This might be complicated by the complex kinetics of biological markers in critical care patients, e.g. sedatives, other medication, comorbidities and possibly the type of brain insult.19,33 Previous studies found NfL levels to increase by over 100 pg/ml after an acute event such as stroke or cardiac arrest, indicating that an effect can be detected within 24 h of onset after acute brain damage.27,28,34,35 In the case of COVID-19 sepsis elevations appear to be less pronounced and at a slower rate. This evidence concerns the gene NEFL and cardiac arrest.