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.

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 150ms. 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.