Around 2.75 billion passengers travel by commercial airlines every year, however medical emergencies on planes are relatively rare, a study has found.

US researchers carried out a review of in-flight medical emergencies involving five large commercial airlines between January 2008 and October 2010.

A number of issues were assessed, such as the type of medical problem, the type of assistance given on board the plane, whether the plane needed to be diverted and what happened to the person after the flight.

Altogether, the researchers looked at almost 12,000 in-flight medical emergencies, which equated to one emergency for every 604 flights.

The most common types of medical emergencies seen on planes were syncope (fainting) and presyncope (feeling faint). These accounted for at least one in three emergencies.

These were followed by respiratory symptoms, which accounted for one in nine emergencies, and nausea or vomiting, which accounted for almost one in 10.

In almost half of all emergencies, assistance was offered by doctors who happened to be travelling as passengers on the same flight.

Meanwhile, just 7% of flights had to be diverted as a result of a medical emergency.

Post-flight information was available for almost 11,000 passengers who experienced a medical emergency on board. Of these, at least one in four were brought to hospital by an ambulance, where just 8% needed to be admitted. Less than 1% died.

The main reasons for being admitted to hospital were suspected stroke, respiratory problems and heart problems.

The researchers concluded that while access to care is limited if a medical emergency occurs on a plane, ‘few in-flight emergencies result in diversion of the aircraft or death'.

Details of these findings were originally published in the New England Journal of Medicine and are also featured in the journal, Hospital Doctor of Ireland.