Where I work, confirming brain death and stopping life support takes about 3-4 days. There are several diagnostics tests that have to be completed and it takes time… I was curious what Dr. Google says about observation period etc. and found the following:
Observation period — The length of observation required to determine brain death varies extensively. A follow-up evaluation after 24 hours was an early requirement for brain death diagnosis in the United States. Later, requirements in this regard were made age dependent: a 48-hour evaluation interval for infants age seven days to two months, 24 hours for those greater than two months to one year, and 12 hours for those between 1 and 18 years.
An observation period for adults is considered optional; six hours is often recommended, with longer periods, up to 24 hours, recommended in cases of hypoxic-ischemic encephalopathy. Guidelines in other countries recommend longer observation periods. The American Academy of Neurology guideline update published in 2010 found insufficient evidence to determine a minimally acceptable observation period.
In patients who have been resuscitated after cardiac arrest, we recommend observation for at least 24 hours from the time of the arrest, as spontaneous improvement in brainstem reflexes can occur hours after cardiac arrest. In such patients who have received induced hypothermia, the recovery time may be further extended, as some motor and brainstem reflexes may recover after being absent for three days. It may be advisable to perform an ancillary test of brain blood flow with such patients; electrophysiologic parameters may also be affected by induced hypothermia.
There are limited studies of serial examinations in this setting upon which to base recommendations for a required length of observation. One case series reviewed data from 1229 adult and 82 pediatric (greater than one year of age) cases of brain death. The interval between first and second examinations ranged from 3 to over 50 hours (mean 19.2 hours).
None of the patients with an initial examination consistent with brain death regained brainstem function on repeat examination. However, rates of organ donation decreased with longer intervals between examinations.
Resource:
https://www.uptodate.com/contents/diagnosis-of-brain-death