Out of those 50 guests, it is a sure bet that you have at least two good, reliable friends in attendance. Let the friends know what has happened, ask them to let others know, and make a quick exit before they do. If everything is set, with food and beverages there, and if you are comfortable with the idea, let them know that they are welcome to continue on without you and your spouse. Let them know your wishes. Ask them to stand in for you as hosts/hostesses (whether guests stay and continue or not) and ask them to secure the home if your guests and they leave before you get back.

I'd get everyone's attention and explain the emergency. It is doubtful that anyone would be upset about having to cancel the party. It's more likely that they would be extremely understanding and make a quick exit. Then, you can follow the last person out, lock up and go be with your spouse.

Or, as windowshopping suggested, you can put someone you trust fully in charge of handling the exit formalities, excuse yourself (offering for everyone to take their time heading out and not let the food go to waste, that way their evening wasn't a total loss) and get up to the hospital as soon as possible. As the host(ess), I wouldn't leave without informing your guests that there's been an emergency with your spouse and making your apologies for needing to exit.

Either way, there shouldn't be a soul in the room who would have the nerve to feel upset or inconvenienced when something so traumatic happens. If there are people who didn't understand (for whatever selfish reasoning they may have), then they'll just have to get glad in the same pants they got mad in.... Shrug it off and get to your spouse anyway.

I had a similar situation on my daughter's 10 th birthday. My husband was taken ill, and needed to be taken to the hospital. I called a friend and had her come over and manage the party for me. If it was early enough to cancel the party, that would be an option- but if you have all the food and beverages and the guests are en route, calling a "substitute" host or hostess might be the best course.