Elsevier

Resuscitation

Volume 84, Issue 10, October 2013, Pages 1375-1381
Resuscitation

Clinical paper
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

https://doi.org/10.1016/j.resuscitation.2013.05.016Get rights and content

Abstract

Background and purpose

We investigated the inter-observer variability in interpretation of median nerve SSEPs with regard to neurological prognosis in survivors of cardiac arrest (CA).

Methods

Four experienced neurologists analyzed 163 median nerve SSEPs on the basis of a pre-defined classification of SSEPs into five patterns (A–E), with consideration of cortical potentials up to a latency of 150 ms. Of these, 133 recordings were from CA survivors and 30 were from healthy volunteers. The experts were blinded to whether a SSEP finding was from a CA survivor or a healthy volunteer. They were also unaware of the neurological outcome for the resuscitated patients. Three categories were defined for decision making. These were “good neurological outcome” represented by patterns A–C, “poor neurological outcome” (patterns D and E), and “not evaluable”. Experts’ agreement was calculated using the kappa-coefficient.

Results

The mean correct prediction by the experts was 81.8% (range 76.3–86.6%) in resuscitated patients with good neurological outcome. In those with poor neurological outcome, however, correct prediction was achieved in only 63% (60.5–66%). All SSEPs from healthy volunteers were classified as “good neurological outcome”. The kappa-coefficient (κ) for all decision-making classifications was 0.75; for patients with poor outcome it was 0.76 and for those with good outcome 0.88. The predictive value for poor neurological outcome of the SSEP pattern D achieved a specificity of 93.5% and that of E a specificity of 98.4%.

Conclusion

Our study demonstrates good inter-observer agreement in the interpretation of median nerve SSEPs in CA survivors on the basis of a pre-defined SSEP evaluation set. The strongest correlation with poor outcome was found for pattern E, bilateral absence of the N20 peak.

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.

References (38)

  • C. Madl et al.

    Detection of nontraumatic comatose patients with no benefit of intensive care treatment by recording of sensory evoked potentials

    Arch Neurol

    (1996)
  • B.G. Carter et al.

    Are somatosensory evoked potentials the best predictor of outcome after severe brain injury: a systematic review

    Intensive Care Med

    (2005)
  • E.G. Zandbergen et al.

    PROPAC Study Group. Prediction of poor outcome within the first 3 days of postanoxic coma

    Neurology

    (2006)
  • B.W. Kaplan

    Electrophysiological prognosticattion and brain injury from cardiac arrest

    Semin Neurol

    (2006)
  • E.F. Wijdicks et al.

    Practice parameter: prediction of outcome in comatose survivors after cardiopulmonary resuscitation: report of the Quality Standards Subcommittee of the American Academy of Neurology

    Neurology

    (2006)
  • T.L. Rothstein

    The utility of median somatosensory evoked potentials in anoxic-ischemic coma

    Rev Neurosci

    (2009)
  • L.L. Bisshops et al.

    Predictors of poor neurologic outcome in patients after cardiac arrest treated with hypothermia: a retrospective study

    Resuscitation

    (2011)
  • A.B. Bouwes et al.

    Prognosis after therapeutic hypothermia: a prospective cohort study

    Ann Neurol

    (2012)
  • A.O. Rossetti et al.

    Prognostication after cardiac arrest and hypothermia: a prospective study

    Ann Neurol

    (2010)
  • Cited by (51)

    • European Resuscitation Council and European Society of Intensive Care Medicine Guidelines 2021: Post-resuscitation care

      2021, Resuscitation
      Citation 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 Neurophysiology
      Citation 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.

    View all citing articles on Scopus

    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.

    View full text