General anesthesia used in surgery can increase post-op pain by activating body’

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General anesthesia used in surgery can increase post-op pain by activating

body’s chemical irritant response, Georgetown researchers discover

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(http://www.immunesupport.com/library/ad.cfm?ad_imp_id=9432340 & redir=2 & article_i\

d=8966 & client_id=1) “The choice of anesthetic appears to be an important

determinant of post-operative pain.†– Gerard Ahern, PhD, Georgetown

University Dept. of Pharmacology

Washington, D.C. - The general anesthesia that puts patients into

unconscious sleep so they do not feel surgical pain can increase the discomfort

they

feel once they wake up, say researchers from Georgetown University Medical

Center. They say their findings, the first to scientifically explain what has

been anecdotally observed in the clinic, may lead to wider use of the few

anesthetics that don’t have this side effect, or to the development of new

ones.

In the June 24 issue of the Proceedings of the National Academy of Sciences

(PNAS)1 the scientists report that “noxious†anesthesia drugs - which most

of these general anesthetics are - activate and then sensitize specific

receptors on neurons in the peripheral nervous system. These are the sensory

nerves

in the inflammation and pain pathway that are not affected by general

anesthesia drugs that target the central nervous system – the brain and the

spinal

cord.

“The choice of anesthetic appears to be an important determinant of

post-operative pain,†says the study’s lead investigator, _Gerard Ahern,

PhD_

(http://pharmacology.georgetown.edu/faculty/facahern.html) , an assistant

professor

in the Department of Pharmacology at Georgetown University Medical Center.

“We

hope these findings are ultimately helpful in providing more comfort to

patients.â€

* It has long been known that general anesthetics cause irritation at

the infusion site or in the airways when inhaled, Dr. 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.

* In fact, anesthesiologists often first use a drug to suppress

inflammation and pain before delivering the anesthesia to put the patient to

sleep.

 

* But what has not been understood is the specific mechanism by which

anesthetics affect sensory neurons, or that they can continue to cause pain

and inflammation even as they are being used during surgery, Dr. Ahern says.

The Hypothesis

The researchers tested the hypothesis that two specific receptors on the

nerve 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,†Dr. Ahern says. In fact,

TRPA1

is more commonly known as the mustard-oil receptor, and is a principal

receptor in the pain pathway, he says.

The Findings

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. Perhaps the strongest evidence is that mice bred without TRPA1 genes

demonstrate no pain when the drugs are administered and used, Ahern says.

“Most general anesthetics activate the mustard oil receptor, and animals

that don’t have the receptor don’t have irritation,†he says.

The research team also found that nerve-mediated inflammation was greater

when pungent (chemical irritants) versus non-pungent inhaled general

anesthetics were used.

The Implications

What both findings suggest is that sensory nerve stimulation throughout the

body just before and during surgery adds to the pain that is felt after the

patient is awake, Ahern says.

“This is a provocative finding in terms of the clinical setting, because it

was not really recognized that use of these drugs results in release of lots

of chemicals that recruit immune cells to the nerves, which causes more pain

or inflammation.â€

Some general anesthetics do not activate the mustard-oil receptor, but they

may not be as effective in other ways, Ahern says. “This tells us that there

is room for improvement in these drugs.â€

The study was funded by National Institutes of Health and the National

Multiple Sclerosis Society. Co-authors include José Matta, PhD, Paul Cornett,

PhD,

Rosa Miyares, BA, Ken Abe, PhD, and Niaz Sahibzada, PhD, from Georgetown

University.

____

1. See _“General anesthetics activate a nociceptive ion channel to enhance

pain and inflammation,â€_ (http://www.pnas.org/content/105/25/8784.abstract)

PNAS (Proceedings of the National Academy of Sciences) June 24; 105:8784-8789.

PMID: 18574153, by Ahern GP, Matta JA, et al. [E-mail: Gerard P Ahern

_gpa3_ (gpa3) ]

Source: Georgetown University Medical Center news release, June 23, 2008

Note: This information has not been evaluated by the FDA. It is generic and

is not meant to prevent, diagnose, treat or cure any disease. It is very

important that you make no change in your healthcare plan without researching

and

discussing it in collaboration with your professional healthcare team