Background <p>Electroencephalograpy (EEG) reactivity may aid functional outcome prediction in the intensive care unit (ICU). Different types of stimuli could vary in their ability to evoke reactivity. This study explored which type of stimulus is best to elicit EEG reactivity in ICU patients with an impaired consciousness. We also investigated associations between reactivity and hospital survival and functional outcome. Lastly, we compared standardized testing with random stimuli application.</p> Methods <p>Adult ICU patients with an impaired consciousness and an EEG with reactivity testing were screened for eligibility. Stimuli were auditory (clapping and calling patient’s name), visual, tactile, and noxious. Three raters, blinded to clinical outcomes, scored each EEG recording and stimulus for reactivity. Interrater reliability was assessed using Fleiss’ kappa. Associations between reactivity and outcomes were analyzed with logistic regression.</p> Results <p>In total, 72 patients were included, most commonly with traumatic brain injury which was present in 19 patients (26.4%) and a median GCS score of 6 (interquartile range, IQR 3–11). EEG reactivity was present in 30.6% of patients. Auditory stimuli were most effective, accounting for 57% of all reactive stimuli. Interrater reliability was highest for clapping (<i>κ</i> = 0.633, 77% raw agreement) and calling the patient’s name (<i>κ</i> = 0.584, 74% raw agreement). Reactivity was not associated with hospital survival or 6-month functional outcome. Standardized testing was applied in 23.6% of patients and improved raters’ certainty in detecting reactivity compared with the application of random stimuli (88.2% vs. 41.8%, p = 0.002).</p> Conclusions <p>Auditory stimuli (clapping and calling the patient’s name) proved most effective in eliciting EEG reactivity. Reactivity was not associated with outcomes. Standardized testing increased raters’ certainty in detecting reactivity.</p>