invasive monitoring. But wait... we must account for the cost of the ultrasound machines and teaching. Interestingly, ultrasound technology has been integrated into critical care medicine without the intense scrutiny of costs. Does what appear to be a "no-brainer" need the same scrutiny of a cost-effective analysis? No longer is a cost-effective analysis as simple as "show me the money." It is a complex model that will only get more complicated as the future expands the surgical, diagnostic, and therapeutic possibilities. It is a good thing that PGDT has now passed this rigorous and important test. Bennett would be proud because the patients now wiU get what was needed all along without excuses.

4. Ebm C, Ceoooni M, Sutton L, et al: A Cost-Effectiveness Analysis of Postoperative Goal-Direoted Therapy for High-Risk Surgioal Patients. Crit Care Med 2014; 42:1194-1 203 5. Pearse R, Dawson D, Fawoett J, et al: Early goal-direoted therapy after major surgery reduces oomplioations and duration of hospital stay. A randomised, oontrolled trial [ISRCTN38797445]. Crit Care 2005; 9:R687-R693 6. Rhodes A, Ceoooni M, Hamilton M, et al: Goal-direoted therapy in high-risk surgioal patients: A 15-year follow-up study. Intensive Care /Wed 2010; 36:1327-1332 7 Bennett ED: Goal-directed therapy is suooessful-ln the right patients. Crit Care Med 2002; 30:1909-1910 8. Briggs A, Gray A: The distribution of health oare oosts and their statistioal analysis for eoonomio evaluation. J Health Serv Res Policy 1998; 3:233-245 9. Birkmeyer JD, Finlayson EV, Birkmeyer CM: Volume standards for high-risk surgioal prooedures: Potential benefits of the Leapfrog initiative. Surgery 2001 ; 130:415-422 1. Watts G: Ephraim David Bennett. Lancet 2012; 379:1294 10. Sohermerhorn ML, O'Malley AJ, Jhaveri A, et al: Endovasoular vs. 2. Boyd C, Grounds RM: Cur study 20 years on: A randomized olinioal trial of open repair of abdominal aortio aneurysms in the Medioare populathe effeot of deliberate perioperative inorease of oxygen delivery on mortaltion. N EngI J Med 2008; 358:464-474 ity in high-risk surgioal patients. Intensive Care Med 2013; 39:2107-2114 11. Lederle FA, Freisohlag JA, Kyriakides TC, et al; OVER Veterans Affairs 3. Boyd O, Grounds RM, Bennett ED: A randomized olinioal trial of the Cooperative Study Group: Long-term comparison of endovasoular effeot of deliberate perioperative inorease of oxygen delivery on morand open repair of abdominal aortic aneurysm. N EngI J Med 2012; tality in high-risk surgioal patients. JAMA 1993; 270:2699-2707 367:1988-1997


Bispectral Index for Prognostication After Cardiac Arrest: The Holy Grail at Last?* C. W. E. Hoedemaekers, MD, PhD W. F.Abdo, MD, PhD Department of Intensive Care Radboud University Medical Centre Nijmegen, The Netherlands

BIS monitoring records both the electroencephalographic (EEG) and electromyographic (EMG) activity from sensors placed across the patient's forehead. The measured signals are filtered, digitized, and processed using the Fast Fourier Transformation to produce the BIS index displayed as a linear scale ranging from 0 to 100. This inherently results in the loss of qualitative data hidden in the raw EEG signals. Such EEG sigarly neurological prognostication after cardiac arrest is nals can have an impact on therapeutic strategies, for examdifficult. It focuses on the identification of variables that ple, antiepileptic treatment. BIS was originally developed predict a poor outcome with a very high specificity and to measure the hypnotic component of anesthesia, and BIS a narrow CI to avoid withdrawal of active treatment in patients reduces the risk of intraoperative awareness and improves with a potentially favorable outcome. anesthetic delivery and postoperative recovery (5). Its use in In this issue of Critical Care Medicine, Burjek et al ( 1) develbrain-injured patients has limitations and is subject to potenoped a model using the bispectral index (BIS) and sedation tial confounders. First, BIS sensors are placed over the unilatrequirements during therapeutic hypothermia to predict neueral or bilateral frontal cortical area, leaving the majority of rological outcome after cardiac arrest. This study confirms earthe brain without monitoring. High EMG activity interferlier findings that lower BIS values (2-4) are associated with a ence may falsely elevate the BIS. This can be counteracted by poor neurological outcome. Despite these studies, uncertainty the continuous use of neuromuscular blockers (6). Electrical remains whether the noninvasive and relatively easy BIS monitor is the most appropriate electrophysiological tool to aid devices such as pacemakers or electrical blankets may interfere with the BIS signal, without indication of disturbances prognostication in these patients. on the signal quality bar (7). Most of these confounding factors cannot easily be detected due to the unavailability of the *Seealsop. 1204. unprocessed EEG signal. Key Words: bispeotral index; oardiao arrest; eleotroenoephalographio; Continuous and standard EEG monitoring has become prognostioation an important tool in the management of comatose surThe authors have disolosed that they do not have any potential oonfliots vivors of cardiac arrest, both in predicting neurological of interest. outcome and in identifying and treating postanoxic staCopyright © 2013 by the Sooiety of Critical Care Medioine and Lippincott tus epilepticus. Continuous EEG allows recording of the Williams & Wilkins evolution of the EEG pattern and is a reliable indicator of


DOI: 10.1097/CCM.0000000000000187

May 2014 • Volume 42 • Number 5 1312



both good and poor neurological outcome. Absence of a continuous pattern within 12 hours after the arrest and the presence of isoelectric or low-voltage EEG after 24 hours predict a poor outcome with high sensitivity and specificity (8-10). Nonreactive EEG background activity during hypothermia and normothermia has a high predictive value for a poor outcome. Prognostication based on these criteria is impossible with the processed EEG signal from the BIS monitor. Postanoxic status epilepticus develops in a large proportion of patients after cardiac arrest (8, 11). Continuous EEG monitoring offers the possibility of early seizure detection and detection of nonconvulsive status epilepticus. Early identification and aggressive treatment of postanoxic status epilepticus may improve outcome (12, 13). BIS monitoring has been reported to detect nonconvulsive status epilepticus in case reports (14). However, changes in BIS cannot discriminate between increased EMG activity and increased neuronal activity due to recovery of the neurons or pathologic states such as seizures. Epilepsy detection and monitoring of treatment using BIS cannot be advised as routine daily practice. The prognostication of comatose patients after cardiac arrest is complex. The predictive value of clinical variables early after the arrest is low since the introduction of therapeutic hypothermia (15). Electrophysiological tests such as somatosensoryevoked potentials and EEG are well studied variables that can facilitate prognostication with high sensitivity and specificity. Previous studies (16) on the prognostic value of BIS in cardiac arrest patients showed a larger overlap between patients with good or bad outcome compared with the study by Burjek et al (1). The study published by Burjek et al (1) provides highly interesting data in need of replication in larger studies. Ideally such studies should include the concomitant use of BIS and continuous EEG to study the association between established EEG patterns associated with poor outcome and the various BIS thresholds at different time points after the arrest that have previously been suggested. In absence of more robust data and in light of data from previous BIS studies, BIS for prognostication of patients after cardiac arrest is not ready for clinical use but remains an interesting research tool. If the data of Burjek et al ( 1 ) could be replicated in well-designed larger studies, BIS could impact the daily clinical practice in patients with cardiac arrest due to its practicality in use compared with the EEG.

Critical Care Medicine

REFERENCES 1. Burjek NE, Wagner CE, Hollenbeck RD, et al: Early Bispectral Index and Sedation Requirements During Therapeutic Hypothermia Predict Neurologic Recovery Following Cardiac Arrest. Crit Care Med 2014; 42:1204-1212 2. Leary M, Fried DA, Gaieski DF, et al: Neurologic prognostication and bispectral index monitoring after resuscitation from cardiac arrest. Resuscitation 2010; 81:1133-1137 3. Riker RR, Stone PC Jr, May T, et al: Initial bispectral index may identify patients who will awaken during therapeutic hypothermia after cardiac arrest: A retrospective pilot study. Resuscitation 2013; 84:794-797 4. Seder DB, Fraser GL, Robbins T, et al: The bispectral index and suppression ratio are very early predictors of neurological outcome during therapeutic hypothermia after cardiac arrest. Intensive Care Med 2010:36:281-288 5. Punjasawadwong Y, Boonjeungmonkol N, Phongchiewboon A: Bispectral index for improving anaesthetic delivery and postoperative recovery. Cochrane Database Syst Rev 2007; 4:CD003843 6. Vivien B, Di Maria S, Ouattara A, et al: Cverestimation of bispectral index in sedated intensive care unit patients revealed by administration of muscle relaxant. Anesthesiology 2003; 99:9-17 7 Duarte LT, Saraiva RA: When the bispectral index (bis) can give false results. Rev Bras Anestesiol 2009; 59:99-109 8. Cloostermans MC, van Meulen FB, Eertman CJ, et al: Continuous electroencephalography monitoring for early prediction of neurological outcome in postanoxic patients after cardiac arrest: A prospective cohort study. Crit Care Med 201 2; 40:2867-2875 9. Crepeau AZ, Rabinstein AA, Fúgate JE, et al: Continuous EEG in therapeutic hypothermia after cardiac arrest: Prognostic and clinical value. Neurology 2013; 80:339-344 10. Rossetti AO, Cddo M, Logroscino G, et al: Prognostication after cardiac arrest and hypothermia: A prospective study. Ann Neurol 2010; 67:301-307 11. Rossetti AC, Urbano LA, Delodder F, et al: Prognostic value of continuous EEG monitoring during therapeutic hypothermia after cardiac arrest. Crit Care 2010; 14:R173 12. Legriel S, Hilly-Ginoux J, Resche-Rigon M, et al: Prognostic value of electrographic postanoxic status epilepticus in comatose cardiacarrest survivors in the therapeutic hypothermia era. Resuscitation 2013; 84:343-350 13. Rossetti AO, Oddo M, Liaudet L, et al: Predictors of awakening from postanoxic status epilepticus after therapeutic hypothermia. Neurology 2009; 72:744-749 14. Fernández-Torre JL, Hernández-Hernández MA: Utility of bilateral bispectral index (BIS) monitoring in a comatose patient with focal nonconvulsive status epilepticus. Seizure 2012; 21:61 -64 15. Kamps MJ, Horn J, Cddo M, et al: Prognostication of neurologic outcome in cardiac arrest patients after mild therapeutic hypothermia: A meta-analysis of the current literature. Intensive Care Med 2013; 39:1671-1682 16. Stammet P, Wagner DR, Gilson G, et al: Modeling serum level of s100ß and bispectral index to predict outcome after cardiac arrest. JAm Coll Cardiol 20:3\ 62:851-858



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Bispectral index for prognostication after cardiac arrest: the holy grail at last?

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