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Inappropriately low bispectral index of the elderly during emergence from sevoflurane anesthesia
Journal of Clinical Anesthesia (2016) 34, 279–281
Correspondence Inappropriately low bispectral index of the elderly during emergence from sevoflurane anesthesia☆,☆☆ To the Editor: Neuromuscular activity has been previously reported to influence bispectral index (BIS) estimations in both awake volunteers [1] and sedated patients [2,3]. The applicability of BIS monitoring for assessing the depth of anesthesia in elderly individuals is also problematic because electroencephalogram (EEG) in the elderly is known to be electrophysiologically different from those in younger individuals [4,5]. We have described here a case of inappropriately low (b 50) BIS in an 87-year-old woman during the emergence period from sevoflurane anesthesia until reversal of muscle relaxation was started. After antagonism of the muscle relaxant with sugammadex, the patients immediately opened their eyes in response to calling their name, accompanied by an abrupt rise in BIS to more than 90. Judging from this situation, the level of anesthesia seemed quite shallow, despite the low BIS, just before antagonism of muscle relaxation. We retrospectively examined the EEG in this case. It appears to offer evidence that BIS monitoring in elderly patients with neuromuscular blockade can include some degree of misappraisal. Before submission of the present case report, written informed consent was obtained from the patient and her family for analyzing EEG data and publishing the case in the journal. The patient had not been prescribed any antipsychotics or antidementia agents. Anesthesia was induced using propofol and remifentanil and was maintained using sevoflurane, remifentanil, and epidural anesthesia. BIS was monitored using an A-2000 BIS monitor (version 4.0; Aspect Medical Systems, Natick, MA), and raw EEG (converted from analog to digital at 128 Hz) was continuously collected. At the completion of surgical operations, we decreased the concentration of sevoflurane to 0.5%, continuing at this level until the end of x-ray imaging. Sevoflurane inhalation was then ended so that the patient can be promptly extubated once the x-ray images are obtained—usually approximately 4 minutes after the end of x-ray imaging. Sugammadex
☆ ☆☆
Conflicts of interest: None declared. Financial support and sponsorship: None declared.
0952-8180/© 2016 Elsevier Inc. All rights reserved.
(200 mg) was injected intravenously once suitable x-ray images have been confirmed. The stored EEG was retrospectively analyzed using BSA version 3.22B2 software [6], and EEG subparameters were examined, in addition to BIS. Analyzed parameters were 95% spectral edge frequency (SEF95); relative β ratio (RBR = log10 [spectral power (30-47 Hz)/ spectral power (11-20 Hz)]); SynchFastSlow (BispR = log10 [bispectral power (40-47 Hz)/bispectral power (0.5-47 Hz)]); and burst suppression ratio (BSR). Figure 1 shows changes in BIS, SEF95, RBR, and BispR during emergence from sevoflurane anesthesia in an 87-year-old woman. EEG waves and power spectra at respective time points are also shown. BIS remained low (approximately 40) during the emergence period until administration of sugammadex (point S) and immediately increased to more than 90 after starting reversal of muscle relaxation. Throughout the course of emergence until Point_S, SEF95, RBR, and BispR likewise remained low (around 10 Hz, − 1, and − 3, respectively) and increased just after Point_S, although the increase in BIS was slightly delayed by approximately 20 seconds and steep. Burst suppression ratio was zero throughout the analysis period. BIS thus remained low until administration of sugammadex, although the patients seemed to already be in a condition of shallow anesthesia from which they could be aroused by light stimulation. Electromyography without neuromuscular blockade has previously been reported to result in elevation of BIS in anesthetized patients [2,3]. Conversely, the present finding indicates that pure EEG of the elderly without the presence of electromyography results in an inappropriately low BIS, agreeing with previous reports [1,3] and providing evidence that monitoring BIS does not allow precise estimation of the depth of anesthesia during emergence in elderly patients under management with muscle relaxants. Accordingly, when the BIS monitor showed an unnaturally deep level of anesthesia during emergence in an elderly patient who has received neuromuscular blockade, anesthesia management should be conducted in consideration of quantitative parameters of anesthetic agents, such as end-expiratory anesthesia concentration and/or the simulated effect site concentration of anesthetics. Although the inappropriately low BIS was observed in very old elderly patient under muscle relaxation, whether similar misappraisal occurs in younger adults remains unclear.
280
Correspondence
Fig. 1 Representative changes in BIS, SEF95, RBR, and BispR during emergence from sevoflurane anesthesia in an 87-year-old woman. EEG waves and power spectra at the respective time points are also shown. S = intravenous administration of sugammadex; BS = 4 minutes before S; AS = 2 minutes after S.
Because EEG changes with age as reported with the predominance of the low-frequency component in the elderly [4], and because BIS uses a heuristically derived algorithm based on EEG data from healthy adults [7], we think this kind of misappraisal may occur more readily for elderly individuals than for younger adults. However, because BIS monitors reportedly require muscle activity to generate awake BIS values in younger awake volunteers [1], we think a similar phenomenon may occur in younger patients. We also found that BIS tended to change at a lag of approximately 20 seconds behind other EEG subparameters. The reason for this delay was not elucidated but may be related to the BIS-
calculating algorithm, which needs several minutes of stable EEG signals. In conclusion, this report indicates that BIS monitoring may not adequately reflect the level of anesthesia during emergence in some elderly patients under neuromuscular paralysis.
Acknowledgments We thank Satoshi Hagihira for supplying BSA software.
Correspondence Kazuko Hayashi MD, PhD (Visiting lecturer) Department of Anesthesiology, Nantan General Hospital Yagi, Nantan, Kyoto, Japan Department of Anesthesiology, Kyoto Prefectural University of Medicine, Kawaramachi, Kyoto, Japan E-mail address: [email protected] Tel: +81 771 42 2510 Fax: +81 771 42 2096 http://dx.doi.org/10.1016/j.jclinane.2016.04.052
References [1] Schuller PJ, Newell S, Strickland PA, Barry JJ. Response of bispectral index to neuromuscular block in awake volunteers. Br J Anaesth 2015; 115(Suppl. 1):i95-i103.
281 [2] Vivien B, Di Maria S, Ouattara A, Langeron O, Coriat P, Riou B. Overestimation of bispectral index in sedated intensive care unit patients revealed by administration of muscle relaxant. Anesthesiology 2003;99:9-17. [3] Dahaba AA, Bornemann H, Hopfgartner E, Ohran M, Kocher K, Liebmann M, et al. Effect of sugammadex or neostigmine neuromuscular block reversal on bispectral index monitoring of propofol/ remifentanil anaesthesia. Br J Anaesth 2012;108:602-6. [4] Sowell ER, Peterson BS, Thompson PM, Welcome SE, Henkenius AL, Toga AW. Mapping cortical change across the human life span. Nat Neurosci 2003;6:309-15. [5] Purdon PL, Pavone KJ, Akeju O, Smith AC, Sampson AL, Lee J, et al. The ageing brain: the ageing brain: age-dependent changes in the electroencephalogram during propofol and sevoflurane general anaesthesia. Br J Anaesth 2015;115(Suppl. 1):i46-57. [6] Hagihira S, Takashina M, Mori T, Mashimo T, Yoshiya I. Practical issues in bispectral analysis of electroencephalographic signals. Anesth Analg 2001;93:966-70. [7] Arnold G, Kluger M, Voss L, Sleigh J. BIS and entropy in the elderly. Anaesthesia 2007;62:907-12.
Correspondence Inappropriately low bispectral index of the elderly during emergence from sevoflurane anesthesia☆,☆☆ To the Editor: Neuromuscular activity has been previously reported to influence bispectral index (BIS) estimations in both awake volunteers [1] and sedated patients [2,3]. The applicability of BIS monitoring for assessing the depth of anesthesia in elderly individuals is also problematic because electroencephalogram (EEG) in the elderly is known to be electrophysiologically different from those in younger individuals [4,5]. We have described here a case of inappropriately low (b 50) BIS in an 87-year-old woman during the emergence period from sevoflurane anesthesia until reversal of muscle relaxation was started. After antagonism of the muscle relaxant with sugammadex, the patients immediately opened their eyes in response to calling their name, accompanied by an abrupt rise in BIS to more than 90. Judging from this situation, the level of anesthesia seemed quite shallow, despite the low BIS, just before antagonism of muscle relaxation. We retrospectively examined the EEG in this case. It appears to offer evidence that BIS monitoring in elderly patients with neuromuscular blockade can include some degree of misappraisal. Before submission of the present case report, written informed consent was obtained from the patient and her family for analyzing EEG data and publishing the case in the journal. The patient had not been prescribed any antipsychotics or antidementia agents. Anesthesia was induced using propofol and remifentanil and was maintained using sevoflurane, remifentanil, and epidural anesthesia. BIS was monitored using an A-2000 BIS monitor (version 4.0; Aspect Medical Systems, Natick, MA), and raw EEG (converted from analog to digital at 128 Hz) was continuously collected. At the completion of surgical operations, we decreased the concentration of sevoflurane to 0.5%, continuing at this level until the end of x-ray imaging. Sevoflurane inhalation was then ended so that the patient can be promptly extubated once the x-ray images are obtained—usually approximately 4 minutes after the end of x-ray imaging. Sugammadex
☆ ☆☆
Conflicts of interest: None declared. Financial support and sponsorship: None declared.
0952-8180/© 2016 Elsevier Inc. All rights reserved.
(200 mg) was injected intravenously once suitable x-ray images have been confirmed. The stored EEG was retrospectively analyzed using BSA version 3.22B2 software [6], and EEG subparameters were examined, in addition to BIS. Analyzed parameters were 95% spectral edge frequency (SEF95); relative β ratio (RBR = log10 [spectral power (30-47 Hz)/ spectral power (11-20 Hz)]); SynchFastSlow (BispR = log10 [bispectral power (40-47 Hz)/bispectral power (0.5-47 Hz)]); and burst suppression ratio (BSR). Figure 1 shows changes in BIS, SEF95, RBR, and BispR during emergence from sevoflurane anesthesia in an 87-year-old woman. EEG waves and power spectra at respective time points are also shown. BIS remained low (approximately 40) during the emergence period until administration of sugammadex (point S) and immediately increased to more than 90 after starting reversal of muscle relaxation. Throughout the course of emergence until Point_S, SEF95, RBR, and BispR likewise remained low (around 10 Hz, − 1, and − 3, respectively) and increased just after Point_S, although the increase in BIS was slightly delayed by approximately 20 seconds and steep. Burst suppression ratio was zero throughout the analysis period. BIS thus remained low until administration of sugammadex, although the patients seemed to already be in a condition of shallow anesthesia from which they could be aroused by light stimulation. Electromyography without neuromuscular blockade has previously been reported to result in elevation of BIS in anesthetized patients [2,3]. Conversely, the present finding indicates that pure EEG of the elderly without the presence of electromyography results in an inappropriately low BIS, agreeing with previous reports [1,3] and providing evidence that monitoring BIS does not allow precise estimation of the depth of anesthesia during emergence in elderly patients under management with muscle relaxants. Accordingly, when the BIS monitor showed an unnaturally deep level of anesthesia during emergence in an elderly patient who has received neuromuscular blockade, anesthesia management should be conducted in consideration of quantitative parameters of anesthetic agents, such as end-expiratory anesthesia concentration and/or the simulated effect site concentration of anesthetics. Although the inappropriately low BIS was observed in very old elderly patient under muscle relaxation, whether similar misappraisal occurs in younger adults remains unclear.
280
Correspondence
Fig. 1 Representative changes in BIS, SEF95, RBR, and BispR during emergence from sevoflurane anesthesia in an 87-year-old woman. EEG waves and power spectra at the respective time points are also shown. S = intravenous administration of sugammadex; BS = 4 minutes before S; AS = 2 minutes after S.
Because EEG changes with age as reported with the predominance of the low-frequency component in the elderly [4], and because BIS uses a heuristically derived algorithm based on EEG data from healthy adults [7], we think this kind of misappraisal may occur more readily for elderly individuals than for younger adults. However, because BIS monitors reportedly require muscle activity to generate awake BIS values in younger awake volunteers [1], we think a similar phenomenon may occur in younger patients. We also found that BIS tended to change at a lag of approximately 20 seconds behind other EEG subparameters. The reason for this delay was not elucidated but may be related to the BIS-
calculating algorithm, which needs several minutes of stable EEG signals. In conclusion, this report indicates that BIS monitoring may not adequately reflect the level of anesthesia during emergence in some elderly patients under neuromuscular paralysis.
Acknowledgments We thank Satoshi Hagihira for supplying BSA software.
Correspondence Kazuko Hayashi MD, PhD (Visiting lecturer) Department of Anesthesiology, Nantan General Hospital Yagi, Nantan, Kyoto, Japan Department of Anesthesiology, Kyoto Prefectural University of Medicine, Kawaramachi, Kyoto, Japan E-mail address: [email protected] Tel: +81 771 42 2510 Fax: +81 771 42 2096 http://dx.doi.org/10.1016/j.jclinane.2016.04.052
References [1] Schuller PJ, Newell S, Strickland PA, Barry JJ. Response of bispectral index to neuromuscular block in awake volunteers. Br J Anaesth 2015; 115(Suppl. 1):i95-i103.
281 [2] Vivien B, Di Maria S, Ouattara A, Langeron O, Coriat P, Riou B. Overestimation of bispectral index in sedated intensive care unit patients revealed by administration of muscle relaxant. Anesthesiology 2003;99:9-17. [3] Dahaba AA, Bornemann H, Hopfgartner E, Ohran M, Kocher K, Liebmann M, et al. Effect of sugammadex or neostigmine neuromuscular block reversal on bispectral index monitoring of propofol/ remifentanil anaesthesia. Br J Anaesth 2012;108:602-6. [4] Sowell ER, Peterson BS, Thompson PM, Welcome SE, Henkenius AL, Toga AW. Mapping cortical change across the human life span. Nat Neurosci 2003;6:309-15. [5] Purdon PL, Pavone KJ, Akeju O, Smith AC, Sampson AL, Lee J, et al. The ageing brain: the ageing brain: age-dependent changes in the electroencephalogram during propofol and sevoflurane general anaesthesia. Br J Anaesth 2015;115(Suppl. 1):i46-57. [6] Hagihira S, Takashina M, Mori T, Mashimo T, Yoshiya I. Practical issues in bispectral analysis of electroencephalographic signals. Anesth Analg 2001;93:966-70. [7] Arnold G, Kluger M, Voss L, Sleigh J. BIS and entropy in the elderly. Anaesthesia 2007;62:907-12.