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Anesth Analg 2004;98:1734-1736 © 2004 International Anesthesia Research Society doi: 10.1213/01.ANE.0000117282.72866.26
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Abstract |
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 Top Abstract IntroductionCase ReportDiscussionReferences |
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We observed abnormal fluctuation in Bispectral Index (BIS) caused by repeated alternations between two electroencephalographic (EEG) waveform patterns in a patient with a recent history of epileptic seizure under sevoflurane anesthesia. The repetitive development of the abnormal EEG changes (slow
with or without spike) and the fluctuation in BIS disappeared almost immediately after administration of anticonvulsants. BIS may give useful information not only on the sedative-hypnotic state, but also on the development of and recovery from abnormal epileptiform EEG activity. IMPLICATIONS: During epileptiform electroencephalographic activity (EEG), the Bispectral Index shows an abnormal fluctuation caused by repeated abrupt alterations between normal EEG and abnormal epileptiform EEG patterns.
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Introduction |
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TopAbstractIntroductionCase ReportDiscussionReferences |
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Several studies have indicated that the electroencephalographic (EEG) Bispectral Index (BIS) can be reliably used to assess the sedative-hypnotic state during anesthesia (1,2). However, there are few reports on the performance of BIS monitoring during abnormal EEG activities (3). We report findings in a patient with epilepsy who developed epileptiform EEG activity during BIS-guided anesthesia.
This case report illustrates how BIS may respond to such abnormal EEG changes.
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Case Report |
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TopAbstractIntroductionCase ReportDiscussionReferences |
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A 52-yr-old man was scheduled for total gastrectomy. His medical history included postencephalitic epilepsy from 4 years old, and chronic treatment with anticonvulsants including phenytoin, cloxazolam, and valproate. He may have experienced a mild epileptic seizure several months before surgery.
On the morning of surgery, he did not receive anticonvulsants. He received IM midazolam 2.5 mg and pentazocine 15 mg as premedication. In addition to routine intraoperative monitoring including electrocardiogram, noninvasive blood pressure and pulse oximetry, BIS was monitored using an Aspect A-1050 EEG monitor (version 3.12; Aspect Medical Systems, Natick, MA). We applied 4 electrodes to the forehead and bilateral temporal areas. Electrode impedances were <2 k
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An epidural catheter was inserted via the Th8/Th9 intervertebral space. Anesthesia was induced with midazolam 1.5 mg, thiamylal 175 mg, and 2% sevoflurane; vecuronium 7 mg was also given (Fig. 1A). After tracheal intubation, ventilation was controlled to keep end-tidal PCO2 approximately 35 mm Hg. Anesthesia was maintained with 0.6%–1.0% sevoflurane and 67% nitrous oxide in addition to intermittent epidural injections of 1% mepivacaine. Vecuronium was given while monitoring train-of-four stimulation.
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The BIS decreased to 40 with this induction sequence and remained stable at this baseline value for about an hour. About 40 min after the start of surgery (Fig. 1C), episodes of abrupt and transient reductions in BIS began to occur. In each episode, BIS decreased abruptly from the baseline value of approximately 40 to a low value of approximately 20 and abruptly returned to baseline within a minute. This consecutive change in BIS repeated at intervals of 1.5 to 5 min for nearly 2 h (10:20–12:15). Throughout this period, the EEG monitor intermittently displayed error messages. We confirmed that electrode impedances were <2 k
; possible contamination with the electromyogram signal was eliminated because vecuronium was used; and no other noise source could be found. The baseline pattern of raw EEG signals before surgical stimuli was high-frequency (10–14 Hz) low-voltage waves. We found that when low-frequency (1.5–2.5 Hz) high-voltage waves emerged, BIS began to reduce to 20 (Fig. 2A). When high-frequency low-voltage waves reappeared, BIS value recovered to baseline (Fig. 2B). The repeated BIS change reflected sudden transitions between high-frequency low-voltage and low-frequency high-voltage EEG waves.
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Because the EEG changes were likely to be epileptogenic, midazolam 1.5 mg and thiamylal 100 mg were administered IV. Almost immediately after this treatment, low-frequency high-voltage EEG waves and abrupt BIS reductions disappeared (Fig. 1D), as did the error messages. The patient emerged from anesthesia uneventfully.
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Discussion |
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TopAbstractIntroductionCase ReportDiscussionReferences |
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We describe herein intraoperative observations of abnormal fluctuations in BIS caused by repeated alternations between two EEG waveform patterns in a patient with a history of epileptic seizure. Although precise EEG diagnosis of the EEG pattern is difficult, the low-frequency high-voltage EEG activities with abrupt onset-offset profiles may be classified as slow
waves, with or without spikes, a common epileptiform EEG pattern (4,5). Worthy of note are the effects of midazolam and thiamylal on the EEG. The repetitive development of abnormal EEG changes, and thus the abnormal fluctuation in BIS, disappeared completely almost immediately after injection of these anticonvulsants. Therefore, it is highly likely that the abnormal fluctuation in BIS resulted from occurrences of epileptiform EEG activity.
Before surgery, the patient received 4 mg of midazolam in total. This dose may not have been sufficient to prevent epileptic seizures throughout anesthesia and perhaps we should have continued the anticonvulsant medications through the morning of surgery (6). Although volatile anesthetics have anticonvulsant actions (7,8), there have been several reports of epileptoid EEG patterns observed during sevoflurane anesthesia (4,9,10). One of them described slow EEG activity, with or without spikes, associated with jerking movements (4). Moreover, studies have shown that sevoflurane has stronger epileptogenic properties than isoflurane (11,12).
Abrupt and transient reductions in BIS can also develop as a result of transient cerebral hypoperfusion (3,13). In our case, however, abnormal BIS reductions did not follow significant hemodynamic derangement. Although BIS is not intended as a monitor of such abnormal EEG activities, development of epileptiform EEG changes and recovery could be conveniently and demonstrably traced using the EEG monitor.
This report shows that BIS monitoring may not only give useful information on the sedative-hypnotic state, but also on the development of abnormal epileptiform EEG activity.
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Acknowledgments |
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The authors thank Paul J. Manberg, PhD, Aspect Medical Systems, Inc., for helpful editorial comments.
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References |
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TopAbstractIntroductionCase ReportDiscussionReferences |
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- Glass PS, Bloom M, Kearse L, et al. Bispectral analysis measures sedation and memory effects of propofol, midazolam, isoflurane, and alfentanil in healthy volunteers. Anesthesiology 1997; 86: 836–47.[Web of Science][Medline]
- Katoh T, Suzuki A, Ikeda K. Electroencephalographic derivatives as a tool for predicting the depth of sedation and anesthesia induced by sevoflurane. Anesthesiology 1998; 88: 642–50.[Web of Science][Medline]
- Tanabe T, Sakai T, Mi W, et al. Electroconvulsive therapy decreased bispectral index: a case report. Masui 1998; 47: 1096–8.[Medline]
- Yli-Hankala A, Vakkuri A, Sarkela M, et al. Epileptiform electroencephalogram during mask induction of anesthesia with sevoflurane. Anesthesiology 1999; 91: 1596–603.[Web of Science][Medline]
- Sperling MR, Morrell MJ. Pediatric and adult electroencephalography. In: Sperling MR, Clancy RR, eds. Atlas of electroencephalography. Amsterdam: Elsevier, 1993: 202–3.
- Roizen MF. Anesthetic implications of concurrent diseases. In: Millar RD, ed. Anesthesia. 5th ed. Philadelphia: Churchill-Livingstone, 2000: 969–70.
- Franks NP, Lieb WR. Molecular and cellular mechanisms of general anesthesia. Nature 1994; 367: 607–14.[Medline]
- Murao K, Shingu K, Tsushima K, et al. The anticonvulsant effects of volatile anesthetics on lidocaine-induced seizure in cat. Anesth Analg 2000; 90: 148–55.
[Abstract/Free Full Text] - Komatsu H, Taie S, Endo S, et al. Electrical seizures during sevoflurane anesthesia in two pediatric patients with epilepsy. Anesthesiology 1994; 81: 1535–7.[Web of Science][Medline]
- Kaisti KK, Jaaskelainen SK, Rinne JO, et al. Epileptiform discharges during 2 MAC sevoflurane anesthesia in two healthy volunteers. Anesthesiology 1999; 91: 1952–5.[Web of Science][Medline]
- Watts ADJ, Herick IA, Mclachlan RS, et al. The effect of sevoflurane and isoflurane anesthesia on interictal spike activity among patients with refractory epilepsy. Anesth Analg 1999; 89: 1275–81.
[Abstract/Free Full Text] - Iijima T, Nakamura Z, Iwao Y, et al. The epileptogenic properties of the volatile anesthetics sevoflurane and isoflurane in patients with epilepsy. Anesth Analg 2000; 91: 989–95.
[Abstract/Free Full Text] - Hayashida M, Chinzei M, Komatsu K, et al. Detection of cerebral hypoperfusion with bispectral index during paediatric cardiac surgery. Br J Anaesth 2003; 90: 694–8.
[Abstract/Free Full Text]
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