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The 10–20 Rule - The 10–20 Rule for Carotid Carotid endarterectomy

Experience with immediate postoperative neurologic defi -cits has shown that there is a “10–20 rule” in effect in EEG monitoring of CEAs. This rule refers to the clinical observations that a signifi cant EEG change seen with cross-clamping (i.e., signifi cant cortical ischemia) can be sustained by the cortex for about 6–10 minutes in most patients without apparent neurologic sequelae. If the EEG change is allowed to persist beyond 6–10 minutes (without

release of the clamp or bypass shunting), there is an increasing incidence of immediate, postoperative signifi -cant neurologic defi cits, so that, by 20 minutes duration of the signifi cant EEG change, there is an almost 100% incidence of postoperative neurologic defi cits (Chiappa et al., 1979; Jenkins et al., 1983). This is concordant with what other authors have reported: EEG changes lasting 19 minutes were associated with profound hemiparesis, which improved within a week (Kaufman et al., 1977). In assessing this incidence, note that clinical strokes may not have an immediate abnormal diffusion-weighted mag-netic resonance image (MRI) (Oppenheim et al., 2000; Pedraza et al. 2002; Sylaja et al., 2008). We believe that, in these patients with negative imaging, the neurophysi-ologic dysfunction signaled by EEG changes and the fol-lowing postoperative clinical defi cits (see Fig. 2-1) refl ect transient neuronal stunning beyond the typical transient ischemic attack (TIA) time window (1 hour).