NEFL and delirium: Increased plasma and CSF NfL have been shown in delirium patients in elective surgery, emergency orthopaedic surgery and critical care settings.17,34-36 In elective surgical patients, no preoperative differences were demonstrated in plasma NfL, but postoperative NfL increased dose dependently with delirium severity.17 This temporal correlation implicates NfL in delirium pathophysiology, as opposed to changes being attributable to prior subclinical pathology.