I suffer from obesity and my specialist doctor may perform Lap Banding surgery on me within few days or perhaps even during Ramadan. After the operation, I may have to break my fast in order to take the medications or because of repeated vomiting. Should I only make up for the missed fasting days or do I have to offer expiation too?
All perfect praise be to Allah, the Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His Slave and Messenger.
If it is necessary for you to take the medications during the daytime and there is no possibility to delay them until night so as not to harm yourself or delay your healing, then you will be allowed to break your fast. In such a case, you are only required to make up for the missed fasting days.
As for vomiting, mere vomiting does not invalidate the fast. However, deliberate vomiting invalidates the fast and necessitates making up for it, as it was narrated on the authority of Abu Hurayrah, may Allah be pleased with him, that the Prophet said: "Whoever cannot help vomiting does not have to make up for the fast, but whoever makes himself vomit deliberately - let him make up for it.” [Ahmad]
Hence, if you become sick after the surgery and fasting will be harmful to your health or unbearably difficult for you, then it would be permissible for you not to fast and only make up for the missed days of fasting. Nevertheless, it is preferable for you to delay the surgery until after Ramadan to be able to fast it all.
However, to the best of our knowledge, and Allah knows best, it is permissible for one to have a surgery during Ramadan if he needs it, even if it is possible for him to delay it.
This ruling is supported by the fact that Allah The Exalted allows the traveler to break the fast even if he is not forced by necessity to travel during Ramadan. According to Al Buhooti from the Hanbali School of Jurisprudence, “If a person intended to fast and then traveled willingly or out of necessity for the distance that allows breaking the fast, then it is permissible for him to break his fast.”
The questioner sister mentioned that a male doctor is following up her case and we want to draw her attention to the fact that it impermissible for her to visit a male doctor if that entails uncover her body in front of him. So, she should visit a female doctor if one is available; otherwise, it is be permissible for her to visit a male doctor out of necessity or dire need.
Allah Knows best.