Hello. Some of the commonly seen causes which cause delirium in elderly persons are: 1. Low sodium or hyponatremia 2. Dehydration and/ malnutrition 3. Fever or severe infection eg. pneumonia, infection of the meninges 4. Bleeding in the brain 5. Sleep deprivation 6. Exacerbation of underlying disorder like Parkinson s or Alzheimer s Of these, very commonly seen in practice are low sodium, dehydration and infection. Since labs are good, I assume that his electrolyte levels have been checked. Infection is also ruled out since labs did not show any sign of infection according to you. At this point, I would suggest urgent hospitalisation as his condition seems quite critical. I would like to first stabilise his condition by correcting his nutritional status as there is bound to be some degree of electrolyte imbalance since he has not eaten nor had liquids for 5 days. In elderly persons, fever may not be as apparent as in normal people and hence there is a possibility of it being missed. Also, viral infections which are very common can cause aseptic meningitis i.e. infection of the brain covering, which may give rise to such symptoms, and even increased blood pressure. They may also not show up on blood tests and also on MRI. Confirmation can be done clinically and by CSF analysis if necessary. Apart from supportive care in an intensive care unit, prophylactic antibiotics may need to be started and all his medications reviewed to ascertain whether this is drug-induced. Wishing him a speedy recovery. Regards, Dr Geeta