Impact of female sex on anaesthetic awareness, depth, and emergence: a systematic review and meta-analysis

Beyond surgery: Repurposing anesthetics for treatment of central nervous system disorders

The development of new drugs is a complex, expensive, and time-consuming process, often fraught with a high likelihood of failure. Amid these obstacles, drug repurposing, which identifies new therapeutic applications for already existing medications, offers a more economical and time-saving approach, particularly in the challenging field of neurological and psychiatric disorders. This narrative review explores both preclinical and clinical studies to examine the potential of anesthetics such as ketamine, nitrous oxide, isoflurane, sevoflurane, propofol, dexmedetomidine, and sodium oxybate in treating central nervous system disorders. Various research highlights the potential of anesthetics to provide rapid antidepressant effects, enhance learning and memory, improve synaptic plasticity, and offer neuroprotective benefits, demonstrating promise for treating depression, post-traumatic stress disorder, cognitive decline, traumatic brain injury, and neurodegenerative disorders. Anesthetics appear to alleviate symptoms in neurological conditions, likely by modulating GABAergic and glutamatergic pathways. However, challenges such as dose-dependent neurotoxicity, variability in preclinical and clinical outcomes, as well as environmental concerns remain significant issues. Future research is essential to optimize dosing strategies, ensure long-term safety, and gain a deeper understanding of the precise mechanisms of action. The concept of anesthetics' repurposing presents a unique solution to tackle the challenges in neurological and psychiatric therapy by providing a platform for the development of new and improved therapies.

Gender-Specific Differences in Sedation-Associated Outcomes During Complex Electrophysiological Procedures

Background: Interventional electrophysiology is a rapidly advancing field, with sedation essential for patient comfort and immobility during complex electrophysiological procedures (EPS). However, sedatives and analgesics can cause respiratory depression and hypotension. Gender-specific differences (GDs) are often overlooked in medical research, as protocols and dosages are typically based on male subjects, potentially compromising treatment safety and efficacy for women. This study examines GDs in CO2 levels, respiratory rate, arterial blood pressure (ABP), and anesthetic requirements during deep sedation for EPS. Methods: This prospective study at Ulm University Heart Center included 702 patients (405 men and 297 women) treated under deep sedation between August 2019 and October 2023. Standard monitoring included an electrocardiogram (ECG) with heart rate, non-invasive ABP, oxygen saturation (SpO2), and a frequent venous blood gas analysis (vBGA). The primary composite endpoint was GDs in SpO2 dips below 90% and pathological vBGA changes. Results: The primary composite endpoint was reached by 177 women (59.6%) and 213 men (52.6%), showing no significant difference (p = 0.102). Women had a 1,6-fold higher risk of experiencing SpO2 dips below 90% (p = 0.001). Additionally, women had 1.7 times higher hypoxia rates (p < 0.001) and were 1.5 times more likely to have a mean ABP below 65 mmHg (p < 0.001). On average, they received 65.3 mg less total propofol than men (p = 0.005) and a higher midazolam dose per kilogram of body weight (p < 0.001). Conclusions: Although the primary composite endpoint showed no significant GDs, secondary outcomes highlight the need to consider gender-specific sedation adjustments, particularly for women. This study underscores the need for personalized sedation management and patient monitoring regarding GDs.

Genetic Variation and Sex-Based Differences: Current Considerations for Anesthetic Management

Biomedical sciences have made immense progress and numerous discoveries aimed at improving the quality of life and life expectancy in modern times. Anesthesiology is typically tailored to individual patients as its clinical effects depend on multiple factors, including a patient's physiological and pathological states, age, environmental exposures, and genetic variations. Sex differences are also paramount for a complete understanding of the effects of specific anesthetic medications on men and women. However, women-specific research and the inclusion of women in clinical trials, specifically during child-bearing years, remain disproportionately low compared to the general population at large. This review describes and summarizes genetic variations, including sex differences, that affect responses to common anesthetic medications such as volatile anesthetics, induction agents, neuromuscular blocking drugs, opioids, and local anesthetics. It also discusses the influence of genetic variations on anesthesia outcomes, such as postoperative nausea and vomiting, allergic reactions, pain, depth of anesthesia, awareness under anesthesia and recall, and postoperative delirium.

Noradrenergic suppression to reduce electroencephalographic arousal after intubation: a randomised, placebo-controlled trial

Background

Intraoperative awareness, without explicit recall, occurs after induction of anaesthesia in approximately 10% of persons under 40 yr of age. Most anaesthetic agents minimally suppress the noradrenergic system. We hypothesised that addition of dexmedetomidine, which suppresses noradrenergic activity, may reduce encephalographic (EEG) arousal in response to tracheal intubation; such an effect would lay the foundation for future studies of dexmedetomidine in reducing intraoperative awareness.

Methods

A single-site randomised, placebo-controlled trial with sex-based stratification was conducted. Participants, aged 18-40 yr old, undergoing intubation for general anaesthesia were eligible for recruitment and randomly allocated to receive dexmedetomidine or placebo. Dexmedetomidine (0.5 μg kg-1) was given as a 5-min loading dose before induction. Bispectral index (BIS) values were collected during the induction phase of anaesthesia and the isolated forearm technique was used to assess patients' responsiveness before and after tracheal intubation. The primary outcome was the effect of dexmedetomidine on changes in BIS from pre-to postintubation.

Results

A total of 51 patients were recruited and included in the primary analysis. We did not observe an effect of dexmedetomidine on changes in BIS after tracheal intubation (mean difference -1.13, 95% confidence interval [CI] -4.87 to 2.62; p=0.556). Dexmedetomidine reduced the estimated plasma propofol concentration at loss of responsiveness (difference [dexmedetomidine - placebo]: -1.06 μg ml-1, 95% CI -1.66 to -0.46; p<0.001) and before intubation (difference [dexmedetomidine - placebo]: -1.84 μg ml-1, 95% CI -2.79 to -0.90; p<0.001). There was one patient in the placebo group who gave positive responses in the isolated forearm test before and after tracheal intubation.

Conclusions

Dexmedetomidine demonstrated an anaesthetic-sparing effect at induction of anaesthesia but did not prevent EEG arousal after tracheal intubation, as defined by an increase in the BIS value.

Clinical Trial Registration

Australia and New Zealand Clinical Trials Registry (Trial ID: ACTRN12622000754741).

Substantia Innominata Glutamatergic Neurons Modulate Sevoflurane Anesthesia in Male Mice

BACKGROUND

Accumulated evidence suggests that brain regions that promote wakefulness also facilitate emergence from general anesthesia (GA). Glutamatergic neurons in the substantia innominata (SI) regulate motivation-related aversive, depressive, and aggressive behaviors relying on heightened arousal. Here, we hypothesize that glutamatergic neurons in the SI are also involved in the regulation of the effects of sevoflurane anesthesia.

METHODS

With a combination of fiber photometry, chemogenetic and optogenetic tools, behavioral tests, and cortical electroencephalogram recordings, we investigated whether and how SI glutamatergic neurons and their projections to the lateral hypothalamus (LH) regulate sevoflurane anesthesia in adult male mice.

RESULTS

Population activity of glutamatergic neurons in the SI gradually decreased upon sevoflurane-induced loss of consciousness (LOC) and slowly returned as soon as inhalation of sevoflurane discontinued before recovery of consciousness (ROC). Chemogenetic activation of SI glutamatergic neurons dampened the animals' sensitivity to sevoflurane exposure, prolonged induction time (mean ± standard deviation [SD]; 389 ± 67 seconds vs 458 ± 53 seconds; P = .047), and shortened emergence time (305 seconds, 95% confidence interval [CI], 242-369 seconds vs 207 seconds, 95% CI, 135-279 seconds; P = .004), whereas chemogenetic inhibition of these neurons facilitated sevoflurane anesthesia. Furthermore, optogenetic activation of SI glutamatergic neurons and their terminals in LH induced cortical activation and behavioral emergence from different depths of sevoflurane anesthesia.

CONCLUSIONS

Our study shows that SI glutamatergic neuronal activity facilitates emergence from sevoflurane anesthesia and provides evidence for the involvement of the SI-LH glutamatergic pathway in the regulation of consciousness during GA.

VCP controls KCC2 degradation through FAF1 recruitment and accelerates emergence from anesthesia

Ubiquitin-proteasomal degradation of K+/Cl- cotransporter 2 (KCC2) in the ventral posteromedial nucleus (VPM) has been demonstrated to serve as a common mechanism by which the brain emerges from anesthesia and regains consciousness. Ubiquitin-proteasomal degradation of KCC2 during anesthesia is driven by E3 ligase Fbxl4. However, the mechanism by which ubiquitinated KCC2 is targeted to the proteasome has not been elucidated. We report in cultured neuro-2a cells that the valosin-containing protein (VCP) transported ubiquitinated KCC2 to the proteasome and in mice in vivo experiments that inhibition of VCP restored KCC2 expression in the VPM and enhanced the effects of anesthesia. In cultured neuro-2a cells, propofol-induced degradation of KCC2 was inhibited by VCP inhibitor DBeQ and VCP knockout plasmid sgRNA(VCP). Propofol-induced enhanced interaction between VCP and KCC2 was inhibited by knockout of Fbxl4 or Fas-associated factor 1 (FAF1). In in vivo studies, pharmacological or genetic inhibition of VCP in the VPM significantly prevented KCC2 degradation and enhanced propofol anesthesia; these effects were abrogated by a KCC2 antagonist VU0463271. These results demonstrate that the VCP controls ubiquitin-proteasomal degradation of KCC2 dependent on FAF1 recruitment and serves as a mechanism for the ubiquitin-proteasomal degradation of KCC2, which is responsible for the subsequent emergence from anesthesia.

Brain health: A concern for anaesthesiologists and intensivists

Damage to the brain can have disastrous and long-lasting consequences. The European Society of Anaesthesiology and Intensive Care (ESAIC) is aware of the importance of taking good care of the brain, both of patients and of anaesthesia and intensive care unit (ICU) caregivers, and has organised a complete learning track on brain health to bring this concern to the attention of practitioners. This learning track included an online Focus Meeting on Brain Health (November 25, 2023). We here provide readers with a digest of the information that was delivered during that meeting in an opinion paper driven by the authors' own reading of the literature. It is divided according to the meeting's sessions, including how to improve the health of an injured brain, how to keep a young or old brain healthy, how to keep a healthy adult brain unimpaired, how monitoring can impact brain health in the operating room and in the intensive care unit, and how to keep the anaesthesia and ICU caregivers' brain healthy. Each part is a brief and focused summary. The main delivered messages are that the management of injured brain patients involves an adequate choice of sedation, adequate brain monitoring, and focused attention to specific points depending on the underlying pathology; that several measures can be undertaken to protect the brain of the very young needing anaesthesia; that it is possible to detect older patients at risk of postoperative neurocognitive disorders, and that dedicated perioperative management by a multidisciplinary expert team may improve their outcomes; that apparently healthy adult brains may suffer during anaesthesia; that the electroencephalogram may track peri-operative brain dysfunction, and that female patients should be given special care in this respect; that multimodal brain monitoring helps to detect pathological processes and to maintain brain homeostasis; and that burnout in anaesthesiologists can be effectively fought using personal, organisational, managerial and legal approaches.

A Narrative Review of the Best Anesthesia Care for Endovascular Thrombectomy: Early Diagnosis of the Ischemic Stroke and Evaluation of Risk Factors in Female Population

Background: The increasing incidence of cerebrovascular accidents represents an emerging problem. The rise in risk factors such as lifestyle choices—smoking, poor nutrition, and metabolic diseases—poses a significant challenge for the global healthcare system. The female population, due to physiological conditions and iatrogenic risks, may be at a greater risk of developing ischemic accidents. In addition to these acquired conditions, life phases such as pregnancy or puerperium, and medical conditions like surgical treatments and hormone therapy, may elevate this risk. Methods: This narrative aims to assess the various risk factors specific to the female population and evaluate the appropriate management strategies, including anesthetic support. Anesthesia plays a crucial role in enabling pharmacological procedures, such as thrombolysis, or surgical procedures like thrombectomy, in the management of ischemic cerebrovascular events. Results: The review emphasizes the importance of early recognition of risk factors to ensure prompt diagnosis and the most appropriate treatment options for ischemic events. Anesthesia support has become essential for carrying out necessary medical interventions effectively. Choosing the right anesthesia technique for endovascular thrombectomy is particularly significant, requiring consideration of the patient’s characteristics, the timing of diagnosis, and the preferences of the interventional neuroradiologists. Conclusions: It is vital to identify risk factors in the female population early to facilitate timely diagnosis and optimize treatment outcomes. Anesthetic support plays a key role in ensuring that critical procedures, such as thrombolysis and thrombectomy, are carried out effectively. Tailoring anesthesia choices to the patient’s individual needs is critical for a successful intervention.

Changes in brain connectivity and neurovascular dynamics during dexmedetomidine-induced loss of consciousness

Understanding the neurophysiological changes that occur during loss and recovery of consciousness is a fundamental aim in neuroscience and has marked clinical relevance. Here, we utilize multimodal magnetic resonance neuroimaging to investigate changes in regional network connectivity and neurovascular dynamics as the brain transitions from wakefulness to dexmedetomidine-induced unconsciousness, and finally into early-stage recovery of consciousness. We observed widespread decreases in functional connectivity strength across the whole brain, and targeted increases in structure-function coupling (SFC) across select networks-especially the cerebellum-as individuals transitioned from wakefulness to hypnosis. We also observed robust decreases in cerebral blood flow (CBF) across the whole brain-especially within the brainstem, thalamus, and cerebellum. Moreover, hypnosis was characterized by significant increases in the amplitude of low-frequency fluctuations (ALFF) of the resting-state blood oxygen level-dependent signal, localized within visual and somatomotor regions. Critically, when transitioning from hypnosis to the early stages of recovery, functional connectivity strength and SFC-but not CBF-started reverting towards their awake levels, even before behavioral arousal. By further testing for a relationship between connectivity and neurovascular alterations, we observed that during wakefulness, brain regions with higher ALFF displayed lower functional connectivity with the rest of the brain. During hypnosis, brain regions with higher ALFF displayed weaker coupling between structural and functional connectivity. Correspondingly, brain regions with stronger functional connectivity strength during wakefulness showed greater reductions in CBF with the onset of hypnosis. Earlier recovery of consciousness was associated with higher baseline (awake) levels of functional connectivity strength, CBF, and ALFF, as well as female sex. Across our findings, we also highlight the role of the cerebellum as a recurrent marker of connectivity and neurovascular changes between states of consciousness. Collectively, these results demonstrate that induction of, and emergence from dexmedetomidine-induced unconsciousness are characterized by widespread changes in connectivity and neurovascular dynamics.

Rényi entropy-complexity causality space: a novel neurocomputational tool for detecting scale-free features in EEG/iEEG data

Scale-free brain activity, linked with learning, the integration of different time scales, and the formation of mental models, is correlated with a metastable cognitive basis. The spectral slope, a key aspect of scale-free dynamics, was proposed as a potential indicator to distinguish between different sleep stages. Studies suggest that brain networks maintain a consistent scale-free structure across wakefulness, anesthesia, and recovery. Although differences in anesthetic sensitivity between the sexes are recognized, these variations are not evident in clinical electroencephalographic recordings of the cortex. Recently, changes in the slope of the power law exponent of neural activity were found to correlate with changes in Rényi entropy, an extended concept of Shannon's information entropy. These findings establish quantifiers as a promising tool for the study of scale-free dynamics in the brain. Our study presents a novel visual representation called the Rényi entropy-complexity causality space, which encapsulates complexity, permutation entropy, and the Rényi parameter q. The main goal of this study is to define this space for classical dynamical systems within theoretical bounds. In addition, the study aims to investigate how well different time series mimicking scale-free activity can be discriminated. Finally, this tool is used to detect dynamic features in intracranial electroencephalography (iEEG) signals. To achieve these goals, the study implementse the Bandt and Pompe method for ordinal patterns. In this process, each signal is associated with a probability distribution, and the causal measures of Rényi entropy and complexity are computed based on the parameter q. This method is a valuable tool for analyzing simulated time series. It effectively distinguishes elements of correlated noise and provides a straightforward means of examining differences in behaviors, characteristics, and classifications. For the iEEG experimental data, the REM state showed a greater number of significant sex-based differences, while the supramarginal gyrus region showed the most variation across different modes and analyzes. Exploring scale-free brain activity with this framework could provide valuable insights into cognition and neurological disorders. The results may have implications for understanding differences in brain function between the sexes and their possible relevance to neurological disorders.

Incidence, Associated Factors, and Behavioral Consequences of Intraoperative Awareness and Dreams During General Anesthesia Among Adult Patients: A Prospective Cohort Study

Background  The intraoperative awareness with recall phenomenon involves the memory of intraoperative events. The reported incidence is 0.001%. Awareness is rare intraoperatively but has profound implications. This research aimed to study intraoperative awareness and dream experiences in the Omani population undergoing general anesthesia. Methods This prospective cohort study involving 300 adult patients was conducted at a tertiary-level hospital between July and December 2021. Awareness was assessed in the post-anesthesia care unit and then at home on the seventh day and one month telephonically using a modified Brice questionnaire. The study's primary outcome was the incidence of IOA and dreams in adult Omani patients undergoing GA. The secondary outcome was identifying the factors associated with intraoperative awareness and dreams under GA. Results In this study, the incidence of awareness was 0.3% while 7.6% of patients reported intraoperative dreams. The patient who experienced IOA underwent an endoscopic retrograde cholangiopancreatography under GA with neuromuscular blockade and had a prolonged recovery. A total of 49.33% developed psychological effects postoperatively; anxiety, irritability, fear of surgery, change in memory, and repetitive nightmares were the most common ones. Because of the limited sample size, no factor associated significantly with these outcomes was found. Conclusion This study observed a higher incidence of intraoperative awareness and dreams. Awareness might be due to prolonged recovery and the use of neuromuscular blocking agents, but a focused study is required to confirm this finding. The incidence of intraoperative dreams and postoperative psychological effects of GA was also high. It may be worth exploring these findings with larger population-based research.

Hormonal basis of sex differences in anesthetic sensitivity

General anesthesia-a pharmacologically induced reversible state of unconsciousness-enables millions of life-saving procedures. Anesthetics induce unconsciousness in part by impinging upon sexually dimorphic and hormonally sensitive hypothalamic circuits regulating sleep and wakefulness. Thus, we hypothesized that anesthetic sensitivity should be sex-dependent and modulated by sex hormones. Using distinct behavioral measures, we show that at identical brain anesthetic concentrations, female mice are more resistant to volatile anesthetics than males. Anesthetic sensitivity is bidirectionally modulated by testosterone. Castration increases anesthetic resistance. Conversely, testosterone administration acutely increases anesthetic sensitivity. Conversion of testosterone to estradiol by aromatase is partially responsible for this effect. In contrast, oophorectomy has no effect. To identify the neuronal circuits underlying sex differences, we performed whole brain c-Fos activity mapping under anesthesia in male and female mice. Consistent with a key role of the hypothalamus, we found fewer active neurons in the ventral hypothalamic sleep-promoting regions in females than in males. In humans, we demonstrate that females regain consciousness and recover cognition faster than males after identical anesthetic exposures. Remarkably, while behavioral and neurocognitive measures in mice and humans point to increased anesthetic resistance in females, cortical activity fails to show sex differences under anesthesia in either species. Cumulatively, we demonstrate that sex differences in anesthetic sensitivity are evolutionarily conserved and not reflected in conventional electroencephalographic-based measures of anesthetic depth. This covert resistance to anesthesia may explain the higher incidence of unintended awareness under general anesthesia in females.