AIM: Delirium is common in patients aged over 70 years after cardiac surgery. Screening to detect delirium in high-risk patients is important, yet hypoactive delirium is often missed in nurse-reported screening. Polymorphic delta waves are associated with delirium, and can be detected with single-channel electroencephalography (SC-EEG). The aim of the study is to assess whether SC-EEG as a screening instrument for delirium will increase the detection rate of postoperative delirium and reduce hospital stay of delirious patients. METHODS AND RESULTS: A prospective quasi-experimental study compared Delirium Observation Screening Scale (DOSS) screening (442 patients) to SC-EEG screening (462 patients) to detect postoperative delirium in cardiac surgery patients aged over 70 years. Delirium was diagnosed using the Diagnostic and Statistical Manual of Mental Disorders 5th edition.Detection of delirium was higher in the SC-EEG group (20%) compared to DOSS group (14%), p = 0.016. A difference in length of stay for delirious patients was attributed to baseline differences as pneumonia and EuroSCORE II, but not delirium screening method. Length of stay for all patients was -0.11 (95% CI -0.18 to -0.04) night shorter for SC-EEG cohort patients compared to DOSS cohort patients, p = 0.002. CONCLUSION: Screening with SC-EEG increased delirium detection after cardiac surgery. Only length of stay for all patients was significantly reduced in the SC-EEG cohort. This reduction in hospital stay is small, yet relevant for high volume cardiac surgery centres and should be further studied in other centres. REGISTRATION: International Clinical Trials Registry Platform: NL-OMON27069.