When the call goes out during an airline flight for a doctor to make themselves known to the cabin crew, there are a few useful things to know.

Emergency specialists Dr Alun Ackery and David Kodama from the University of Toronto say medical practitioners can often find themselves outside their comfort zone when they volunteer to assist on a commercial airline flight.

Writing in the Canadian Association Medical Journal, they say that as many as one in 600 flights involves a medical emergency, so it pays to know what to expect.

After reviewing the evidence and previous reports on in flight emergencies, they provide the following tips:

1. The top five causes of inflight emergencies are syncope/presyncope” (37%), “respiratory symptoms” (12%),“nausea or vomiting” (10%), “cardiac symptoms” (8%) and “seizures” (6%).
2. The aircraft cabin is difficult to work in due to noise, lack of space and privacy. Most patients can be managed in their seats. You may need to ask other passengers to move, or move the patient to the galley for more space. Lighting should be turned on full.
3. Many doctors complain that the stethoscope in the first aid kit is broken or faulty. But the loud noise of an aircraft cabin means that performing auscultation for breath sounds or taking blood pressure measurements can be difficult, if not impossible. More practical methods for confirming systolic BP include palpating the radial artery as the cuff deflates, or watching for the return of the waveform if using a pulse oximeter.
4. Vital signs are different in a pressured aircraft cabin: normal oxygen saturation is about 90% at 2-3000m. Oxygen canisters will not achieve 100% fraction of inspired oxygen even at high flow.
5. Injectable medications are supplied in stand-alone ampoules, which must be prepared carefully. Adrenaline carries the highest risk of error, especially if given intravenously. The authors suggest it is only used IV for patients in cardiac arrest.
6. Make full use of other volunteers, who may include nurses and paramedics. Assign clear roles and responsibilities. Flight attendants are also crucial  resource. They are trained in first aid and CPR, including use of defibrillators. They are also important for smooth communication with aircrew and familiarity with aircraft resources and procedures.
7. Ground support may be available from telemedical agencies via  satellite communication. In the US, 7% of medical emergencies resulted in diversion. The decision to divert (which may cost between $3000 and $900,000) ultimately lies with the captain of the aircraft.
8. Medical practitioners who voluntarily provide emergency medical assistance on a commercial aircraft are protected from liability. While airlines have been sued over emergency treatment, no physician who has volunteered assistance has been known to be sued.

“The incidence of in-flight medical emergencies continues to rise and it is likely that many physicians will hear a call to attend to a fellow passenger. Knowing what to expect may help physicians be better prepared the next time that fateful call goes out at 36 000 feet,” they conclude.

You can see their video, unpacking an inflight first aid kit here: