Letter to the Editor Re: Outcomes of Combined Somatosensory Evoked Potential, Motor Evoked Potential, and Electroencephalography Monitoring during Carotid Endarterectomy
To the Editor: We read with great interest, the article by Alcantara et al.1 and appreciated it as a further description of a neurophysiologic methodology in the field of monitoring cerebral ischemia during carotid endarterectomy (CEA). The authors aimed to evaluate the rate of detection and prevention of neurologic events by using a combination of cortical somatosensory evoked potential (SSEP), motor evoked potential (MEP), and processed electroencephalography (EEG). Although this study was described as a prospective study and it is clearly a retrospective investigation, it shows evidence that MEP monitoring is a reliable method in addition to SSEP monitoring in patients undergoing carotid surgery. Thus, it supports results we published recently in a multicenter study of 600 patients.2 However, there are 2 things that remain unclear in the present article: 1) How can the authors argue that their results do not justify the implementation of intraoperative neurophysiologic monitoring (IONM) when they used a protocol for intervention in case of defined changes in EEG, SSEP, or transcranial electrical stimulated MEP recordings? Following this, all patients showing IONM changes were either treated by increasing the blood pressure or shunt insertion. Therefore, no postoperative neurologic deficit was found in their cohort. Because it remains unclear what would happen in the case of no intervention, it is not correct to conclude that IONM is not useful for detection of cerebral ischemia. Only a prospective trial including a control group could clearly show significant differences in sensitivity and specificity of one or the other monitoring techniques, and the design of the study did not incorporate such statistical calculation. 2) The comparison of shunting rate data obtained by Alcantara et al.1 during asleep CEA with the authors’ data obtained during awake CEA is invalid. This
Ann Vasc Surg 2014; -: 1 http://dx.doi.org/10.1016/j.avsg.2014.03.008 Ó 2014 Elsevier Inc. All rights reserved. Published online: --,-
is because the criteria for shunt application are different for evaluating awake patients neurologically (e.g., loss of consciousness, speech disturbance, muscle strength) than judging from IONM changes under general anesthesia. Furthermore, inhomogeneity of both cohorts makes a comparison even harder. Results of Alcantara et al.,1 our own experiences, and the results from the literature in the field of aneurysm surgery3e5 suggest that the implementation of both SSEP and MEP monitoring should be a subject of further discussions with regard to detecting ischemic events in anesthetized patients. This is to develop stronger evidence for patient’s safety and to justify cost-effectiveness in the future. Michael J. Malcharek* Division of Neuroanesthesia and Intraoperative Neuromonitoring, Department of Anesthesiology, Intensive care and Pain therapy, Klinikum St. Georg gGmbH, Affiliated Hospital of the University of Leipzig, Leipzig, Germany *Correspondence to: Michael J. Malcharek, MD, Division of Neuroanesthesia and Intraoperative Neuromonitoring, Department of Anesthesiology, Intensive care and Pain therapy, Klinikum St. Georg gGmbH, Affiliated Hospital of the University of Leipzig, Delitzscher Street 141, 04129 Leipzig, Germany. E-mail: [email protected]
REFERENCES 1. Alcantara SD, Wuamett JC, Lantis JC, et al. Outcomes of combined somatosensory evoked potential, motor evoked potential, and electroencephalography monitoring during carotid endarterectomy. Ann Vasc Surg 2013;. http://dx.doi. org/10.1016/j.avsg.2013.09.005. 2. Malcharek MJ, Ulkatan S, Marin o V, et al. Intraoperative monitoring of carotid endarterectomy by transcranial motor evoked potential: a multicenter study of 600 patients. Clin Neurophysiol 2013;124:1025e30. 3. Neuloh G, Schramm J. Monitoring of motor evoked potentials compared with somatosensory evoked potentials and microvascular Doppler ultrasonography in cerebral aneurysm surgery. J Neurosurg 2004;100:389e99. 4. Szelenyi A, de Camargo AB, Flamm E, et al. Neurophysiological criteria for intraoperative prediction of motor hemiplegia during aneurysm surgery: case report. J Neurosurg 2003;99: 575e8. 5. Szelenyi A, Langer D, Kothbauer K, et al. Monitoring of muscle evoked potentials during cerebral aneurysm surgery: intraoperative changes and postoperative outcome. J Neurosurg 2006;105:675e81.
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To the Editor: We read with great interest, the article by Alcantara et al.1 and appreciated it as a further description of a neurophysiologic methodology in the field of monitoring cerebral ischemia during carotid endarterectomy (CEA). The authors aimed to evaluate the rate of detection and prevention of neurologic events by using a combination of cortical somatosensory evoked potential (SSEP), motor evoked potential (MEP), and processed electroencephalography (EEG). Although this study was described as a prospective study and it is clearly a retrospective investigation, it shows evidence that MEP monitoring is a reliable method in addition to SSEP monitoring in patients undergoing carotid surgery. Thus, it supports results we published recently in a multicenter study of 600 patients.2 However, there are 2 things that remain unclear in the present article: 1) How can the authors argue that their results do not justify the implementation of intraoperative neurophysiologic monitoring (IONM) when they used a protocol for intervention in case of defined changes in EEG, SSEP, or transcranial electrical stimulated MEP recordings? Following this, all patients showing IONM changes were either treated by increasing the blood pressure or shunt insertion. Therefore, no postoperative neurologic deficit was found in their cohort. Because it remains unclear what would happen in the case of no intervention, it is not correct to conclude that IONM is not useful for detection of cerebral ischemia. Only a prospective trial including a control group could clearly show significant differences in sensitivity and specificity of one or the other monitoring techniques, and the design of the study did not incorporate such statistical calculation. 2) The comparison of shunting rate data obtained by Alcantara et al.1 during asleep CEA with the authors’ data obtained during awake CEA is invalid. This
Ann Vasc Surg 2014; -: 1 http://dx.doi.org/10.1016/j.avsg.2014.03.008 Ó 2014 Elsevier Inc. All rights reserved. Published online: --,-
is because the criteria for shunt application are different for evaluating awake patients neurologically (e.g., loss of consciousness, speech disturbance, muscle strength) than judging from IONM changes under general anesthesia. Furthermore, inhomogeneity of both cohorts makes a comparison even harder. Results of Alcantara et al.,1 our own experiences, and the results from the literature in the field of aneurysm surgery3e5 suggest that the implementation of both SSEP and MEP monitoring should be a subject of further discussions with regard to detecting ischemic events in anesthetized patients. This is to develop stronger evidence for patient’s safety and to justify cost-effectiveness in the future. Michael J. Malcharek* Division of Neuroanesthesia and Intraoperative Neuromonitoring, Department of Anesthesiology, Intensive care and Pain therapy, Klinikum St. Georg gGmbH, Affiliated Hospital of the University of Leipzig, Leipzig, Germany *Correspondence to: Michael J. Malcharek, MD, Division of Neuroanesthesia and Intraoperative Neuromonitoring, Department of Anesthesiology, Intensive care and Pain therapy, Klinikum St. Georg gGmbH, Affiliated Hospital of the University of Leipzig, Delitzscher Street 141, 04129 Leipzig, Germany. E-mail: [email protected]
REFERENCES 1. Alcantara SD, Wuamett JC, Lantis JC, et al. Outcomes of combined somatosensory evoked potential, motor evoked potential, and electroencephalography monitoring during carotid endarterectomy. Ann Vasc Surg 2013;. http://dx.doi. org/10.1016/j.avsg.2013.09.005. 2. Malcharek MJ, Ulkatan S, Marin o V, et al. Intraoperative monitoring of carotid endarterectomy by transcranial motor evoked potential: a multicenter study of 600 patients. Clin Neurophysiol 2013;124:1025e30. 3. Neuloh G, Schramm J. Monitoring of motor evoked potentials compared with somatosensory evoked potentials and microvascular Doppler ultrasonography in cerebral aneurysm surgery. J Neurosurg 2004;100:389e99. 4. Szelenyi A, de Camargo AB, Flamm E, et al. Neurophysiological criteria for intraoperative prediction of motor hemiplegia during aneurysm surgery: case report. J Neurosurg 2003;99: 575e8. 5. Szelenyi A, Langer D, Kothbauer K, et al. Monitoring of muscle evoked potentials during cerebral aneurysm surgery: intraoperative changes and postoperative outcome. J Neurosurg 2006;105:675e81.
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