NEFL and delirium: In a mixed cohort of elective and emergency surgical patients, activation of the kynurenine pathway and elevated quinolinic acid was associated with delirium, high NfL and mortality.15 Increased NfL indicating neuroaxonal damage fits with our previous report of reduced CSF ApoE, which has an important role in neuroaxonal membrane repair.13 Our finding that CSF P-tau181 was not increased in persistent delirium supports the idea that pre-existing subclinical dementia was less likely to be a contributing factor.