Extreme BP drops after Aortic root aneurysm.and aortic valve replaceme

My husband had Bentall procedure two days ago … he is having extreme blood pressure drops , especially when they try to get him to stand up .. it dropped extremely low this morning , he became non responsive .. there were 9 providers in here doing interventions.. still unstable, though BP is improving … he has Afib now , and they just made an adjustment to his external pace maker …
Anyone else had these kinds of side effects after surgery?

Thanks