Three blind mice: a tail of discordant trials

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).

Spinal Anesthesia with Targeted Sedation based on Bispectral Index Values Compared with General Anesthesia with Masked Bispectral Index Values to Reduce Delirium: The SHARP Randomized Controlled Trial

BACKGROUND

Reducing depth of anesthesia and anesthetic exposure may help prevent delirium, but trials have been conflicting. Most studies were conducted under general anesthesia or in cognitively impaired patients. It is unclear whether reducing depth of anesthesia beyond levels consistent with general anesthesia reduces delirium in cognitively intact patients. The authors' objective was to determine whether a bundled approach to reduce anesthetic agent exposure as determined by Bispectral Index (BIS) values (spinal anesthesia with targeted sedation based on BIS values) compared with general anesthesia (masked BIS) reduces delirium.

METHODS

Important eligibility criteria for this parallel-arm randomized trial were patients 65 yr or greater undergoing lumbar spine fusion. The intervention group received spinal anesthesia with targeted sedation to BIS greater than 60 to 70. The control group received general anesthesia (masked BIS). The primary outcome was delirium using the Confusion Assessment Method daily through postoperative day 3, with blinded assessment.

RESULTS

The median age of 217 patients in the analysis was 72 (interquartile range, 69 to 77). The median BIS value in the spinal anesthesia with targeted sedation based on BIS values group was 62 (interquartile range, 53 to 70) and in the general anesthesia with masked BIS values group was 45 (interquartile range, 41 to 50; P < 0.001). Incident delirium was not different in the spinal anesthesia with targeted sedation based on BIS values group (25.2% [28 of 111] vs. the general anesthesia with masked BIS values group (18.9% [20 of 106]; P = 0.259; relative risk, 1.22 [95% CI, 0.85 to 1.76]). In prespecified subgroup analyses, the effect of anesthetic strategy differed according to the Mini-Mental State Examination, but not the Charlson Comorbidity Index or age. Two strokes occurred among patients receiving spinal anesthesia and one death among patients receiving general anesthesia.

CONCLUSIONS

Spinal anesthesia with targeted sedation based on BIS values compared with general anesthesia with masked BIS values did not reduce delirium after lumbar fusion.

EDITOR’S PERSPECTIVE

Anaesthetic depth and delirium: a challenging balancing act

This editorial highlights the findings of the Balanced Anaesthesia Delirium study, a 515-patient substudy of the 6644 patient Balanced Anaesthesia trial, which found that targeting deep anaesthesia in patients undergoing major noncardiac surgery was not associated with significantly increased postoperative death or major morbidity. The substudy found that using bispectral index (BIS) guidance with the intention of deliberately achieving deep volatile agent-based anaesthesia (target BIS reading 35 vs 50) significantly increased delirium incidence (28% vs 19%), although not subsyndromal delirium incidence (45% vs 49%). We discuss the implications of these findings for anaesthetic practice, and address whether the BIS should be used as a guide to deliver precision anaesthesia for delirium prevention. We posit that subpopulation-based differences within this multicentre substudy could have affected delirium occurrence, since the findings appeared to rest on outcomes in patients from East Asia. We conclude that questions of whether and for whom deep anaesthesia is deliriogenic remain unanswered.

Poincaré Plot Area of Gamma-Band EEG as a Measure of Emergence From Inhalational General Anesthesia

The Poincaré plot obtained from electroencephalography (EEG) has been used to evaluate the depth of anesthesia. A standalone EEG Analyzer application was developed; raw EEG signals obtained from a bispectral index (BIS) monitor were analyzed using an on-line monitoring system. Correlations between Poincaré plot parameters and other measurements associated with anesthesia depth were evaluated during emergence from inhalational general anesthesia. Of the participants, 20 were adults anesthetized with sevoflurane (adult_{_SEV}), 20 were adults anesthetized with desflurane (adult_{_DES}), and 20 were pediatric patients anesthetized with sevoflurane (ped_{_SEV}). EEG signals were preprocessed through six bandpass digital filters (f0: 0.5–47 Hz, f1: 0.5–8 Hz, f2: 8–13 Hz, f3: 13–20 Hz, f4: 20–30 Hz, and f5: 30–47 Hz). The Poincaré plot-area ratio (PP_AR = PP_{A_fx}/PP_{A_f0}, fx = f1∼f5) was analyzed at five frequency ranges. Regardless of the inhalational anesthetic used, there were strong linear correlations between the logarithm of PP_AR at f5 and BIS (R² = 0.67, 0.79, and 0.71, in the adult_{_SEV}, adult_{_DES}, and ped_{_SEV} groups, respectively). As an additional observation, a part of EMG activity at the gamma range of 30–47 Hz probably influenced the calculations of BIS and PP_{AR_f5} with a non-negligible level. The logarithm of PP_AR in the gamma band was most sensitive to state changes during the emergence process and could provide a new non-proprietary parameter that correlates with changes in BIS during measurement of anesthesia depth.

Reducing Perioperative Neurocognitive Disorders (PND) Through Depth of Anesthesia Monitoring: A Critical Review

General anesthesia has been administered for over 150 years, and in that time, has become progressively safer. Improvements in outcomes have been driven by multiple advances, including the use of non-invasive monitors to assess cardiovascular and respiratory status. More recent advances have included the development and use of monitors to measure neurologic status by means of “processed” electroencephalography (pEEG), wherein the frontal EEG signal is analyzed by proprietary algorithms to produce a dimensionless number (scaled from 0 to 100), wherein low values are associated with deepening levels of sedation that progresses to loss of consciousness. Such monitors have been shown to enable anesthetic titration so as to expedite emergence and early recovery, and their use is advocated for the prevention of intraoperative awareness in the setting of administration of total intravenous anesthesia and neuromuscular blockade. Whether their use can minimize, or prevent, longer term adverse events is a matter of debate. In this narrative review of the most recent literature, we provide an assessment on the use of pEEG monitors in the prevention of a notable, and important, postoperative adverse outcome – delirium – in elderly patients. As we will discuss, the existing data do not support its routine use for the prevention of postoperative delirium in this, or any other, patient population.