Clinical paperInvestigation 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☆
Introduction
Approximately 50–60% of CA survivors die during the first four weeks after cardiopulmonary resuscitation (CPR) or develop severe neurological impairment due to hypoxia-induced brain damage.1, 2 Early and reliable prognosis of neurological outcome after CA is thus of major importance for health care systems and the families of patients. Numerous clinical investigations have proved that, for predicting an unfavourable neurological prognosis in CA survivors, the detection of bilateral absence of N20 peak of the median nerve SSEP is superior to all other parameters investigated in this field, particularly after introduction of therapeutic hypothermia in post cardiac arrest care.3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 Moreover, bilateral loss or a time delay >130 ms of the middle long latency cortical potentials (e.g. N70 peak) was also associated with poor neurological outcome in several investigations.9, 15, 16, 17
Since poor SSEP findings may result in a decision to withdraw intensive care from comatose CA survivors, it is fundamental that there is consistency in interpreting SSEP recordings for determining cerebral prognosis for CA survivors between experts.
High inter-expert agreement was not always achieved. Only moderate agreement was obtained, for example, between five neurologists in identifying the presence of the N20 peak.18 We therefore investigated the degree of inter-expert variability in interpretation of median nerve SSEPs with special regard to their use for predicting neurological outcome. The interpretation was on the basis of pre-defined SSEP patterns that takes into consideration all cortical potentials up to a latency of 150 ms. Furthermore, we investigated whether the SSEP findings of healthy volunteers could be unequivocally differentiated from those of resuscitated patients with poor neurological prognosis.
Section snippets
Materials and methods
We analyzed a total of 163 median nerve SSEP recordings taken from a local registry. Of these, 133 were recorded from 133 successfully resuscitated patients (95 males, 38 females, mean age 62.7 ± 13.9 yrs) treated in the medical intensive care unit of the University Hospital of Jena between 1998 and 2007. In addition, 30 SSEPs were recorded under comparable conditions from 30 neurologically healthy volunteers (25 males, 5 females, mean age 35.0 ± SD 14.3 yrs). The ethics committee of the University
Statistical analysis
Statistical analysis was performed using SPSS© version 17 (SPSS Inc., Chicago, IL, USA). Data were expressed as mean and standard deviation. Categorical data were represented as numbers or percentages. The degree of inter-observer agreement was calculated using the kappa-coefficient and the limit values taken from the literature. Consequently, κ-values of 0–0.21 represent slight inter-observer agreement, 0.21–0.40 fair, 0.41–0.6 moderate, 0.61–0.8 good, and 0.81–1.0 very good agreement.18, 23,
Results
Of the 133 resuscitated patients, 63 (47.4%) died within the first four weeks and 31 (23.3%) remained comatose. 39 patients (29.3%) regained consciousness and survived for at least four weeks with a CPC of 1–3.
Two-thirds of patients were resuscitated in non-hospital surroundings, and in 75% of patients cardiovascular diseases were the cause of the cardiac arrest (Table 2). The mean latency between ROSC and SSEP recording was 3.5 ± 2.5 days.
The SSEP patterns A–C were allocated 370 (56.7%) times
Discussion
Bilateral absence of the N20 peak in median nerve SSEP is a well-established predictor of poor neurological outcome in CA survivors. In contrast to EEG, the N20 peak (and also the middle long cortical responses) are less influenced by sedatives frequently administered within the first 24–72 h following resuscitation.26, 27, 28 However, the absence of N20 identifies only a fraction of the CA survivors who remain comatose or die within the first weeks after ROSC.4 Additional survivors of CA with
Summary
On the basis of five pre-defined SSEP pattern, four independent experts predicted the individual outcome for CA survivors. Although several pattern were associated with a moderate rate of mis-interpretation, this classification achieved 75% agreement of all four experts within the three decision-making classifications, and better inter-observer agreement than other studies. Determining the absence of middle long latency cortical potentials provided additional prognostic information for CA
Conflict of interest statement
The authors declare that they have no competing interests.
Acknowledgements
We thank Nasim Krögel, Michelle Wilbraham and Dr. Andrew Davis for their comprehensive revision of the English of the manuscript.
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Cited by (51)
European Resuscitation Council and European Society of Intensive Care Medicine Guidelines 2021: Post-resuscitation care
2021, ResuscitationCitation Excerpt :Occasional false positive predictions were reported.367 The interrater reliability for interpretation of SSEPs was moderate to good.368,369 The quality of the recording is very important and noise from muscle activity is an important limiting factor which may be eliminated by neuromuscular blocking drugs.357,368
Reliability in the assessment of paediatric somatosensory evoked potentials post cardiac arrest
2021, Clinical NeurophysiologyCitation Excerpt :This can result in bias which could inflate test specificity and underestimate the rate of false positives reported in the literature (Amorim et al, 2018), which appear to be greater in paediatric age (Carrai et al, 2010; Carter and Butt, 2001; Kane and Oware, 2015; Robinson et al, 2003). Secondly, inter-rater agreement amongst experts interpreting SSEPs is not unanimous (Bouwes et al, 2012; Hakimi et al, 2009; Pfeifer et al., 2013; Zandbergen et al, 2006), and has not been assessed between professionals who record and identify the presence/absence of the N20 component of the SSEP (technical/scientific staff) and those who provide the final clinical interpretation (clinical neurophysiologists). This is important because correct interpretation relies on identification of the N20 component and agreement should be near perfect for a test used to support WLST.
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A Spanish translated version of the summary of this article appears as Appendix in the final online version at http://dx.doi.org/10.1016/j.resuscitation.2013.05.016.