Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
This is routine poison advice and does not always mean an emergency department visit will be needed.
Call emergency services now if the person:
Place an unconscious but breathing person on their side if you can do so safely, and follow the emergency call handler's instructions.
And for anyone, someone who:
Contact a poison information service promptly whenever rhubarb leaf has been swallowed, even if there are no symptoms.
Seek urgent medical assessment if there is repeated vomiting, worsening abdominal pain, marked weakness, muscle cramps, confusion, blood in the urine, or much less urine than usual.
These symptoms may require blood tests and monitoring.
The article also says
Do not give food, drink, or activated charcoal to someone who is unconscious, having a seizure, or unable to swallow safely.
Every sign above is quoted from the sofidex article on Rhubarb leaves poisoning. If you are not sure, err upward — it is always reasonable to be checked.