My son is going under general anesthesia for wisdom teeth extraction. He always gets horrible indigestion from anesthesia. Whats the best thing to give him? He wakes up immediately with dry heaves.

Talk to MD. Your anesthesiologist should be able to treat this in a preventative manner before the operation. Discuss previous anesthetics and your concerns before the operation.
PONV. Post operative nausea and vomiting (ponv) is a frequent ocurrence after surgery and anesthesia. You should get to know your anesthesia doctor and inform him or her that your son is prone to experience ponv. There are medications alone and in combination that are used by anesthesia doctors to help to prevent or ameliorate this condition.
Nausea . Nausea and vomiting after general anesthesia is a common enough complication that it has its own abbreviation ("ponv: post operative nausea and vomiting"). Although most common in young women, nonsmokers, and people who get motion sickness, anyone can get this miserable problem after anesthesia. For most, it is a temporary and self-resolving problem. For some it can be severe enough to slow the process of going home and recovering. Unfortunately, people having wisdom tooth extraction often swallow some blood -- which can cause vomiting by itself. The choice of anesthetic is a complicated one which depends on many more variables than the liklihood of ponv. Provider experience, patient health status, length of procedure, and medication availability may all play into this decision. There are general anesthetic agents which are less likely to cause ponv than others, but these may not be the right choice for your son. The most important thing you can do is make sure that your son's provider knows that he has had nausea/vomiting after previous anesthetics, and discuss your concern and the provider's management plan in detail. This allows the provider to make appropriate management plans ahead of time. In addition to potentially altering the anesthetic, a provider may choose to administer antiemetic (anti-nausea) medication before the anesthetic has worn off -- or even before starting. Sometimes multiple medications are combined to try to prevent ponv. If ponv persists after going home, under-the-tongue tablets or suppositories can be used to treat the nausea. Be careful to follow the provider's instructions regarding restrictions on food and water before the procedure. Although ponv by itself is not life-threatening, undergoing general anesthesia with a full stomach can be life threatening and should not be undertaken except in an emergency.