The American Society of Anesthesiologists reports more than 25 million surgical procedures are performed in the U.S. annually. Surgery may be performed in a hospital, outpatient clinic, ambulatory care facility or, sometimes, even in the physician’s office. No matter where the procedure takes place, patient safety, comfort and pain control are of utmost importance.

Anesthetics are medications that control pain. They may be given in an IV or in the form of an injection, gas or vapor. A local anesthetic provides pain control in a very specific part of the body (for example, the hand or foot). It is often injected. But for very small areas, it may be applied in the form of a cream or spray.

Regional anesthetics are drugs that are injected near a cluster of nerves for pain control over a larger area of the body, like a limb or lower waist. A patient may be fully awake for regional anesthesia or may be sedated. Examples are spinal anesthesia and epidural anesthesia.

General anesthetics are used to promote sleep and loss of consciousness. The patient is completely unaware of what is happening while under general anesthesia and has no sensations or memory of the surgery. A tube may be inserted into the throat to maintain breathing. Patients are carefully monitored by the anesthesiologist to ensure the patient remains unconscious and doesn’t develop problems with vital functions.

The Paradox of Anesthesia

Post-operative pain is a common consequence of surgery. It occurs in response to tissue disruption or damage. But researchers say some types of general anesthetics, used to control pain during surgery, may actually contribute to pain after surgery.

Brian Freeman, M.D., an Anesthesiologist with Georgetown University Medical Center, says doctors have known for some time that some injected anesthetics are irritating to the skin and some inhaled anesthetics irritate the airways. These effects were believed to be temporary. Thus, lingering post-operative pain has always been attributed to tissue disruption and damage caused by surgery.

To further investigate the nature of pain after surgery, Freeman and his colleagues looked at two specific pain receptors on sensory nerve cells, TRP (Transient Receptor Potential)V1 and TRPA1. These receptors help the body sense pain from irritants in plants, like capsaicin, mustard oil, wasabi and garlic. Laboratory studies confirmed that TRPA1, also called the mustard oil receptor, becomes activated when exposed to noxious anesthetics. In turn, this would stimulate the sensory nerves, causing increased inflammation and pain.

To confirm the findings, researchers used mice genetically bred without the TRPA1 receptor. Georgetown Pharmacologist Gerard Ahern, Ph.D., says these mice had no problems when given noxious anesthetics.

Ahern says the mustard oil receptor is located in the peripheral nervous system. General anesthetics that target the central nervous system do not activate this pain receptor and are not believed to cause post-surgical pain. Patients who have any concerns about the potential side effects of anesthesia should talk with their anesthesiologist about the risks and benefits of the different kinds of anesthetic medications.

For general information on anesthesia:

American Association of Nurse Anesthetists

American Society of Anesthesiologists