Resuscitation 85 (2014) e137
Contents lists available at ScienceDirect
Resuscitation journal homepage: www.elsevier.com/locate/resuscitation
Reply to Letter to the Editor Reply to letter: False positive absent somatosensory evoked potentials in cardiac arrest with therapeutic hypothermia
Conflict of interest statement The authors of this manuscript declare that there are no conflicts of interest.
Sir, References Arch et al. recently described a comatose patient after cardiac arrest (CA) with absent cortical responses (N20) in median nervederived somatosensory evoked potentials (SSEP) recording, who eventually showed good neurological recovery.1 This patient was treated with therapeutic hypothermia for 24 h and SSEPs were performed one day after termination of cooling (i.e., 49 h post-arrest). Neurological examination at 72 h after arrest showed a persistent coma with minimal brain stem reflexes. The SSEP recording showed positive responses at Erb and cervical regions and very poor traces from the cerebral cortex. Based on that registration the authors concluded that the N20 was bilaterally absent. We think the level of noise on the cortical traces was so high that this recording should not lead to any conclusions. The SSEPs is a very reliable tool to determine the prognosis of comatose patients after CA, when performed after 48–72 h from the anoxic injury.2 However, results of SSEP are influences by two well-known confounders: interference (i.e., the noise of the electronic devices on the ICU or muscle activity) and inter-observer variability.3,4 The higher the level of interference and noise, the higher the inter-observer variability.3 By repeated recordings with high voltage, noise can be reduced. Muscular noise can be diminished by the administration of neuromuscular-blocking agents. If the interference level remains too high despite adequate measures, then no conclusion can be given regarding the cortical N20 response on neurological outcome after CA. Such a strategy would prevent a false positive SSEP results or, far more worse, an incorrect withdrawal of treatment. We think that the case described is not of a patient with a false positive SSEP, but of a false conclusion based on a SSEP registration with too much interference.
http://dx.doi.org/10.1016/j.resuscitation.2014.04.030 0300-9572/© 2014 Elsevier Ireland Ltd. All rights reserved.
1. Arch AE, Chiappa K, Greer DM. False positive absent somatosensory evoked potentials in cardiac arrest with therapeutic hypothermia. Resuscitation 2014;85:e97–8. 2. Kamps MJ, Horn J, Oddo 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;39:1671–82. 3. Zandbergen EG, Hijdra A, de Haan RJ, et al. Interobserver variation in the interpretation of SSEPs in anoxic-ischaemic coma. Clin Neurophysiol 2006;117: 1529–35. 4. Pfeifer R, Weitzel S, Gunther A, et al. Investigation of the inter-observer variability effect on the prognostic value of somatosensory evoked potentials of the median nerve (SSEP) in cardiac arrest survivors using an SSEP classification. Resuscitation 2013;84:1375–81.
Janneke Horn a,∗ Fabio Silvio Taccone b Hans Koelman c a Department of Intensive Care Medicine, Academical Medical Center, Amsterdam, the Netherlands b Department of Intensive care, Hopital Erasme, Brussels, Belgium c Department of Neurology, Academical Medical Center, Amsterdam, the Netherlands ∗ Corresponding author. E-mail address: [email protected] (J. Horn)
1 April 2014
Contents lists available at ScienceDirect
Resuscitation journal homepage: www.elsevier.com/locate/resuscitation
Reply to Letter to the Editor Reply to letter: False positive absent somatosensory evoked potentials in cardiac arrest with therapeutic hypothermia
Conflict of interest statement The authors of this manuscript declare that there are no conflicts of interest.
Sir, References Arch et al. recently described a comatose patient after cardiac arrest (CA) with absent cortical responses (N20) in median nervederived somatosensory evoked potentials (SSEP) recording, who eventually showed good neurological recovery.1 This patient was treated with therapeutic hypothermia for 24 h and SSEPs were performed one day after termination of cooling (i.e., 49 h post-arrest). Neurological examination at 72 h after arrest showed a persistent coma with minimal brain stem reflexes. The SSEP recording showed positive responses at Erb and cervical regions and very poor traces from the cerebral cortex. Based on that registration the authors concluded that the N20 was bilaterally absent. We think the level of noise on the cortical traces was so high that this recording should not lead to any conclusions. The SSEPs is a very reliable tool to determine the prognosis of comatose patients after CA, when performed after 48–72 h from the anoxic injury.2 However, results of SSEP are influences by two well-known confounders: interference (i.e., the noise of the electronic devices on the ICU or muscle activity) and inter-observer variability.3,4 The higher the level of interference and noise, the higher the inter-observer variability.3 By repeated recordings with high voltage, noise can be reduced. Muscular noise can be diminished by the administration of neuromuscular-blocking agents. If the interference level remains too high despite adequate measures, then no conclusion can be given regarding the cortical N20 response on neurological outcome after CA. Such a strategy would prevent a false positive SSEP results or, far more worse, an incorrect withdrawal of treatment. We think that the case described is not of a patient with a false positive SSEP, but of a false conclusion based on a SSEP registration with too much interference.
http://dx.doi.org/10.1016/j.resuscitation.2014.04.030 0300-9572/© 2014 Elsevier Ireland Ltd. All rights reserved.
1. Arch AE, Chiappa K, Greer DM. False positive absent somatosensory evoked potentials in cardiac arrest with therapeutic hypothermia. Resuscitation 2014;85:e97–8. 2. Kamps MJ, Horn J, Oddo 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;39:1671–82. 3. Zandbergen EG, Hijdra A, de Haan RJ, et al. Interobserver variation in the interpretation of SSEPs in anoxic-ischaemic coma. Clin Neurophysiol 2006;117: 1529–35. 4. Pfeifer R, Weitzel S, Gunther A, et al. Investigation of the inter-observer variability effect on the prognostic value of somatosensory evoked potentials of the median nerve (SSEP) in cardiac arrest survivors using an SSEP classification. Resuscitation 2013;84:1375–81.
Janneke Horn a,∗ Fabio Silvio Taccone b Hans Koelman c a Department of Intensive Care Medicine, Academical Medical Center, Amsterdam, the Netherlands b Department of Intensive care, Hopital Erasme, Brussels, Belgium c Department of Neurology, Academical Medical Center, Amsterdam, the Netherlands ∗ Corresponding author. E-mail address: [email protected] (J. Horn)
1 April 2014
