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Anesthetics May Increase Pain After Surgery

Posted on: Tuesday, 24 June 2008, 10:59 CDT

Anesthetics given to patients during surgery could cause an increase in pain following the procedure, according a new study.

Published in the June 23 issue of the Proceedings of the National Academy of Sciences, the study is the first to scientifically explain what doctors have noticed in clinics, researchers said.

They hope their findings will lead to the development of new anesthetics that don’t cause post-surgical pain.

Gerard Ahern of Georgetown University Medical Center in Washington and the study’s lead author, said that “noxious” anesthesia drugs activate and then sensitize specific receptors on neurons in the peripheral nervous system.

“The choice of anesthetic appears to be an important determinant of post-operative pain,” Ahern said.

“We hope these findings are ultimately helpful in providing more comfort to patients.”

Although doctors have been aware of pain caused at the infusion site or in the airways when inhaled, anesthesiologists often first use an additional drug to suppress inflammation and pain before delivering the anesthesia to put the patient to sleep.

"That was thought to be a temporary thing," Ahern said.

Researchers studied two specific receptors on the nerves cells, known as TRPV1 and TRPA1, which they believed were activated by the noxious drugs.

TRPV1 and TRPA1 are two receptors that are often expressed together and are known to react to irritants like garlic and wasabi.

“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 Ahern. In fact, TRPA1 is more commonly known as the mustard-oil receptor, and is a principal receptor in the pain pathway, Ahern says.

Studies confirmed that TRPA1 was activated by noxious anesthetics.

“It's a major pain receptor on peripheral nerves," Ahern said. "When they are activated they cause burning pain."

To see if TRPA1 was involved, they tested the drugs on mice bred to lack the TRPA1 gene and found they showed no pain when the drugs were used, unlike normal animals.

“Most general anesthetics activate the mustard oil receptor, and animals that don’t have the receptor don’t have irritation,” Ahern said.

Although the findings have yet to be determined in human studies, Ahern said they do help explain why these drugs cause pain and suggest the need for more study on ways to prevent or avoid it.

"I think it's a factor that should be considered," he said.

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On the Net:

Proceedings of the National Academy of Sciences

Georgetown University Medical Center

Source: redOrbit Staff & Wire Reports

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