A new study conducted by the researchers from Georgetown University Medical Center revealed a paradox: the general anesthesia drugs given to a patient to put him into unconscious sleep could be related to the level of post-op pain.

This effect is well known is the surgery clinics, but this is the first attempt to explain the mechanism. It has long been known that general anesthetics cause irritation at the infusion site or in the airways when inhaled, Ahern says. And investigators have also known that while they suppress the central nervous system, they can activate so called "pain-sensing" or nociceptive nerve cells on the peripheral nervous system.

According to the findings of this new study published in the June 23rd issue of the Proceedings of the National Academy of Sciences (PNAS), anesthetics affect sensory neurons and they can continue to cause pain and inflammation even as they are being used during surgery.

The researchers tested the hypothesis that two specific receptor on the nerves cells (TRPV1 and TRPA1) which are often expressed together and which also react to other irritants, such as garlic and wasabi, were the ones activated by the noxious drugs.

"Plants produce chemicals such as capsaicin, mustard and garlic that were meant to stop animals from eating them. When they are eaten, the two main receptors that react to them are TRPV1 and TRPA1," said Gerard Ahern, Ph.D., an assistant professor in the Department of Pharmacology at Georgetown University Medical Center.
Experiments showed that general anesthetics appear to regulate TRPA1 in a direct fashion, and are thus responsible for the acute noxious effects of the drugs

The research team also found that nerve-mediated inflammation was greater when pungent (chemical irritants) versus non-pungent inhaled general anesthetics were used.

What both findings suggest is that sensory nerve stimulation throughout the body just before and during surgery ads to the pain that is felt after the patient is awake, Ahern explained.

The scientists explained that their study could lead to improvements to the anesthesia drugs.