Side Effects of General Anesthesia

General anesthesia -- a combination of medications that decrease brain activity and pain receptor response -- creates a lack of consciousness, immobility and loss of feeling. Even though newer medications used in general anesthesia disappear from the bloodstream much faster than older medications, some people continue to experience side effects such as confusion, nausea, vomiting, shivering, urinary retention and constipation.

General anesthesia can be inhaled or given intravenously.
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The side effect of confusion is triggered by medications used in anesthesia to prevent awareness and pain during surgery. Clear thinking requires a smooth relay of messages from 1 brain cell to the next. Chemical substances, called neurotransmitters, are responsible for this smooth connection. A general anesthesia may affect the ability of neurotransmitters to smoothly connect and transmit messages after surgery and may contribute to confusion. The effects of pain medications used before, during and after surgery may also contribute to confusion because they, too, leave your body in stages and prevent clear thinking during the process.

Nausea and Vomiting

The side effect of nausea and vomiting is triggered by medications used in anesthesia to prevent muscle movement during surgery. Because anesthesia drugs take time to leave the body, nausea and vomiting may occur after surgery and even after you've left the hospital. Even though you are awake and can move around, it takes more time for the muscles of the digestive tract, which were made sluggish by the anesthesia, to become fully operational. Body secretions, such as saliva, and stomach contents depend on the digestive muscles to push them along. When the muscles for pushing are still inactive from the general anesthesia, the contents often roll back up and you throw up. The authors of a review in the September 2012 issue of "Anesthesia & Analgesia" report that 20 to 30 percent of people experience nausea and vomiting after surgery compared to 80 percent who experienced nausea and vomiting 90 years ago.

Constipation and Urinary Retention

The effects of the medications used in anesthesia to prevent muscle movement during surgery can cause constipation and urinary retention -- that is, the inability to partly or completely empty the bladder -- after surgery. The urinary and bowel muscles are sluggish from the anesthesia and the nerves that send messages to the muscles to void or have a bowel movement are slow to resume activity. Voiding and bowel movements may also be affected by decreased fluid and food intake and lack of physical movement, both before and after surgery.


Shivering is a side effect of a general anesthetic. Medications in the general anesthetic affect the body's "thermostat" and cause the body temperature to drop. Other factors contributing to the drop in body temperature include the temperature of the operating room, which may be required to be cool -- either by the type of surgery or comfort of personnel -- and the cold temperature of intravenous medications. Shivering is the body's way of warming up and creates an increased demand for oxygen. If the oxygen demand is too great, it could potentially cause problems for people with heart and lung conditions. The authors of an August 2013 article in "International Journal of Medical Sciences" investigated the effectiveness of adding a medication, called dexmedetomidine, to general anesthetics to prevent postoperative shivering. The authors found that the addition of dexmedetomidine was effective in controlling both shivering and pain after surgery.

Is This an Emergency?

If you are experiencing serious medical symptoms, seek emergency treatment immediately.
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