened the acidosis in a dose-dependent manner and, at the higher Xenon concentration (70%), prevented induced apoptosis. Lactate remained normal in our animals suggesting severe circulatory failure was not present, and the pH we report is in keeping with a recent study showing induced apoptosis in rats exposed to six hours of 2.5% sevoflurane (mean arterial blood pH: 7.04).4 The relationships between RR and PCO2, and pH and induced apoptosis were estimated using Spearman's Rank correlation coefficient. There was a very strong negative correlation between respiratory rate and pCO2 of mixed arterio-venous blood (−0.99, P < .001). There was less acidosis with increased xenon/decreased sevoflurane (P < .001). Lactate was not raised in any animal (<3 mmol/L), and there was no difference between the three groups (P = .282). There was a moderate negative correlation between pH and apoptotic cell count in the sensory cortex (−0.50, P = .028), but not in the hippocampus or the pre-frontal cortex (P = .092 and P = .342, respectively). Our study shows that xenon-co-administration in neonatal rats, used to reduce sevoflurane exposure, lessened physiological disturbances and this was accompanied by reduced apoptosis in the brain. Further pre-clinical studies are needed where cardiorespiratory derangement is minimized and equal between groups. HG and AEP have no conflicts of interest. This work was presented at The Anaesthetic Research Society/ British Journal of Anaesthesia Research Forum, Royal College of Anaesthetists, London, May 2019. The abstract was published in the BJA.