Aspiration pneumonia also is one of the leading causes of death in pregnant women, who are at risk of developing the condition when they give birth under general anesthesia or undergo other surgery.

Researchers in the Department of Anesthesiology have found that inhaled nitric oxide, a new therapy being tested to treat serious respiratory ailments, may do more harm than good if used for aspiration pneumonia, and reported new information about the progression of this potentially fatal form of lung inflammation.

Results of their studies were presented recently at the American Society of Anesthesiologists annual meeting in San Diego.

"We're looking at the mechanisms involved in aspiration-induced lung injury, how we can treat this disease, and how to avoid things that make the injury worse," said Paul Knight, professor and chair of the Department of Anesthesiology and senior researcher on the studies.

Aspiration of stomach contents occurs during unconsciousness brought on by anesthesia, trauma, drug overdose or other circumstances. When unconscious, a person loses the natural reflexes that prevent food particles and/or stomach juices from entering the respiratory system.

Stomach contents often are highly acidic. When acidic matter comes in contact with tissue lining the air passages of the lungs, a cascade of events results that can lead to a decreased ability of the lungs to transport oxygen. Even when the process is interrupted, the initial damage inflicted eventually may be fatal, due to later-occurring reactions, Knight said.

One of the newest therapies for treating inflammatory lung injury is inhaled nitric oxide. This gas can bring dramatic improvement in oxygenation in some patients. Giving supplemental oxygen also is a standard therapy to improve oxidation during lung injury.

Knight and colleagues examined administration of oxygen and nitric oxide together in acid-injured and normal lungs, using rats as an animal model.

Results showed that when lung injury was caused by aspiration of acidic liquid, nitric oxide and oxygen worked synergistically to produce an increase in reactive nitrogen species that are toxic to lung tissue. There was no effect of the combined therapies on lung injury from aspiration of gastric particles. Knight said these two etiologic agents have been shown to use different pathways in producing inflammatory lung injury.

"This observation, along with our previous findings of microvascular and functional changes with exposure to nitric oxide and oxygen, suggests that caution should be taken in using nitric oxide in acute inflammatory lung injuries that also require oxygen therapy," he said.

Another study by the same team centered on the relationship of the concentration of food particles aspired to the severity of lung damage and the progression of the damage. Results showed that most of the damage occurred during the first five hours after aspiration, and remained unchanged after 15 days. "Not surprisingly," Knight said, "the higher the concentration of particles, the greater the damage."

Researchers on the studies, in addition to Knight, were Nader Nader-Djalal, Bruce A. Davidson, and Jerzy Cio of the UB Department of Anesthesiology; David Steinhorn of the UB Department of Pediatrics, and Kent Johnson of the University of Michigan Department of Pathology.