Correlating in vivo anaesthetic effects with ex vivo receptor density data supports a GABAergic mechanism of action for propofol, but not for isoflurane

Serotonin and Consciousness-A Reappraisal

The serotonergic system of the brain is a major modulator of behaviour. Here we describe a re-appraisal of its function for consciousness based on anatomical, functional and pharmacological data. For a better understanding, the current model of consciousness is expanded. Two parallel streams of conscious flow are distinguished. A flow of conscious content and an affective consciousness flow. While conscious content flow has its functional equivalent in the activity of higher cortico-cortical and cortico-thalamic networks, affective conscious flow originates in segregated deeper brain structures for single emotions. It is hypothesized that single emotional networks converge on serotonergic and other modulatory transmitter neurons in the brainstem where a bound percept of an affective conscious flow is formed. This is then dispersed to cortical and thalamic networks, where it is time locked with conscious content flow at the level of these networks. Serotonin acts in concert with other modulatory systems of the brain stem with some possible specialization on single emotions. Together, these systems signal a bound percept of affective conscious flow. Dysfunctions in the serotonergic system may not only give rise to behavioural and somatic symptoms, but also essentially affect the coupling of conscious affective flow with conscious content flow, leading to the affect-stained subjective side of mental disorders like anxiety, depression, or schizophrenia. The present model is an attempt to integrate the growing insights into serotonergic system function. However, it is acknowledged, that several key claims are still at a heuristic level that need further empirical support.

Cerebrospinal fluid metabolic profiling reveals divergent modulation of pentose phosphate pathway by midazolam, propofol and dexmedetomidine in patients with subarachnoid hemorrhage: a cohort study

BACKGROUND

Agitation is common in subarachnoid hemorrhage (SAH), and sedation with midazolam, propofol and dexmedetomidine is essential in agitation management. Previous research shows the tendency of dexmedetomidine and propofol in improving long-term outcome of SAH patients, whereas midazolam might be detrimental. Brain metabolism derangement after SAH might be interfered by sedatives. However, how sedatives work and whether the drugs interfere with patient outcome by altering cerebral metabolism is unclear, and the comprehensive view of how sedatives regulate brain metabolism remains to be elucidated.

METHODS

For cerebrospinal fluid (CSF) and extracellular space of the brain exchange instantly, we performed a cohort study, applying CSF of SAH patients utilizing different sedatives or no sedation to metabolomics. Baseline CSF metabolome was corrected by selecting patients of the same SAH and agitation severity. CSF components were analyzed to identify the most affected metabolic pathways and sensitive biomarkers of each sedative. Markers might represent the outcome of the patients were also investigated.

RESULTS

Pentose phosphate pathway was the most significantly interfered (upregulated) pathway in midazolam (p = 0.0000107, impact = 0.35348) and propofol (p = 0.00000000000746, impact = 0.41604) groups. On the contrary, dexmedetomidine decreased levels of sedoheptulose 7-phosphate (p = 0.002) and NADP (p = 0.024), and NADP is the key metabolite and regulator in pentose phosphate pathway. Midazolam additionally augmented purine synthesis (p = 0.00175, impact = 0.13481) and propofol enhanced pyrimidine synthesis (p = 0.000203, impact = 0.20046), whereas dexmedetomidine weakened pyrimidine synthesis (p = 0.000000000594, impact = 0.24922). Reduced guanosine diphosphate (AUC of ROC 0.857, 95%CI 0.617-1, p = 0.00506) was the significant CSF biomarker for midazolam, and uridine diphosphate glucose (AUC of ROC 0.877, 95%CI 0.631-1, p = 0.00980) for propofol, and succinyl-CoA (AUC of ROC 0.923, 95%CI 0.785-1, p = 0.000810) plus adenosine triphosphate (AUC of ROC 0.908, 95%CI 0.6921, p = 0.00315) for dexmedetomidine. Down-regulated CSF succinyl-CoA was also associated with favorable outcome (AUC of ROC 0.708, 95% CI: 0.524-0.865, p = 0.029333).

CONCLUSION

Pentose phosphate pathway was a crucial target for sedatives which alter brain metabolism. Midazolam and propofol enhanced the pentose phosphate pathway and nucleotide synthesis in poor-grade SAH patients, as presented in the CSF. The situation of dexmedetomidine was the opposite. The divergent modulation of cerebral metabolism might further explain sedative pharmacology and how sedatives affect the outcome of SAH patients.

A comparison of GABA-ergic (propofol) and non-GABA-ergic (dexmedetomidine) sedation on visual and motor cortical oscillations, using magnetoencephalography

Studying changes in cortical oscillations can help elucidate the mechanistic link between receptor physiology and the clinical effects of anaesthetic drugs. Propofol, a GABA-ergic drug produces divergent effects on visual cortical activity: increasing induced gamma-band responses (GBR) while decreasing evoked responses. Dexmedetomidine, an α2- adrenergic agonist, differs from GABA-ergic sedatives both mechanistically and clinically as it allows easy arousability from deep sedation with less cognitive side-effects. Here we use magnetoencephalography (MEG) to characterize and compare the effects of GABA-ergic (propofol) and non-GABA-ergic (dexmedetomidine) sedation, on visual and motor cortical oscillations. Sixteen male participants received target-controlled infusions of propofol and dexmedetomidine, producing mild-sedation, in a placebo-controlled, cross-over study. MEG data was collected during a combined visuomotor task. The key findings were that propofol significantly enhanced visual stimulus induced GBR (44% increase in amplitude) while dexmedetomidine decreased it (40%). Propofol also decreased the amplitudes of the Mv100 (visual M100) (27%) and Mv150 (52%) visual evoked fields (VEF), whilst dexmedetomidine had no effect on these. During the motor task, neither drug had any significant effect on movement related gamma synchrony (MRGS), movement related beta de-synchronisation (MRBD) or Mm100 (movement-related M100) movement-related evoked fields (MEF), although dexmedetomidine slowed the Mm300. Dexmedetomidine increased (92%) post-movement beta synchronisation/rebound (PMBR) power while propofol reduced it (70%, statistically non- significant). Overall, dexmedetomidine and propofol, at equi-sedative doses, produce contrasting effects on visual induced GBR, VEF, PMBR and MEF. These findings provide a mechanistic link between the known receptor physiology of these sedative drugs with their known clinical effects and may be used to explore mechanisms of other anaesthetic drugs on human consciousness.

Multimodal pathophysiological dataset of gradual cerebral ischemia in a cohort of juvenile pigs

Ischemic brain injuries are frequent and difficult to detect reliably or early. We present the multi-modal data set containing cardiovascular (blood pressure, blood flow, electrocardiogram) and brain electrical activities to derive electroencephalogram (EEG) biomarkers of corticothalamic communication under normal, sedation, and hypoxic/ischemic conditions with ensuing recovery. We provide technical validation using EEGLAB. We also delineate the corresponding changes in the electrocardiogram (ECG)-derived heart rate variability (HRV) with the potential for future in-depth analyses of joint EEG-ECG dynamics. We review an open-source methodology to derive signatures of coupling between the ECoG and electrothalamogram (EThG) signals contained in the presented data set to better characterize the dynamics of thalamocortical communication during these clinically relevant states. The data set is presented in full band sampled at 2000 Hz, so the additional potential exists for insights from the full-band EEG and high-frequency oscillations under the bespoke experimental conditions. Future studies on the dataset may contribute to the development of new brain monitoring technologies, which will facilitate the prevention of neurological injuries.

Measurement(s)	EEG with persistent abnormal rhythmic activity • electrocardiogram • Electrothalamogram • cerebral blood flow measurement • positive regulation of heart rate involved in baroreceptor response to decreased systemic arterial blood pressure • cerebral metabolic rate of oxygen • cerebral perfusion pressure
Technology Type(s)	electrophysiology assay • extracellular electrophysiology recording assay • fluorescent colormicrospheres • Electrophysiology
Factor Type(s)	sedation • cerebral ischemia • recovery
Sample Characteristic - Organism	Sus scrofa
Sample Characteristic - Environment	laboratory environment

Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.13251176

Effects of sevoflurane anaesthesia on radioligand binding to monoamine oxidase-B in vivo

Background

The molecular actions underlying the clinical effects of inhaled anaesthetics such as sevoflurane and isoflurane are not fully understood. Unexpected observations in positron emission tomography (PET) studies with [¹¹C]AZD9272, a metabotropic glutamate receptor 5 (mGluR5) radioligand with possible affinity for monoamine oxidase-B (MAO-B), suggest that its binding is sensitive to anaesthesia with sevoflurane. The objective of the present study was to assess the effects of sevoflurane anaesthesia on the binding of [¹¹C]AZD9272 and of [¹¹C]L-deprenyl-D₂, a radioligand selective for MAO-B in non-human primates (NHPs).

Methods

Altogether, 12 PET measurements were conducted with a high-resolution research tomograph using the ligands [¹¹C]AZD9272 or [¹¹C]L-deprenyl-D₂ in six cynomolgus monkeys anaesthetised with sevoflurane or ketamine/xylazine.

Results

The specific binding of [¹¹C]AZD9272 and [¹¹C]L-deprenyl-D₂ was markedly reduced during anaesthesia with sevoflurane compared with ketamine/xylazine. The reduction was 80–90% (n=3) for [¹¹C]AZD9272 and 77–80% (n=3) for [¹¹C]L-deprenyl-D₂.

Conclusions

Sevoflurane anaesthesia inhibited radioligand binding to MAO-B in the primate brain. The observation of lower MAO-B binding at clinically relevant concentrations of sevoflurane warrants further exploration of the potential role of MAO-B related mechanisms in regulation of systemic blood pressure during anaesthesia.

Analgesia, sedation, and delirium in pediatric surgical critical care

The alleviation of discomfort and distress is an essential component of the management of critically ill surgical patients. Pain and anxiety have multifocal etiologies that may be related to an underlying disease or surgical procedure, ongoing medical therapy, invasive monitors, an unfamiliar, complex and chaotic environment, as well as fear. Pharmacologic and non-pharmacologic therapies have complex risk benefit profiles. A fundamental understanding of analgesia, sedation, and delirium is essential for optimizing important outcomes in critically ill pediatric surgical patients. There has been a recent emphasis on goal directed, evidence based, and patient-centered management of the physical and psychological needs of these children. The purpose of this article is to review and summarize recent advances and describe current practice of these important subjects in the pediatric surgical intensive care environment.

Using Positron Emission Tomography in Revealing the Mystery of General Anesthesia: Study Design Challenges and Opportunities

Functional neuroimaging with positron emission tomography (PET) is one of the cornerstones for studying the central nervous system effects of general anesthetics and anesthesia mechanisms. General anesthesia offers a unique and safe way to directly manipulate consciousness, and can thus be used as a powerful research tool to study the neurobiology of human consciousness. In this chapter, we will address the possibilities of PET imaging in revealing the mysteries of general anesthesia and anesthetic induced unconsciousness and summarize some of the recent advancements in the field. Importantly, we will discuss possible ways to separate brain activity changes associated with the changing level of consciousness from the concentration or dose-dependent direct or indirect drug effects on the brain. We will try to demonstrate how state-of-the-art clinical pharmacology, use of specific anesthetic drugs, and innovative study design solutions could be utilized.

Sedation in Critically Ill Children with Respiratory Failure

This article discusses the rationale of sedation in respiratory failure, sedation goals, how to assess the need for sedation as well as effectiveness of interventions in critically ill children, with validated observational sedation scales. The drugs and non-pharmacological approaches used for optimal sedation in ventilated children are reviewed, and specifically the rationale for drug selection, including short- and long-term efficacy and safety aspects of the selected drugs. The specific pharmacokinetic and pharmacodynamic aspects of sedative drugs in the critically ill child and consequences for dosing are presented. Furthermore, we discuss different sedation strategies and their adverse events, such as iatrogenic withdrawal syndrome and delirium. These principles can guide clinicians in the choice of sedative drugs in pediatric respiratory failure.

Cerebral mechanisms of general anesthesia

How does general anesthesia (GA) work? Anesthetics are pharmacological agents that target specific central nervous system receptors. Once they bind to their brain receptors, anesthetics modulate remote brain areas and end up interfering with global neuronal networks, leading to a controlled and reversible loss of consciousness. This remarkable manipulation of consciousness allows millions of people every year to undergo surgery safely most of the time. However, despite all the progress that has been made, we still lack a clear and comprehensive insight into the specific neurophysiological mechanisms of GA, from the molecular level to the global brain propagation. During the last decade, the exponential progress in neuroscience and neuro-imaging led to a significant step in the understanding of the neural correlates of consciousness, with direct consequences for clinical anesthesia. Far from shutting down all brain activity, anesthetics lead to a shift in the brain state to a distinct, highly specific and complex state, which is being increasingly characterized by modern neuro-imaging techniques. There are several clinical consequences and challenges that are arising from the current efforts to dissect GA mechanisms: the improvement of anesthetic depth monitoring, the characterization and avoidance of intra-operative awareness and post-anesthesia cognitive disorders, and the development of future generations of anesthetics.

Changes in effective connectivity by propofol sedation

Mechanisms of propofol-induced loss of consciousness remain poorly understood. Recent fMRI studies have shown decreases in functional connectivity during unconsciousness induced by this anesthetic agent. Functional connectivity does not provide information of directional changes in the dynamics observed during unconsciousness. The aim of the present study was to investigate, in healthy humans during an auditory task, the changes in effective connectivity resulting from propofol induced loss of consciousness. We used Dynamic Causal Modeling for fMRI (fMRI-DCM) to assess how causal connectivity is influenced by the anesthetic agent in the auditory system. Our results suggest that the dynamic observed in the auditory system during unconsciousness induced by propofol, can result in a mixture of two effects: a local inhibitory connectivity increase and a decrease in the effective connectivity in sensory cortices.

Propofol stimulates noradrenalin-inhibited neurons in the ventrolateral preoptic nucleus by reducing GABAergic inhibition

BACKGROUND

The cellular mechanisms underlying the sedative effect of general anesthetics are not completely understood. Accumulating evidence indicates that the ventrolateral preoptic area (VLPO) of the hypothalamus plays a critical role. The VLPO contains 2 major types of neurons, the noradrenalin-inhibited GABAergic projecting neurons (NA(-) neurons) and the noradrenalin-excited interneurons (NA(+) neurons) which are probably also γ-aminobutyric acid (GABA)-containing neurons. Our previous work suggests that NA(-) neurons are normally under the inhibitory control of NA(+) neurons. Previous studies also show that GABAergic agents including propofol activate GABAergic projecting neurons in the VLPO, which is believed to lead to the inhibition of the arousal-producing nuclei in the tuberomammillary nucleus and sedation. However, how propofol activates VLPO neurons remains unclear. We explored the possibility that propofol activates NA(-) neurons indirectly, by inhibiting GABAergic transmission including those from VLPO NA(+) neurons.

METHODS

Electrophysiological activities were recorded from VLPO cells in acute brain slices of rats.

RESULTS

Propofol facilitates the discharges of NA(-) neurons and reduces the frequency, but not the amplitude of spontaneous GABAergic inhibitory postsynaptic currents in NA(-) neurons. Conversely, propofol suppressed the discharges of NA(+) neurons.

CONCLUSION

Propofol excites VLPO NA(-) neurons by reducing GABAergic transmission, at least in part by inhibiting VLPO NA(+) neurons. This may be a critical mechanism contributing to propofol-induced sedation.

Spatiotemporal reconfiguration of large-scale brain functional networks during propofol-induced loss of consciousness

Applying graph theoretical analysis of spontaneous BOLD fluctuations in functional magnetic resonance imaging (fMRI), we investigated whole-brain functional connectivity of 11 healthy volunteers during wakefulness and propofol-induced loss of consciousness (PI-LOC). After extraction of regional fMRI time series from 110 cortical and subcortical regions, we applied a maximum overlap discrete wavelet transformation and investigated changes in the brain's intrinsic spatiotemporal organization. During PI-LOC, we observed a breakdown of subcortico-cortical and corticocortical connectivity. Decrease of connectivity was pronounced in thalamocortical connections, whereas no changes were found for connectivity within primary sensory cortices. Graph theoretical analyses revealed significant changes in the degree distribution and local organization metrics of brain functional networks during PI-LOC: compared with a random network, normalized clustering was significantly increased, as was small-worldness. Furthermore we observed a profound decline in long-range connections and a reduction in whole-brain spatiotemporal integration, supporting a topological reconfiguration during PI-LOC. Our findings shed light on the functional significance of intrinsic brain activity as measured by spontaneous BOLD signal fluctuations and help to understand propofol-induced loss of consciousness.

Balanced propofol sedation administered by nonanesthesiologists: The first Italian experience

AIM: To assess the efficacy and safety of a balanced approach using midazolam in combination with propofol, administered by non-anesthesiologists, in a large series of diagnostic colonoscopies.

METHODS: Consecutive patients undergoing diagnostic colonoscopy were sedated with a single dose of midazolam (0.05 mg/kg) and low-dose propofol (starter bolus of 0.5 mg/kg and repeated boluses of 10 to 20 mg). Induction time and deepest level of sedation, adverse and serious adverse events, as well as recovery times, were prospectively assessed. Cecal intubation and adenoma detection rates were also collected.

RESULTS: Overall, 1593 eligible patients were included. The median dose of propofol administered was 70 mg (range: 40-120 mg), and the median dose of midazolam was 2.3 mg (range: 2-4 mg). Median induction time of sedation was 3 min (range: 1-4 min), and median recovery time was 23 min (range: 10-40 min). A moderate level of sedation was achieved in 1561 (98%) patients, whilst a deep sedation occurred in 32 (2%) cases. Transient oxygen desaturation requiring further oxygen supplementation occurred in 8 (0.46%; 95% CI: 0.2%-0.8%) patients. No serious adverse event was observed. Cecal intubation and adenoma detection rates were 93.5% and 23.4% (27.8% for male and 18.5% for female, subjects), respectively.

CONCLUSION: A balanced sedation protocol provided a minimalization of the dose of propofol needed to target a moderate sedation for colonoscopy, resulting in a high safety profile for non-anesthesiologist propofol sedation.

Balanced Propofol Sedation in Patients Undergoing EUS-FNA: A Pilot Study to Assess Feasibility and Safety

Introduction and aims. Balanced propofol sedation (BPS) administered by gastroenterologists has gained popularity in endoscopic procedures. Few studies exist about the safety of this approach during endosonography with fine needle aspiration (EUS-FNA). We assessed the safety of BPS in EUS-FNA. Materials and methods. 112 consecutive patients, referred to our unit to perform EUS-FNA, from February 2008 to December 2009, were sedated with BPS. A second gastroenterologist administered the drugs and monitorized the patient. Results. All the 112 patients (62 males, mean age 58.35) completed the examination. The mean dose of midazolam and propofol was, respectively, of 2.1 mg (range 1–4 mg) and 350 mg (range 180–400). All patients received oxygen with a mean flux of 4 liter/minute (range 2–6 liters/minute). The mean recovery time after procedure was 25 minutes (range 18–45 minutes). No major complications related to sedation were registered during all procedures. The oxygen saturation of all patients never reduced to less than 85%. Blood systolic pressure during and after the procedure never reduced to less than 100 mmHg. Conclusions. In our experience BPS administered by non-anaesthesiologists provided safe and successful sedation in patients undergoing EUS-FNA.

Sedation and Analgesia in Critically Ill Neurologic Patients

Critically ill neurologic patients can pose a challenge when it comes to providing sedation and analgesia, primarily with the balance of maintaining sedation to provide patient comfort while still allowing a neurological examination. Determination of the optimal agent requires assessment and understanding of the underlying requirement for sedation: provision of analgesia, anxiolysis, or treatment of delirium. Pharmacological options exist that can affect individual or multiple underlying sedation requirements. Numerous evaluation tools exist to monitor the efficacy of sedation as well as help clinicians titrate agents to predefined goals; these tools allow the safe administration of drugs that can otherwise have serious adverse effects. Sedation regimens must ultimately be individualized to each patient to account for differences in pharmacokinetics and dynamics of the various agents, and this is particularly true in sedating neurologically injured patients. The agents frequently used to provide sedation and analgesia in the critically ill neurologic patient will be reviewed.

Effects of anesthetic protocol on normal canine brain uptake of 18F-FDG assessed by PET/CT

The purpose of this study was to assess the effects of four anesthetic protocols on normal canine brain uptake of 2-deoxy-2-[18F]fluoro-D-glucose (FDG) using positron emission tomography/computed tomography (PET/CT). Five clinically normal beagle dogs were anesthetized with (1) propofol/isoflurane, (2) medetomidine/pentobarbital, (3) xylazine/ketamine, and (4) medetomidine/tiletamine-zolazepam in a randomized cross-over design. The standard uptake value (SUV) of FDG was obtained in the frontal, parietal, temporal and occipital lobes, cerebellum, brainstem and whole brain, and compared within and between anesthetic protocols using the Friedman test with significance set at P < 0.05. Significant differences in SUVs were observed in various part of the brain associated with each anesthetic protocol. The SUV for the frontal and occipital lobes was significantly higher than in the brainstem in all dogs. Dogs receiving medetomidine/tiletamine-zolazepam also had significantly higher whole brain SUVs than the propofol/isoflurane group. We concluded that each anesthetic protocol exerted a different regional brain glucose uptake pattern. As a result, when comparing brain glucose uptake using PET/CT, one should consider the effects of anesthetic protocols on different regions of the glucose uptake in the dog's brain.

Activation of orexin signal in basal forebrain facilitates the emergence from sevoflurane anesthesia in rat

Orexinergic system may play an important role in the regulation of anesthesia-arousal. However, which region or which pathway mediated the effect of orexins was still unclear. In current study, we investigated whether activation of orexin signals in basal forebrain (BF) may alter electroencephalographic activity, induction and emergence time to sevoflurane anesthesia in rats. Either orexin-A or orexin-B was injected into the BF while measuring electroencephalogram (EEG) under 1.0 minimum alveolar concentration (2.4%) sevoflurane anesthesia. The induction and emergence time of sevoflurane anesthesia were measured respectively after an injection of orexin receptor agonist (orexin-A or orexin-B) or antagonist (SB-334867A) into the BF also. We found that the administration of orexin-A (30, 100 pmol) and orexin-B (100 pmol) changed the burst and suppression patterns to arousal EEG in rat under sevoflurane anesthesia. Comparing with orexin-B, injection of lower dose of orexin-A induced more arousal EEG. Intrabasalis microinjection of orexin-A shorted the emergence time, whereas intrabasalis microinjection of SB-334867A (5 microg, 20 microg) delayed the emergence time to sevoflurane anesthesia, without changing anesthetic induction. These findings indicate that the orexin signals in basal forebrain, a middle region of the cholinergic ventral ascending arousal system, plays a crucial role in the anesthesia-arousal regulation.

Propofol: neuroprotection in an in vitro model of traumatic brain injury

Introduction

The anaesthetic agent propofol (2,6-diisopropylphenol) has been shown to be an effective neuroprotective agent in different in vitro models of brain injury induced by oxygen and glucose deprivation. We examined its neuroprotective properties in an in vitro model of traumatic brain injury.

Methods

In this controlled laboratory study organotypic hippocampal brain-slice cultures were gained from six- to eight-day-old mice pups. After 14 days in culture, hippocampal brain slices were subjected to a focal mechanical trauma and subsequently treated with different molar concentrations of propofol under both normo- and hypothermic conditions. After 72 hours of incubation, tissue injury assessment was performed using propidium iodide (PI), a staining agent that becomes fluorescent only when it enters damaged cells via perforated cell membranes. Inside the cell, PI forms a fluorescent complex with nuclear DNA.

Results

A dose-dependent reduction of both total and secondary tissue injury could be observed in the presence of propofol under both normo- and hypothermic conditions. This effect was further amplified when the slices were incubated at 32°C after trauma.

Conclusions

When used in combination, the dose-dependent neuroprotective effect of propofol is additive to the neuroprotective effect of hypothermia in an in vitro model of traumatic brain injury.

Nurse-administered propofol sedation compared with midazolam and meperidine for EUS: a prospective, randomized trial

BACKGROUND

The utility of nurse-administered propofol sedation (NAPS) compared with midazolam and meperidine (M/M) for EUS is not known.

OBJECTIVE

To compare recovery times, costs, safety, health personnel, and patient satisfaction of NAPS and M/M for EUS.

DESIGN

Prospective, randomized, single-blinded trial.

SETTING

Tertiary-referral hospital in Indianapolis, Indiana.

PATIENTS

Outpatients referred for EUS.

INTERVENTIONS

Sedation with M/M or NAPS. The patient and recovery nurse were blinded; however, the sedating nurse, endoscopist, and recording research nurse were unblinded to the sedatives used. A capnography, in addition to standard monitoring, was used. A questionnaire and visual analog scale assessed patient, endoscopist, and sedating nurse satisfaction.

MAIN OUTCOME MEASUREMENTS

Recovery times, costs, safety, health personnel, and patient satisfaction in both groups.

RESULTS

Eighty consecutive patients were randomized to NAPS (n = 40) or M/M (n = 40). More patients in the propofol group were current tobacco users; patient demographics, procedures performed, mean procedure length, and the overall frequency of adverse events were otherwise similar. Compared with M/M, NAPS was associated with a faster induction of sedation (2.3 vs 5.7 minutes, respectively; P = .001) and full recovery time (29 vs 49 minutes, respectively; P = .001), higher postprocedure patient satisfaction, and quicker anticipated return to baseline function. At discharge, total costs (recovery plus medications) were similar between the propofol ($406) and M/M groups ($399; P = .79).

LIMITATION

Low-risk patient population.

CONCLUSIONS

Compared with M/M, NAPS for an EUS offered a faster sedation induction and full recovery time, higher postprocedure patient satisfaction, and a quicker anticipated return to baseline function. Total costs were similar between the groups.

Nurse-administered propofol sedation for upper endoscopic ultrasonography

BACKGROUND

Limited data exist regarding the safety of nurse-administered propofol sedation (NAPS) for advanced endoscopy.

AIMS

To evaluate the frequency of and the risk factors for complications associated with NAPS for upper endoscopic ultrasound (EUS).

METHODS

Consecutive upper EUS examinations using NAPS were retrospectively identified. Clinical data and adverse events were recorded. Univariate and multivariable repeated measures logistic regression models were used to identify independent risk factors for complications.

RESULTS

Among 806 EUS procedures, the mean procedure duration, time for sedation induction, and postprocedure recovery time were: 34 +/- 20 min, 3.6 +/- 1.4 min, and 27 +/- 23 min, respectively. A decline in systolic blood pressure (SBP) to <90 mm Hg occurred in 104 patients (13%). Six patients (0.7%) had a decline in oxygen saturation (SpO(2)) to <90%. Four patients (0.5%; 95% confidence interval [CI] 0.14-1.27) required assisted positive pressure ventilation. There were no major complications. The minor complication rate from sedation was 21% (95% CI 17.2-25.3). All of the complications were clinically insignificant. Overall complication risk was not related to age, dose, or procedure time. Sedation-related complication rates for advanced experience-level (> or =100 NAPS procedures) nurses were lower compared to the least-experienced (< or =30 NAPS procedures) nurses (17.2%vs 25.4%, odds ratio [OR] 0.61, 95% CI 0.41-0.92).

CONCLUSIONS

NAPS for upper EUS is safe and may be performed without major complications. Four patients (0.5%) required assisted ventilation. Minor complications occurred in 21% of patients, but were not associated with patient age, propofol dose, or procedure time.

[Propofol-induced myocardial depression: possible role of atrial muscarinic cholinergic receptors]

OBJECTIVE

To investigate the possible role of muscarinic cholinergic receptors (MCRs) in the depression of myocardial function induced by propofol, an intravenous anesthetic chemically unrelated to other drugs. Although adverse effects are rare, bradycardia has been reported and this can lead to cardiac arrest in some patients. The mechanism behind this effect is still unknown but a possible role for MCRs has been suggested.

MATERIAL AND METHODS

The interaction of propofol with human atrial MCRs was determined by means of inhibition tests using [3H] quinuclidinyl benzilate ([3H] QNB).

RESULTS

The displacement of [3H] QNB binding to human atrial MCRs by propofol was concentration dependent but the observed effect was not consistent with a model of simple competition between propofol and [3H] QNB.

CONCLUSION

Propofol appears to have the ability to modify the activity of human atrial MCRs and this effect may be related to its ability to induce bradycardia.

Positron emission tomography and target-controlled infusion for precise modulation of brain drug concentration

INTRODUCTION

There are several instances when it is desirable to control brain concentration of pharmaceuticals, e.g., to modulate the concentration of anesthetic agents to different desired levels fitting to different needs during the course of surgery. This has so far only been possible using indirect estimates of drug concentration such as assuming constant relation between tissue and blood including extrapolations from animals.

METHODS

A system for controlling target tissue concentration (UIPump) was used to regulate whole-brain concentrations of a central benzodiazepine receptor antagonist at therapeutic levels with input from brain kinetics as determined with PET. The system was tested by using pharmacological doses of flumazenil mixed with tracer amounts of [11C]flumazenil. Flumazenil was used as a model compound for anesthesia. An infusion scheme to produce three different steady-state levels in sequence was designed based on kinetic curves obtained after bolus injection. The subjects (Sprague-Dawley rats, n=6) were monitored in a microPET scanner during the whole experiment to verify resulting brain kinetic curves.

RESULTS

A steady-state brain concentration was rapidly achieved corresponding to a whole-brain concentration of 118+/-6 ng/ml. As the infusion rate decreased to lower the exposure by a factor of 2, the brain concentration decreased to 56+/-4 ng/ml. A third increased steady-state level of anesthesia corresponding to a whole-brain concentration of 107+/-7 ng/ml was rapidly achieved.

CONCLUSION

The experimental setup with computerized pump infusion and PET supervision enables accurate setting of target tissue drug concentration.

Beautiful minds (i.e., brains) and the neural basis of intelligence

The commentaries address conceptual issues ranging from our narrow focus on neuroimaging to the various definitions of intelligence. The integration of the P-FIT and data from cognitive neuroscience is particularly important and considerable consistency is found. Overall, the commentaries affirm that advances in neuroscience techniques have caused intelligence research to enter a new phase. The P-FIT is recognized as a reasonable empirical framework to test hypotheses about the relationship of brain structure and function with intelligence and reasoning.

Critical care sedation for neuroscience patients

In 2000, the Joint Commission on Accreditation of Healthcare Organizations (JCAHO) introduced the mandate for the implementation of standards for both pain assessment and need for therapy in hospitalized patients. The need for the appropriate titration of sedation and analgesia is particularly poignant in an intensive care unit (ICU) setting where iatrogenic discomfort often complicates patient management. Neurologically ill patients in ICUs present particularly complex sedation issues, owing to the need to monitor these patients with serial neurological exams. Hence, maximal comfort without diminishing neurological responsiveness is desirable. Here, we review the frequently applied methods of evaluating levels of pain and agitation in critically ill patients as well as discuss the appropriate classes of pharmaceutical agents common to this population, with particular emphasis on the potential neurophysiological impact of such therapy.

Cholinergic modulation of response properties and orientation tuning of neurons in primary visual cortex of anaesthetized Marmoset monkeys

Cortical processing is strongly influenced by the actions of neuromodulators such as acetylcholine (ACh). Early studies in anaesthetized cats argued that acetylcholine can cause a sharpening of orientation tuning functions and an improvement of the signal-to-noise ratio (SNR) of neuronal responses in primary visual cortex (V1). Recent in vitro studies have demonstrated that acetylcholine reduces the efficacy of feedback and intracortical connections via the activation of muscarinic receptors, and increases the efficacy of feed-forward connections via the activation of nicotinic receptors. If orientation tuning is mediated or enhanced by intracortical connections, high levels of acetylcholine should diminish orientation tuning. Here we investigate the effects of acetylcholine on orientation tuning and neuronal responsiveness in anaesthetized marmoset monkeys. We found that acetylcholine caused a broadening of the orientation tuning in the majority of cells, while tuning functions became sharper in only a minority of cells. Moreover, acetylcholine generally facilitated neuronal responses, but neither improved signal-to-noise ratio, nor reduced trial-to-trial firing rate variance systematically. Acetylcholine did however, reduce variability of spike occurrences within spike trains. We discuss these findings in the context of dynamic control of feed-forward and lateral/feedback connectivity by acetylcholine.

Ketamine, but not propofol, anaesthesia is regulated by metabotropic glutamate 5 receptors

BACKGROUND

Group I metabotropic glutamate receptors (mGluRs) have been reported to regulate N-methyl-d-aspartate (NMDA) receptor function in various brain regions. The selective mGluR5 antagonist 2-methyl-6-(phenylethynyl)-pyridine (MPEP) can potentiate NMDA antagonists such as PCP and MK-801-induced behavioural responses. In the present study, the role of group I mGluRs on ketamine- and propofol-induced general anaesthesia was examined.

METHODS

Mice were pretreated with various doses of the group I mGluR agonist (S)-3,5-dihydroxyphenylglycine (DHPG), selective mGluR5 agonist (RS)-2-chloro-5-hydroxyphenylglycine (CHPG), mGluR1 antagonist 7-(hydroxyimino)cyclopropa[b]chromen-1a-carboxylate ethyl ester (CPCCOEt) and mGluR5 antagonist MPEP followed by administration of ketamine (120 mg kg(-1)) or propofol (140 mg kg(-1)) to induce anaesthesia. The duration of loss of righting reflex was recorded.

RESULTS

DHPG and CHPG antagonized and MPEP potentiated ketamine-induced anaesthesia in a dose-dependent manner. CPCCOEt was ineffective. However, propofol-induced anaesthesia was not affected after manipulating mGluR1 and mGluR5 receptors.

CONCLUSIONS

mGluR5 receptors play an important role in modulation of anaesthesia induced by ketamine, but not propofol.

Correlation of EEG spectral entropy with regional cerebral blood flow during sevoflurane and propofol anaesthesia

ENTROPY index monitoring, based on spectral entropy of the electroencephalogram, is a promising new method to measure the depth of anaesthesia. We examined the association between spectral entropy and regional cerebral blood flow in healthy subjects anaesthetised with 2%, 3% and 4% end-expiratory concentrations of sevoflurane and 7.6, 12.5 and 19.0 microg.ml(-1) plasma drug concentrations of propofol. Spectral entropy from the frequency band 0.8-32 Hz was calculated and cerebral blood flow assessed using positron emission tomography and [(15)O]-labelled water at baseline and at each anaesthesia level. Both drugs induced significant reductions in spectral entropy and cortical and global cerebral blood flow. Midfrontal-central spectral entropy was associated with individual frontal and whole brain blood flow values across all conditions, suggesting that this novel measure of anaesthetic depth can depict global changes in neuronal activity induced by the drugs. The cortical areas of the most significant associations were remarkably similar for both drugs.

General anesthesia and the neural correlates of consciousness

The neural correlates of consciousness must be identified, but how? Anesthetics can be used as tools to dissect the nervous system. Anesthetics not only allow for the experimental investigation into the conscious-unconscious state transition, but they can also be titrated to subanesthetic doses in order to affect selected components of consciousness such as memory, attention, pain processing, or emotion. A number of basic neuroimaging examinations of various anesthetic agents have now been completed. A common pattern of regional activity suppression is emerging for which the thalamus is identified as a key target of anesthetic effects on consciousness. It has been proposed that a neuronal hyperpolarization block at the level of the thalamus, or thalamocortical and corticocortical reverberant loops, could contribute to anesthetic-induced unconsciousness. However, all anesthetics do not suppress global cerebral metabolism and cause a regionally specific effect on thalamic activity. Ketamine, a so-called dissociative anesthetic agent, increases global cerebral metabolism in humans at doses associated with a loss of consciousness. Nevertheless, it is proposed that those few anesthetics not associated with a global metabolic suppression effect might still have their effects on consciousness mediated at the level of thalamocortical interactions, if such agents scramble the signals associated with normal neuronal network reverberant activity. Functional and effective connectivity are analysis techniques that can be used with neuroimaging to investigate the signal scrambling effects of various anesthetics on network interactions. Whereas network interactions have yet to be investigated with ketamine, a thalamocortical and corticocortical disconnection effect during unconsciousness has been found for both suppressive anesthetic agents and for patients who are in the persistent vegetative state. Furthermore, recovery from a vegetative state is associated with a reconnection of functional connectivity. Taken together these intriguing observations offer strong empirical support that the thalamus and thalamocortical reverberant network loop interactions are at the heart of the neurobiology of consciousness.

Molecular and neuronal substrates for general anaesthetics

Although general anaesthesia has been of tremendous importance for the development of surgery, the underlying mechanisms by which this state is achieved are only just beginning to be understood in detail. In this review, we describe the neuronal systems that are thought to be involved in mediating clinically relevant actions of general anaesthetics, and we go on to discuss how the function of individual drug targets, in particular GABA(A)-receptor subtypes, can be revealed by genetic studies in vivo.

Effects of ketamine anesthesia on central nociceptive processing in the rat: a 2-deoxyglucose study

Ketamine is a dissociative anesthetic with complex actions on the CNS. We investigated here the effects of ketamine anesthesia on somatosensory processing in the rat spinal cord, thalamus, and cerebral cortex, using the quantitative 2-deoxyglucose mapping technique. Unanesthetized or ketamine-anesthetized male Sprague-Dawley rats received a s.c. injection of a dilute formaldehyde solution (5%, 0.08 ml) into a forepaw, inducing prolonged noxious afferent input, or an equal volume of isotonic saline as a control stimulus. The 2-deoxyglucose experiments started 30 min after the injection. In the cervical enlargement of the spinal cord, ketamine had no significant effect on glucose metabolic rates in saline-injected animals, whereas it prevented the metabolic increases elicited by prolonged noxious stimulation in unanesthetized animals. At the thalamic level, ketamine increased glucose uptake in both saline- and formalin-injected rats in the lateral posterior, lateral dorsal, medial dorsal, gelatinosus, antero-ventral and antero-medial thalamic nuclei, whereas it decreased metabolic activity in the ventro-basal complex. At the cortical level, the drug increased metabolic activity in both control and formalin groups in the lacunosus-molecularis layer of the dorsal hippocampus, posterior parietal, retrosplenial, cingulate and frontal cortex; significant metabolic decreases were found in the CA1 region of the dorsal hippocampus and in the parietal 1 and 2 cortical areas. In the investigated brain regions, ketamine did not abolish noxious-evoked increases in glucose uptake, which were in fact enhanced in the forelimb cortex and in the lacunosus-molecularis layer of the hippocampus. The dissociation between the spinal and supraspinal effects of ketamine suggests a specific antinociceptive action on spinal circuits, in parallel with complex changes of the activity of brain circuits involved in somatosensory processing. More generally, this study shows that functional imaging techniques are able to quantitatively assess the effects of anesthetic drugs on nociceptive processing at different levels of the neuraxis.

Intravenous Subhypnotic Propofol in Central Pain

OBJECTIVE

To validate IV subhypnotic propofol, a gamma-aminobutyric acid A (GABA-A) agonist, as a diagnostic test for central pain.

METHODS

The efficacy of systemic propofol (0.2 mg/kg IV bolus) was evaluated in a double-blind, placebo-controlled and crossover fashion on both spontaneous ongoing pain and allodynia in 44 patients with chronic central pain of both brain and cord origin.

RESULTS

Propofol was significantly superior to the placebo (Intralipid, Kabi Pharmacia) in reducing the intensity of spontaneous ongoing pain for up to 1 hour after the injection: 24 of 44 patients (55%) receiving propofol showed a significant reduction in spontaneous pain, whereas only 6 patients showed this after the placebo. Propofol also significantly reduced the intensity of both mechanical and cold allodynia. In a few cases, only the evoked components were abolished but not the spontaneous pain. In general, the side effects were minimal and consisted mainly of transitory burning upon injection of both propofol and placebo and slight lightheadedness in a few cases.

CONCLUSIONS

Systemic propofol induces analgesic effects on all studied components of central pain and highlights the key role of GABA modulation in central pain.

PET quantification of muscarinic cholinergic receptors with [N-11C-methyl]-benztropine and application to studies of propofol-induced unconsciousness in healthy human volunteers

This work evaluated kinetic analysis methods for estimation of the receptor availability of the muscarinic receptor using dynamic positron emission tomography (PET) studies with [N-(11)C-methyl]-benztropine. The study also investigated the effect of propofol on central muscarinic receptor availability during general anesthesia. Six volunteers were scanned three times, once for baseline while awake, once during unconsciousness, and once after recovery to conscious level. An irreversible two-tissue compartment model was used to estimate the [N-(11)C-methyl]-benztropine specific binding rate constant k(3), a measure of muscarinic receptor availability. Two different estimation methods were used: 1) optimization with positivity constraints on all the parameters; 2) optimization with additional constraints determined from a one-tissue compartment fit to the cerebellum. In regions with low to middle muscarinic receptor density, the k(3) values from method (2) had lower standard errors than that for method (1) and gave a higher correlation with the density of muscarinic receptors measured in human tissue by in vitro studies (r(2) of 0.98 for Method 2 and r(2) of 0.72 for Method 1). But the k(3) values determined by Method 2 had higher errors for regions with high muscarinic receptor density compared to Method 1. For both methods the mean k(3) values during unconsciousness were generally lower than those during awake for most regions evaluated. Therefore, the method with additional constraints derived from the cerebellum (Method 2) was deemed superior for regions with low to middle muscarinic receptor density, while the method with positivity constraint is the better choice in the regions with high muscarinic receptor density. Our results also suggest the existence of propofol-related reductions in muscarinic receptor availability.