Role of cortical feedback signalling in consciousness and anaesthetic-induced unconsciousness

Separation of responsive and unresponsive patients under clinical conditions: comparison of symbolic transfer entropy and permutation entropy

Electroencephalogram (EEG)-based monitoring during general anesthesia may help prevent harmful effects of high or low doses of general anesthetics. There is currently no convincing evidence in this regard for the proprietary algorithms of commercially available monitors. The purpose of this study was to investigate whether a more mechanism-based parameter of EEG analysis (symbolic transfer entropy, STE) can separate responsive from unresponsive patients better than a strictly probabilistic parameter (permutation entropy, PE) under clinical conditions. In this prospective single-center study, the EEG of 60 surgical ASA I-III patients was recorded perioperatively. During induction of and emergence from anesthesia, patients were asked to squeeze the investigators' hand every 15s. Time of loss of responsiveness (LoR) during induction and return of responsiveness (RoR) during emergence from anesthesia were registered. PE and STE were calculated at -15s and +30s of LoR and RoR and their ability to separate responsive from unresponsive patients was evaluated using accuracy statistics. 56 patients were included in the final analysis. STE and PE values decreased during anesthesia induction and increased during emergence. Intra-individual consistency was higher during induction than during emergence. Accuracy values during LoR and RoR were 0.71 (0.62-0.79) and 0.60 (0.51-0.69), respectively for STE and 0.74 (0.66-0.82) and 0.62 (0.53-0.71), respectively for PE. For the combination of LoR and RoR, values were 0.65 (0.59-0.71) for STE and 0.68 (0.62-0.74) for PE. The ability to differentiate between the clinical status of (un)responsiveness did not significantly differ between STE and PE at any time. Mechanism-based EEG analysis did not improve differentiation of responsive from unresponsive patients compared to the probabilistic PE.Trial registration: German Clinical Trials Register ID: DRKS00030562, November 4, 2022, retrospectively registered.

Protective effect of isoflurane preconditioning on neurological function in rats with HIE

Hypoxic-ischemic encephalopathy (HIE) is an important cause of neonatal death and disability, which can lead to long-term neurological and motor dysfunction. Currently, inhalation anesthetics are widely used in surgery, and some studies have found that isoflurane (ISO) may have a positive effect on neuroprotection. In this paper, we investigated whether ISO pretreatment has a neuroprotective effect on the neurological function of HIE rats. Here, 7-day-old neonatal rats were randomly divided into a sham group, a hypoxic-ischemic (HI) group, and an ISO pretreatment (pretreatment) group. The pretreatment group was pretreated with 2% ISO for 1 h, followed by the HI group to establish an HI animal model. The HI‑induced neurological injury was evaluated by Zea‑Longa scores and triphenyltetrazolium (TTC) staining. Neuronal number and histomorphological changes were observed with Nissl staining and Hematoxylin-eosin (HE) staining. In addition, motor learning memory function was evaluated by the Morris water maze (MWM), the Y-maze, and the rotarod tests. HI induced severe neurological dysfunction, brain infarction, and cell apoptosis as well as obvious neuron loss in neonatal rats. In the MWM, the rats in the pretreatment group showed a decrease in escape latency (p = 0.042), indicating that pretreatment with ISO could improve the learning ability of HI rats. The results of Nissl staining showed that in the HI group, there was an irregular arrangement of neurons and nuclear fixation; however, the cell damage was significantly reduced and the total number of neurons was increased after ISO pretreatment (p < 0.001). In conclusion, ISO pretreatment improved cognitive function and attenuated HI-induced reduction of Nissl-positive cells and spatial memory impairment, suggesting that pretreatment with ISO before HI modeling could reduce neuronal cell death in the hippocampus after HI.