Dreaming during anaesthesia has been documented for over a century, yet it remains poorly understood. This scoping review synthesises evidence on the frequency, phenomenology, predictors, outcomes, and neural correlates of anaesthesia dreaming. We systematically searched multiple databases for studies examining anaesthesia dreaming, including clinical trials, observational studies, and...
Postoperative delirium and other forms of perioperative neurocognitive deficits occur commonly in older adult patients. Ketamine, administered either before or during general anaesthesia, may have cognitive-sparing properties owing to its ability to reduce neuroinflammation, increase neurotrophin levels, or allow reductions in the doses of other general anaesthetic drugs. However, the efficacy...
Orexin can induce arousal from general anaesthesia; however, the underlying mechanisms are not fully understood. Nucleus accumbens (NAc), a downstream target of orexinergic neurones, plays a role in regulating consciousness. We aimed to clarify whether and how the NAc mediates the arousal effects of orexin. Fibre photometry was used to track changes of orexinergic afferent activity during...
Ketamine, in doses suitable to induce anaesthesia in humans, gives rise to a unique state of unresponsiveness accompanied by vivid experiences and sensations, making it possible to disentangle the correlated but distinct concepts of conscious awareness and behavioural responsiveness. This distinction is often overlooked in the study of consciousness. The mathematical framework of connectome...
Ketamine, an N-methyl-D-aspartic acid receptor antagonist that was first discovered in 1962, has become established in anaesthesia providing dose-dependent anaesthetic, sedative, and analgesic effects. Ketamine, however, also acts on a wide range of other cellular targets, resulting in interesting and diverse effects on both physiological and pathological processes. Potential beneficial...
The acute hypoxic ventilatory response is a critical chemoreflex originating at the carotid bodies. This study investigates the impact of low-dose i.v. esketamine on the ventilatory response to 20 min of isocapnic hypoxia to test the hypothesis that esketamine does not affect hypoxic ventilation. In this open-label study, 18 healthy subjects received a 3-h escalating i.v. infusion of...
Information integration and network science are important theories for quantifying consciousness. However, whether these theories propose drug- or conscious state-related changes in EEG during anaesthesia-induced unresponsiveness remains unknown. A total of 72 participants were randomised to receive i.v. infusion of propofol, dexmedetomidine, or ketamine at a constant infusion rate until loss...
Understanding the neural correlates of consciousness has important ramifications for the theoretical understanding of consciousness and for clinical anaesthesia. A major limitation of prior studies is the use of responsiveness as an index of consciousness. We identified a collection of measures derived from unresponsive subjects and more specifically their association with consciousness (any...
BACKGROUND Delayed emergence from general anaesthesia poses a significant perioperative safety hazard. Subanaesthetic doses of ketamine not only deepen anaesthesia but also accelerate recovery from isoflurane anaesthesia; however, the mechanisms underlying this phenomenon remain elusive. Esketamine exhibits a more potent receptor affinity and fewer adverse effects than ketamine and exhibits...
Sensory disconnection is a key feature of sleep and anaesthesia. We have proposed that predictive coding offers a framework for understanding the mechanisms of disconnection. Low doses of ketamine that do not induce disconnection should thus diminish predictive coding, but not abolish it. Ketamine was administered to 14 participants up to a blood concentration of 0.3 μg ml-1 Participants were...
The subjective experiences of sedation or anaesthesia are underexplored. A recent study by Valli and colleagues (Br J Anaesth 2023; 131: 348-59) found similar frequency and content of recalled experiences after both non-rapid eye movement sleep and target-controlled infusions of propofol or dexmedetomidine titrated to verbal unresponsiveness. The authors find that the phenomenological...
Anaesthetic-induced unresponsiveness and non-rapid eye movement (NREM) sleep share common neural pathways and neurophysiological features. We hypothesised that these states bear resemblance also at the experiential level. We compared, in a within-subject design, the prevalence and content of experiences in reports obtained after anaesthetic-induced unresponsiveness and NREM sleep. Healthy males...
Whilst the general presumption of the public is that general anaesthesia prevents awareness of any sensory stimuli, Lennertz and colleagues have shown in this issue of the British Journal of Anaesthesia that 11% of young adults were able to respond to auditory commands when neuromuscular blocking drugs were prevented from reaching one arm using the isolated forearm technique. This occurred with...
Background: How conscious experience becomes disconnected from the environment, or disappears, across arousal states is unknown. We sought to identify the neural correlates of sensory disconnection and unconsciousness using a novel serial awakening paradigm. Methods: Volunteers were recruited for sedation with dexmedetomidine i.v., propofol i.v., or natural sleep with high-density EEG...
Ketamine is a general anaesthetic with anti-depressant effects at subanaesthetic doses. We hypothesised that intraoperative administration of ketamine would prevent or mitigate postoperative depressive symptoms in surgical patients. We conducted an international, randomised clinical trial testing the effects of intraoperative administration of ketamine [0.5 mg kg-1 (Lo-K) or 1.0 mg kg-1 (Hi-K)]...
Background: Impaired consciousness has been associated with impaired cortical signal propagation after transcranial magnetic stimulation (TMS). We hypothesised that the reduced current propagation under propofol-induced unresponsiveness is associated with changes in both feedforward and feedback connectivity across the cortical hierarchy. Methods: Eight subjects underwent left occipital TMS...
Experiences during anaesthetic-induced unresponsiveness have previously been investigated by interviews after recovery. To explore whether experiences occur during drug administration, we interviewed participants during target-controlled infusion (TCI) of dexmedetomidine or propofol and after recovery. Healthy participants received dexmedetomidine (n=23) or propofol (n=24) in stepwise...
BackgroundDespite its designation as a 'dissociative anaesthetic,' the dissociative and psychoactive effects of ketamine remain incompletely understood. The goal of this study was to characterise the subjective experiences and accompanying EEG changes with subanaesthetic doses of ketamine.MethodsHigh-density EEG was recorded in 15 human volunteers before, during, and after subanaesthetic...
Selfhood is linked to brain processes that enable the experience of a person as a distinct entity, capable of agency. This framework naturally incorporates a continuum of both non-conscious and conscious self-related information processing, and includes a hierarchy of components, such as awareness of existence (core self), embodied self (sentience), executive self (agency/volition), and various...
Since the late 1980s 'Ecstasy' (3,4-methylenedioxymethamphetamine, MDMA) has become established as a popular recreational drug in western Europe. The UK National Criminal Intelligence Service estimates that 0.5-2 million tablets are consumed weekly in Britain. It has been reported that 4.5% of young adults (15-34 yr) in the UK have used MDMA in the previous 12 months. Clinically important toxic...
To determine if learning occurs during general anaesthesia, 72 women undergoing surgery were given postoperative implicit memory tests in which performance could be influenced by auditory information presented during general anaesthesia. Two methods of anaesthesia were used: nitrous oxide and opioids (n = 24) or nitrous oxide and isoflurane (1, 1.3 and 1.5 MAC for n = 12, 24 and 12,...
This study has examined the effects of inhaled nitrous oxide on the N1 and P2 components of the cortical auditory evoked potentials (AEP) in the latency interval 80-300 ms after the stimulus. The amplitudes, latencies and thresholds of the AEP were measured at a range of end-tidal nitrous oxide concentrations (0%, 10%, 20%, 40%) in 10 subjects with normal hearing. Systematic decreases in...
The possibility that nitrous oxide releases endogenous opioid peptides into the circulation has been tested in 10 pain-free, unstressed volunteers breathing 30% nitrous oxide in oxygen. Despite achieving plateau concentrations in venous blood, accompanied by subjective effects, there were no significant changes in plasma concentrations of immunoreactive beta-endorphin, methionine-enkephalin or...