If your asthma is optimally controlled the risk is very small and you can undergo major surgery without significant asthma complications. Most anesthesiologists I have worked with will recommend that you take your asthma medicine the prior to surgery with a sip of water and bring your inhalers to the surgery center. In addition, steroids are given just prior to anesthesia in most patients any way which helps prevent asthmatic complications.
On the other hand, if your asthma is poorly controlled, or you are steroid-dependent, you are at increased risk and therefore it is recommended that your asthma specialist provide any needed specific medical preparation prior to surgery including a written plan to give to your surgeon and anesthesiologist regarding asthma medication recommendations pre- and post-surgery. This will include a complete pre-surgical evaluation including pulmonary function test results, physical examination, and review of your medications and past medical problems. If your pulmonary function tests are not optimal your asthma doctor and/or anesthesiologist may choose to postpone surgery until your asthma is under optimal control prior to giving surgical clearance. In addition, it is advisable that you contact that anesthesiologist beforehand to discuss any issues that might arise and their management. . This is because surgery may cause an asthma flare or related bronchospasm during or immediately after surgery. Make sure you tell the anesthesiologist and your surgeon the amount and type of steroids you take so additional steroids can be given to prevent adrenal insufficiency which can result in a sudden blood pressure drop.