You have essentially two choices for what type of an anesthetic to have during shoulder surgery: a regional or a general anesthetic. The word "anesthesia" comes from two Greek words that literally mean "without pain", and this situation can be created in either a part of your body (a regional anesthetic) or in your entire body (called a general anesthetic, or "going to sleep").
Regional anesthesia involves having your anesthesiologist perform a procedure called a "nerve block", where medications are injected in the area around the nerves that travel to the part of your body that is being operated on. The most common type of regional anesthesia that is used for shoulder surgery is called an inter-scalene block. This type of anesthesia is administered just before your operation. The procedure for an inter-scalene block usually begins when you are lying down on a hospital bed or in a semi-sitting position. Your head is then turned towards the opposite shoulder (the one that is not being operated on). Your anesthesiologist will then palpate the side of your neck in order to identify several important anatomic landmarks that guide the correct placement of a needle.
The correct location for injecting medications is between the scalene muscles of the neck, and this why this block is called an inter-scalene block. The needle that is used for the injection is often attached to a special electrical simulator that allows the anesthesiologist to stimulate the nerve that is to be blocked. This stimulator will cause small twitches in the muscles that are supplied by that nerve and may also cause small "electric-shock" like sensations in the arm. The stimulator is used to verify that the needle is in the correct position before the anesthetic agent is injected. A long acting local anesthetic - like Mepivacaine or Ropivacaine - is then injected in the area of the nerve, causing the entire arm to become numb. The length of time that entire arm is numb depends upon the type of anesthetic that is used and whether or not epinephrine is added to the mixture. This type of a nerve block will generally provide up to 3 hours of "surgical" anesthesia, during which time your surgeon can operate on your arm, and up to 24 hours of pain relief in some situations.
In contrast, a general anesthetic involves going to sleep. In this situation, your anesthesiologist will give you medications that will completely relax your entire body and stop you from feeling any pain. During general anesthesia you will need to have a machine breath for you by gently pushing air into your lungs through a tube in your throat. This most commonly involves placing an "endo-tracheal" tube in your throat and then connecting it to a ventilator. When your surgical procedure is over, your anesthesiologist will reverse the effects of the medication, the tube is removed from your throat, and you are able to breath for yourself again. There are several advantages and disadvantages to each type of anesthesia for shoulder surgery.
There are some shoulder surgeries, like certain rotator cuff repairs, that may require a general anesthetic in order to position the patient correctly. These surgeries typically involve the patient lying on their side, and this is a very difficult position to be comfortable in during the entire procedure. When the shoulder surgery is usually expected to last more than an hour or so, most surgeons generally prefer that the patient have a general anesthetic so that they do not start to "squirm" around during the operation. It can be very difficult to hold still for more than an hour, and while a regional anesthetic can take away pain for much longer than an hour, many patients start to get quite restless.
However, the main advantage of a regional anesthetic is that you do not have to go to sleep, and many patients find that the medications that are used for general anesthesia can make them nauseated and sick to their stomach. The pain relief from a regional anesthetic can also be designed to last for up to 24 hours, and this does facilitate pain control during the first day after shoulder surgery and during outpatient surgery. However, some people are slightly bothered by the sensation of having a completely numb arm, which often feels like it is not even attached to their body. In addition, anesthesia has become much more "gentle" over the past 10 years and now several medications that help to prevent nausea after the operation are routinely given during the procedure. If you have strong feelings one way or another about what type of anesthetic you would like to have you should discuss them with your surgeon before your operation. Ultimately, your anesthesiologist and your surgeon will make a joint decision about what type of anesthetic is safest for you and will make you comfortable during the procedure.