Sewer Gas, Rotten Eggs and Suspended Animation: Researchers Probing Possibilities of Breathing Hydrogen Sulfide

Newswise — Imagine a substance that could facilitate safe long-term space travel in "suspended animation" without using resources such as oxygen or food in the space capsule, a substance to help with organ preservation during surgery, and one that offers an on-demand decrease in metabolism while preserving cardiovascular function, especially after major wounding on the battlefield.

It sounds like science fiction, but researchers at Massachusetts General Hospital (MGH) are excited about the science facts that they found in a study on the effects of inhaled hydrogen sulfide (H2S) in mice. H2S is a major component of sewer or swamp gas and is the stinky component of rotten eggs.

"Our research showed that breathing low concentrations of H2S rapidly and reversibly depresses metabolism in mice, yet preserves cardiovascular function," said Warren Zapol, M.D., Chief of Anesthesia and Critical Care at MGH. "These properties may be exploitable to protect organ function when supplies of oxygen are limited, such as during or after major trauma or during surgery."

Previous studies had shown that H2S acted as a metabolic depressant, but the cardiovascular effects of the substance have remained largely unknown until Dr. Zapol's study, which used sophisticated procedures such echocardiography. He and his MGH colleagues were surprised to find that when H2S was inhaled by mice, the heart rate fell by more than 50 percent " but blood pressure did not fall.

"Blood pressure needs to remain high enough to ensure blood supply to vital organs," said Dr. Zapol's colleague Gian Paolo Volpato, M.D., the study's lead author. "If we could repeat this combination of lowering metabolism without altering blood pressure in cardiac, brain or transplant surgery, inhaled H2S or intravenous chemical H2S donors could have therapeutic potential, because we could balance oxygen transport and tissue metabolism in these patients during periods of inadequate circulation."

Currently, hypothermia is one of the only safe methods of decreasing the metabolic rate and has been used in situations such as stroke, cardiac arrest, organ transplantation and coronary artery bypass surgery. But hypothermia impairs clotting and can increase infection rates. The reduction in metabolic rate produced by H2S does not depend on any change in body temperature.

"Thus, the ability to induce a reversible hypometabolic state, avoiding the damaging effects of hypothermia, could be a valuable and novel field tool for treatment of severely injured patients," said Dr. Zapol. "It could buy time to transport soldiers to a field hospital for major surgery."

Dr. Zapol and his colleagues were surprised by their findings on H2S and they and others remain excited about its potential use in humans. But much more research needs to be performed before such lofty goals as suspended-animation in people can become a reality.

"Further studies of the safety of H2S inhalation and the ability of H2S inhalation to be effective in larger species will be required," he said.

For more information visit the Anesthesiology Web site at http://www.anesthesiology.org.

Founded in 1905, the American Society of Anesthesiologists is an educational, research and scientific association with 43,000 members organized to raise and maintain the standards of the medical practice of anesthesiology and improve the care of the patient.

Visit the ASA Web site at http://www.asahq.org.