Brain Monitoring of Anesthetic Effect

Transcription

1 Brain Monitoring of Anesthetic Effect An Evidence-Based Assessment of Clinical Impact and Safe Use Release Date: October 1, 2010 Expiration Date: April 1, 2012 Goal The goal of this educational activity is to provide physicians and nurse anesthetists with information on the clinical rationale and recent evidence supporting the use of brain monitoring during anesthesia. Learning Objectives At the completion of this activity, participants should be better prepared to: 1 Describe brain monitoring terminology, technology, and concepts. 2 Evaluate current research documenting the effects of brain monitoring on patient care during anesthesia. 3 Identify differences among available technologies and their effects in various clinical situations. 4 List the potential benefits of brain monitoring technology on emergence and recovery from general anesthesia. 5 Apply appropriate management strategies based on patients clinical profiles and brain monitoring information. Needs Statement Excessive anesthetic effect can prolong recovery and cause cardiovascular depression, cardiac arrest, and postoperative mortality. Inadequate anesthetic effect can cause unintentional intraoperative awareness. With the goal of avoiding these consequences, brain monitoring helps guide the clinician in managing anesthetic medications. However, terms and concepts related to brain monitoring are not used consistently, many anesthesia providers were trained before such advances were used, and although several technologies are available, they all do not have the same evidence base and may differ in impact on various clinical situations. Thus, clinicians require education to maximize their use of brain monitoring to improve patient outcomes. Accreditation Statements Physician: This activity has been planned and implemented in accordance with the Essential Areas and policies of the Accreditation Council for Continuing Medical Education (ACCME) through the joint sponsorship of AKH Inc., Advancing Knowledge in Healthcare, and Applied Clinical Education. AKH Inc. is accredited by the ACCME to provide continuing medical education for physicians. AKH Inc. designates this educational activity for a maximum of 1.0 AMA PRA Category 1 Credit. Physicians should only claim credit commensurate with the extent of their participation in the activity. Conflict of Interest Statement It is the policy of AKH Inc. to ensure independence, balance, objectivity, scientific rigor, and integrity in all continuing education activities. The faculty must disclose any significant relationship with a commercial interest whose product or device may be mentioned in the activity or with the commercial supporter of this activity. Identified conflicts of interest are resolved by AKH Inc. prior to accreditation of the activity. Financial Disclosures Marc J. Bloom, MD: Covidien (speakers bureau) Tong J. Gan, MD: Baxter, Eisai, Fresenius, Xanodyne (speakers bureaus); Cheetah Medical, Durect, Eisai (grant/research support) Oren Traub, PhD, MD (medical writer): Nothing to disclose AKH planners and reviewers: Nothing to disclose Disclosure of Unlabeled Use This educational activity contains discussion of some technology and devices that have been studied but not FDA-approved for brain monitoring of anesthetic effect. This discussion is noted within the text. Please refer to all official product information for discussion of approved indications, contraindications, and warnings. Estimated Time of Completion 60 minutes. Method of Participation There are no fees for participating in and receiving credit for this activity. The participant should, in order, read the objectives and monograph and complete the multiple-choice post-test. Participation Faculty Marc J. Bloom, MD Clinical Associate Professor Department of Anesthesiology New York University Langone Medical Center New York, New York Tong J. Gan, MD Professor Vice Chair for Clinical Research Department of Anesthesiology Duke University School of Medicine Durham, North Carolina Medical Writer Oren Traub, PhD, MD is available online at CMEZone.com (availability may be delayed from original print date). Enter the project number SR1058 in the keyword field to access this activity directly. Or, complete the answer sheet with registration and evaluation on page 8 and mail to: AKH Inc., PO Box 2187, Orange Park, FL ; or fax to (904) Statements of participation will be mailed/ ed approximately 6 to 8 weeks after receipt of mailed or faxed submissions. A score of at least 70% is required to complete this program successfully. One retake is allowed. The corrected answer sheet will be provided for comparison with course information. Credit is available through April 1, Disclaimer This course is designed solely to provide the health care professional with information to assist in his or her practice and professional development and is not to be considered a diagnostic tool to replace professional advice or treatment. The course serves as a general guide to the health care professional, and therefore, cannot be considered as giving legal, nursing, medical, or other professional advice in specific cases. AKH Inc., the authors, and the publisher specifically disclaim responsibility for any adverse consequences resulting directly or indirectly from information in the course, for undetected error, or through the reader s misunderstanding of the content. Copyright 2010 AKH Inc. and Applied Clinical Education. Sponsored by Supported by an educational grant from Distributed via

2 Introduction The goals of anesthesia in surgical patients include the induction and maintenance of a decreased level of consciousness (sedative component), amnesia, analgesia, prevention of muscular activity in response to noxious stimuli, and avoidance of autonomic responses (eg, hypertension, tachycardia, lacrimation, diaphoresis) to various stimuli. 1 The dynamic nature of surgical anesthesia makes maintaining the appropriate delivery of anesthesia within an optimal range (ie, neither too light nor too deep ) particularly challenging. Insufficient anesthesia is associated with multiple concerns, including intraoperative awareness. This problem is exacerbated by the use of neuromuscular blocking agents during general anesthesia, leaving patients unable to communicate. Anesthesia awareness has been found in multiple studies to occur in 0.1% to 0.2% of patients undergoing general anesthesia. 2 General anesthesia is administered to approximately 21 million US patients annually, translating to 20,000 to 40,000 cases of anesthesia awareness each year. 3 Several risk factors for this complication have been identified. For example, some procedures (eg, cardiac, obstetric, major trauma) are associated with hypotension, which may limit the use of anesthetic agents. 4 Specifically, cesarean delivery, cardiac surgery (eg, patients with ejection fraction <30%, cardiac index <2.1 L/min/m 2, severe aortic stenosis, pulmonary hypertension, or undergoing offpump coronary artery bypass graft surgery), or rigid bronchoscopy correspond with a high risk for anesthesia awareness. 5 Patients at increased risk include those with acute trauma with hypovolemia, significant impairment of cardiovascular status and expected intraoperative hypotension requiring treatment, severe end-stage lung disease, past history of awareness, anticipated difficult intubation where an awake intubation technique was not planned, known or suspected heavy alcohol intake, chronic benzodiazepine or opioid use, or current protease inhibitor therapy. In patients with these conditions or undergoing these procedures, the rate of intraoperative awareness (0.9%) was 5- to 9-fold higher than that described in the general surgical population. Clinicians may underestimate the incidence of anesthesia awareness. Moerman and colleagues studied 26 patients referred to them because of anesthesia awareness and found that in 65% of cases, and for a variety of reasons, the anesthesia provider was not informed about the occurrence. 6 Thus, unless clinicians specifically and deliberately seek a history of anesthesia awareness from their patients, many cases are missed in routine clinical practice. Anesthesia awareness causes severe distress, and long-term consequences can be profound. Patients report auditory recollections (48%), sensations of being unable to breathe (48%), and pain (28%). 7 More than 50% of these patients report experiencing mental distress following surgery, including an indeterminate number who develop post-traumatic stress disorder (PTSD). 8 Some patients describe these occurrences as their worst hospital experience, 5 and determine never again to undergo surgery. Other patients may minimize the impact of intraoperative awareness on their mental health initially, but find that they are suffering, sometimes years later. This was highlighted in a study in which patients who had expericed intraoperative awareness declared, at a 3-week follow-up, that all symptoms related to their experience had disappeared and that they did not require mental health counseling. 9 At the 2-year mark, however, the majority had psychological sequelae related to the episode, including either transient mental symptoms or severe PTSD-related disability. As a result of these and other observations, the Joint Commission issued a Sentinel Event Alert regarding the issue of intraoperative awareness in Excessive delivery of anesthetic agents is associated with adverse outcomes as well. Various studies suggest that deep anesthesia results in an increased incidence of postoperative nausea and vomiting (PONV) and related aspiration events, as well as prolonged recovery times, leading to an increased probability of cardiopulmonary complications. Furthermore, excessive anesthesia results in increased costs of care due to complications and need for extended monitoring Some investigators also have demonstrated that excessive delivery of anesthetic agents is associated with increased perioperative mortality. For example, a prospective observational study of 1-year postoperative mortality in 1,064 patients found that deep hypnotic time was an independent predictor of increased mortality. 14 Due to various patient and clinical factors, the optimal delivery of anesthetic agents cannot be predicted on the basis of drug dose/ concentration alone. Furthermore, anesthetic agent needs change throughout surgical procedures, requiring a dynamic response on the part of the anesthesia provider. Traditionally, clinicians have used a variety of indicators to measure depth of anesthesia. Many rely on changes in normal physiologic variables such as heart rate and blood pressure. Although variations in these parameters can be associated with differences in the level of anesthesia, they may not be reliable. 13 These challenges have prompted various groups to identify and develop objective strategies to help monitor anesthetic effect and guide the delivery of anesthetic agents. This monograph provides an overview of technologies used for electroencephalography (EEG)- based monitoring of anesthetic effect and explores clinical data describing their efficacy. Assessing Depth of Anesthesia Increasing doses of anesthetic agents result in defined and predictable changes in several EEG parameters, including multimodal changes in EEG amplitude and EEG frequency. 15 The challenge facing anesthesia providers is how to translate the multitude of gross and subtle changes in EEG parameters in real time to yield an accurate and clinically meaningful measure of level of consciousness in response to the dynamic administration of these agents. Several brain monitors, each using specific EEG-based indices, are available to help providers assess the appropriate use of anesthetic agents. These devices and their respective indices differ in methodology, evidence base, and utility in various clinical situations. The following is a description of several technologies but is not an exhaustive list; numerous others, including those based on auditory evoked potentials (AEPs), are in various stages of development, testing, and clinical use, and not all are available currently in the United States. Bispectral Index 13,15-18 The Bispectral Index (BIS) is the most widely used brain monitoring technology to assess depth of anesthesia in surgical patients. BIS is a statistically based, complex parameter that is composed of a combination of time domain, frequency domain, and high-order spectral subparameters. The index is calculated using a proprietary algorithm that was derived empirically by recording EEG data from healthy adults who underwent repeated transitions between consciousness and unconsciousness using several different anesthetic regimens. The raw EEG data were time-stamped at various clinical end points, and a multivariate logistic regression was used in offline analyses to identify those features of the EEG recordings that best correlated with clinical depth of sedation/anesthesia. These were then fitted to a model. 2

3 Why wait? Access this program and CMEZone.com The BIS is unique in that it integrates several disparate descriptors from a single channel of frontal EEG into a single variable, based on a large volume of clinical data, to synthesize an index that correlates with behavioral assessments of sedation and hypnosis, yet is insensitive to the specific anesthetic or sedative agent chosen. Furthermore, with use of 2 frontal leads, the BIS monitor allows simultaneous assessment of bilateral EEG activity. The BIS monitor generates a dimensionless number on a continuous scale of 0 to 100, with 100 representing alert cortical electrical activity and 0 indicating cortical electrical silence. Validation studies have demonstrated that a BIS value between 45 and 60 (optimal target, 50) is considered suitable for surgical anesthesia and reflects a decreased cerebral metabolic rate and a very low probability of consciousness. In addition to displaying the BIS index, the monitor shows a signal quality index and an indicator of electromyography (EMG) interference, which helps the operator detect erroneous readings resulting from insufficient or inappropriate signals. As with any physiologic signal, BIS is subject to interference and artifact, particularly from EMG activity, which can elevate the recorded BIS artifactually. Furthermore, BIS is a cortical function indicator that does not reflect the direct activity of the subcortical structures (including the spinal cord) that primarily mediate motor response to a noxious stimulus; thus, BIS may not be reliable for predicting movement due to noxious stimuli. Several other factors have been reported to result in inaccurate BIS readings, including the presence of senile dementia and the use of nitrous oxide, ketamine, or esmolol. Entropy Index 13,15,19,20 Generally speaking, the EEG and frontalis EMG signals are most complex in the awake state and become more regular as anesthetic depth increases. Thus, entropic scales, which describe the irregularity, complexity, or unpredictability characteristics of a signal, may be used to indicate anesthetic effect. The Entropy Index calculates entropy of processed EEG and frontalis EMG variables that have been shown to correlate with the amount of certain anesthetic agents administered to patients. More specifically, its algorithm presents 2 different entropy numbers, designated as state entropy (SE) and response entropy (RE), to yield an assessment of anesthetic effects. RE combines the frequency ranges of EEG and EMG. The reasoning behind this approach is that an increase in EMG activity may indicate that the patient is responding to a stimulus by increasing tone in the facial muscle near the sensor electrodes, possibly serving as an early warning of impending arousal. Essentially, this approach attempts to use EMG activity as useful information rather than as a nuisance artifact contaminating the EEG signal. In terms of measured parameters, SE is an index ranging from 0 (deeply anesthetized) to 91 (awake), computed over the frequency range from 0.8 to 32 Hz, reflecting the cortical state of the patient. By contrast, RE is an index ranging from 0 (deeply anesthetized) to 100 (awake), computed over a frequency range from 0.8 to 47 Hz, containing the higher EMG-dominated frequencies, and thus also will respond to the increased EMG activity resulting from inadequate muscle relaxant effect. A clinically practical level of anesthesia is achieved when entropy values are between 40 and 60. The functionality of the Entropy Index has been validated with the use of propofol, thiopental, sevoflurane, and desflurane anesthesia, but has not yet been validated reliably with ketamine anesthesia. Narcotrend Index 13,15,21,22 The Narcotrend monitor is another EEG monitor designed to measure the depth of anesthesia. This apparatus uses 2 commercially available electrodes that are placed on the patient s forehead with a third electrode serving as a reference. The original version of the monitor recorded raw EEG signals using standard electrodes for single- and double-channel registration, and after artifact exclusion and Fourier transformation, a multivariate statistical algorithm transformed the raw EEG data in a 6-letter classification reflecting the anesthetic effect, as follows: A (awake), B (sedated), C (light anesthesia), D (general anesthesia), E (general anesthesia with deep hypnosis), and F (general anesthesia with increasing burst suppression). However, in the most recent version of the Narcotrend software, the alphabet-based scale has been translated to a numeric index system (Narcotrend Index). It is scaled quantitatively, similar to the BIS scale, with 0 reflecting the deeply anesthetized state and 100 representing the awake state. Other Indices Other devices for the assessment of anesthetic effects are at various stages of development, although there is comparatively less experience with their use, and several of them may not enter the US market or may be withdrawn due to difficulties with their commercialization. For example, the Patient State Index monitor, now known as the SEDLine monitor, is based on the observation that there are reversible changes in power distribution of quantitative EEG at loss and return of consciousness. 15 This monitor generates an index based on a proprietary algorithm, using changes in power distribution collected from a high-resolution EEG monitor. Similarly, the SNAP monitor calculates an index from a singlechannel device intended to monitor a patient s EEG. It samples raw EEG signals and uses its own unique algorithm, which analyzes both high- ( Hz) and low- (0-20 Hz) frequency signal components. 15,23 Its most noteworthy feature appears to be compact size. The Cerebral State Index (CSI) monitor is another compact device that analyzes frequency shifts that take place in the EEG signal in response to changes in level of consciousness. Calculation of the CSI is based on the analysis of several factors, including the frequency content (2-35 Hz) of the EEG signal, 2 different energy ratios (called alpha and beta), the relationship between these quantities (alpha-beta shift), and the amount of instantaneous burst suppression in each 30-second period of the EEG. 23 An EMG bar also shows the energy of the EMG level in the 75- to 85-Hz frequency band. Similar to the BIS monitor, it provides the EEG suppression percentage and a measure of EMG activity as a reflection of signal quality and artifact. Finally, various entities are developing level-of-consciousness monitors based on evoked potentials primarily AEP. These monitors detect electrical responses of auditory processing pathways and centers of the brain in response to sound stimuli (clicks) delivered to the patient via headphones. Investigators have demonstrated that early auditory cortical responses, known as middle-latency AEPs, change predictably with increasing concentrations of both volatile and IV anesthetics. 23 The typical AEP response to increasing anesthetic concentrations is increased latency and decreased amplitude of the various waveform components. Various generations of AEP monitors (eg, A-line monitor, AEP/2 monitor) capitalize on this phenomenon by using a propriety algorithm to calculate an index that correlates with different levels of consciousness induced in response to anesthesia. 15 3

4 Utility of Brain Monitoring: Clinical Data Studies assessing the utility of EEG for measuring the adequacy of anesthesia were published as early as 1957, 24 but the development and validation of modern EEG indices has spurred significant debate during the past decade. Due to its relatively early introduction in the marketplace and increasingly common use, the overwhelming majority of modern investigations describe the utility of BIS, whereas comparatively few data are available for the other indices and monitors. For example, BIS has been shown to reduce emergence and recovery time and reduce primary anesthetic use. In one study, 302 patients receiving a propofol-alfentanil-nitrous oxide anesthetic at 4 institutions were randomized to standard clinical practice or standard practice plus BIS monitoring (BIS group). 25 Those who were monitored with BIS had better outcomes than those who received standard clinical practice. Specifically, the BIS group required lower normalized propofol infusion rates (134 vs 116 mcg/kg per minute; P<0.001), was extubated sooner (11.22 vs 7.25 minutes; P<0.003), had a higher percentage of patients oriented on arrival to the post-anesthesia care unit (PACU; 43% vs 23%; P<0.02), had better PACU nursing assessments (P<0.001), and became eligible for discharge sooner (37.77 vs minutes; P<0.04). Similarly, in a meta-analysis of 1,380 patients from 11 trials, Liu and colleagues reported that the use of BIS monitoring reduced anesthetic consumption by 19%, reduced the incidence of PONV (32% vs 38%; odds ratio [OR], 0.77; 95% confidence interval [CI], ), and reduced time in the recovery room, even for ambulatory surgery. 11 Individual studies have documented a larger effect of BIS in terms of reducing PONV. For example, Nelskylä and colleagues reported that PONV-related vomiting occurred in 16% of patients who received BIS monitoring and 40% who did not (P<0.05) (Figure 1). 26 In this study, more BIS-monitored patients also were able to tolerate oral fluids 30 minutes after anesthesia compared with the control group (44% vs 13%, respectively; P<0.05). This effect may be particularly important in postoperative patient satisfaction; studies have shown that the avoidance of PONV is considered more important than pain relief. 27 A cost benefit analysis found that patients were willing to spend as much as $100 to avoid this common and unpleasant surgical complication. 28 Patients, % P<0.05 BIS No BIS n=32 n=30 Figure 1. Incidence of vomiting in Phase 2 a recovery. 26 a Patients transferred to Phase 2 recovery after 120 minutes in PACU, when vital signs stable, SaO2 >95% without extra oxygen supply, severity of pain and PONV mild, 15 minutes passed since last medication. BIS, Bispectral Index; PACU, postanesthesia care unit; PONV, postoperative nausea and vomiting Adapted from reference 26. Patients Reporting Anesthesia Awareness, % BIS n=4,945 P<0.038 No BIS n=7,826 Figure 2. Incidence of awareness in patients with and without BIS monitoring, Eckman BIS, Bispectral Index Reprinted with permission from reference 29. Other studies have documented a decreased incidence of anesthesia awareness and recall with the use of brain awareness monitoring. 3,29,30 In a prospective investigation, Ekman and colleagues compared the incidence of anesthesia awareness in 4,945 consecutive BIS-monitored surgical patients who required muscle relaxants and/ or intubation with that observed in a historical control population. 29 The investigators reported that the incidence of anesthesia awareness was significantly lower in the BIS-monitored population (0.04% vs 0.18%; P<0.038) (Figure 2). 29 Furthermore, all patients in the BIS group who did experience anesthesia awareness had a BIS level of greater than 60 at the time, indicating insufficient levels of anesthesia that should have prompted additional anesthetic delivery. Similarly, the B-Aware Trial was a prospective, randomized, double-blind, multicenter trial of BIS (n=1,225) versus standard practice monitoring (n=1,238) in patients at high risk for anesthesia awareness. 5 Investigators reported that 2 patients experienced anesthesia awareness in the BIS-guided group, as did 11 in the standard practice group (P=0.022) (Figure 3). This corresponded to an anesthesia awareness risk reduction of 82% (95% CI, 17%- 98%) in response to BIS monitoring. One small study also suggested that the benefit of BIS extends to patients in the intensive care unit; these investigators studied 24 sedated, mechanically ventilated, critically ill patients and found that BIS correlated well with the Richmond Agitation-Sedation Scale and reliably differentiated adequate from inadequate sedation. 31 In a 2007 Cochrane review, Punjasawadwong and colleagues analyzed data from 20 studies of BIS monitoring in 4,056 participants. 32 They found that BIS-guided anesthesia reduced anesthesia requirements, reduced recovery and emergence times, shortened PACU stay, and reduced the incidence of intraoperative recall awareness in surgical patients with a high risk for awareness (OR, 0.20; 95% CI, ). Based on these data, the investigators concluded that, Anesthesia guided by BIS within the recommended range (40 to 60) could improve anesthetic delivery and postoperative recovery from relatively deep anesthesia. In addition, BIS-guided anesthesia has a significant impact on reduction of the incidence of intraoperative recall in surgical patients with high risk of awareness. 32 Of note, a 2008 study of 2,000 patients randomly assigned to BIS-guided anesthesia (target BIS range, 40-60) or end-tidal anesthetic gas (ETAG)-guided anesthesia (target range, minimum 4

5 Why wait? Access this program and CMEZone.com Patients Reporting Anesthesia Awareness, n BIS n=1,225 No BIS n=1,238 Figure 3. Incidence of awareness in patients with and without BIS monitoring, Myles BIS, Bispectral Index Adapted from reference 5. P=0.022 alveolar concentration) did not find any reduction in anesthesia awareness with BIS. 3 However, the findings of this study have raised considerable controversy, with at least 6 different groups of investigators publishing responses in peer-reviewed journals suggesting that the design and methodology of this study were flawed. 30,33-37 For example, some assert that the use of both very deep narcosis 33 and liberal inclusion criteria which were allowed in subjects with a low risk for awareness 30 reduced the likelihood of awareness events, leading to an underpowered result that does not justify sweeping conclusions that are neither supported by data nor consistent with the preponderance of clinical evidence. 34 Some questioned the use of inhaled anesthetics only, indicating that both the induction and maintenance of anesthesia usually are achieved using IV agents, 35 and others disagreed with the use of an ETAG-guided protocol, considering it outside standard clinical practice, and potentially an intervention in itself. 36 Finally, more than 50% of patients in the BIS group and 75% of those in the control group breached the study protocol with BIS ratings greater than Regardless, more recent studies provide further, and potentially more important, evidence of a beneficial effect of EEG-based brain monitoring by demonstrating improvements in long-term morbidity and mortality. For example, Kertai and colleagues studied 460 patients who underwent cardiac surgery and reported that cumulative duration of low BIS scores (<45), suggesting overuse of anesthetic agents, was independently associated with intermediate-term mortality. 38 Specifically, 17.8% of patients died in the first 3 years after cardiac surgery, with the risk for death increasing by 29% for every cumulative hour for which the BIS was less than 45 during surgery. These observations were consistent with those of Monk and colleagues, who found an association between cumulative deep hypnotic time (BIS <45) and 1-year mortality after major noncardiac surgery. 14 Furthermore, at the 2009 annual meeting of the American Society of Anesthesiologists (ASA), Saager and colleagues presented data suggesting that a concordance of low mean arterial pressure, low endtidal volatile anesthetic concentration, and low BIS index (ie, triplelow ) was associated with a 3-fold risk for mortality at 30 days, and a 2-fold risk for mortality at 1 year. 39 This combination of risk factors was a much more powerful predictor of poor outcomes when compared with any 1 or 2 of these risk factors alone. The question logically raised by these studies is whether avoiding deep anesthesia through BIS monitoring can improve outcomes or whether low BIS levels simply are a marker of comorbidity associated with a greater risk for postoperative death. Leslie and colleagues explored this issue in a recent study. 40 Following up (after a median of 4.1 years) on the B-Aware Trial, which had randomly allocated 2,463 patients at high risk for anesthesia awareness to BIS-guided anesthesia or routine care, these investigators found that monitoring with BIS and absence of BIS values less than 40 for more than 5 minutes were associated with improved survival and reduced morbidity. An overview of BIS and mortality by Monk and colleagues analyzed the data reported by Leslie s group and noted that the researchers found that the optimal BIS group had significantly lower mortality and morbidity rates compared with both the no BIS and the low BIS groups. 41 These results suggest that although BIS monitoring per se did not affect important outcomes, the maintenance of BIS values between 40 and 60 reduced the risk of morbidity and mortality. 41 Other than BIS, with its long record of clinical study, few clinical trials or other comparative studies have investigated the effect of brain monitoring technologies on the incidence of anesthesia awareness; in fact, the 2006 ASA practice advisory reported that only BIS had been studied sufficiently in that context. 2 For example, a clinical trial of the Entropy Monitor (N=368) demonstrated shorter recovery times and reduced consumption of anesthetic drugs in patients for whom entropy values were shown to the anesthesia provider relative to those for whom such values were not shown. 42 However, a more recent case report described a patient who experienced anesthesia awareness despite low spectral entropy values. 43 Furthermore, a small study (N=12) using the isolated forearm technique of assessing consciousness found that the Narcotrend Index monitor could not reliably detect consciousness during general anesthesia when neuromuscular blocking agents were used. 21 Some studies have focused on the correlations between different technologies. For example, one investigation found a correlation between the SNAP index and BIS (although not in agreement with each other numerically and therefore not interchangeable), 44 although others reported a correlation between CSI and BIS. 45 However, investigators have not yet studied the effect of these other technologies on long-term patient morbidity and mortality. Because of the potential benefits of EEG-based monitoring to help guide the delivery of anesthesia during surgical procedures, further investigation of these less well-studied technologies is likely and should help to delineate their specific strengths, limitations, and overall clinical utility. Clinical Recommendations In response to increasing interest in the role of EEG-based brain monitoring in the delivery of anesthesia, the ASA created the Task Force on Intraoperative Awareness to review available data (studies published as of 2005) and provide recommendations regarding its appropriate use. The task force issued recommendations in 2006 (Table 1, page 6). 2 The group suggested that the use of EEG-based intraoperative monitoring may be appropriate for some (but not all) patients and that these devices should be used in combination with other monitoring modalities (eg, clinical techniques, such as checking for purposeful or reflex movement; conventional monitoring systems). 5

6 Table 1. EEG-Based Brain Monitoring of Anesthetic Effect: ASA Recommendations 2 Intraoperative monitoring of depth of anesthesia, for the purpose of minimizing the occurrence of awareness, should rely on multiple modalities Clinical techniques Checking for clinical signs such as purposeful or reflex movement Conventional monitoring systems Electrocardiography Blood pressure monitoring Heart rate monitoring End-tidal anesthetic analysis Capnography Use of neuromuscular blocking drugs may mask purposeful or reflex movements Adds additional importance to use of monitoring methods that assure adequate delivery of anesthesia Brain electrical activity monitoring valuable in monitoring depth of anesthesia in selected patients Those at risk for awareness Those requiring smaller doses of general anesthetics Brain function monitoring not routinely indicated for patients undergoing general anesthesia, either to reduce frequency of intraoperative awareness or to monitor depth of anesthesia. Use on case-by-case basis for selected patients Those at risk for awareness Those requiring smaller doses of general anesthetics Trauma surgery Cesarean delivery Total IV anesthesia ASA, American Society of Anesthesiologists; EEG, electroencephalography Adapted from reference 2. In essence, these recommendations stressed that, when used, EEG-based brain monitoring should serve as an adjunct to clinical judgment and training and that data generated by these devices must be integrated with other information available for assessment of the patient. 2 The anesthesia provider must be sure that the index monitor number is consistent with the apparent state of the patient, doses of anesthetic drugs, degrees of surgical stimulation, and appearance of the raw EEG signal. Discrepancies should prompt critical examination of the patient s state using all available information. For example, in interpreting BIS data, the clinician must be aware of potential artifacts that may be caused by poor skin contact, muscle activity or rigidity, improper sensor placement, and electrical interference. 17 Recommendations from the Joint Commission 2004 Sentinel Alert regarding anesthesia awareness also support the ASA s recommendations, stating that providers should consider the effective application of available anesthesia monitoring techniques, including the timely maintenance of anesthesia equipment [to reduce the incidence of anesthesia awareness] (Table 2). 10 Table 2. Prevention and Management of Anesthesia Awareness: Joint Commission Recommendations 10 Develop and implement an anesthesia awareness policy that addresses the following: Education of clinical staff about anesthesia awareness and how to manage patients who have experienced awareness. Identification of patients at proportionately higher risk for an awareness experience, and discussion with such patients, before surgery, of the potential for anesthesia awareness. The effective application of available anesthesia monitoring techniques, including the timely maintenance of anesthesia equipment. Appropriate postoperative follow-up of all patients who have undergone general anesthesia, including children. The identification, management and, if appropriate, referral of patients who have experienced awareness. Assure access to necessary counseling or other support for patients who are experiencing post-traumatic stress disorder or other mental distress. The Joint Commission, Reprinted with permission. One scenario in which the technology may be of particular benefit is in the intraoperative management of hemodynamics. 46 For example, instances of hypotension combined with low BIS may indicate a need for decreased rate of anesthetic delivery, whereas hypotension in the context of therapeutic or high BIS might suggest the need for pressors. Similarly, intraoperative hypertension in the context of therapeutic or low BIS may reflect the need for antihypertensive agents, whereas hypertension combined with high BIS should prompt increased delivery of anesthetic agents. Whether data generated from large-scale randomized trials and comprehensive meta-analyses that have been reported since publication of the ASA recommendations would result in more definitive guidance regarding the use of EEG-based brain monitoring is unclear. Certainly, the conclusions from the ASA task force statement were limited by a lack of comparative data involving different devices and indices a deficiency that persists. That said, the timing of any reevaluation of medical literature and the publication of the next iteration of recommendations is not known. In the interim, it is incumbent on practicing clinicians to familiarize themselves with recent data as to the potential benefits and limitations of this technology. Conclusion Delivery of anesthesia must be monitored carefully to avoid over- or underuse, as both excessive and inadequate anesthetic effect can have serious consequences. EEG-based brain monitoring can help guide the provider to optimize anesthetic effect and may result in improved short- and long-term outcomes, but this technology cannot supplant clinical judgment or obviate the use of adjunctive monitoring techniques. Among monitoring technologies, BIS is supported by the largest body of data and longest track record. Further large, randomized controlled trials are required to confirm the benefit of and identify optimal indications and protocols for the use of brain monitoring in guiding anesthesia. 6

7 Why wait? Access this program and CMEZone.com References 1. Guignard B. Best Pract Res Clin Anaesthesiol. 2006;20(1): American Society of Anesthesiologists Task Force on Intraoperative Awareness. Anesthesiology. 2006;104(4): Avidan MS, et al. N Engl J Med. 2008;358(11): Ghoneim MM. Anesthesiology. 2000;92(2): Myles PS, et al. Lancet. 2004;363(9423): Moerman N, et al. Anesthesiology. 1993;79(3): Sebel PS, et al. Anesth Analg. 2004;99(3): Osterman JE, et al. Gen Hosp Psychiatry. 2001;23(4): Lennmarken C, et al. Acta Anaesthesiol Scand. 2002;46(3): Joint Commission. Accessed August 1, Liu SS. Anesthesiology. 2004;101(2): White PF. Anesth Analg. 2010;110(2): Bruhn J, et al. Br J Anaesth. 2006;7(1): Monk TG, et al. Anesth Analg. 2005;100: Bowdle TA. Anesthesiol Clin. 2006;24(4): Rampil IJ. Curr Opin Anaesthesiol. 2001;14(6): Aspect Medical Systems. BISVIEW_operatingmanual_ENGLISH.pdf. Accessed August 1, Johansen JW. Best Pract Res Clin Anaesthesiol. 2006;20(1): Schmidt GN, et al. Anesthesiology. 2004;101(6): Kotur PF. Indian J. Anaesth. 2004;48(3): Russell IF. Br J Anaesth. 2006;96(3): Kreuer S, Wilhelm W. Best Pract Res Clin Anaesthesiol. 2006;20(1): Sinha PK, Koshy T. Indian J Anaesth. 2007;51(5): Wyke BD. Anaesthesia. 1957;12(3): Gan TJ, et al. Anesthesiology. 1997;87(4): Nelskylä KA, et al. Anesth Analg. 2001;93(5): Gold BS, et al. JAMA. 1999;262: Gan T, et al. Anesth Analg. 2001;92: Ekman A, et al. Acta Anaesthesiol Scand. 2004;48(1): Myles PS, et al. N Engl J Med. 2008;359(4): ; author reply Karamchandani K, et al. J Anesth. 2010;24(3): Punjasawadwong Y, et al. Cochrane Database Syst Rev. 2007;(4):CD Pavlovic D. Eur J Anaesthesiol. 2009;26(1): Kelley SD, et al. N Engl J Med. 2008;359(4): ; author reply Aretha D, et al. N Engl J Med. 2008;359(4): ; author reply Bo L, et al. N Engl J Med. 2008;359(4):429; author reply Cook TM. N Engl J Med. 2008;359(4):430; author reply Kertai MD, et al. Anesthesiology. 2010;112(5): Saager L, et al. Anesthesiology 2009;111:A Leslie K, et al. Anesth Analg. 2010;110(3): Monk TG, Weldon BC. Anesthesiology. 2010;112(5): Vakkuri A, et al. Anesthesiology. 2005;103(2): Vassiliadis M, et al. Anesth Analg. 2007;105(2): Hrelec C, et al. J Clin Monit Comput July 22. [Epub ahead of print] 45. Nishiyama T, Komatsu K. J Anesth. 2010;24(3): Aspect Medical Systems. ConsciousnessUsingtheBispectralIndexDuringAnesthesia-PocketGuide.pdf. Accessed August 1, Post-Test The incidence of intraoperative awareness is estimated as. a. 0.01% to 0.02% b. 0.1% to 0.2% c. 1% to 2% d. 10% to 20% surgery should be regarded as particularly high risk for intraoperative awareness. a. Abdominal b. Cardiac c. Cosmetic d. Gynecologic When using the Bispectral Index (BIS), represents the most clinically appropriate target for optimal delivery of anesthetic agents? a. 0 to 15 b. 25 to 40 c. 45 to 60 d. 85 to 100 Use of electroencephalography (EEG)- based brain monitoring of anesthetic effect may reduce. a. incidence of postoperative nausea and vomiting b. need for clinical judgment by the anesthesiologist c. long-term survival rates d. procedural time The majority of EEG-based monitors for the assessment of anesthetic effect express their index in. a. Hertz (Hz) b. Microvolt (mcv) c. MilliHertz (mhz) d. Dimensionless units Hypotension combined with a normal or high BIS score may indicate a need for. a. decreased delivery of anesthetic agents b. increased delivery of anesthetic agents c. administration of pressors d. administration of antihypertensive agents Hypertension combined with a high BIS score may indicate a need for. a. decreased delivery of anesthetic agents b. increased delivery of anesthetic agents c. administration of vasopressors d. none of the above According to various meta-analyses and the majority of studies, which of the following statements is true? a. EEG-based brain monitoring to guide anesthetic delivery results in a decreased incidence of intraoperative awareness. b. EEG-based brain monitoring to guide anesthetic delivery results in no difference in the incidence of intraoperative awareness. c. EEG-based brain monitoring to guide anesthetic delivery results in a slight increase in the incidence of intraoperative awareness. d. EEG-based brain monitoring to guide anesthetic delivery results in a large increase in intraoperative awareness. 9. Several studies have demonstrated that the cumulative intraoperative time of low BIS (<45) is associated with. a. decreased intermediate mortality b. decreased long-term mortality c. increased intermediate and long-term mortality d. none of the above 10. Which of the following statements most accurately reflects the American Society of Anesthesiologists 2006 statement on the use of brain monitoring for delivery of anesthesia? a. EEG-based brain monitoring should be used for all patients. b. EEG-based brain monitoring alone is sufficient to guide delivery of anesthetic agents. c. EEG-based brain monitoring technology should be used as an adjunct to clinical judgment and traditional monitoring techniques in some patients. d. EEG-based brain monitoring should never be used. 7

8 Answer Sheet and Evaluation Form Brain Monitoring of Anesthetic Effect An Evidence-Based Assessment of Clinical Impact and Safe Use Release Date: October 1, 2010 Expiration Date: April 1, 2012 Participate online at: CMEZone.com Type SR1058 in the keyword field (availability may be delayed from print date). Or fax to: (904) Or mail to: AKH Inc. Advancing Knowledge in Healthcare PO Box 2187 Orange Park, FL Participant Information (please print) First Name: Last Name: Degree: Address: City: State: ZIP: Daytime Phone: Fax: License #: State of Licensure: o Physician I am claiming AMA PRA Category 1 Credit o Other (specify): Evaluation Questions Please answer the following questions by circling the appropriate rating. 4 = Strongly Agree 3 = Agree 2 = Disagree 1 = Strongly Disagree 1. After participating in this activity, I am better prepared to: a. Describe brain monitoring terminology, technology, and concepts b. Evaluate current research documenting the effects of brain monitoring on patient care during anesthesia c. Identify differences among available technologies and their effects in various clinical situations d. List the potential benefits of brain monitoring technology on emergence and recovery from general anesthesia e. Apply appropriate management strategies based on patients clinical profiles and brain monitoring information The activity met my educational needs The faculty were knowledgeable and effective in the presentation of content The teaching method and educational materials were effective The learning activities were effective and incorporated active learning methods Post-Test Answer Section Please circle the correct answer for each question. (A score of at least 70% is required to receive credit.) 1. a b c d 2. a b c d 3. a b c d 4. a b c d 5. a b c d 6. a b c d 7. a b c d 6. The post-test accurately assessed learning The content was objective, current, scientifically based, and free of commercial bias. o Yes o No (please explain): 8. a b c d 9. a b c d 10. a b c d 8. Based on information presented in this activity, I will: o do nothing, as the content was not convincing. o seek additional information on this topic. o change my practice. o do nothing, as current practice reflects the program s recommendations. 9. The most important concept learned during this activity that may effect a change in patient care is: _ 10. What issue(s) related to the therapeutic area discussed in this activity, or other topics, would you like addressed in future continuing education? 11. Additional comments: 8 CMEZone.com is powered by CECity. SR1058