Anesthesia

What Happens During Anesthesia

You likely will be given anesthesia by an anesthesia specialist. Final preparations before your surgery may include:

• Attaching monitoring instruments to check your breathing, oxygen level, heart rate, blood pressure, and other body functions.
• Positioning your body for surgery. You will be placed in a position that allows your surgeon access to the appropriate body area and avoids unnecessary pressure on any parts of your body.

The three main phases of anesthesia are induction, maintenance, and emergence.

Induction

The first phase of anesthesia, when you first begin receiving an anesthetic, is called induction.

For local anesthesia and many types of regional anesthesia, induction occurs when a local anesthetic is injected into the part of your body that needs to be anesthetized. Local and regional anesthesia often are given with other medicines that make you relaxed or sleepy (sedatives) or relieve pain (analgesics). These medicines are often given through a vein (intravenously, IV) before the local anesthetic is given.

Induction of epidural and spinal anesthesia may require the insertion of a needle into the space around the spinal nerves in the lower back. You will receive an injection of local anesthetic to reduce discomfort before the needle is inserted.

General anesthesia is often induced with intravenous anesthetics, but inhalation anesthetics also may be used.

• Because they enter directly into the bloodstream, intravenous anesthetics usually cause unconsciousness in less than 1 minute.
• Inhalation anesthetics also act quickly, but you must inhale them for a short time before they cause unconsciousness. Inhalation anesthetics are usually given through a mask that covers your nose and mouth. Induction with inhalation agents is mainly used for small children and adults who do not yet have an intravenous (IV) catheter.

Maintenance and monitoring

The second phase of anesthesia is called maintenance. During maintenance, the anesthesia specialist maintains a balance of medicines while carefully monitoring your breathing, heart rate, blood pressure, and other vital functions. Anesthesia is adjusted based on your responses during the procedure.

With local anesthesia and regional nerve blocks, maintenance frequently requires additional injections of sedatives to prolong the effects for more lengthy procedures.

For general anesthesia, after you are unconscious, anesthesia may be maintained with an inhalation anesthetic alone, with intravenous anesthetics, or most commonly with a combination of the two. Very often, inhalation anesthetics are given through an endotracheal (ET) tube or a laryngeal mask airway (LMA), which is an airway placed at the back of your throat but not in your windpipe like an ET tube. The airway is inserted after you become unconscious.

It also is common during general anesthesia for you to be given other medicines intravenously to maintain stable vital functions and to help prevent or decrease pain or nausea after the procedure.

Emergence

The final phase of anesthesia is called emergence. When your procedure is completed, the anesthesia specialist will stop giving the anesthetic. As your body clears the anesthetic medicines from your system, the effects begin to wear off, and your body functions begin to return. How quickly you emerge from anesthesia depends on the anesthetics and other medicines used and on your response to the medicines.

With local and regional anesthesia, emergence occurs as the effect of the injected anesthetic wears off and sensation returns. How long it takes for sensation to return depends on the type of anesthetic used, how much you were given, and the area of your body that was affected. Local anesthesia and some regional nerve blocks may wear off within 1 to 2 hours. Emergence from epidural or spinal blocks may take longer.

Emergence from general anesthesia begins when the intravenous or inhalation anesthetic is stopped. It may take a short time before your body clears the anesthetic from your system. You will be closely monitored during emergence to make sure that you are breathing well on your own; your heartbeat, blood pressure, and other vital functions stay at normal levels; and your muscle control has returned. If an endotracheal tube (ET) or laryngeal mask airway (LMA) was used, it will be removed as soon as you are breathing on your own.

In some cases, to help speed emergence, reversal agents are used to counteract, or reverse, the effects of certain anesthetics. These agents may help reduce the time it takes for you to recover from anesthesia.

Emergence does not mean you will have completely recovered from all the effects of anesthesia. Some effects may persist for many hours after anesthesia has ended. For example, you may have some numbness or reduced sensation in the part of your body that was anesthetized until the anesthetic wears off completely. Even if you feel alert and normal, your judgment and reflexes may still be affected for some time after your procedure, especially if you continue to take medicines, such as those to control pain or nausea. But if you experience numbness or reduced sensation longer than expected, contact your anesthesia specialist.

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Author:	Caroline Rea, RN, BS, MS	Last Updated: February 4, 2008
Medical Review:	E. Gregory Thompson, MD - Internal Medicine John M. Freedman, MD - Anesthesiology
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