Anaesthetic depth and delirium: a challenging balancing act

Depth of Anesthesia and Nociception Monitoring: Current State and Vision For 2050

Anesthesia objectives have evolved into combining hypnosis, amnesia, analgesia, paralysis, and suppression of the sympathetic autonomic nervous system. Technological improvements have led to new monitoring strategies, aimed at translating a qualitative physiological state into quantitative metrics, but the optimal strategies for depth of anesthesia (DoA) and analgesia monitoring continue to stimulate debate. Historically, DoA monitoring used patient's movement as a surrogate of awareness. Pharmacokinetic models and metrics, including minimum alveolar concentration for inhaled anesthetics and target-controlled infusion models for intravenous anesthesia, provided further insights to clinicians, but electroencephalography and its derivatives (processed EEG; pEEG) offer the potential for personalization of anesthesia care. Current studies appear to affirm that pEEG monitoring decreases the quantity of anesthetics administered, diminishes postanesthesia care unit duration, and may reduce the occurrence of postoperative delirium (notwithstanding the difficulties of defining this condition). Major trials are underway to further elucidate the impact on postoperative cognitive dysfunction. In this manuscript, we discuss the Bispectral (BIS) index, Narcotrend monitor, Patient State Index, entropy-based monitoring, and Neurosense monitor, as well as middle latency evoked auditory potential, before exploring how these technologies could evolve in the upcoming years. In contrast to developments in pEEG monitors, nociception monitors remain by comparison underdeveloped and underutilized. Just as with anesthetic agents, excessive analgesia can lead to harmful side effects, whereas inadequate analgesia is associated with increased stress response, poorer hemodynamic conditions and coagulation, metabolic, and immune system dysregulation. Broadly, 3 distinct monitoring strategies have emerged: motor reflex, central nervous system, and autonomic nervous system monitoring. Generally, nociceptive monitors outperform basic clinical vital sign monitoring in reducing perioperative opioid use. This manuscript describes pupillometry, surgical pleth index, analgesia nociception index, and nociception level index, and suggest how future developments could impact their use. The final section of this review explores the profound implications of future monitoring technologies on anesthesiology practice and envisages 3 transformative scenarios: helping in creation of an optimal analgesic drug, the advent of bidirectional neuron-microelectronic interfaces, and the synergistic combination of hypnosis and virtual reality.

Pharmacokinetic and Pharmacodynamic Changes in the Elderly: Impact on Anesthetics

Anesthesiologists are increasingly required to care for frail elderly patients. A detailed knowledge of the influence of age on the pharmacokinetics and dynamics of the anesthetic drugs is essential for optimal safety and care. For most of the anesthetic drugs, the elderly need lower doses to achieve the same plasma concentrations, and at any given plasma and effect-site concentration, they will have more profound clinical effects than younger patients. Caution is required, with close monitoring of clinical effects and active titration of dose administration to achieve the desired level of effect, ideally following the "start low, go slow" principle.

A Real-Time Neurophysiologic Stress Test for the Aging Brain: Novel Perioperative and ICU Applications of EEG in Older Surgical Patients

As of 2022, individuals age 65 and older represent approximately 10% of the global population [1], and older adults make up more than one third of anesthesia and surgical cases in developed countries [2, 3]. With approximately > 234 million major surgical procedures performed annually worldwide [4], this suggests that > 70 million surgeries are performed on older adults across the globe each year. The most common postoperative complications seen in these older surgical patients are perioperative neurocognitive disorders including postoperative delirium, which are associated with an increased risk for mortality [5], greater economic burden [6, 7], and greater risk for developing long-term cognitive decline [8] such as Alzheimer's disease and/or related dementias (ADRD). Thus, anesthesia, surgery, and postoperative hospitalization have been viewed as a biological "stress test" for the aging brain, in which postoperative delirium indicates a failed stress test and consequent risk for later cognitive decline (see Fig. 3). Further, it has been hypothesized that interventions that prevent postoperative delirium might reduce the risk of long-term cognitive decline. Recent advances suggest that rather than waiting for the development of postoperative delirium to indicate whether a patient "passed" or "failed" this stress test, the status of the brain can be monitored in real-time via electroencephalography (EEG) in the perioperative period. Beyond the traditional intraoperative use of EEG monitoring for anesthetic titration, perioperative EEG may be a viable tool for identifying waveforms indicative of reduced brain integrity and potential risk for postoperative delirium and long-term cognitive decline. In principle, research incorporating routine perioperative EEG monitoring may provide insight into neuronal patterns of dysfunction associated with risk of postoperative delirium, long-term cognitive decline, or even specific types of aging-related neurodegenerative disease pathology. This research would accelerate our understanding of which waveforms or neuronal patterns necessitate diagnostic workup and intervention in the perioperative period, which could potentially reduce postoperative delirium and/or dementia risk. Thus, here we present recommendations for the use of perioperative EEG as a "predictor" of delirium and perioperative cognitive decline in older surgical patients.

Effects of qCON and qNOX-guided general anaesthesia management on patient opioid use and prognosis: a study protocol

INTRODUCTION

The adverse effects of general anaesthetic drugs (especially opioids) cannot be ignored. However, current nociceptive-monitoring techniques still lack consistency in guiding the use of opioids. This trial will study the demand for opioid use and patient prognosis in qCON and qNOX-guided general anaesthesia management.

METHODS AND ANALYSIS

This prospective, randomised, controlled trial will randomly recruit 124 patients undergoing general anaesthesia for non-cardiac surgery in equal numbers to either the qCON or BIS group. The qCON group will adjust intraoperative propofol and remifentanil dosage according to qCON and qNOX values, while the BIS group will adjust according to BIS values and haemodynamic fluctuations. The differences between the two groups will be observed in remifentanil dosing and prognosis. The primary outcome will be intraoperative remifentanil use. Secondary outcomes will include propofol consumption; the predictive ability of BIS, qCON and qNOX on conscious responses, noxious stimulus and body movements; and changes in cognitive function at 90 days postoperatively.

ETHICS AND DISSEMINATION

This study involves human participants and was approved by the Ethics Committee of the Tianjin Medical University General Hospital (IRB2022-YX-075-01). Participants gave informed consent to participate in the study before taking part. The study results will be published in peer-reviewed journals and presented at relevant academic conferences.

TRIAL REGISTRATION NUMBER

ChiCTR2200059877.

Processed electroencephalography-guided general anaesthesia to reduce postoperative delirium: a systematic review and meta-analysis

BACKGROUND

Postoperative delirium (POD) is the most common serious postoperative complication in older adults. It has uncertain aetiology, limited preventative strategies, and poor long-term outcomes. This updated systematic review and meta-analysis aimed to estimate the effect of processed electroencephalography (pEEG)-guided general anaesthesia during surgery on POD incidence.

METHODS

We performed a systematic review and meta-analysis by searching OVID MEDLINE, EMBASE, and the Cochrane Central Register of Controlled Trials (CENTRAL) electronic databases. Studies of adult patients having general anaesthesia for any surgery where pEEG was used and POD was an outcome measure were included. Full-text reports of RCTs published from database inception until August 28, 2021, were included. Trials were excluded if sedation rather than general anaesthesia was administered, or the setting was intensive care. The primary outcome was POD assessed by validated tools. The study was prospectively registered with PROSPERO.

RESULTS

Nine studies, which included 4648 eligible subjects, were identified. The incidence of POD in the pEEG-guided general anaesthesia or lighter pEEG target group was 19.0% (440/2310) compared with 23.3% (545/2338) in the usual care or deeper pEEG target group (pooled odds ratio=0.78; 95% confidence interval, 0.60-1.00; P=0.054). Significant heterogeneity was detected (I²=53%).

CONCLUSIONS

Our primary analysis demonstrated a highly sensitive result with a pooled analysis of trials in which the intervention group adhered to manufacturer's recommended guidelines, showing reduced incidence of POD with pEEG guidance. High clinical heterogeneity limits inferences from this and any future meta-analyses.

CLINICAL TRIAL REGISTRATION

CRD42020199404 (PROSPERO).

Sevoflurane dose and postoperative delirium: a prospective cohort analysis

BACKGROUND

Recent trials are conflicting as to whether titration of anaesthetic dose using electroencephalography monitoring reduces postoperative delirium. Titration to anaesthetic dose itself might yield clearer conclusions. We analysed our observational cohort to clarify both dose ranges for trials of anaesthetic dose and biological plausibility of anaesthetic dose influencing delirium.

METHODS

We analysed the use of sevoflurane in an ongoing prospective cohort of non-intracranial surgery. Of 167 participants, 118 received sevoflurane and were aged >65 yr. We tested associations between age-adjusted median sevoflurane (AMS) minimum alveolar concentration fraction or area under the sevoflurane time×dose curve (AUC-S) and delirium severity (Delirium Rating Scale-98). Delirium incidence was measured with 3-minute Diagnostic Confusion Assessment Method (3D-CAM) or CAM-ICU. Associations with previously identified delirium biomarkers (interleukin-8, neurofilament light, total tau, or S100B) were tested.

RESULTS

Delirium severity did not correlate with AMS (Spearman's ρ=-0.014, P=0.89) or AUC-S (ρ=0.093, P=0.35), nor did delirium incidence (AMS Wilcoxon P=0.86, AUC-S P=0.78). Further sensitivity analyses including propofol dose also demonstrated no relationship. Linear regression confirmed no association for AMS in unadjusted (log (IRR)=-0.06 P=0.645) or adjusted models (log (IRR)=-0.0454, P=0.735). No association was observed for AUC-S in unadjusted (log (IRR)=0.00, P=0.054) or adjusted models (log (IRR)=0.00, P=0.832). No association of anaesthetic dose with delirium biomarkers was identified (P>0.05).

CONCLUSION

Sevoflurane dose was not associated with delirium severity or incidence. Other biological mechanisms of delirium, such as inflammation and neuronal injury, appear more plausible than dose of sevoflurane.

CLINICAL TRIAL REGISTRATION

NCT03124303, NCT01980511.

Differential regional cerebrovascular reactivity to end-tidal gas combinations commonly seen during anaesthesia: A blood oxygenation level-dependent MRI observational study in awake adult subjects

BACKGROUND

Regional cerebrovascular reactivity (rCVR) is highly variable in the human brain as measured by blood oxygenation level-dependent (BOLD) MRI to changes in both end-tidal CO 2 and O 2 .

OBJECTIVES

We examined awake participants under carefully controlled end-tidal gas concentrations to assess how regional CVR changes may present with end-tidal gas changes seen commonly with anaesthesia.

DESIGN

Observational study.

SETTING

Tertiary care centre, Winnipeg, Canada. The imaging for the study occurred in 2019.

SUBJECTS

Twelve healthy adult subjects.

INTERVENTIONS

Cerebral BOLD response was studied under two end-tidal gas paradigms. First end-tidal oxygen (ETO 2 ) maintained stable whereas ETCO 2 increased incrementally from hypocapnia to hypercapnia (CO 2 ramp); second ETCO 2 maintained stable whereas ETO 2 increased from normoxia to hyperoxia (O 2 ramp). BOLD images were modeled with end-tidal gas sequences split into two equal segments to examine regional CVR.

MAIN OUTCOME MEASURES

The voxel distribution comparing hypocapnia to mild hypercapnia and mild hyperoxia (mean F I O 2  = 0.3) to marked hyperoxia (mean F I O 2  = 0.7) were compared in a paired fashion ( P  < 0.005 to reach threshold for voxel display). Additionally, type analysis was conducted on CO 2 ramp data. This stratifies the BOLD response to the CO 2 ramp into four categories of CVR slope based on segmentation (type A; +/+slope: normal response, type B +/-, type C -/-: intracranial steal, type D -/+.) Types B to D represent altered responses to the CO 2 stimulus.

RESULTS

Differential regional responsiveness was seen for both end-tidal gases. Hypocapnic regional CVR was more marked than hypercapnic CVR in 0.3% of voxels examined ( P  < 0.005, paired comparison); the converse occurred in 2.3% of voxels. For O 2 , mild hyperoxia had more marked CVR in 0.2% of voxels compared with greater hyperoxia; the converse occurred in 0.5% of voxels. All subjects had altered regional CO 2 response based on Type Analysis ranging from 4 ± 2 to 7 ± 3% of voxels.

CONCLUSION

In awake subjects, regional differences and abnormalities in CVR were observed with changes in end-tidal gases common during the conduct of anaesthesia. On the basis of these findings, consideration could be given to minimising regional CVR fluctuations in patients-at-risk of neurological complications by tighter control of end-tidal gases near the individual's resting values.