Effects of anesthesia on the response to sleep deprivation

Effect of desflurane maintenance on postoperative sleep quality in patients undergoing elective breast surgery: A non-inferiority randomized controlled trial

BACKGROUND

Postoperative sleep disturbance (PSD) is prevalent in perioperative patients，and has significant impact on postoperative recovery and prognosis. The aim of this study was to investigate the effect of desflurane maintenance on postoperative sleep quality, in order to optimize patients' perioperative sleep management.

METHOD

A total of 118 patients undergoing elective breast surgery were randomized to receive either desflurane-based volatile anesthesia (desflurane group) or propofol-based total intravenous anesthesia (propofol group) for anesthesia maintenance. The primary outcome was the quality of sleep, which was assessed by the Pittsburgh Sleep Quality Index (PSQI) on 3 days after operation (POD3). Secondary outcomes were PSQI on postoperative day 7 (POD7) and 30 (POD30), and postoperative anxiety, depression, and pain score, as well as objective sleep parameters including total sleep time (TST), WASO (Wakefulness after sleep onset), REM (Rapid eye movement) and NREM (Non-rapid Eye Movement) measured by Fitbit Charge 2TM during the initial 3 postoperative days.

RESULTS

The global PSQI scores on POD3 in the desflurane group was non-inferior to that in the propofol group [mean (SD) 8.47 (3.46) vs. 7.65 (3.16); mean difference (95 % CI) 0.82 (-0.43, 2.07); p < 0.001 for non-inferiority]. There were no significant differences in PSQI scores on POD3 and POD7. In addition, the score of anxiety, depression, and pain on the 3rd, 7th, and 30th day after surgery have no significant differences between the propofol and the desflurane group, respectively. The postoperative NREM was higher in the desflurane group than that in the propofol group.

CONCLUSION

The effects of desflurane-based volatile anesthesia maintenance on postoperative sleep quality is not inferior to that of propofol-based total intravenous anesthesia, and these two drugs may have different effects on the sleep structure.

TRIAL REGISTRATION

ClinicalTrials.gov Identifier: NCT04805775.

Isoflurane anesthesia and sleep deprivation trigger delayed and selective sleep alterations

Isoflurane anesthesia (IA) partially compensates NREM sleep (NREMS) and not REM sleep (REMS) requirement, eliciting post-anesthetic REMS rebound. Sleep deprivation triggers compensatory NREMS rebounds and REMS rebounds during recovery sleep as a result of the body's homeostatic mechanisms. A combination of sleep deprivation and isoflurane anesthesia is common in clinical settings, especially prior to surgeries. This study investigates the effects of pre-anesthetic sleep deprivation on post-anesthetic sleep-wake architecture. The effects of isoflurane exposure (90 min) alone were compared with the effects of isoflurane exposure preceded by experimental sleep deprivation (6 h, gentle handling) on recovery sleep in adult mice by studying the architecture of post-anesthetic sleep for 3 consecutive post-anesthetic days. Effects of isoflurane anesthesia on recovery sleep developed only during the first dark period after anesthesia, the active phase in mice. During this time, mice irrespective of preceding sleep pressure, showed NREMS and REMS rebound and decreased wakefulness during recovery sleep. Additionally, sleep deprivation prior to isoflurane treatment caused a persistent reduction of theta power during post-anesthetic REMS at least for 3 post-anesthetic days. We showed that isoflurane causes NREMS rebound during recovery sleep which suggests that isoflurane may not fully compensate for natural NREMS. The study also reveals that isoflurane exposure preceded by sleep deprivation caused a persistent disruption of REMS quality. We suggest that preoperative sleep deprivation may impair postoperative recovery through lasting disruption in sleep quality.

General anesthesia and sleep: like and unlike

General anesthesia and sleep have long been discussed in the neurobiological context owingto their commonalities, such as unconsciousness, immobility, non-responsiveness to externalstimuli, and lack of memory upon returning to consciousness. Sleep is regulated bycomplex interactions between wake-promoting and sleep-promoting neural circuits. Anestheticsexert their effects partly by inhibiting wake-promoting neurons or activating sleep-promotingneurons. Unconscious but arousable sedation is more related to sleep-wake circuitries,whereas unconscious and unarousable anesthesia is independent of them. Generalanesthesia is notable for its ability to decrease sleep propensity. Conversely, increasedsleep propensity due to insufficient sleep potentiates anesthetic effects. Taken together, it isplausible that sleep and anesthesia are closely related phenomena but not the same ones.Further investigations on the relationship between sleep and anesthesia are warranted.

Sleep from acute to chronic traumatic brain injury and cognitive outcomes

STUDY OBJECTIVES

Traumatic brain injuries (TBIs) cause persistent cerebral damage and cognitive deficits. Because sleep may be a critical factor for brain recovery, we characterized the sleep of patients with TBI from early hospitalization to years post-injury and explored the hypothesis that better sleep during hospitalization predicts more favorable long-term cognitive outcomes.

METHODS

We tested patients with moderate-to-severe TBI in the hospitalized (n = 11) and chronic (n = 43) stages using full-night polysomnography, with 82% of the hospitalized group being retested years post-injury. Hospitalized patients with severe orthopedic and/or spinal cord injury (n = 14) and healthy participants (n = 36) were tested as controls for the hospitalized and chronic TBI groups, respectively. Groups had similar age and sex and were compared for sleep characteristics, including slow waves and spindles. For patients with TBI, associations between sleep during hospitalization and long-term memory and executive function were assessed.

RESULTS

Hospitalized patients with TBI or orthopedic injuries had lower sleep efficiency, higher wake after sleep onset, and lower spindle density than the chronic TBI and healthy control groups, but only hospitalized patients with brain injury had an increased proportion of slow-wave sleep. During hospitalization for TBI, less fragmented sleep, more slow-wave sleep, and higher spindle density were associated to more favorable cognitive outcomes years post-injury, while injury severity markers were not associated with these outcomes.

CONCLUSION

These findings highlight the importance of sleep following TBI, as it could be a strong predictor of neurological recovery, either as a promoter or an early marker of cognitive outcomes.

Sleep, Narcolepsy, and Sodium Oxybate

Sodium oxybate (SO) has been in use for many decades to treat narcolepsy with cataplexy. It functions as a weak GABAB agonist but also as an energy source for the brain as a result of its metabolism to succinate and as a powerful antioxidant because of its capacity to induce the formation of NADPH. Its actions at thalamic GABAB receptors can induce slow-wave activity, while its actions at GABAB receptors on monoaminergic neurons can induce or delay REM sleep. By altering the balance between monoaminergic and cholinergic neuronal activity, SO uniquely can induce and prevent cataplexy. The formation of NADPH may enhance sleep’s restorative process by accelerating the removal of the reactive oxygen species (ROS), which accumulate during wakefulness. SO improves alertness in normal subjects and in patients with narcolepsy. SO may allay severe psychological stress - an inflammatory state triggered by increased levels of ROS and characterized by cholinergic supersensitivity and monoaminergic deficiency. SO may be able to eliminate the inflammatory state and correct the cholinergic/ monoaminergic imbalance.

Preoptic Area Modulation of Arousal in Natural and Drug Induced Unconscious States

The role of the hypothalamic preoptic area (POA) in arousal state regulation has been studied since Constantin von Economo first recognized its importance in the early twentieth century. Over the intervening decades, the POA has been shown to modulate arousal in both natural (sleep and wake) as well as drug-induced (anesthetic-induced unconsciousness) states. While the POA is well known for its role in sleep promotion, populations of wake-promoting neurons within the region have also been identified. However, the complexity and molecular heterogeneity of the POA has made distinguishing these two populations difficult. Though multiple lines of evidence demonstrate that general anesthetics modulate the activity of the POA, the region's heterogeneity has also made it challenging to determine whether the same neurons involved in sleep/wake regulation also modulate arousal in response to general anesthetics. While a number of studies show that sleep-promoting POA neurons are activated by various anesthetics, recent work suggests this is not universal to all arousal-regulating POA neurons. Technical innovations are making it increasingly possible to classify and distinguish the molecular identities of neurons involved in sleep/wake regulation as well as anesthetic-induced unconsciousness. Here, we review the current understanding of the POA's role in arousal state regulation of both natural and drug-induced forms of unconsciousness, including its molecular organization and connectivity to other known sleep and wake promoting regions. Further insights into the molecular identities and connectivity of arousal-regulating POA neurons will be critical in fully understanding how this complex region regulates arousal states.

The Biology of General Anesthesia from Paramecium to Primate

General anesthesia serves a critically important function in the clinical care of human patients. However, the anesthetized state has foundational implications for biology because anesthetic drugs are effective in organisms ranging from paramecia, to plants, to primates. Although unconsciousness is typically considered the cardinal feature of general anesthesia, this endpoint is only strictly applicable to a select subset of organisms that are susceptible to being anesthetized. We review the behavioral endpoints of general anesthetics across species and propose the isolation of an organism from its environment - both in terms of the afferent arm of sensation and the efferent arm of action - as a generalizable definition. We also consider the various targets and putative mechanisms of general anesthetics across biology and identify key substrates that are conserved, including cytoskeletal elements, ion channels, mitochondria, and functionally coupled electrical or neural activity. We conclude with a unifying framework related to network function and suggest that general anesthetics - from single cells to complex brains - create inefficiency and enhance modularity, leading to the dissociation of functions both within an organism and between the organism and its surroundings. Collectively, we demonstrate that general anesthesia is not restricted to the domain of modern medicine but has broad biological relevance with wide-ranging implications for a diverse array of species.

Cortical zeta-inhibitory peptide injection reduces local sleep need

Local sleep need within cortical circuits exhibits extensive interregional variability and appears to increase following learning during preceding waking. Although the biological mechanisms responsible for generating sleep need are unclear, this local variability could arise as a consequence of wake-dependent synaptic plasticity. To test whether cortical synaptic strength is a proximate driver of sleep homeostasis, we developed a novel experimental approach to alter local sleep need. One hour prior to light onset, we injected zeta-inhibitory peptide (ZIP), a pharmacological antagonist of protein kinase Mζ, which can produce pronounced synaptic depotentiation, into the right motor cortex of freely behaving rats. When compared with saline control, ZIP selectively reduced slow-wave activity (SWA; the best electrophysiological marker of sleep need) within the injected motor cortex without affecting SWA in a distal cortical site. This local reduction in SWA was associated with a significant reduction in the slope and amplitude of individual slow waves. Local ZIP injection did not significantly alter the amount of time spent in each behavioral state, locomotor activity, or EEG/LFP power during waking or REM sleep. Thus, local ZIP injection selectively produced a local reduction in sleep need; synaptic strength, therefore, may play a causal role in generating local homeostatic sleep need within the cortex.

Disruption of Rapid Eye Movement Sleep Homeostasis in Adolescent Rats after Neonatal Anesthesia

BACKGROUND

Previous studies suggest that rapid eye movement sleep rebound and disruption of rapid eye movement sleep architecture occur during the first 24 h after general anesthesia with volatile anesthetics in adult rats. However, it is unknown whether rapid eye movement sleep alterations persist beyond the anesthetic recovery phase in neonatal rats. This study tested the hypothesis that rapid eye movement sleep disturbances would be present in adolescent rats treated with anesthesia on postnatal day 7.

METHODS

Forty-four neonatal rats were randomly allocated to treatment with anesthesia consisting of midazolam, nitrous oxide, and isoflurane or control conditions for 2 h or 6 h. Electroencephalographic and electromyographic electrodes were implanted and recordings obtained between postnatal days 26 and 34. The primary outcome was time spent in rapid eye movement sleep. Data were analyzed using two-tailed unpaired t tests and two-way repeated measures analysis of variance.

RESULTS

Rats treated with midazolam, nitrous oxide, and isoflurane exhibited a significant increase in rapid eye movement sleep three weeks later when compared with control rats, regardless of whether they were treated for 2 h (174.0 ± 7.2 min in anesthetized, 108.6 ± 5.3 in controls, P < 0.0001) or 6 h (151.6 ± 9.9 min in anesthetized, 108.8 ± 7.1 in controls, P = 0.002).

CONCLUSIONS

Treatment with midazolam, nitrous oxide, and isoflurane on postnatal day 7 increases rapid eye movement sleep three weeks later in rats.

Glymphatic System Function in Relation to Anesthesia and Sleep States

The brain is one of the most metabolically active organs in the body. The brain's high energy demand associated with wakefulness persists during rapid eye movement sleep, and even during non-rapid eye movement sleep, cerebral oxygen consumption is only reduced by 20%. The active bioenergetic state parallels metabolic waste production at a higher rate than in other organs, and the lack of lymphatic vasculature in brain parenchyma is therefore a conundrum. A common assumption has been that with a tight blood-brain barrier restricting solute and fluid movements, a lymphatic system is superfluous in the central nervous system. Cerebrospinal fluid (CSF) flow has long been thought to facilitate central nervous system tissue "detoxification" in place of lymphatics. Nonetheless, while CSF production and transport have been studied for decades, the exact processes involved in toxic waste clearance remain poorly understood. Over the past 5 years, emerging data have begun to shed new light on these processes in the form of the "glymphatic system," a novel brain-wide perivascular transit passageway dedicated to CSF transport and metabolic waste drainage from the brain. Here, we review the key anatomical components and operational drivers of the brain's glymphatic system, with a focus on its unique functional dependence on the state of arousal and anesthetic regimens. We also discuss evidence for why clinical exploration of this novel system may in the future provide valuable insight into new strategies for preventing delirium and cognitive dysfunction in perioperative and critical care settings.

Alpha rhythm collapse predicts iso-electric suppressions during anesthesia

Could an overly deep sedation be anticipated from ElectroEncephaloGram (EEG) patterns? We report here motifs hidden in the EEG signal that predict the appearance of Iso-Electric Suppressions (IES), observed during epileptic encephalopathies, drug intoxications, comatose, brain death or during anesthetic over-dosage that are considered to be detrimental. To show that IES occurrences can be predicted from EEG traces dynamics, we focus on transient suppression of the alpha rhythm (8-14 Hz) recorded for 80 patients, that had a Propofol target controlled infusion of 5 μg/ml during a general anesthesia. We found that the first time of appearance as well as changes in duration of these Alpha-Suppressions (αS) are two parameters that anticipate the appearance of IES. Using machine learning, we predicted IES appearance from the first 10 min of EEG (AUC of 0.93). To conclude, transient motifs in the alpha rhythm predict IES during anesthesia and can be used to identify patients, with higher risks of post-operative complications.

Bird-like propagating brain activity in anesthetized Nile crocodiles

Study Objectives

The changes in electroencephalogram (EEG) activity that characterize sleep and its sub-states-slow-wave sleep (SWS) and rapid eye movement (REM) sleep-are similar in mammals and birds. SWS is characterized by EEG slow waves resulting from the synchronous alternation of neuronal membrane potentials between hyperpolarized down-states with neuronal quiescence and depolarized up-states associated with action potentials. By contrast, studies of non-avian reptiles report the presence of high-voltage sharp waves (HShW) during sleep. How HShW relate to EEG phenomena occurring during mammalian and avian sleep is unclear. We investigated the spatiotemporal patterns of electrophysiological phenomena in Nile crocodiles (Crocodylus niloticus) anesthetized with isoflurane to determine whether they share similar spatiotemporal patterns to mammalian and avian slow waves.

Methods

Recordings of anesthetized crocodiles were made using 64-channel penetrating arrays with electrodes arranged in an 8 × 8 equally spaced grid. The arrays were placed in the dorsal ventricular ridge (DVR), a region implicated in the genesis of HShW. Various aspects of the spatiotemporal distribution of recorded signals were investigated.

Results

Recorded signals revealed the presence of HShW resembling those reported in earlier studies of naturally sleeping reptiles. HShW propagated in complex and variable patterns across the DVR.

Conclusions

We demonstrate that HShW within the DVR propagate in complex patterns similar to those observed for avian slow waves recorded from homologous brain regions. Consequently, sleep with HShW may represent an ancestral form of SWS, characterized by up-states occurring less often and for a shorter duration than in mammals and birds.

Optogenetic reactivation of memory ensembles in the retrosplenial cortex induces systems consolidation

The neural circuits underlying memory change over prolonged periods after learning, in a process known as systems consolidation. Postlearning spontaneous reactivation of memory-related neural ensembles is thought to mediate this process, although a causal link has not been established. Here we test this hypothesis in mice by using optogenetics to selectively reactivate neural ensembles representing a contextual fear memory (sometimes referred to as engram neurons). High-frequency stimulation of these ensembles in the retrosplenial cortex 1 day after learning produced a recent memory with features normally observed in consolidated remote memories, including higher engagement of neocortical areas during retrieval, contextual generalization, and decreased hippocampal dependence. Moreover, this effect was only present if memory ensembles were reactivated during sleep or light anesthesia. These results provide direct support for postlearning memory ensemble reactivation as a mechanism of systems consolidation, and show that this process can be accelerated by ensemble reactivation in an unconscious state.

Spectral Properties of Brain Activity Under Two Anesthetics and Their Potential for Inducing Natural Sleep in Birds

Both mammals and birds exhibit two sleep states, slow wave sleep (SWS) and rapid eye movement (REM) sleep. Studying certain aspects of sleep-related electrophysiology in freely behaving animals can present numerous methodological constraints, particularly when even fine body movements interfere with electrophysiological signals. Interestingly, under light general anesthesia, mammals and birds also exhibit slow waves similar to those observed during natural SWS. For these reasons, slow waves occurring under general anesthesia are commonly used in the investigation of sleep-related neurophysiology. However, how spectral properties of slow waves induced by anesthesia correspond to those occurring during natural SWS in birds has yet to be investigated systematically. In this study, we systematically analyzed spectral properties of electroencephalographic (EEG) patterns of pigeons (Columba livia) occurring under two commonly used anesthetics, isoflurane and urethane. These data were compared with EEG patterns during natural sleep. Slow waves occurring during spontaneous SWS, and those induced with isoflurane and urethane all showed greatest absolute power in the slowest frequencies (<3 Hz). Isoflurane and urethane-induced slow waves had near-identical power spectra, and both had higher mean power than that observed during SWS for all frequencies examined (0–25 Hz). Interestingly, burst suppression EEG activity observed under deeper planes of isoflurane anesthesia could occur bihemispherically or unihemispherically. Electrophysiological patterns while under isoflurane and urethane share phenomenological and spectral similarities to those occurring during SWS, notably the generation of high amplitude, slow waves, and peak low-frequency power. These results build upon other studies which suggest that some anesthetics exert their effects by acting on natural sleep pathways. As such, anesthesia-induced slow waves appear to provide an acceptable model for researchers interested in investigating sleep-related slow waves utilizing electrophysiological methods not suitable for use in freely behaving birds.

Melatonin in Critically Ill Children

Melatonin, while best known for its chronobiologic functions, has multiple effects that may be relevant in critical illness. It has been used for circadian rhythm maintenance, analgesia, and sedation, and has antihypertensive, anti-inflammatory, antioxidant, antiapoptotic, and antiexcitatory effects. This review examines melatonin physiology in health, the current state of knowledge regarding endogenous melatonin production in pediatric critical illness, and the potential uses of exogenous melatonin in this population, including relevant information from basic sciences and other fields of medicine. Pineal melatonin production and secretion appears to be altered in critical illness, though understanding in pediatric critical illness is in early stages, with only 102 children reported in the current literature. Exogenous melatonin may be used for circadian rhythm disturbances and, within the critically ill population, holds promise for diseases involving oxidant stress. There are no studies of exogenous melatonin administration to critically ill children beyond the neonatal period.

Melatonin and melatonin agonists to prevent and treat delirium in critical illness: a systematic review protocol

BACKGROUND

Delirium is a syndrome characterized by acute fluctuations and alterations in attention and arousal. Critically ill patients are at particularly high risk, and those that develop delirium are more likely to experience poor clinical outcomes such as prolonged duration of ICU and hospital length of stay, and increased mortality. Melatonin and melatonin agonists (MMA) have the potential to decrease the incidence and severity of delirium through their hypnotic and sedative-sparing effects, thus improving health-related outcomes. The objective of this review is to synthesize the available evidence pertaining to the efficacy and safety of MMA for the prevention and treatment of ICU delirium.

METHODS

We will search Ovid MEDLINE, Web of Science, EMBASE, PsycINFO, the Cochrane Central Register of Controlled Trials (CENTRAL), and CINAHL to identify studies evaluating MMA in critically ill populations. We will also search http://apps.who.int/trialsearch for ongoing and unpublished studies and PROSPERO for registered reviews. We will not impose restrictions on language, date, or journal of publication. Authors will independently screen for eligible studies using pre-defined criteria; data extraction from eligible studies will be performed in duplicate. The Cochrane Risk of Bias Scale and the Newcastle-Ottawa Scale will be used to assess the risk of bias and quality of randomized and non-randomized studies, respectively. Our primary outcome of interest is delirium incidence, and secondary outcomes include duration of delirium, number of delirium- and coma-free days, use of physical and chemical (e.g., antipsychotics or benzodiazepines) restraints, duration of mechanical ventilation, ICU and hospital length of stay, mortality, long-term neurocognitive outcomes, hospital discharge disposition, and adverse events. We will use Review Manager (RevMan) to pool effect estimates from included studies. We will present results as relative risks with 95% confidence intervals for dichotomous outcomes and as mean differences, or standardized mean differences, for continuous outcomes.

DISCUSSION

Current guidelines make no pharmacological recommendations for either the prevention or treatment of ICU delirium. This systematic review will synthesize the available evidence on the efficacy and safety of MMA for this purpose, thus potentially informing clinical decision-making and improving patient outcomes.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42015024713.

Sleep Homeostasis and General Anesthesia: Are Fruit Flies Well Rested after Emergence from Propofol?

BACKGROUND

Shared neurophysiologic features between sleep and anesthetic-induced hypnosis indicate a potential overlap in neuronal circuitry underlying both states. Previous studies in rodents indicate that preexisting sleep debt discharges under propofol anesthesia. The authors explored the hypothesis that propofol anesthesia also dispels sleep pressure in the fruit fly. To the authors' knowledge, this constitutes the first time propofol has been tested in the genetically tractable model, Drosophila melanogaster.

METHODS

Daily sleep was measured in Drosophila by using a standard locomotor activity assay. Propofol was administered by transferring flies onto food containing various doses of propofol or equivalent concentrations of vehicle. High-performance liquid chromatography was used to measure the tissue concentrations of ingested propofol. To determine whether propofol anesthesia substitutes for natural sleep, the flies were subjected to 10-h sleep deprivation (SD), followed by 6-h propofol exposure, and monitored for subsequent sleep.

RESULTS

Oral propofol treatment causes anesthesia in flies as indicated by a dose-dependent reduction in locomotor activity (n = 11 to 41 flies from each group) and increased arousal threshold (n = 79 to 137). Recovery sleep in flies fed propofol after SD was delayed until after flies had emerged from anesthesia (n = 30 to 48). SD was also associated with a significant increase in mortality in propofol-fed flies (n = 44 to 46).

CONCLUSIONS

Together, these data indicate that fruit flies are effectively anesthetized by ingestion of propofol and suggest that homologous molecular and neuronal targets of propofol are conserved in Drosophila. However, behavioral measurements indicate that propofol anesthesia does not satisfy the homeostatic need for sleep and may compromise the restorative properties of sleep.

Qualitative and Quantitative Characteristics of the Electroencephalogram in Normal Horses during Administration of Inhaled Anesthesia

BACKGROUND

The effects of anesthesia on the equine electroencephalogram (EEG) after administration of various drugs for sedation, induction, and maintenance are known, but not that the effect of inhaled anesthetics alone for EEG recording.

OBJECTIVE

To determine the effects of isoflurane and halothane, administered as single agents at multiple levels, on the EEG and quantitative EEG (qEEG) of normal horses.

ANIMALS

Six healthy horses.

METHODS

Prospective study. Digital EEG with video and quantitative EEG (qEEG) were recorded after the administration of one of the 2 anesthetics, isoflurane or halothane, at 3 alveolar doses (1.2, 1.4 and 1.6 MAC). Segments of EEG during controlled ventilation (CV), spontaneous ventilation (SV), and with peroneal nerve stimulation (ST) at each MAC multiple for each anesthetic were selected, analyzed, and compared. Multiple non-EEG measurements were also recorded.

RESULTS

Specific raw EEG findings were indicative of changes in the depth of anesthesia. However, there was considerable variability in EEG between horses at identical MAC multiples/conditions and within individual horses over segments of a given epoch. Statistical significance for qEEG variables differed between anesthetics with bispectral index (BIS) CV MAC and 95% spectral edge frequency (SEF95) SV MAC differences in isoflurane only and median frequency (MED) differences in SV MAC with halothane only.

CONCLUSIONS AND CLINICAL IMPORTANCE

Unprocessed EEG features (background and transients) appear to be beneficial for monitoring the depth of a particular anesthetic, but offer little advantage over the use of changes in mean arterial pressure for this purpose.

Impact of traumatic brain injury on sleep structure, electrocorticographic activity and transcriptome in mice

Traumatic brain injury (TBI), including mild TBI (mTBI), is importantly associated with vigilance and sleep complaints. Because sleep is required for learning, plasticity and recovery, we here evaluated the bidirectional relationship between mTBI and sleep with two specific objectives: (1) Test that mTBI rapidly impairs sleep-wake architecture and the dynamics of the electrophysiological marker of sleep homeostasis (i.e., non-rapid eye movement sleep delta (1-4Hz) activity); (2) evaluate the impact of sleep loss following mTBI on the expression of plasticity markers that have been linked to sleep homeostasis and on genome-wide gene expression. A closed-head injury model was used to perform a 48h electrocorticographic (ECoG) recording in mice submitted to mTBI or Sham surgery. mTBI was found to immediately decrease the capacity to sustain long bouts of wakefulness as well as the amplitude of the time course of ECoG delta activity during wakefulness. Significant changes in ECoG spectral activity during wakefulness, non-rapid eye movement and rapid eye movement sleep were observed mainly on the second recorded day. A second experiment was performed to measure gene expression in the cerebral cortex and hippocampus after a mTBI followed either by two consecutive days of 6h sleep deprivation (SD) or of undisturbed behavior (quantitative PCR and next-generation sequencing). mTBI modified the expression of genes involved in immunity, inflammation and glial function (e.g., chemokines, glial markers) and SD changed that of genes linked to circadian rhythms, synaptic activity/neuronal plasticity, neuroprotection and cell death and survival. SD appeared to affect gene expression in the cerebral cortex more importantly after mTBI than Sham surgery including that of the astrocytic marker Gfap, which was proposed as a marker of clinical outcome after TBI. Interestingly, SD impacted the hippocampal expression of the plasticity elements Arc and EfnA3 only after mTBI. Overall, our findings reveal alterations in spectral signature across all vigilance states in the first days after mTBI, and show that sleep loss post-mTBI reprograms the transcriptome in a brain area-specific manner and in a way that could be deleterious to brain recovery.

Cortical neuronal activity does not regulate sleep homeostasis

The neural substrate of sleep homeostasis is unclear, but both cortical and subcortical structures are thought to be involved in sleep regulation. To test whether prior neuronal activity in the cortex or in subcortical regions drives sleep rebound, we systemically administered atropine (100mg/kg) to rats, producing a dissociated state with slow-wave cortical electroencephalogram (EEG) but waking behavior (e.g. locomotion). Atropine injections during the light period produced 6h of slow-wave cortical EEG but also subcortical arousal. Afterward, rats showed a significant increase in non-rapid eye movement (NREM) sleep, compared to the same period on a baseline day. Consistent with the behavioral and cortical EEG state produced by systemic atropine, c-Fos expression was low in the cortex but high in multiple subcortical arousal systems. These data suggest that subcortical arousal and behavior are sufficient to drive sleep homeostasis, while a sleep-like pattern of cortical activity is not sufficient to satisfy sleep homeostasis.

Learning-related brain hemispheric dominance in sleeping songbirds

There are striking behavioural and neural parallels between the acquisition of speech in humans and song learning in songbirds. In humans, language-related brain activation is mostly lateralised to the left hemisphere. During language acquisition in humans, brain hemispheric lateralisation develops as language proficiency increases. Sleep is important for the formation of long-term memory, in humans as well as in other animals, including songbirds. Here, we measured neuronal activation (as the expression pattern of the immediate early gene ZENK) during sleep in juvenile zebra finch males that were still learning their songs from a tutor. We found that during sleep, there was learning-dependent lateralisation of spontaneous neuronal activation in the caudomedial nidopallium (NCM), a secondary auditory brain region that is involved in tutor song memory, while there was right hemisphere dominance of neuronal activation in HVC (used as a proper name), a premotor nucleus that is involved in song production and sensorimotor learning. Specifically, in the NCM, birds that imitated their tutors well were left dominant, while poor imitators were right dominant, similar to language-proficiency related lateralisation in humans. Given the avian-human parallels, lateralised neural activation during sleep may also be important for speech and language acquisition in human infants.

Sleep, recovery, and metaregulation: explaining the benefits of sleep

A commonly held view is that extended wakefulness is causal for a broad spectrum of deleterious effects at molecular, cellular, network, physiological, psychological, and behavioral levels. Consequently, it is often presumed that sleep plays an active role in providing renormalization of the changes incurred during preceding waking. Not surprisingly, unequivocal empirical evidence supporting such a simple bi-directional interaction between waking and sleep is often limited or controversial. One difficulty is that, invariably, a constellation of many intricately interrelated factors, including the time of day, specific activities or behaviors during preceding waking, metabolic status and stress are present at the time of measurement, shaping the overall effect observed. In addition to this, although insufficient or disrupted sleep is thought to prevent efficient recovery of specific physiological variables, it is also often difficult to attribute specific changes to the lack of sleep proper. Furthermore, sleep is a complex phenomenon characterized by a multitude of processes, whose unique and distinct contributions to the purported functions of sleep are difficult to determine, because they are interrelated. Intensive research effort over the last decades has greatly progressed current understanding of the cellular and physiological processes underlying the regulation of vigilance states. Notably, it also highlighted the infinite complexity within both waking and sleep, and revealed a number of fundamental conceptual and technical obstacles that need to be overcome in order to fully understand these processes. A promising approach could be to view sleep not as an entity, which has specific function(s) and is subject to direct regulation, but as a manifestation of the process of metaregulation, which enables efficient moment-to-moment integration between internal and external factors, preceding history and current homeostatic needs.

Distinctive recruitment of endogenous sleep-promoting neurons by volatile anesthetics and a nonimmobilizer

BACKGROUND

Numerous studies demonstrate that anesthetic-induced unconsciousness is accompanied by activation of hypothalamic sleep-promoting neurons, which occurs through both pre- and postsynaptic mechanisms. However, the correlation between drug exposure, neuronal activation, and onset of hypnosis remains incompletely understood. Moreover, the degree to which anesthetics activate both endogenous populations of γ-aminobutyric acid (GABA)ergic sleep-promoting neurons within the ventrolateral preoptic (VLPO) and median preoptic nuclei remains unknown.

METHODS

Mice were exposed to oxygen, hypnotic doses of isoflurane or halothane, or 1,2-dichlorohexafluorocyclobutane (F6), a nonimmobilizer. Hypothalamic brain slices prepared from anesthetic-naive mice were also exposed to oxygen, volatile anesthetics, or F6 ex vivo, both in the presence and absence of tetrodotoxin. Double-label immunohistochemistry was performed to quantify the number of c-Fos-immunoreactive nuclei in the GABAergic subpopulation of neurons in the VLPO and the median preoptic areas to test the hypothesis that volatile anesthetics, but not nonimmobilizers, activate sleep-promoting neurons in both nuclei.

RESULTS

In vivo exposure to isoflurane and halothane doubled the fraction of active, c-Fos-expressing GABAergic neurons in the VLPO, whereas F6 failed to affect VLPO c-Fos expression. Both in the presence and absence of tetrodotoxin, isoflurane dose-dependently increased c-Fos expression in GABAergic neurons ex vivo, whereas F6 failed to alter expression. In GABAergic neurons of the median preoptic area, c-Fos expression increased with isoflurane and F6, but not with halothane exposure.

CONCLUSIONS

Anesthetic unconsciousness is not accompanied by global activation of all putative sleep-promoting neurons. However, within the VLPO hypnotic doses of volatile anesthetics, but not nonimmobilizers, activate putative sleep-promoting neurons, correlating with the appearance of the hypnotic state.

Plumes of neuronal activity propagate in three dimensions through the nuclear avian brain

BACKGROUND

In mammals, the slow-oscillations of neuronal membrane potentials (reflected in the electroencephalogram as high-amplitude, slow-waves), which occur during non-rapid eye movement sleep and anesthesia, propagate across the neocortex largely as two-dimensional traveling waves. However, it remains unknown if the traveling nature of slow-waves is unique to the laminar cytoarchitecture and associated computational properties of the neocortex.

RESULTS

We demonstrate that local field potential slow-waves and correlated multiunit activity propagate as complex three-dimensional plumes of neuronal activity through the avian brain, owing to its non-laminar, nuclear neuronal cytoarchitecture.

CONCLUSIONS

The traveling nature of slow-waves is not dependent upon the laminar organization of the neocortex, and is unlikely to subserve functions unique to this pattern of neuronal organization. Finally, the three-dimensional geometry of propagating plumes may reflect computational properties not found in mammals that contributed to the evolution of nuclear neuronal organization and complex cognition in birds.

Burst suppression in sleep in a routine outpatient EEG

Burst suppression (BS) is an electroencephalogram (EEG) pattern that is characterized by brief bursts of spikes, sharp waves, or slow waves of relatively high amplitude alternating with periods of relatively flat EEG or isoelectric periods. The pattern is usually associated with coma, severe encephalopathy of various etiologies, or general anesthesia. We describe an unusual case of anoxic brain injury in which a BS pattern was seen during behaviorally defined sleep during a routine outpatient EEG study.

Explaining general anesthesia: a two-step hypothesis linking sleep circuits and the synaptic release machinery

Several general anesthetics produce their sedative effect by activating endogenous sleep pathways. We propose that general anesthesia is a two-step process targeting sleep circuits at low doses, and synaptic release mechanisms across the entire brain at the higher doses required for surgery. Our hypothesis synthesizes data from a variety of model systems, some which require sleep (e.g. rodents and adult flies) and others that probably do not sleep (e.g. adult nematodes and cultured cell lines). Non-sleeping systems can be made insensitive (or hypersensitive) to some anesthetics by modifying a single pre-synaptic protein, syntaxin1A. This suggests that the synaptic release machinery, centered on the highly conserved SNARE complex, is an important target of general anesthetics in all animals. A careful consideration of SNARE architecture uncovers a potential mechanism for general anesthesia, which may be the primary target in animals that do not sleep, but a secondary target in animals that sleep.

Sleep and the single neuron: the role of global slow oscillations in individual cell rest

Sleep is universal in animals, but its specific functions remain elusive. We propose that sleep's primary function is to allow individual neurons to perform prophylactic cellular maintenance. Just as muscle cells must rest after strenuous exercise to prevent long-term damage, brain cells must rest after intense synaptic activity. We suggest that periods of reduced synaptic input ('off periods' or 'down states') are necessary for such maintenance. This in turn requires a state of globally synchronized neuronal activity, reduced sensory input and behavioural immobility - the well-known manifestations of sleep.

A novel telemetric system to measure polysomnographic biopotentials in freely moving animals

Mice are by far the most widely used species for scientific research and have been used in many studies involving biopotentials, such as the electroencephalogram (EEG) and electromyogram (EMG) signals monitored for sleep analysis. Unfortunately, current methods for the analysis of these signals involve either tethered systems that are restrictive and heavy for the animal or wireless systems that use transponders that are large relative to the animal and require invasive surgery for implantation; as a result, natural behavior/activity is altered. Here, we propose a novel and inexpensive system for measuring electroencephalographic signals and other biopotentials in mice that allows for natural movement. We also evaluate the new system for the analysis of sleep architecture and EEG power during both spontaneous sleep and the sleep that follows sleep deprivation in mice. Using our new system, vigilance states including non-rapid eye movement sleep (NREMS), rapid eye movement sleep (REMS), and wakefulness, as well as EEG power and NREMS EEG delta power in the 0.5-4 Hz range (an indicator of sleep intensity) showed the diurnal rhythms typically found in mice. These values were also similar to values obtained in mice using telemetry transponders. Mice that used the new system also demonstrated enhanced NREMS EEG delta power responses that are typical following sleep deprivation and few signal artifacts. Moreover, similar movement activity counts were found when using the new system compared to a wireless system. This novel system for measuring biopotentials can be used for polysomnography, infusion, microdialysis, and optogenetic studies, reduces artifacts, and allows for a more natural moving environment and a more accurate investigation of biological systems and pharmaceutical development.

Neurologic Implications of Critical Illness and Organ Dysfunction

Critical illness has consequences for the nervous system. Patients experiencing critical illness are at risk for common global neurologic disturbances, such as delirium, long-term cognitive dysfunction, ICU-acquired weakness, sleep disturbances, recurrent seizures, and coma. In addition, complications related to specific organ dysfunction may be anticipated. Cardiovascular disease presents the possibility for CNS injury after cardiac arrest, sequelae of endocarditis, aberrancies of blood flow autoregulation, and malperfusion. Respiratory disease is known to cause short-term effects of hypoxia and long-term effects after ARDS. Sepsis encephalopathy and sickness behavior syndrome are early signs of infection in patients. In addition, commonly encountered organ dysfunction including uremia, hepatic failure, endocrine, and metabolic disturbances present with neurologic findings which may manifest in the critically ill patient as well.

Sleep and Anesthesia Interactions: A Pharmacological Appraisal

Anesthetics have been used in clinical practice for over a hundred years, yet their mechanisms of action remain poorly understood. One tempting hypothesis to explain their hypnotic properties posits that anesthetics exert a component of their effects by "hijacking" the endogenous arousal circuitry of the brain. Modulation of activity within sleep- and wake-related neuroanatomic systems could thus explain some of the varied effects produced by anesthetics. There has been a recent explosion of research into the neuroanatomic substrates affected by various anesthetics. In this review, we will highlight the relevant sleep architecture and systems and focus on studies over the past few years that implicate these sleep-related structures as targets of anesthetics. These studies highlight a promising area of investigation regarding the mechanisms of action of anesthetics and provide an important model for future study.

Temporal disorganization of circadian rhythmicity and sleep-wake regulation in mechanically ventilated patients receiving continuous intravenous sedation

OBJECTIVES

Sleep is regulated by circadian and homeostatic processes and is highly organized temporally. Our study was designed to determine whether this organization is preserved in patients receiving mechanical ventilation (MV) and intravenous sedation.

DESIGN

Observational study.

SETTING

Academic medical intensive care unit.

PATIENTS

Critically ill patients receiving MV and intravenous sedation.

METHODS

Continuous polysomnography (PSG) was initiated an average of 2.0 (1.0, 3.0) days after ICU admission and continued ≥ 36 h or until the patient was extubated. Sleep staging and power spectral analysis were performed using standard approaches. We also calculated the electroencephalography spectral edge frequency 95% SEF₉₅, a parameter that is normally higher during wakefulness than during sleep. Circadian rhythmicity was assessed in 16 subjects through the measurement of aMT6s in urine samples collected hourly for 24-48 hours. Light intensity at the head of the bed was measured continuously.

MEASUREMENTS AND RESULTS

We analyzed 819.7 h of PSG recordings from 21 subjects. REM sleep was identified in only 2/21 subjects. Slow wave activity lacked the normal diurnal and ultradian periodicity and homeostatic decline found in healthy adults. In nearly all patients, SEF₉₅ was consistently low without evidence of diurnal rhythmicity (median 6.3 [5.3, 7.8] Hz, n = 18). A circadian rhythm of aMT6s excretion was present in most (13/16, 81.3%) patients, but only 4 subjects had normal timing. Comparison of the SEF₉₅ during the melatonin-based biological night and day revealed no difference between the 2 periods (P = 0.64).

CONCLUSIONS

The circadian rhythms and PSG of patients receiving mechanical ventilation and intravenous sedation exhibit pronounced temporal disorganization. The finding that most subjects exhibited preserved, but phase delayed, excretion of aMT6s suggests that the circadian pacemaker of such patients may be free-running.

Interfaces of sleep and anesthesia

In the past decades there has been an increasing focus on the relationship of sleep and anesthesia. This relationship bears on the fundamental scientific questions in anesthesiology, such as the mechanism of anesthetic-induced unconsciousness. However, given the increasing prevalence of sleep disorders in surgical patients, the interfaces of sleep and anesthesia are now a pressing clinical concern. This article discusses sleep and anesthesia from the perspective of phenotype, mechanism and function, with some concluding thoughts on the relevance to neuroanesthesiology.

Rapid eye movement sleep debt accrues in mice exposed to volatile anesthetics

BACKGROUND

General anesthesia has been likened to a state in which anesthetized subjects are locked out of access to both rapid eye movement (REM) sleep and wakefulness. Were this true for all anesthetics, a significant REM rebound after anesthetic exposure might be expected. However, for the intravenous anesthetic propofol, studies demonstrate that no sleep debt accrues. Moreover, preexisting sleep debts dissipate during propofol anesthesia. To determine whether these effects are specific to propofol or are typical of volatile anesthetics, the authors tested the hypothesis that REM sleep debt would accrue in rodents anesthetized with volatile anesthetics.

METHODS

Electroencephalographic and electromyographic electrodes were implanted in 10 mice. After 9-11 days of recovery and habituation to a 12 h:12 h light-dark cycle, baseline states of wakefulness, nonrapid eye movement sleep, and REM sleep were recorded in mice exposed to 6 h of an oxygen control and on separate days to 6 h of isoflurane, sevoflurane, or halothane in oxygen. All exposures were conducted at the onset of light.

RESULTS

Mice in all three anesthetized groups exhibited a significant doubling of REM sleep during the first 6 h of the dark phase of the circadian schedule, whereas only mice exposed to halothane displayed a significant increase in nonrapid eye movement sleep that peaked at 152% of baseline.

CONCLUSION

REM sleep rebound after exposure to volatile anesthetics suggests that these volatile anesthetics do not fully substitute for natural sleep. This result contrasts with the published actions of propofol for which no REM sleep rebound occurred.

Delta oscillations induced by ketamine increase energy levels in sleep-wake related brain regions

Neuronal signaling consumes much of the brain energy, mainly through the restoration of the membrane potential (MP) by ATP-consuming ionic pumps. We have reported that, compared with waking, ATP levels increase during the initial hours of natural slow-wave sleep, a time with prominent electroencephalogram (EEG) delta oscillations (0.5-4.5 Hz). We have hypothesized that there is a delta oscillation-ATP increase coupling, since, during delta waves, neurons exhibit a prolonged hyperpolarizing phase followed by a very brief phase of action potentials. However, direct proof of this hypothesis is lacking, and rapid changes in EEG/neuronal activity preclude measurement in the naturally sleeping brain. Thus, to induce a uniform state with pure delta oscillations and one previously shown to be accompanied by a similar pattern of neuronal activity during delta waves as natural sleep, we used ketamine-xylazine treatment in rats. We here report that, with this treatment, the high-energy molecules ATP and ADP increased in frontal and cingulate cortices, basal forebrain, and hippocampus compared with spontaneous waking. Moreover, the degree of ATP increase positively and significantly correlated with the degree of EEG delta activity. Supporting the hypothesis of decreased ATP consumption during delta activity, the ATP-consuming Na+-K+-ATPase mRNA levels were significantly decreased, whereas the mRNAs for the ATP-producing cytochrome c oxidase (COX) subunits COX III and COX IVa were unchanged. Taken together, these data support the hypothesis of a cortical delta oscillation-dependent reduction in ATP consumption, thus providing the brain with increased ATP availability, and likely occurring because of reduced Na+-K+-ATPase-related energy consumption.