Monitoring depth of anaesthesia: is it worth the effort?:

The role of entropy monitoring in reducing propofol requirements during open heart surgeries. A prospective randomized study

Background:

Hypotension, which is commonly associated with propofol induction of general anesthesia in coronary artery bypass grafting (CABG) surgery, may cause adverse consequences in patients with coronary artery diseases undergoing this type of surgeries. The clinical absence of verbal response and eyelash reflex was used as an endpoint for hypnosis. Spectral entropy, as a novel monitoring method for the endpoint of hypnosis, affect the dose of required anesthetic agents for induction as well as the hemodynamic profile during general anesthesia in CABG surgery.

Aims:

We hypothesized that entropy monitoring might reduce the dose of propofol required for induction of anesthesia during CABG surgery and could maintain hemodynamic stability when compared with the conventional clinical monitoring.

Materials and Methods:

Sixty adult patients of both sexes, aged 30–60 years, ASA II and III, and scheduled for CABG surgery were enrolled in this prospective, controlled, randomized, double-blind study. These patients were randomly divided into two equal groups to receive intravenous propofol for induction of anesthesia guided by either the patients’ clinical response (Group I) or by entropy monitoring (Group II). The total dose of propofol used for induction of anesthesia was recorded. Hemodynamic parameters and entropy values were also recorded.

Results:

Propofol consumption was significantly reduced in Group II than Group I (P = 0.000*). Heart rate showed no statistical significance between the two groups, whereas the mean arterial pressure significantly decreased at induction in group I compared to Group II (P = 0.000*). The entropy values were significantly lower in Group I than Group II at induction (P = 0.036* for state entropy; 0.002* for response entropy). However, during intubation, and after 1 and 5 min, entropy indices displayed a significant increase in Group I than Group II.

Conclusions:

Entropy monitoring significantly reduced the dose of propofol required for induction of anesthesia and maintained hemodynamic stability compared to the conventional clinical monitoring during CABG surgeries.

Efficacy of the bispectral index and Observer's Assessment of Alertness/Sedation Scale in monitoring sedation during spinal anesthesia: A randomized clinical trial

OBJECTIVE

The bispectral index (BIS) has been used to monitor sedation during spinal anesthesia. We evaluated the correlation between BIS and the Observer's Assessment of Alertness/Sedation Scale (OAA/S) in patients sedated with dexmedetomidine, propofol, or midazolam.

METHODS

This prospective, randomized study included 46 patients scheduled for knee arthroplasty under spinal anesthesia with sedation. The patients were randomized to receive sedation with dexmedetomidine (n = 15), propofol (n = 15), or midazolam (n = 16). Correlation between BIS and OAA/S was assessed during sedation in the three groups.

RESULTS

A linear correlation was observed between BIS and OAA/S, and there was no significant difference in BIS score between the groups during mild to moderate sedation status (OAA/S 3-5). During deep sedation (OAA/S 1-2), the BIS score in the midazolam group was significantly higher than that in the propofol and dexmedetomidine groups (74.4 ± 11.9 vs 67.7 ±  9.5 vs 62.6 ± 12.2).

CONCLUSIONS

BIS values differed at the same level of sedation between different sedative agents. Objective sedation scores should therefore be used in combination with BIS values for the assessment of sedation levels during spinal anesthesia.

Anesthesia Adverse Events Voluntarily Reported in the Veterans Health Administration and Lessons Learned

BACKGROUND

Anesthesia providers have long been pioneers in patient safety. Despite remarkable efforts, anesthesia errors still occur, resulting in complications, injuries, and even death. The Veterans Health Administration (VHA) National Center of Patient Safety uses root cause analysis (RCA) to examine why system-related adverse events occur and how to prevent future similar events. This study describes the types of anesthesia adverse events reported in VHA hospitals and their root causes and preventative actions.

METHODS

RCA reports from VHA hospitals from May 30, 2012, to May 1, 2015, were reviewed for root causes, severity of patient outcomes, and actions. These elements were coded by consensus and analyzed using descriptive statistics.

RESULTS

During the study period, 3228 RCAs were submitted, of which 292 involved an anesthesia provider. Thirty-six of these were specific to anesthesia care. We reviewed these 36 RCA reports of adverse events specific to anesthesia care. Types of event included medication errors (28%, 10), regional blocks (14%, 5), airway management (14%, 5), skin integrity or position (11%, 4), other (11%, 4), consent issues (8%, 3), equipment (8%, 3), and intravenous access and anesthesia awareness (3%, 1 each). Of the 36 anesthesia events reported, 5 (14%) were identified as being catastrophic, 10 (28%) major, 12 (34%) moderate, and 9 (26%) minor. The majority of root causes identified a need for improved standardization of processes.

CONCLUSIONS

This analysis points to the need for systemwide implementation of human factors engineering-based approaches to work toward further eliminating anesthesia-related adverse events. Such actions include standardization of processes, forcing functions, separating storage of look-alike sound-alike medications, limiting stock of high-risk medication strengths, bar coding medications, use of cognitive aids such as checklists, and high-fidelity simulation.

Clinical neurophysiology of hepatic encephalopathy

BACKGROUND/OBJECTIVES

Hepatic encephalopathy (HE) has relevant impact on the quality of life of patients and their caregivers and causes relevant costs because of hospitalizations and work days lost. Its quantification is important to perform adequate clinical trials on this relevant complication of cirrhosis and portal-systemic shunting. Clinical neurophysiology, which detects functional alterations of the nervous system, has been applied to the study of HE for over 60 years. This review aims at summarizing and clarifying the role of neurophysiologic techniques in the study of HE.

METHODS

A narrative review was performed aiming at interpreting the cited papers and the techniques on the basis of their physiological and pathophysiological meaning.

RESULTS

The potential role of EEG, quantified EEG, evoked potentials-both exogenous, endogenous and motor-have been clarified to the reader that may be unfamiliar with neurophysiology.

CONCLUSIONS

The EEG, reflecting the oscillatory changes of neural network is the preferable tool to detect and monitor HE, with the exception of its most severe stage, when EEG flattens. SSEP and MEP have indication to detect and monitor transmission alterations that are likely related to myelin changes and microedema.

The Alaris auditory evoked potential monitor as an indicator of seizure inducibility and duration during electroconvulsive therapy: an observational study

Background

Precise control of anesthetic depth during electroconvulsive therapy (ECT) is crucial because most intravenous anesthetics have anticonvulsant effects. In this study, we investigated the association between anesthetic depth measured by the Alaris auditory evoked potential index (AAI) and seizure inducibility and seizure duration during ECT.

Methods

Sixty-four ECTs were evaluated in 12 consecutive patients. General anesthesia was performed with a thiopental-based method. The relationship between the pre-ictal AAI, seizure activity and seizure duration was analyzed, and a possible threshold pre-ictal AAI to induce a seizure duration of at least 25 seconds was calculated.

Results

Forty-one of the 64 ECT stimuli successfully induced seizure activity that lasted longer than 25 seconds. Pre-ictal AAI was significantly correlated to seizure duration (r = 0.54, p < 0.001) and the threshold pre-ictal AAi value was calculated to be 26 (area under curve: 0.76, sensitivity: 70.3% and specificity: 73.9%, p < 0.001). ECT with a pre-ictal AAI ≧ 26 had a higher incidence of successful seizure activity ( p < 0.001) and a longer seizure duration (55 ± 35 v.s. 21 ± 27 seconds, p < 0.001).

Conclusion

Maintenance of a pre-ictal AAI value ≧ 26 was associated with an increased incidence of successful seizure activities and a longer seizure duration. This is the first report to investigate Alaris AEP monitoring during ECT.

How electroencephalography serves the anesthesiologist

Major clinical endpoints of general anesthesia, such as the alteration of consciousness, are achieved through effects of anesthetic agents on the central nervous system, and, more precisely, on the brain. Historically, clinicians and researchers have always been interested in quantifying and characterizing those effects through recordings of surface brain electrical activity, namely electroencephalography (EEG). Over decades of research, the complex signal has been dissected to extract its core substance, with significant advances in the interpretation of the information it may contain. Methodological, engineering, statistical, mathematical, and computer progress now furnishes advanced tools that not only allow quantification of the effects of anesthesia, but also shed light on some aspects of anesthetic mechanisms. In this article, we will review how advanced EEG serves the anesthesiologist in that respect, but will not review other intraoperative utilities that have no direct relationship with consciousness, such as monitoring of brain and spinal cord integrity. We will start with a reminder of anesthestic effects on raw EEG and its time and frequency domain components, as well as a summary of the EEG analysis techniques of use for the anesthesiologist. This will introduce the description of the use of EEG to assess the depth of the hypnotic and anti-nociceptive components of anesthesia, and its clinical utility. The last part will describe the use of EEG for the understanding of mechanisms of anesthesia-induced alteration of consciousness. We will see how, eventually in association with transcranial magnetic stimulation, it allows exploring functional cerebral networks during anesthesia. We will also see how EEG recordings during anesthesia, and their sophisticated analysis, may help corroborate current theories of mental content generation.

Relationship of bispectral index to minimum alveolar concentration during isoflurane, sevoflurane or desflurane anaesthesia

OBJECTIVE

To determine bispectral index (BIS) values produced by equipotent concentrations of commonly used volatile anaesthetics.

METHODS

Female patients undergoing thyroidectomy were randomly assigned to receive isoflurane, sevoflurane or desflurane anaesthesia. After induction, anaesthesia was maintained by the volatile agent at 1 minimum alveolar concentration and supplemented with remifentanil infusion. BIS values were recorded during 1 h surgical anaesthesia after a 15 min equilibrium phase.

RESULTS

Time-averaged BIS value during the study period was significantly lower in the desflurane group (n = 29) than the sevoflurane group (n = 27) (37.0 ± 4.9 vs 41.5 ± 5.9). Duration of deep hypnosis (BIS < 40) was significantly longer in the desflurane group than the sevoflurane group (40.2 ± 20.7 vs 24.3 ± 22.5 min). There were no significant differences in any parameter between the isoflurane group (n = 27) and any other group.

CONCLUSIONS

Desflurane produces a greater hypnotic effect than sevoflurane during equipotent anaesthesia. Management of volatile anaesthesia using predetermined minimum alveolar concentration targets can lead to an unnecessarily long duration of deep hypnosis.

Monitoring with EEG entropy decreases propofol requirement and maintains cardiovascular stability during induction of anaesthesia in elderly patients

BACKGROUND AND OBJECTIVES

Electroencephalographic entropy is used to measure the degree of brain hypnosis and anaesthesia depth. Two parameters are displayed in the monitor, state entropy (SE) and response entropy (RE). Ageing leads to reduction in liver mass as well as hepatic blood flow, which decreases clearance of propofol and increases the risk of cardiovascular adverse effects. The aim of this study is to demonstrate the effect of electroencephalographic entropy on propofol requirement and haemodynamic parameters during induction of anaesthesia in elderly patients.

METHODS

We studied 72 elderly patients. Standard monitoring was performed for all patients together with entropy monitor. Patients were allocated randomly either to the control group, which were given the recommended induction dose of propofol, or to the entropy group which was induced with propofol based on entropy reading where the end-point was SE 50 and SE-RE difference less than 10. Propofol induction doses and haemodynamic changes were recorded. Anaesthesia was maintained using sevoflurane and O2 air mixture.

RESULTS

After induction of anaesthesia, the systolic, diastolic, mean arterial pressure, RE and SE were significantly lower in the control group (P value < 0.05). Total dose of propofol and the dose kg-1 were significantly reduced by 37.1% and 31.8%, respectively, in the entropy group (P value < 0.01).

CONCLUSION

The use of electroencephalographic entropy during induction of anaesthesia in elderly patients reduces propofol requirements and maintains cardiovascular stability.

L'entropie: un moyen d'apprécier le défaut d'analgésie?

OBJECTIVE

Comparison between BIS (Bispectral Index) and state (SE) and response (RE) entropy during laparotomy for inflammatory bowel disease patients (IBD) and evaluation of the variations of RE and SE during nociceptive stimulation.

STUDY DESIGN

Prospective, observational study.

PATIENTS AND METHODS

Fourteen IBD's patients undergoing laparotomy were included. Anaesthesia aimed to maintain BIS between 40 and 60 by isoflurane and nitrous oxide. Analgesia was performed by sufentanil bolus administrated according to an increase of 20% of systolic blood pressure (SBP) and heart rate compared with the baseline values. BIS, RE and SE were measured at each nociceptive stimulation. A variance analysis (Anova) was used to assess BIS, RE and SE variations throughout surgery (p<0.05 as significant). Relationship between BIS, RE and SE was assessed by Pearson correlation (p<0.01 as significant). The ability for SE and RE to predict depth of anaesthesia and intraoperative analgesia was performed by calculating area under the receiver operated curves (AUC).

RESULTS

BIS and entropy parameters had strictly the same evolution during anaesthesia. SBP increased significantly during nociceptive stimulation while no variation of RE was observed. A significant correlation was shown between BIS, RE and SE. The evaluation of anaesthesia depth was good for RE (AUC: 0.932+/-0.26) and SE (AUC: 0.926+/-0.27). There was however no difference between RE and SE to predict analgesic requirement.

CONCLUSION

Because RE includes muscular frequency analysis, it does not allow analgesic requirement evaluation in paralyzed patients.

Correlation and agreement between bispectral index and state entropy of the electroencephalogram during propofol anaesthesia

BACKGROUND

Bispectral index (BIS) and state entropy (SE) monitor hypnosis. We evaluated the correlation and the agreement between those parameters during propofol anaesthesia and laryngoscopy with and without muscle relaxation.

METHODS

A total of 25 patients were anaesthetized with propofol. At steady state (SS: BIS 40-50), they randomly received rocuronium (R) or saline (S); 3 min thereafter, a 20 s laryngoscopy was performed. Correlation (regression analysis) and agreement (Bland-Altman analysis) were evaluated before induction (baseline), at loss of eyelash reflex (LER), at SS and during the first 3 min after laryngoscopy (L).

RESULTS

The correlation coefficient r (95% CI), the mean difference (MD) (95% CI), and the limits of agreement [lower-upper limits of 95% CI of MD (sd 1.96)] between BIS and SE were as follows. Overall recordings: 0.87 (0.83 to 0.90), 2.5 (1.2 to 3.0), and [-19.5 to 24.6]; Baseline: 0.45 (0.06 to 0.72), 7.6 (6.0 to 9.2), and [-2.7 to 17.9]; LER: 0.74 (0.47 to 0.88), 8.3 (3.5 to 13.2), and [-22.6 to 39.3]; SS, all patients: 0.41 (0.14 to 0.63), 2.0 (-0.5 to 4.6), and [-19.0 to 23.3]; SS, Group S: 0.36 (-0.07 to 0.68), 1.9 (-2.5 to 6.3), and [-25.0 to 28.8]; SS, Group R: 0.63 (0.32 to 0.82), 0.2 (-2.0 to 2.3), and [-14.0 to 14.4]; L, all patients: 0.49 (0.32 to 0.63), 0.7 (-1.6 to 3.0), and [-25.6 to 27.1]; L, Group S: 0.41 (0.13 to 0.63), 2.3 (-2.4 to 7.1), and [-36.7 to 41.3]; L, Group R: 0.72 (0.56 to 0.83), -0.6 (-2.2 to 1.0), and [-14.3 to 13.1]. The correlation was good except for SS in Group S. The MD was significantly different from 0 for overall recordings, during baseline and LER, but not for the other conditions. The agreement was poor except for baseline, and SS and L in Group R.

CONCLUSIONS

BIS and SE are globally well correlated. In contrast, agreement is poor as differences of more than 20 units are frequently observed, except for awake and paralysed patients.

Monitoring consciousness in intensive care medicine

Sedation and analgesia are important components of care for critically ill patients. Avoiding over-as well as undersedation is of utmost importance as both states carry considerable risks and may influence outcome. The management of sedation has changed dramatically over the past two decades from providing a dosage level by which the patient was kept in a deep stage of anaesthesia to a current dosing strategy allowing the administration of drugs in line with individual need, resulting in most cases in a slightly sedated, cooperative patient. The importance of monitoring the level of sedation and analgesia has only recently been realised. Most importantly, regularly determining the appropriate level of sedation and analgesia as well as monitoring the desired level of sedation will help to minimise the adverse effects of sedation. Clinical sedation scales are, however, subjective, and most lack proper validation. Thus, an objective measure of sedation, such as the use of processed electroencephalogram (EEG) parameters is desirable. Processed EEG algorithms such as the bispectral index were initially introduced into clinical practice as a tool to assess the depth of anaesthesia objectively in the operating room. However, patients under general anaesthesia differ from those in an intensive care unit. Accordingly, most results from studies evaluating the performance of processed EEG parameters in critically ill patients have not been satisfactory. At present, monitoring sedation with processed EEG parameters cannot generally be recommended. However, in special situations such as deep sedation and neuromuscular blockade, in which clinical sedation scales are prone to failure, the bispectral index may help to assess the level of sedation.

Neurophysiological investigation of hepatic encephalopathy

The neurophysiological tools used to study hepatic encephalopathy (HE) are the electroencephalogram (EEG) and the evoked potentials (EPs), both exogenous and endogenous. These tools are used (1) to diagnose HE in patients with severe liver disease and mental alteration, (2) to grade overt HE and monitor the effect of treatment for HE, (3) to diagnose minimal HE (4) to predict the occurrence of episodes of overt HE or liver-related death. The rationale for the use of each of these tools together with their theoretical and practical role is reviewed.