Monitoring the brain: processed electroencephalogram and peri‐operative outcomes

Electroencephalogram monitoring during anesthesia and critical care: a guide for the clinician

Perioperative anesthetic, surgical and critical careinterventions can affect brain physiology and overall brain health. The clinical utility of electroencephalogram (EEG) monitoring in anesthesia and intensive care settings is multifaceted, offering critical insights into the level of consciousness and depth of anesthesia, facilitating the titration of anesthetic doses, and enabling the detection of ischemic events and epileptic activity. Additionally, EEG monitoring can aid in predicting perioperative neurocognitive disorders, assessing the impact of systemic insults on cerebral function, and informing neuroprognostication. This review provides a comprehensive overview of the fundamental principles of electroencephalography, including the foundations of processed and quantitative electroencephalography. It further explores the characteristic EEG signatures associated wtih anesthetic drugs, the interpretation of the EEG data during anesthesia, and the broader clinical benefits and applications of EEG monitoring in both anesthetic practice and intensive care environments.

Evaluating Midazolam's Influence on Bispectral Index and Propofol Concentrations Using Schnider and Eleveld Models in Target-Controlled Infusion General Anesthesia: A Prospective Observational Study

BACKGROUND

Midazolam is widely used in clinical anesthesia, but its effects on the Bispectral Index (BIS) and propofol concentration at the effector site (CeP) are underexplored. This study investigates the pharmacodynamic interaction between midazolam and propofol in total intravenous anesthesia (TIVA) with target-controlled infusion (TCI), focusing on Schnider and Eleveld models.

METHODS

This prospective study included breast surgery patients receiving TIVA-TCI. BIS and CeP were assessed at loss of responsiveness (LoR), during maintenance (MA), and at return of responsiveness (RoR). Incidences of unwanted spontaneous responsiveness (USRE), burst suppression episodes (BSuppE), and postoperative delirium (POD) were recorded.

RESULTS

Midazolam premedication significantly reduced propofol doses and CeP at LoR and during MA, without affecting CeP at RoR. In the Schnider model, midazolam reduced total propofol dose, while in the Eleveld model, it lowered BIS at LoR. Unwanted anesthesia events occurred in 36.2% of patients, including USRE (10%), BSuppE (26.2%), and POD (1.2%). BSuppE rates were lower in the Schnider model and reduced in the midazolam group in the Eleveld model.

CONCLUSIONS

Midazolam premedication influences CeP and BIS in TIVA-TCI, with model-specific variations, optimizing propofol management and improving patient outcomes.

Intraoperative use of processed electroencephalogram in a quaternary center: a quality improvement audit

Although intraoperative electroencephalography (EEG) is not consensual among anesthesiologists, growing evidence supports its use to titrate anesthetic drugs, assess the level of arousal/consciousness, and detect ischemic cerebrovascular events; in addition, intraoperative EEG monitoring may decrease the incidence of postoperative neurocognitive disorders. Based on the known and potential benefits of intraoperative EEG monitoring, an educational program dedicated to staff anesthesiologists, residents of Anesthesiology and anesthesia technicians was started at Cleveland Clinic Abu Dhabi in May 2022 and completed in June 2022, aiming to have all patients undergoing general anesthesia with adequate brain monitoring and following international initiatives promoting perioperative brain health. All the surgical cases performed under General Anesthesia at 24 daily locations were prospectively inspected during 15 consecutive working days in March 2023. The use or absence of a processed EEG monitor was registered. Of 379 surgical cases distributed by 24 locations under General Anesthesia, 233 cases (61%) had processed EEG monitoring. The specialty with the highest use of EEG monitoring was Cardiothoracic Surgery, with 100% of cases, followed by interventional Cardiology (90%) and Vascular Surgery (75%). Otorhinolaryngology (29%), Gastrointestinal Endoscopy (25%), and Interventional Pulmonology (20%) were the areas with the lowest use of EEG monitoring. Of note, in the Neuroradiology suite, no processed EEG monitor was used in cases under General Anesthesia. We identified a reasonable use of EEG monitoring during general anesthesia, unfortunately not reaching our target of 100%. The educational and support program previously implemented within the Anesthesiology Institute needs to be continued and improved, including workshops, online discussions, and journal club sessions, to increase the use of EEG monitoring in underused areas.

Schnider and Eleveld Models for Propofol Target-Controlled Infusion Anesthesia: A Clinical Comparison

BACKGROUND

Various pharmacokinetic/pharmacodynamic (PK/PD) models have been developed to accurately dose propofol administration during total intravenous anesthesia with target-controlled infusion (TIVA-TCI). We aim to clinically compare the performance of the Schnider model and the new and general-purpose Eleveld PK/PD model during TIVA-TCI.

METHODS

We conducted a prospective observational study at a single center, enrolling 78 female patients, including 37 adults (aged < 65 years) and 41 elderly patients (aged ≥ 65 years). These patients underwent breast surgery with propofol-remifentanil TIVA-TCI guided by the bispectral index (BIS) for depth of anesthesia monitoring (target value 40-60) and the surgical plethysmographic index (SPI) for antinociception monitoring (target value 20-50) without neuromuscular blockade. The concentration at the effect site of propofol (CeP) at loss of responsiveness (LoR) during anesthesia maintenance (MA) and at return of responsiveness (RoR), the duration of surgery and anesthesia (min), the time to RoR (min), the propofol total dose (mg), the deepening of anesthesia events (DAEs), burst suppression events (BSEs), light anesthesia events (LAEs) and unwanted spontaneous responsiveness events (USREs) were considered to compare the two PK/PD models.

RESULTS

Patients undergoing BIS-SPI-guided TIVA-TCI with the Eleveld PK/PD model showed a lower CeP at LoR (1.7 (1.36-2.25) vs. 3.60 (3.00-4.18) μg/mL, p < 0.001), higher CePMA (2.80 (2.55-3.40) vs. 2.30 (1.80-2.50) μg/mL, p < 0.001) and at RoR (1.48 (1.08-1.80) vs. 0.64 (0.55-0.81) μg/mL, p < 0.001) than with the Schnider PK/PD model. Anesthetic hysteresis was observed only in the Schnider PK/PD model group (p < 0.001). DAEs (69.2% vs. 30.8%, p = 0.001) and BSEs (28.2% vs. 5.1%, p = 0.013) were more frequent with the Eleveld PK/PD model than with the Schnider PK/PD model in the general patient population. DAEs (63.2% vs. 27.3%, p = 0.030) and BSEs (31.6% vs. 4.5%, p = 0.036) were more frequent with the Eleveld PK/PD model than with the Schnider PK/PD model in the elderly.

CONCLUSIONS

The Schnider and Eleveld PK/PD models impact CePs differently. A greater incidence of DAEs and BSEs in the elderly suggests more attention is necessary in this group of patients undergoing BIS-SPI-guided TIVA-TCI with the Eleveld PK/PD than with the Schnider model.

Effect of sugammadex on processed EEG parameters in patients undergoing robot-assisted radical prostatectomy

BACKGROUND

Sugammadex has been associated with increases in the bispectral index (BIS). We evaluated the effects of sugammadex administration on quantitative electroencephalographic (EEG) and electromyographic (EMG) measures.

METHODS

We performed a prospective observational study of adult male patients undergoing robot-assisted radical prostatectomy. All patients received a sevoflurane-based general anaesthetic and a continuous infusion of rocuronium, which was reversed with 2 mg kg-1 of sugammadex i.v. BIS, EEG, and EMG measures were captured with the BIS Vista™ monitor.

RESULTS

Twenty-five patients were included in this study. Compared with baseline, BIS increased at 4-6 min (β coefficient: 3.63; 95% confidence interval [CI]: 2.22-5.04; P<0.001), spectral edge frequency 95 (SEF95) increased at 2-4 min (β coefficient: 0.29; 95% CI: 0.05-0.52; P=0.016) and 4-6 min (β coefficient: 0.71; 95% CI: 0.47-0.94; P<0.001), and EMG increased at 4-6 min (β coefficient: 1.91; 95% CI: 1.00-2.81; P<0.001) after sugammadex administration. Compared with baseline, increased beta power was observed at 2-4 min (β coefficient: 93; 95% CI: 1-185; P=0.046) and 4-6 min (β coefficient: 208; 95% CI: 116-300; P<0.001), and decreased delta power was observed at 4-6 min (β coefficient: -526.72; 95% CI: -778 to -276; P<0.001) after sugammadex administration. Neither SEF95 nor frequency band data analysis adjusted for EMG showed substantial differences. None of the patients showed clinical signs of awakening.

CONCLUSIONS

After neuromuscular block reversal with 2 mg kg-1 sugammadex, BIS, SEF95, EMG, and beta power showed small but statistically significant increases over time, while delta power decreased.

Changes in SedLine-derived processed electroencephalographic parameters during hypothermia in patients undergoing cardiac surgery with cardiopulmonary bypass

Objective

Processed electroencephalography (pEEG) is used to monitor depth-of-anesthesia during cardiopulmonary bypass (CPB). The SedLine device has been recently introduced for pEEG monitoring. However, the effect of hypothermia on its parameters during CPB is unknown. Accordingly, we aimed to investigate temperature-induced changes in SedLine-derived pEEG parameters during CPB.

Design

Prospective observational study.

Setting

Cardiac surgery operating theatre.

Participants

28 patients undergoing elective cardiac surgery with CPB.

Interventions

We continuously measured patient state index (PSI), suppression ratio (SR), bilateral spectral edge frequency (SEF) and temperature. We used linear mixed modelling with fixed and random effects to study the interactions between pEEG parameters and core temperature.

Measurements and main results

During CPB maintenance, the median temperature was 32.1°C [interquartile range (IQR): 29.8-33.6] at the end of cooling and 32.8°C (IQR: 30.1-34.0) at rewarming initiation. For each degree Celsius change in temperature during cooling and rewarming the PSI either decreased by 0.8 points [95% confidence interval (CI): 0.7-1.0; p < 0.001] or increased by 0.7 points (95% CI: 0.6-0.8; p < 0.001). The SR increased by 2.9 (95% CI: 2.3-3.4); p < 0.001) during cooling and decreased by 2.2 (95% CI: 1.7-2.7; p < 0.001) during rewarming. Changes in the SEF were not related to changes in temperature.

Conclusions

During hypothermic CPB, temperature changes led to concordant changes in the PSI. The SR increased during cooling and decreased during rewarming. Clinicians using SedLine for depth-of-anesthesia monitoring should be aware of these effects when interpreting the PSI and SR values.

The Effect of Low-Dose Esketamine on Postoperative Neurocognitive Dysfunction in Elderly Patients Undergoing General Anesthesia for Gastrointestinal Tumors: A Randomized Controlled Trial

Purpose

This study aims to evaluate the effects of the intraoperative application of low-dose esketamine on postoperative neurocognitive dysfunction (PND) in elderly patients undergoing general anesthesia for gastrointestinal tumors.

Methods

Sixty-eight elderly patients were randomly allocated to two groups: the esketamine group (group Es) (0.25 mg/kg loading, 0.125mg/kg/h infusion) and the control group (group C) (received normal saline). The primary outcome was the incidence of delayed neurocognitive recovery (DNR). The secondary outcomes were intraoperative blood loss, the total amount of fluid given during surgery, propofol and remifentanil consumption, cardiovascular adverse events, use of vasoactive drugs, operating and anesthesia time, the number of cases of sufentanil remedial analgesia, the incidence of postoperative delirium (POD), the intraoperative hemodynamics, bispectral index (BIS) value at 0, 1, 2 h after operation and numeric rating scale (NRS) pain scores within 3 d after surgery.

Results

The incidence of DNR in group Es (16.13%) was lower than in group C (38.71%) (P <0.05). The intraoperative remifentanil dosage and the number of cases of dopamine used in group Es were lower than in group C (P <0.05). Compared with group C, DBP was higher at 3 min after intubation, and MAP was lower at 30 min after extubation in group Es (P<0.05). The incidence of hypotension and tachycardia in group Es was lower than in group C (P <0.05). The NRS pain score at 3 d after surgery in group Es was lower than in group C (P <0.05).

Conclusion

Low-dose esketamine infusion reduced to some extent the incidence of DNR in elderly patients undergoing general anesthesia for gastrointestinal tumors, improved intraoperative hemodynamics and BIS value, decreased the incidence of cardiovascular adverse events and the intraoperative consumption of opioids, and relieved postoperative pain.

Processed Electroencephalogram-Based Monitoring to Guide Sedation in Critically Ill Adult Patients: Recommendations from an International Expert Panel-Based Consensus

BACKGROUND

The use of processed electroencephalography (pEEG) for depth of sedation (DOS) monitoring is increasing in anesthesia; however, how to use of this type of monitoring for critical care adult patients within the intensive care unit (ICU) remains unclear.

METHODS

A multidisciplinary panel of international experts consisting of 21 clinicians involved in monitoring DOS in ICU patients was carefully selected on the basis of their expertise in neurocritical care and neuroanesthesiology. Panelists were assigned four domains (techniques for electroencephalography [EEG] monitoring, patient selection, use of the EEG monitors, competency, and training the principles of pEEG monitoring) from which a list of questions and statements was created to be addressed. A Delphi method based on iterative approach was used to produce the final statements. Statements were classified as highly appropriate or highly inappropriate (median rating ≥ 8), appropriate (median rating ≥ 7 but < 8), or uncertain (median rating < 7) and with a strong disagreement index (DI) (DI < 0.5) or weak DI (DI ≥ 0.5 but < 1) consensus.

RESULTS

According to the statements evaluated by the panel, frontal pEEG (which includes a continuous colored density spectrogram) has been considered adequate to monitor the level of sedation (strong consensus), and it is recommended by the panel that all sedated patients (paralyzed or nonparalyzed) unfit for clinical evaluation would benefit from DOS monitoring (strong consensus) after a specific training program has been performed by the ICU staff. To cover the gap between knowledge/rational and routine application, some barriers must be broken, including lack of knowledge, validation for prolonged sedation, standardization between monitors based on different EEG analysis algorithms, and economic issues.

CONCLUSIONS

Evidence on using DOS monitors in ICU is still scarce, and further research is required to better define the benefits of using pEEG. This consensus highlights that some critically ill patients may benefit from this type of neuromonitoring.

Resting State Functional Connectivity Analysis During General Anesthesia: A High-Density EEG Study

The depth of anesthesia monitoring is helpful to guide administrations of general anesthetics during surgical procedures,however, the conventional 2-4 channels electroencephalogram (EEG) derived monitors have their limitations in monitoring conscious states due to low spatial resolution and suboptimal algorithm. In this study, 256-channel high-density EEG signals in 24 subjects receiving three types of general anesthetics (propofol, sevoflurane and ketamine) respectively were recorded both before and after anesthesia. The raw EEG signals were preprocessed by EEGLAB 14.0. Functional connectivity (FC) analysis by traditional coherence analysis (CA) method and a novel sparse representation (SR) method. And the network parameters, average clustering coefficient (ACC) and average shortest path length (ASPL) before and after anesthesia were calculated. The results show SR method find more significant FC differences in frontal and occipital cortices, and whole brain network (p<0.05). In contrast, CA can hardly obtain consistent ASPL in the whole brain network (p>0.05). Further, ASPL calculated by SR for whole brain connections in all of three anesthesia groups increased, which can be a unified EEG biomarker of general anesthetics-induced loss of consciousness (LOC). Therefore FC analysis based on SR analysis has better performance in distinguishing anesthetic-induced LOC from awake state.

A survey of current practices, attitudes and demands of anaesthesiologists regarding the depth of anaesthesia monitoring in China

Background

In this study, we aimed to analyse survey data to explore two different hypotheses; and for this purpose, we distributed an online survey to Chinese anaesthesiologists. The hypothetical questions in this survey include: (1) Chinese anaesthesiologists mainly use the depth of anaesthesia (DoA) monitors to prevent intraoperative awareness and (2) the accuracy of these monitors is the most crucial performance factor during the clinical daily practice of Chinese anaesthesiologists.

Methods

We collected and statistically analysed the response of a total of 12,750 anesthesiologists who were invited to participate in an anonymous online survey. The Chinese Society of Anaesthesiologists (CSA) trial group provided the email address of each anaesthesiologist, and the selection of respondents was random from the computerized system.

Results

The overall response rate was 32.0% (4037 respondents). Only 9.1% (95% confidence interval, 8.2-10.0%) of the respondents routinely used DoA monitors. Academic respondents (91.5, 90.3-92.7%) most frequently used DoA monitoring to prevent awareness, whereas nonacademic respondents (88.8, 87.4-90.2%) most frequently used DoA monitoring to guide the delivery of anaesthetic agents. In total, the number of respondents who did not use a DoA monitor and whose patients experienced awareness (61.7, 57.8-65.6%) was significantly greater than those who used one or several DoA monitors (51.5, 49.8-53.2%). Overall, the crucial performance factor during DoA monitoring was considered by 61.9% (60.4-63.4%) of the respondents to be accuracy. However, most respondents (95.7, 95.1-96.3%) demanded improvements in the accuracy of the monitors for DoA monitoring. In addition, broad application in patients of all ages (86.3, 85.2-87.4%), analgesia monitoring (80.4, 79.2-81.6%), and all types of anaesthetic agents (75.6, 74.3-76.9%) was reported. In total, 65.0% (63.6-66.5%) of the respondents believed that DoA monitors should be combined with EEG and vital sign monitoring, and 53.7% (52.1-55.2%) believed that advanced DoA monitors should include artificial intelligence.

Conclusions

Academic anaesthesiologists primarily use DoA monitoring to prevent awareness, whereas nonacademic anaesthesiologists use DoA monitoring to guide the delivery of anaesthetics. Anaesthesiologists demand high-accuracy DoA monitors incorporating EEG signals, multiple vital signs, and antinociceptive indicators. DoA monitors with artificial intelligence may represent a new direction for future research on DoA monitoring.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12871-021-01510-7.

Influence of rate of administration on the mechanism behind propofol induced loss of consciousness

BACKGROUND

Propofol effect-site time course models included in TCI systems have been under discussion. We hypothesized that the rate of administration is a major contributor affecting the construction of a useful effect-site model: yielding different plasmatic concentrations, loss of consciousness may occur by different mechanisms more complex than the pharmacological effect-site.

METHODOLOGY

ASA III patients were randomized in two groups: rapid induction (RI) received TCI of propofol effect-site (CeCALC) 5.4 μg/mL (modified Marsh model), and slow induction (SI) propofol infusion of 10 mg/kg/hour. A neurologist, blinded to induction method, performed neurological assessments using the FOUR score until the loss of consciousness (LOC). At LOC, the presence of brain stem reflexes, EEG index (PSI) and infusion time/mass of drug were registered. Fisher's exact test was used to describe differences between brain stem reflexes and respiration components of the FOUR score and CeCALC for 4 propofo models at LOC time.

RESULTS

16 patients divided in two groups were included. All patient in SI had brainstem reflexes free at LOC. In the RI, all patients had brain stem reflexes abolished and 1 patient had B and R of 4 points in the FOUR score (brain stem reflexes unaffected; P < .001). CeCALC at LOC time were contradictory at LOC in both groups and using 4 different Pk/Pd models.

CONCLUSIONS

Depending of the infusion rate, propofol CeCALC at LOC calculated by different Pk/Pd models could be the source of confuse data to be used to guide the state of general anesthesia.

Influence of rate of administration on the mechanism behind propofol induced loss of consciousness

BACKGROUND

Propofol effect-site time course models included in TCI systems have been under discussion. We hypothesized that the rate of administration is a major contributor affecting the construction of a useful effect-site model: yielding different plasmatic concentrations, loss of consciousness may occur by different mechanisms more complex than the pharmacological effect-site.

METHODOLOGY

ASA III patients were randomized in two groups: rapid induction (RI) received TCI of propofol effect-site (CeCALC) 5.4 μg/mL (modified Marsh model), and slow induction (SI) propofol infusion of 10 mg/kg/hour. A neurologist, blinded to induction method, performed neurological assessments using the FOUR score until the loss of consciousness (LOC). At LOC, the presence of brain stem reflexes, EEG index (PSI) and infusion time/mass of drug were registered. Fisher's exact test was used to describe differences between brain stem reflexes and respiration components of the FOUR score and CeCALC for 4 propofo models at LOC time.

RESULTS

16 patients divided in two groups were included. All patient in SI had brainstem reflexes free at LOC. In the RI, all patients had brain stem reflexes abolished and 1 patient had B and R of 4 points in the FOUR score (brain stem reflexes unaffected; P < .001). CeCALC at LOC time were contradictory at LOC in both groups and using 4 different Pk/Pd models.

CONCLUSIONS

Depending of the infusion rate, propofol CeCALC at LOC calculated by different Pk/Pd models could be the source of confuse data to be used to guide the state of general anesthesia.

Influence of noninvasive central blood pressure devices for afterload monitoring with aortic velocity-pressure Loop in anesthetized patients

BACKGROUND

Global afterload angle (GALA) is a parameter derived from velocity-pressure loop (VP Loop), for continuous assessment of cardiac afterload in the operating room. It has been validated with invasive measure of central pressure. The aim of this study was to evaluate the feasibility of noninvasive VP Loop obtained with central pressure measured with two different noninvasive tonometers.

METHODS

A prospective, observational, monocentric study was conducted in 51 patients under general anesthesia. Invasive central pressure (cPINV) was measured with a fulfilled intravascular catheter, and noninvasive central pressure signals were obtained with two applanation tonometry devices: radial artery tonometry (cPSHYG: Sphygmocor tonometer) and carotid tonometry (cPCOMP: Complior tonometer). Three VP Loops were built: VP LoopINV, VP LoopSPHYG and VP LoopCOMP. Patients were separated according to cardiovascular risk factors.

RESULTS

In the 51 patients under general anesthesia, cPSHYG was adequately obtained in 48 patients (89%) but, compared to cPINV, SBP was underestimated (-4 ± 6 mmHg, P < 0.0001), augmentation index (AIXSPHYG) and a GALASPHYG were overestimated (+13 ± 19%, P = 0.0077 and +4 ± 8°, P = 0.0024, respectively) with large limit of agreement (LOA) (-21 to 47% and -13 to 21° for AIXSPHYG and GALASPHYG, respectively). With the Complior, the failure rate of measurement for cPCOMP was 41%. SBP was similar (3 ± 17 mmHg, P = 0.32), AIXCOMP was underestimated (-11 ± 19%, P = 0.0046) and GALACOMP was similar but with large LOA (-50 to 26% and -20 to 18° for AIXCOMP and GALACOMP, respectively).

CONCLUSION

In anesthetized patient, the reliability of noninvasive central pressure monitoring by tonometry seems too limited to monitor cardiac afterload with VP Loop.

Normative values for SedLine-based processed electroencephalography parameters in awake volunteers: a prospective observational study

Processed electroencephalography (pEEG) is used to monitor depth of anaesthesia and/or sedation. A novel device (SedLine®) has been recently introduced into clinical practice. However, there are no published data on baseline SedLine values for awake adult subjects. We aimed to determine baseline values for SedLine-derived parameters in eyes-open and eyes-closed states. We performed a prospective observational study in healthy volunteers. SedLine EEG-derived parameters were recorded for 2 min with eyes closed and 8 min with eyes open. We determined the overall reference range for each value, as well as the reference range in each phase. We investigated changes in recorded parameters between the two phases, and the interaction between EMG, baseline characteristics, and Patient State Index (PSI). We collected data from 50 healthy volunteers, aged 23-63 years. Median PSI was 94 (92-95) with eyes open and 88 (87-91) with eyes closed (p < 0.001 for open versus close). EMG activity decreased from 47.2% (46.6-47.9) with eyes open to 28.6% (28.0-29.3) with eyes closing (p < 0.001). There was a significant positive correlation between EMG and PSI with eyes closed (p = 0.01) but not with eyes open, which was confirmed with linear regression analysis (p = 0.01). In awake volunteers, keeping eyes open induces significant changes to SedLine-derived parameters, most likely due to increased EMG activity (e.g. eye blinking). These findings have implications for the clinical interpretation of PSI parameters and for the planning of future research.

Predicting unconsciousness after propofol administration: qCON, BIS, and ALPHA band frequency power

During anesthesia induction with propofol the level of arousal progressively decreases until reaching loss of consciousness (LOC). In addition, there is a shift of alpha activity from parieto-occipital to frontal zones, defined as anteriorization. Whilst monitoring LOC and anteriorization would be useful to improve propofol dosage and patient safety, the current devices for anesthetic depth monitoring are unable to detect these events. The aim of this study was to observe LOC and anteriorization during anesthesia induction with propofol by applying electrodes placed in the frontal and parietal areas. Bispectral index (BIS) and quantium consciousness index (qCON) monitors were simultaneously employed. BIS™ and qCON sensors were placed in the frontal and parieto-occipital regions of 10 alopecic patients who underwent anesthesia with propofol, alfentanil, and remifentanil. The initial biophase target of propofol was 2.5 mcg/mL which was gradually increased until reaching LOC. Wilcoxon signed-rank test was used to study differences in alpha power and qCON/BIS indices along the study; and Pk value to evaluate predictive capability of anteriorization of BIS, qCON, and alpha waves. Parietal BIS and qCON values became significantly higher than frontal values 15 min after loss of eye reflex. Anteriorization was observed with both monitors. Pk values for BIS and qCON were strongly predictive of frontal alpha absolute power. During anesthesia induction with propofol it is possible to identify anteriorization with BIS and qCON in the frontal and parieto-occipital regions. Both indices showed different patterns which need to be further studied.

Evaluating NeuroSENSE for assessing depth of hypnosis during desflurane anesthesia: an adaptive, randomized-controlled trial

PURPOSE

Processed electroencephalography (EEG) monitors support depth-of-hypnosis assessment during anesthesia. This randomized-controlled trial investigated the performance of the NeuroSENSE electroencephalography (EEG) monitor to determine whether its wavelet anesthetic value for central nervous system (WAVCNS) index distinguishes consciousness from unconsciousness during induction of anesthesia (as assessed by the anesthesiologist) and emergence from anesthesia (indicated by patient responsiveness), and whether it correlates with changes in desflurane minimum alveolar concentration (MAC) during maintenance of anesthesia.

METHODS

EEG was collected using a fronto-temporal bilateral montage. The WAVCNS was continuously recorded by the NeuroSENSE monitor, to which the anesthesiologist was blinded. Anesthesia was induced with propofol/remifentanil and maintained with desflurane, with randomized changes of -0.4, 0, or +0.4 MAC every 7.5 min within the 0.8-1.6 MAC range, if clinically acceptable to the anesthesiologist. During emergence from anesthesia, desflurane was stepped down by 0.2 MAC every five minutes.

RESULTS

Data from 75 patients with a median [interquartile range] age of 41[35-52] yr were obtained. The WAVCNS distinguished consciousness from unconsciousness as assessed by the anesthesiologist, with area under the receiver operating characteristic curve of 99.5% (95% confidence interval [CI], 98.5 to 100.0) at loss of consciousness and 99.4% (95% CI, 98.5 to 100.0) at return of consciousness. Bilateral WAVCNS changes correlated with desflurane concentrations, with -8.0 and -8.6 WAVCNS units, respectively, per 1 MAC change in the 0.8-1.6 MAC range during maintenance of anesthesia and -10.0 and -10.5 WAVCNS units, respectively, in the 0.4-1.6 MAC range including emergence from anesthesia.

CONCLUSION

The NeuroSENSE monitor can reliably discriminate between consciousness and unconsciousness, as assessed by the anesthesiologist, during induction of anesthesia and with a lower level of reliability during emergence from anesthesia. The WAVCNS correlates with desflurane concentration but plateaus at higher concentrations, similar to other EEG monitors, which suggests limited utility to titrate higher concentrations of anesthetic vapour.

TRIAL REGISTRATION

clinicaltrials.gov, NCT02088671; registered 17 March, 2014.

Is the bispectral index monitoring protective against postoperative cognitive decline? A systematic review with meta-analysis

BACKGROUND

Several studies have suggested that monitoring the depth of anaesthesia might prevent the development of postoperative cognitive decline. We aimed to conduct a meta-analysis to investigate the effects of bispectral index (BIS) monitoring in anaesthesia.

METHODS

We searched in six major electronic databases. Trials were included if they discussed anaesthesia with and without BIS monitoring or low (<50) and high (≥50) BIS levels and which measured the risk of postoperative delirium (POD) and/or postoperative cognitive dysfunction (POCD).

RESULTS

We included fourteen studies in the systematic review, eight of which were eligible for meta-analysis. BIS proved to be protective against POD at 1 day postoperatively in a cohort of 2138 patients (16.1% vs. 22.8% for BIS vs. no BIS groups, respectively; relative risk [RR] 0.71; 95% confidence interval [CI] 0.59 to 0.85, without significant between-study heterogeneity I2 = 0.0%, P = 0.590). The use of BIS was neutral for POCD at 1 week but protective for POCD at 12 weeks (15.8% vs. 18.8% for BIS vs. no BIS groups, respectively; RR = 0.84, CI: 0.66 to 1.08), without significant between-study heterogeneity (I2 = 25.8%, P = 0.260). The neutral association at 1 week proved to be underpowered with trial sequential analysis. In the comparison of low BIS versus high BIS, the incidence of POD at 1 day was similar in the groups.

CONCLUSION

Our findings suggest a protective effect of BIS compared to not using BIS regarding the incidence of POD at 1 day and POCD at 12 weeks. However, limitations of the evidence warrant further investigation to identify those groups of patients by age, comorbid conditions and other individual variables who would benefit the most from the use of BIS monitoring.

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.

Using velocity-pressure loops in the operating room: a new approach of arterial mechanics for cardiac afterload monitoring under general anesthesia

Cardiac afterload is usually assessed in the ascending aorta and can be defined by the association of peripheral vascular resistance (PVR), total arterial compliance (Ctot), and aortic wave reflection (WR). We recently proposed the global afterload angle (GALA) and β-angle derived from the aortic velocity-pressure (VP) loop as continuous cardiac afterload monitoring in the descending thoracic aorta. The aim of this study was to 1) describe the arterial mechanic properties by studying the velocity-pressure relations according to cardiovascular risk (low-risk and high-risk patients) in the ascending and descending thoracic aorta and 2) analyze the association between the VP loop (GALA and β-angle) and cardiac afterload parameters (PVR, Ctot, and WR). PVR, Ctot, WR, and VP loop parameters were measured in the ascending and descending thoracic aorta in 50 anesthetized patients. At each aortic level, the mean arterial pressure (MAP), cardiac output (CO), and PVR were similar between low-risk and high-risk patients. In contrast, Ctot, WR, GALA, and β-angle were strongly influenced by cardiovascular risk factors regardless of the site of measurement along the aorta. The GALA angle was inversely related to aortic compliance, and the β-angle reflected the magnitude of wave reflection in both the ascending and descending aortas (P < 0.001). Under general anesthesia, the VP loop can provide new visual insights into arterial mechanical properties compared with the traditional MAP and CO for the assessment of cardiac afterload. Further studies are necessary to demonstrate the clinical utility of the VP loop in the operating room.NEW & NOTEWORTHY Our team recently proposed the global afterload angle (GALA) and β-angle derived from the aortic velocity-pressure (VP) loop as continuous cardiac afterload monitoring in the descending thoracic aorta under general anesthesia. However, the evaluation of cardiac afterload at this location is unusual. The present study shows that VP loop parameters can describe the components of cardiac afterload both in the ascending and descending thoracic aorta in the operating room. Aging and cardiovascular risk factors strongly influence VP loop parameters. The VP loop could provide continuous visual additional information on the arterial system than the traditional mean arterial pressure and cardiac output during the general anesthesia.

Combined Monitoring-Brain Function Monitoring and Cerebral Oximetry

Peri-operative brain function monitoring is still seen by most clinicians as complex, difficult to interpret and is therefore adopted very slowly. Current available technology mainly focusses on either a processed parameter based on the electroencephalogram to titrate anesthetics and central acting agents or on cerebral oximetry, a wider term to obtain information on the cerebral oxygen balance. There is still a lack of technological offerings that allow to monitor both entities in one device. However, there is scientific evidence that it is possible to combine measurements in an algorithmic approach that allows to better manage brain function in the surgical setting. Such integrated solutions should be made available to clinicians as they are likely to optimize patient care dependent on a sound health technology assessment.

Use, applicability and reliability of depth of hypnosis monitors in children - a survey among members of the European Society for Paediatric Anaesthesiology

Background

To assess the thoughts of practicing anaesthesiologists about the use of depth of hypnosis monitors in children.

Methods

Members of the European Society for Paediatric Anaesthesiology were invited to participate in an online survey about their thoughts regarding the use, applicability and reliability of hypnosis monitoring in children.

Results

The survey achieved a response rate of 30% (N = 168). A total of 138 completed surveys were included for further analysis. Sixty-eight respondents used hypnosis monitoring in children (Users) and 70 did not (Non-users). Sixty-five percent of the Users reported prevention of intra-operative awareness as their main reason to apply hypnosis monitoring. Among the Non-users, the most frequently given reason (43%) not to use hypnosis monitoring in children was the perceived lack or reliability of the devices in children. Hypnosis monitoring is used with a higher frequency during propofol anaesthesia than during inhalation anaesthesia. Hypnosis monitoring is furthermore used more frequently in children > 4 years than in younger children. An ideal hypnosis monitor should be reliable for all age groups and any (combination of) anaesthetic drug. We found no agreement in the interpretation of monitor index values and subsequent anaesthetic interventions following from it.

Conclusions

Prevention of intraoperative awareness appears to be the most important reason to use hypnosis monitoring in children. The perceived lack of reliability of hypnosis monitoring in children is the most important reasons not to use it. No consensus currently exists on how to adjust anaesthesia according to hypnosis monitor index values in children.

Electronic supplementary material

The online version of this article (10.1186/s12871-018-0503-y) contains supplementary material, which is available to authorized users.

Effects of hyperventilation on cerebral oxygen saturation estimated using near-infrared spectroscopy: A randomised comparison between propofol and sevoflurane anaesthesia

BACKGROUND

Near-infrared spectroscopy estimates cerebral regional tissue oxygen saturation (rSO2), which may decrease under hyperventilation. Propofol and sevoflurane act differently on cerebral blood vessels. Consequently, cerebral blood flow during hyperventilation with propofol and sevoflurane anaesthesia may differ.

OBJECTIVES

The first aim of this study was to compare the changes in rSO2 between propofol and sevoflurane anaesthesia during hyperventilation. The second aim was to assess changes in rSO2 with ventilation changes.

DESIGN

A randomised, open-label study.

SETTING

University of Yamanashi Hospital, Yamanashi, Japan from January 2014 to September 2014.

PARTICIPANTS

Fifty American Society of Anesthesiologists physical status 1 or 2 adult patients who were scheduled for elective abdominal surgery were assigned randomly to receive either propofol or sevoflurane anaesthesia. Exclusion criterion was a known history of cerebral disease such as cerebral infarction, cerebral haemorrhage, transient ischaemic attack and subarachnoid haemorrhage.

INTERVENTIONS

After induction of anaesthesia but before the start of surgery, rSO2, arterial carbon dioxide partial pressure (PaCO2) and arterial oxygen saturation were measured. Measurements were repeated at 5-min intervals during 15 min of hyperventilation with a PaCO2 around 30 mmHg (4 kPa), and again after ventilation was normalised.

MAIN OUTCOME MEASURES

The primary outcome was the difference of changes in rSO2 between propofol anaesthesia and sevoflurane anaesthesia during and after hyperventilation. The second outcome was change in rSO2 after the initiation of hyperventilation and after the normalisation of ventilation.

RESULTS

Changes of rSO2 during hyperventilation were -10 ± 7% (left) and -11 ± 8% (right) in the propofol group, and -10 ± 8% (left) and -9 ± 7% (right) in the sevoflurane group. After normalisation of PaCO2, rSO2 returned to baseline values. Arterial oxygen saturation remained stable throughout the measurement period. The rSO2 values were similar in the propofol and the sevoflurane groups at each time point.

CONCLUSION

The effects of hyperventilation on estimated rSO2 were similar with propofol and sevoflurane anaesthesia. Changes in rSO2 correlated well with ventilation changes.

TRIAL REGISTRATION

Japan Primary Registries Network (JPRN); UMIN-CTR ID; UMIN000010640.

Inhalation of volatile anesthetics via a laryngeal mask is associated with lower incidence of intraoperative awareness in non-critically ill patients

BACKGROUND

Increased incidence of intraoperative awareness was reported in critically ill patients during major operations, particularly under total intravenous (TIVA) or endotracheal general anesthesia (ETGA). However, the incidence and effect of anesthesia techniques on awareness in generally healthy, non-critically ill patients during operations have yet to receive significant attention.

METHODS AND RESULTS

This retrospective matched case-control study was conducted between January 2009 to December 2014. Surgical patients (ASA physical status I-III) whom reported intraoperative awareness during this study period were interviewed and their medical records were reviewed. The potential risk factors for awareness were compared with the non-case matched controls, who were randomly selected from the database. A total of 61436 patients were included and 16 definite cases of intraoperative awareness were identified. Patients who received ETGA and TIVA had significantly higher incidence of developing awareness compared to those who were anesthetized using laryngeal masks (LMA) (P = 0.03). Compared with the matched controls (n = 80), longer anesthesia time was associated with increased incidence of awareness (odds ratio 2.04; 95% CI 1.30-3.20, per hour increase). Perioperative use of muscle relaxant was also associated with increased incidence of awareness, while significantly lower incidence of awareness was found in patients who were anesthetized with volatile anesthetics.

CONCLUSIONS

The overall incidence of awareness was 0.023% in the ASA≤ III surgical patients who received general anesthesia. Anesthesia with a laryngeal mask under spontaneous ventilation and supplemented with volatile anesthetics may be the preferred anesthesia technique in generally healthy patients in order to provide a lower risk of intraoperative awareness.

Noninvasive Neuromonitoring: Current Utility in Subarachnoid Hemorrhage, Traumatic Brain Injury, and Stroke

Noninvasive neuromonitoring is increasingly being used to monitor the course of primary brain injury and limit secondary brain damage of patients in the neurocritical care unit. Proposed advantages over invasive neuromonitoring methods include a lower risk of infection and bleeding, no need for surgical installation, mobility and portability of some devices, and safety. The question, however, is whether noninvasive neuromonitoring is practical and trustworthy enough already. We searched the recent literature and reviewed English-language studies on noninvasive neuromonitoring in subarachnoid hemorrhage, traumatic brain injury, and ischemic and hemorrhagic stroke between the years 2010 and 2015. We found 88 studies that were eligible for review including the methods transcranial ultrasound, electroencephalography, evoked potentials, near-infrared spectroscopy, bispectral index, and pupillometry. Noninvasive neuromonitoring cannot yet completely replace invasive methods in most situations, but has great potential being complementarily integrated into multimodality monitoring, for guiding management, and for limiting the use of invasive devices and in-hospital transports for imaging.

The Feasibility and Utility of Continuous Sleep Monitoring in Critically Ill Patients Using a Portable Electroencephalography Monitor

BACKGROUND

Sleep disruption in critically ill adults can result in acute decrements in cognitive function, including delirium, but it is underdiagnosed in the setting of the intensive care unit (ICU). Although sleep stages can be assessed by polysomnography (PSG), acquisition and interpretation of PSG is costly, is labor intensive, is difficult to do over an extended period of time with critically ill patients (multiple days of continuous recording), and may interfere with patient care. In this pilot study, we investigated the feasibility and utility of monitoring sleep in the ICU setting using a portable electroencephalography (EEG) monitor, the SedLine brain monitor.

METHODS

We first performed a baseline comparison study of the SedLine brain monitor by comparing its recordings to PSG recorded in a sleep laboratory (n = 3). In a separate patient cohort, we enrolled patients in the ICU who were monitored continuously with the SedLine monitor for sleep disruption (n = 23). In all enrolled patients, we continuously monitored their EEG. The raw EEG was retrieved and sleep stages and arousals were analyzed by a board-certified technologist. Delirium was measured by a trained research nurse using the Confusion Assessment Method developed for the ICU.

RESULTS

For all enrolled patients, we continuously monitored their EEGs and were able to retrieve the raw EEGs for analysis of sleep stages. Overall, the SedLine brain monitor was able to differentiate sleep stages, as well as capture arousals and transitions between sleep stages compared with the PSG performed in the sleep laboratory. The percentage agreement was 67% for the wake stage, 77% for the non-rapid eye movement (REM) stage (N1 = 29%, N2 = 88%, and N3 = 6%), and 89% for the REM stage. The overall agreement was measured with the use of weighted kappa, which was 0.61, 95% confidence interval, 0.58 to 0.64. In the ICU study, the mean recording time for the 23 enrolled patients was 19.10 hours. There were several signs indicative of poor-quality sleep, where sleep was distributed throughout the day, with reduced time spent in REM (1.38% ± 2.74% of total sleep time), and stage N3 (2.17% ± 5.53% of total sleep time) coupled with a high arousal index (34.63 ± 19.04 arousals per hour). The occurrence of ICU delirium was not significantly different between patients with and without sleep disruption.

CONCLUSIONS

Our results suggest the utility of a portable EEG monitor to measure different sleep stages, transitions, and arousals; however, the accuracy in measuring different sleep stages by the SedLine monitor varies compared with PSG. Our results also support previous findings that sleep is fragmented in critically ill patients. Further research is necessary to develop portable EEG monitors that have higher agreement with PSG.

[Anesthesiological care of trauma patients in orthogeriatric co-management]

Elderly patients increasingly need to undergo surgery under anesthesia, especially following trauma. A timely interdisciplinary approach to the perioperative management of these patients is decisive for the long-term outcome. Orthogeriatric co-management, which includes geriatricians and anesthesiologists from an early stage, is of great benefit for geriatric patients. Patient age, comorbidities and self-sufficiency in activities of daily life are decisive for an anesthesiological assessment of the state of health and preoperative risk stratification. If necessary additional investigations, such as echocardiography must be carried out, in order to guarantee optimal perioperative anesthesiological management. Certain medical factors can delay the initiation of anesthesia and it is absolutely necessary that these are taken into consideration for surgical management. Not every form of anesthesia is equally suitable for every geriatric patient.

[Perioperative patient management in orthogeriatrics]

The management of major orthopedic surgery in the elderly prototypically reflects the perioperative risks of geriatric, often very frail patients reflecting an aging population. To improve outcome, the risks of anesthesia and surgery as well as of patient comorbidities must be thoroughly assessed and balanced using a multidisciplinary approach. Particular risks include cardiopulmonary morbidity, anemia, risk of hemorrhage and the management by anticoagulation, cerebral impairments as well as frailty and limited physiological reserves in general. Accordingly, an optimized therapy prior to, during, and after surgery will likely influence not only the immediate postoperative course but also hospital mortality and long-term outcome. Publications on the topic of perioperative management of geriatric patients are fortunately gaining in quality and quantity, not least against the background of the demographic developments. Accordingly, specific influencing factors relevant for perioperative management can be increasingly more identified. This short review summarizes the current state of knowledge to provide an overview and rationale for clinical decision making.

Effect of the severity of liver dysfunction on the minimum alveolar concentration of sevoflurane responding to an electronic stimulation in cirrhotic patients

BACKGROUND

It has been observed that patients with liver dysfunction need lower dose anesthetic compared patients with normal liver function. The minimum amount of volatile anesthetic to achieve an optimal depth of anesthesia for these patients is still unclear. In this study, Minimum alveolar concentration (MAC) of the sevoflurane was determined using an electric stimulation and the effect of severity of liver dysfunction on the MAC was observed in cirrhotic patients.

METHODS

Thirty patients undergoing upper abdominal surgery were divided into the following groups: group N (normal liver function), group A (Child-Pugh grade A) and group B (Child-Pugh grade B-C). Neuropsychological tests were performed before surgery. We measured MAC_electric (minimum alveolar concentration that prevents movement in response to an electric stimulation in 50 % of patients) of sevoflurane in cirrhotic patients with liver dysfunction using an electrical stimulation of 80 mA at 50 Hz, and analyzed factors that associated change of MAC.

RESULTS

According to the neuropsychological tests, there were 7 and 4 patients with minimal hepatic encephalopathy in Groups B and A, respectively. MAC_electric in cirrhotic patients with liver dysfunction decreased significantly compared to that in healthy liver patients (1.51 ± 0.16 vol. %, 1.33 ± 0.14 vol. % and 1.17 ± 0.13 vol. % in Group N, A and B, respectively), while MAC_electric was comparable between the cirrhotic patients with different Child-Pugh grade. The Alanine Aminotransferase (ALT) and baseline values of bispectral index (BIS) were risk factors associated with the lowering of MAC_electric (p < 0.05).

CONCLUSION

MAC_electric of sevoflurane in cirrhotic patients was significantly lower than that of patients with a healthy liver. The severity of liver dysfunction had no effect on the MAC_electric of sevoflurane in cirrhotic patients.

TRIAL REGISTRATION

This study has been registered in the Chinese Clinical Trial Register in August 3, 2011 (No. ChiCTR-TRC-11001507 ).

[Anesthesiological care in orthogeriatric co-management. Perioperative treatment of geriatric trauma patients]

Elderly patients increasingly need to undergo surgery under anesthesia, especially following trauma. A timely interdisciplinary approach to the perioperative management of these patients is decisive for the long-term outcome. Orthogeriatric co-management, which includes geriatricians and anesthesiologists from an early stage, is of great benefit for geriatric patients. Patient age, comorbidities and self-sufficiency in activities of daily life are decisive for an anesthesiological assessment of the state of health and preoperative risk stratification. If necessary additional investigations, such as echocardiography must be carried out, in order to guarantee optimal perioperative anesthesiological management. Certain medical factors can delay the initiation of anesthesia and it is absolutely necessary that these are taken into consideration for surgical management. Not every form of anesthesia is equally suitable for every geriatric patient.

Decoding motor responses from the EEG during altered states of consciousness induced by propofol

OBJECTIVE

Patients undergoing general anesthesia may awaken and become aware of the surgical procedure. Due to neuromuscular blocking agents, patients could be conscious yet unable to move. Using brain-computer interface (BCI) technology, it may be possible to detect movement attempts from the EEG. However, it is unknown how an anesthetic influences the brain response to motor tasks.

APPROACH

We tested the offline classification performance of a movement-based BCI in 12 healthy subjects at two effect-site concentrations of propofol. For each subject a second classifier was trained on the subject's data obtained before sedation, then tested on the data obtained during sedation ('transfer classification').

MAIN RESULTS

At concentration 0.5 μg ml(-1), despite an overall propofol EEG effect, the mean single trial classification accuracy was 85% (95% CI 81%-89%), and 83% (79%-88%) for the transfer classification. At 1.0 μg ml(-1), the accuracies were 81% (76%-86%), and 72% (66%-79%), respectively. At the highest propofol concentration for four subjects, unlike the remaining subjects, the movement-related brain response had been largely diminished, and the transfer classification accuracy was not significantly above chance. These subjects showed a slower and more erratic task response, indicating an altered state of consciousness distinct from that of the other subjects.

SIGNIFICANCE

The results show the potential of using a BCI to detect intra-operative awareness and justify further development of this paradigm. At the same time, the relationship between motor responses and consciousness and its clinical relevance for intraoperative awareness requires further investigation.

Relationship between Sevoflurane Plasma Concentration, Clinical Variables and Bispectral Index Values during Cardiopulmonary Bypass

Background

Anesthetic administration is increasingly guided by electroencephalography (EEG)-based monitoring, such as the bispectral index (BIS). However, during cardiopulmonary bypass (CPB), factors other than the administered hypnotic agents may influence EEG signals, and their effects on BIS values are unknown.

Methods

This report is a secondary analysis of data from a prospective, controlled interventional study comparing the effect of sevoflurane administration guided by BIS monitoring (group Sevo_BIS) and constant administration of sevoflurane (group Sevo_1.8Vol%) during CPB. Sevoflurane plasma concentration (SPC) was measured using gas chromatography. The relationships of BIS to SPC, CPB pump flow, arterial pressure, hematocrit, temperature, time on CPB, and patient characteristics were analysed.

Results

No association was observed between BIS values and SPC in group Sevo_BIS. In group Sevo_1.8Vol%, a 40 μg ml^-1 increase in SPC, which encompassed the entire range of observed values of the SPC in this analysis, was associated with a decrease of 3.6 (95% confidence interval (CI): 1.1–6.1) in BIS values (p = 0.005). Each increase in CPB time of 10 minutes was associated with an increase in BIS values of 0.25 (95%CI: 0.11–0.39, p<0.001). Path analysis revealed that the BIS values of Sevo_BIS patients were 5.3 (95%CI: 3.2–7.5) units higher than those of Sevo_1.8Vol% patients (p<0.001), which was the strongest effect on BIS values. Path analysis revealed a slope of 0.5 (95%CI: 0.3–0.7) BIS units per 1°C body temperature (p<0.001).

Conclusion

BIS monitoring is insensitive to clinically relevant changes in SPC in individual patients during CPB.