Mid-air. It’s the last place anyone wants to have a medical emergency, but a study published in the New England Journal of Medicine on Thursday claims that’s exactly what happens on about one out of every 604 flights. More surprising still, in three out of four emergencies, a trained health professional aboard the plane will step forward to help out.

Researchers from the University of Pittsburgh reviewed in-flight medical emergency calls to their on-campus, physician-directed communications center from five domestic and international airlines between Jan. 1, 2008, and Oct. 31, 2010. The Federal Aviation Administration doesn't require airlines to consult with medical professionals on the ground at the 24-hour center in Pittsburgh, but most airlines do.

During the period of study, the researchers counted 11,920 in-flight medical emergencies resulting in calls to Pittsburgh, which, considering that 2.75 billion passengers fly on commercial airlines each year, equates to about 44,000 in-flight emergencies annually, and nearly 50 a day in the U.S. alone. A passenger physician came to the rescue nearly 50 percent of the time, while other medical professionals such as nurses and emergency medical technicians stepped in to assist in 28 percent of the cases. The study notes that a Good Samaritan law protects those who may fear liability if they help in such situations.

The most common problems were syncope (fainting) or presyncope (37.4 percent), respiratory symptoms (12.1 percent) and nausea or vomiting (9.5 percent). The mid-air medical emergencies only resulted in an aircraft diversion 7.3 percent of the time, and just 0.3 percent of the 10,914 patients for whom post-flight follow-up data was available died. Emergency medical service personnel transported another 25.8 percent to a hospital, where 8.6 were admitted, mostly for possible stroke, respiratory or cardiac symptoms.

The American College of Obstetrics and Gynecology claims air travel should be avoided after the 36th week of pregnancy, but that didn’t stop a few women from flying anyway. During the study period, 11 cases involved women in late pregnancy who were in labor. Three of those flights were diverted as a result.

Christian Martin-Gill, assistant professor of emergency medicine at the University of Pittsburgh, led the team of researchers. He said that the study proved that physicians and others obtain a basic knowledge and awareness of the resources available to them in an unfamiliar and cramped setting to be effective volunteers during an in-flight emergency.

“We wanted to provide a description of the type of emergencies commonly treated on aircraft, identify the outcomes of these patients and provide an understanding of the treatment capabilities available on the aircraft in the medical kit and through experts on the ground,” Martin-Gill explained. “We hope to look more closely at the most common conditions and which ones require follow-up care so we can better tailor treatment recommendations for passengers.”

Most flights are equipped with medical supplies including pain relievers and intravenous fluids, and the study found that flight attendants were adequately trained in emergency protocols and prepared to treat patients using advice from the ground-based consultants. All in all, Martin-Gill concluded, “Commercial air travel is generally safe, and in-flight deaths are rare.”