National Institute for Clinical Excellence guidance on measuring depth of anaesthesia: limitations of EEG-based technology

Isoflurane effects on the N1 and other long-latency auditory evoked potentials in Wistar rats

Long-latency auditory evoked potentials (LLAEPs) may help further advances in understanding consciousness under general anesthesia and promote more objective means of assessing sedation depth than conventional clinical signs. Among the LLAEP components, the auditory N1 shows promise as a measure of sedation depth and a marker of consciousness, but findings are so far inconclusive. Research with animals can help elucidate the effects of various anesthetics on the N1 and other LLAEPs, but investigations of LLAEPs under anesthesia in animals is lacking. To address this deficit, we examined the P1, N1, P2, and N2, along with their corresponding peak-to-peak complexes, in 10 Wistar rats anesthetized with 1.5-2 % isoflurane in pure oxygen and again after recovery. While under anesthesia, subdermal needle electrodes were inserted and secured for electroencephalographic (EEG) recordings. LLAEPs were assessed during a 20-min, passive, two-tone (500 ms inter-tone interval) paradigm with randomized short (1 s) and long (5 s) inter-pair intervals (IPIs). Overall, while the LLAEP peaks under isoflurane were less defined, they were not eliminated. The peak-to-peak amplitudes, particularly the P1-N1, were significantly smaller under isoflurane than during post-recovery. Our preliminary findings indicate that isoflurane produces global suppression across LLAEP components, presumably reflecting impaired integration of top-down and bottom-up attention and sensory systems under profound sedation with isoflurane.

Incidence of accidental awareness during general anaesthesia in obstetrics: a multicentre, prospective cohort study

General anaesthesia for obstetric surgery has distinct characteristics that may contribute towards a higher risk of accidental awareness during general anaesthesia. The primary aim of this study was to investigate the incidence, experience and psychological implications of unintended conscious awareness during general anaesthesia in obstetric patients. From May 2017 to August 2018, 3115 consenting patients receiving general anaesthesia for obstetric surgery in 72 hospitals in England were recruited to the study. Patients received three repetitions of standardised questioning over 30 days, with responses indicating memories during general anaesthesia that were verified using interviews and record interrogation. A total of 12 patients had certain/probable or possible awareness, an incidence of 1 in 256 (95%CI 149-500) for all obstetric surgery. The incidence was 1 in 212 (95%CI 122-417) for caesarean section surgery. Distressing experiences were reported by seven (58.3%) patients, paralysis by five (41.7%) and paralysis with pain by two (16.7%). Accidental awareness occurred during induction and emergence in nine (75%) of the patients who reported awareness. Factors associated with accidental awareness during general anaesthesia were: high BMI (25-30 kg.m^-2 ); low BMI (<18.5 kg.m^-2 ); out-of-hours surgery; and use of ketamine or thiopental for induction. Standardised psychological impact scores at 30 days were significantly higher in awareness patients (median (IQR [range]) 15 (2.7-52.0 [2-56]) than in patients without awareness 3 (1-9 [0-64]), p = 0.010. Four patients had a provisional diagnosis of post-traumatic stress disorder. We conclude that direct postoperative questioning reveals high rates of accidental awareness during general anaesthesia for obstetric surgery, which has implications for anaesthetic practice, consent and follow-up.

Continuous EEG monitoring by a new simplified wireless headset in intensive care unit

Background

In critically ill patients continuous EEG (cEEG) is recommended in several conditions. Recently, a new wireless EEG headset (CerebAir®,Nihon-Kohden) is available. It has 8 electrodes, and its positioning seems to be easier than conventional systems.

Aim of this study was to evaluate the feasibility of this device for cEEG monitoring, if positioned by ICU physician.

Methods

Neurological patients were divided in two groups according with the admission to Neuro-ICU (Study-group:20 patients) or General-ICU (Control-group:20 patients). In Study group, cEEG was recorded by CerebAir® assembled by an ICU physician, while in Control group a simplified 8-electrodes-EEG recording positioned by an EEG technician was performed.

Results

Time for electrodes applying was shorter in Study-group than in Control-group: 6.2 ± 1.1′ vs 10.4 ± 2.3′; p < 0.0001. Thirty five interventions were necessary to correct artifacts in Study-group and 11 in Control-group. EEG abnormalities with or without epileptic meaning were respectively 7(35%) and 7(35%) in Study-group, and 5(25%) and 9(45%) in Control-group;p > 0.05. In Study-group, cEEG was interrupted for risk of skin lesions in 4 cases after 52 ± 4 h. cEEG was obtained without EEG technician in all cases in Study-group; quality of EEG was similar.

Conclusions

Although several limitations should be considered, this simplified EEG system could be feasible even if EEG technician was not present. It was faster to position if compared with standard techniques, and can be used for continuous EEG monitoring. It could be very useful as part of diagnostic process in an emergency setting.

The Effects of Anesthetics on the Cortex-Lessons From Event-Related Potentials

Consciousness while under general anesthesia is a dreadful condition. Various electroencephalogram (EEG)-based technologies have been developed, on the basis of empirical evidence, in order to identify this condition. However, certain electrophysiological phenomena, which seem strongly related with depth of anesthesia in some drugs, appear less consistent with those of other anesthetic drugs. There is a gap between the complexity of the phenomenon of consciousness and its behavioral manifestations, on the one hand, and the empirical nature of the reported electrophysiological markers, which are associated with it, on the other hand. In fact, such a gap might prevent us from progressing toward unified electrophysiological markers of consciousness while under anesthesia, which are applicable to all anesthetic drugs. We believe that there is a need to bridge this conceptual gap. Therefore, in this work, we will try to present a theoretical framework for such bridging. First, we suggest focusing on neuropsychological processes, which seem to have a clear role in the behavioral manifestations of consciousness while under anesthesia but seem, nevertheless, better defined than consciousness itself-such as perception and attention. Then, we suggest analyzing the effects of anesthesia upon these neuropsychological processes, as they are manifested in the EEG signal. Specifically, we will focus on the effects of anesthesia on event-related potentials (ERPs), which seem more easily associable with neuropsychological modeling.

Electroencephalography and Brain Oxygenation Monitoring in the Perioperative Period

Maintaining brain function and integrity is a pivotal part of anesthesiological practice. The present overview aims to describe the current role of the 2 most frequently used monitoring methods for evaluation brain function in the perioperative period, ie, electroencephalography (EEG) and brain oxygenation monitoring. Available evidence suggests that EEG-derived parameters give additional information about depth of anesthesia for optimizing anesthetic titration. The effects on reduction of drug consumption or recovery time are heterogeneous, but most studies show a reduction of recovery times if anesthesia is titrated along processed EEG. It has been hypothesized that future EEG-derived indices will allow a better understanding of the neurophysiological principles of anesthetic-induced alteration of consciousness instead of the probabilistic approach most often used nowadays.Brain oxygenation can be either measured directly in brain parenchyma via a surgical burr hole, estimated from the venous outflow of the brain via a catheter in the jugular bulb, or assessed noninvasively by near-infrared spectroscopy. The latter method has increasingly been accepted clinically due to its ease of use and increasing evidence that near-infrared spectroscopy-derived cerebral oxygen saturation levels are associated with neurological and/or general perioperative complications and increased mortality. Furthermore, a goal-directed strategy aiming to avoid cerebral desaturations might help to reduce these complications. Recent evidence points out that this technology may additionally be used to assess autoregulation of cerebral blood flow and thereby help to titrate arterial blood pressure to the individual needs and for bedside diagnosis of disturbed autoregulation.

Median Nerve Stimulation Based BCI: A New Approach to Detect Intraoperative Awareness During General Anesthesia

Hundreds of millions of general anesthesia are performed each year on patients all over the world. Among these patients, 0.1–0.2% are victims of Accidental Awareness during General Anesthesia (AAGA), i.e., an unexpected awakening during a surgical procedure under general anesthesia. Although anesthesiologists try to closely monitor patients using various techniques to prevent this terrifying phenomenon, there is currently no efficient solution to accurately detect its occurrence. We propose the conception of an innovative passive brain-computer interface (BCI) based on an intention of movement to prevent AAGA. Indeed, patients typically try to move to alert the medical staff during an AAGA, only to discover that they are unable to. First, we examine the challenges of such a BCI, i.e., the lack of a trigger to facilitate when to look for an intention to move, as well as the necessity for a high classification accuracy. Then, we present a solution that incorporates Median Nerve Stimulation (MNS). We investigate the specific modulations that MNS causes in the motor cortex and confirm that they can be altered by an intention of movement. Finally, we perform experiments on 16 healthy participants to assess whether an MI-based BCI using MNS is able to generate high classification accuracies. Our results show that MNS may provide a foundation for an innovative BCI that would allow the detection of AAGA.

Multimodal Neuromonitoring in Neurocritical Care

Neuromonitoring is important for patients with acute brain injury. The bedside neurologic examination is standard for neurologic monitoring; however, a clinical examination may not reliably detect subtle changes in intracranial physiology. Changes found during neurologic examinations are often late signs. The assessment of multiple physiological variables in real time can provide new clinical insights into treatment decisions. No single monitoring modality is ideal for all patients. Simultaneous assessment of cerebral hemodynamics, oxygenation, and metabolism, such as in multimodal monitoring, allows an innovative approach to individualized patient care.

Protocol for the Electroencephalography Guidance of Anesthesia to Alleviate Geriatric Syndromes (ENGAGES) study: a pragmatic, randomised clinical trial

INTRODUCTION

Postoperative delirium, arbitrarily defined as occurring within 5 days of surgery, affects up to 50% of patients older than 60 after a major operation. This geriatric syndrome is associated with longer intensive care unit and hospital stay, readmission, persistent cognitive deterioration and mortality. No effective preventive methods have been identified, but preliminary evidence suggests that EEG monitoring during general anaesthesia, by facilitating reduced anaesthetic exposure and EEG suppression, might decrease incident postoperative delirium. This study hypothesises that EEG-guidance of anaesthetic administration prevents postoperative delirium and downstream sequelae, including falls and decreased quality of life.

METHODS AND ANALYSIS

This is a 1232 patient, block-randomised, double-blinded, comparative effectiveness trial. Patients older than 60, undergoing volatile agent-based general anaesthesia for major surgery, are eligible. Patients are randomised to 1 of 2 anaesthetic approaches. One group receives general anaesthesia with clinicians blinded to EEG monitoring. The other group receives EEG-guidance of anaesthetic agent administration. The outcomes of postoperative delirium (≤5 days), falls at 1 and 12 months and health-related quality of life at 1 and 12 months will be compared between groups. Postoperative delirium is assessed with the confusion assessment method, falls with ProFaNE consensus questions and quality of life with the Veteran's RAND 12-item Health Survey. The intention-to-treat principle will be followed for all analyses. Differences between groups will be presented with 95% CIs and will be considered statistically significant at a two-sided p<0.05.

ETHICS AND DISSEMINATION

Electroencephalography Guidance of Anesthesia to Alleviate Geriatric Syndromes (ENGAGES) is approved by the ethics board at Washington University. Recruitment began in January 2015. Dissemination plans include presentations at scientific conferences, scientific publications, internet-based educational materials and mass media.

TRIAL REGISTRATION NUMBER

NCT02241655; Pre-results.

Anaesthetic considerations for pectus repair surgery

Repair of pectus is one of the most common congenital abnormality for which patient presents for thoracic surgery. In recent years, innovative minimally invasive techniques involving video assisted thoracoscopy for pectus repair have become the norm. Similarly, anaesthetic techniques have evolved to include principles of enhanced recovery, multimodal analgesia and innovative ultrasound guided neuraxial and nerve blocks. Adequate anaesthetic set up and monitoring including the use of real time intraoperative monitoring with transesophageal echocardiography (TOE) has enabled the anaesthetist to enhance patient safety by providing instantaneous imaging of cardiac compression and complications during surgery. In this review article we aim to provide non-systematic review and institutional experience of our anaesthetic strategy to provide effective peri-operative care in this patient group.

Recommendations for standards of monitoring during anaesthesia and recovery 2015: Association of Anaesthetists of Great Britain and Ireland

This guideline updates and replaces the 4th edition of the AAGBI Standards of Monitoring published in 2007. The aim of this document is to provide guidance on the minimum standards for physiological monitoring of any patient undergoing anaesthesia or sedation under the care of an anaesthetist. The recommendations are primarily aimed at anaesthetists practising in the United Kingdom and Ireland. Minimum standards for monitoring patients during anaesthesia and in the recovery phase are included. There is also guidance on monitoring patients undergoing sedation and also during transfer of anaesthetised or sedated patients. There are new sections discussing the role of monitoring depth of anaesthesia, neuromuscular blockade and cardiac output. The indications for end-tidal carbon dioxide monitoring have been updated.

An observational study of the 'isolated forearm technique' in unparalysed, spontaneously breathing patients

The isolated forearm technique enables a patient, otherwise paralysed by neuromuscular blockade, to communicate by movement if wakeful during surgery. The positive response rate to verbal command is high (~32%). The 5th National Audit Project recommended that this monitoring technique should become more widely taught and considered, so this study was designed to assess its utility as a standard of care in unparalysed patients. A positive response rate as high as in the paralysed would justify local adoption. Therefore, 100 consecutive patients undergoing urology surgery were given verbal commands to move at two-minute intervals from induction of anaesthesia (fentanyl and propofol) to full emergence and extubation of the supraglottic airway. Anaesthesia was maintained with isoflurane in oxygen/nitrous oxide. Although 24 patients moved during surgery (and therefore needed additional anaesthetic), none moved to verbal command. Even at extubation, when patients moved to expel the airway, there was no response to command until after wakening. These results suggest that in contrast to its use in paralysed patients, the isolated forearm technique does not yield useful information about the patient's state of wakefulness in the unparalysed. Another interpretation is that unparalysed patients are less prone to wakefulness than the paralysed.

Awareness under general anaesthesia

Awareness under anaesthesia is a rare but important phenomenon which has become a source of fear - and of fascination - to the public and anaesthetists alike. This article discusses the incidence, aetiology, sequelae and prevention of awareness.