i work with fresh heart surgeries everyday. most of the patients come back from surgery on a ventilator mode of SIMV, which is a weaning mode. we draw blood gases upon return to the unit to check their status, then periodically. when the ABG is no longer acidotic or alkolotic, we begin the weaning process, which can take around 4-5 hours. However some pts. with respiratory problems, mainly those who smoke, can take signigicantly longer. Most however are extubated in less than 6 hours. I hope your dad does great, and the best advice i can give u for after the surgery is to not let him lay around. Get him out of the bed and get him moving and push the IS. Take care and i hope this helped.