My Dad Had A Emergency Brain Surgery To Remove A

My dad had a emergency brain surgery to remove a clot two days ago. He was doing well yesterday, but last night he started feeling worse with a headache. They are saying he's got an air bubble that happened due to the surgery. That say it's not big enough to go in and will wait for his body to absorb it. What are the risks and how fast does that kind of bubble usually take to absorb?