You have a medical emergency on a flight. Here’s what the crew can do.

Airplane passengers have fainted, thrown up their breakfast, broken bones and suffered heart attacks. One woman even gave birth to twins - one in the air and the other on land. Recently, a passenger suffered a severe allergic reaction, which has renewed calls for EpiPens on commercial flights.

Any medical crisis is alarming, but more so when you are so far from a hospital. But airlines are prepared for urgent-care situations, regardless of their severity. Flight attendants are trained in basic first aid, CPR and the use of automated external defibrillators, and have medical kits packed with supplies at their disposal (though not everything on a doctor’s wish list).

The cabin crew may also consult with professionals with medical degrees - onboard volunteers or physicians affiliated with an advisory service on the ground (think “Succession”). A passenger’s recovery and, in extreme cases, survival depends on these high-altitude clinics.

“Airplanes have planned ahead for those emergencies,” said Karl Hess, chair of the Pharmacist Professional Group with the International Society of Travel Medicine. “[Very rarely] does the plane need to be diverted, does the person need to be hospitalized when they land or does the individual actually die.”

Here’s how an onboard medical kit and flight crew might just save your life.

The No. 1 medical issue on planes

Considering how many millions of people fly a day, medical issues that transpire during a flight are rare. Dire situations, such as cardiac arrest and strokes, are even less common.

“We prefer to call them events and not emergencies, because most of them are manageable,” said Paulo Alves, global medical director of aviation health with MedAire, which provides land-based medical support to more than 180 domestic and international airlines. “They are not true life-threatening emergencies. Less than 2 percent are severe enough for the plane to be diverted.”

In the 2013 study “Outcomes of Medical Emergencies on Commercial Airline Flights,” researchers analyzed emergency medical data from five domestic and international airlines between January 2008 and October 2010. They determined that medical problems crop up in one out of 604 flights. The number-one issue was presyncope or syncope, or fainting, followed by respiratory problems, and nausea or vomiting.

Alves said fainting can stem from a fear of flying, too much booze or exhaustion. The remedy, he added, is to lie down with your feet up and rest.

What’s in an onboard first-aid kit

For ailments or injuries that require medication or medical equipment, the flight attendants will crack open the first-aid or medical emergency kit, both of which the Federal Aviation Administration mandates.

Since 1986, the agency has required airlines to carry an emergency medical kit and has amended its rule over the years. The FAA, which seeks advice from the Aerospace Medical Association, has assembled a minimum checklist of items that cover the key fields of medicine, such as respiratory, cardiovascular and neurological. For example, there are bandages and splints for cuts and battered limbs, aspirin and analgesics for headaches and pain, antihistamine for allergies, dextrose for a deficiency in liquids or carbohydrates, and an AED for sudden cardiac arrest. There are also such basic supplies as syringes, needles, tourniquets, tape, alcohol sponges and scissors.

“Sometimes the equipment is not state of the art,” said Clayton T. Cowl, a specialist in pulmonary and aerospace medicine at the Mayo Clinic in Minnesota. “It’s not like calling a paramedic or EMT with all of the latest and greatest items.”

Most carriers supplement their kits with additional medicines and instruments, a decision that does not need the FAA’s approval. Last summer, Delta Air Lines introduced several advanced diagnostic tools, including automated blood pressure cuffs, medical-grade stethoscopes, pulse oximeters and a temporal thermometer. Boston physician Andrea Merrill had called out the airline’s medical provisions on Twitter after she assisted with an emergency on a flight to Portugal.

“The kit was quite bare-bones, which surprised me,” said the surgical oncologist, who had volunteered to help a passenger who had passed out a few hours into the trip. “You would think they’d have a higher-quality kit up in the air, where you are far from medical help.”

One absence is particularly notable from flight emergency kits: EpiPens. Though planes must carry epinephrine and syringes, medical organizations have been urging the FAA to require aircraft to carry the auto-injector, a lifesaving device for allergy suffers.

“We have been recommending the EpiPen for many years because it is easier to use,” Alves said.

Last month, Lindsey Ulin, a physician in Boston, suffered an anaphylaxis reaction on a Southwest flight from Phoenix to Austin. “I am only alive today because another physician on the plane figured out how to safely give me the form of epi in your kit,” she tweeted, calling for carriers to add the device to their kits.

In 2018, the agency asked the Aerospace Medical Association to evaluate the emergency medical kit and first-aid kit and share suggestions on how to improve or update their contents. The association’s Air Transport Medicine Committee (Alves was the lead on its task force) proposed the auto-injector in its Guidance Document, which it submitted to the FAA in 2019.

The agency said it is still reviewing the group’s recommendations and that any changes to the kits would involve a “rulemaking process.”

Don’t fly when sick or with symptoms

Some in-flight medical emergencies can be preventable, especially if you listen to your body before boarding. Obviously, if you are sniffling or coughing, make sure you are well enough to travel and won’t spread your sickness. . Though airlines no longer require masking, face coverings can protect yourself and others.

Flying while sick can make you feel even worse. Travelers with sinus infections may experience “the worst headache of their life,” Cowl said, because of the trapped pressure in their eardrums.

Equally important, do not dismiss or ignore even the slightest symptom. In extreme cases, your “pre-departure nerves” could actually be heart disease.

“Initial symptoms aren’t so obvious, and we disregard them,” Alves said. “The latest case that we had was a massive heart attack. He was diagnosed with anxiety over the previous months and explained away the symptoms as anxiety.”

Passengers who have preexisting conditions or recently underwent a surgical treatment should also be cautious when flying. Cowl said the reduced atmospheric pressure at higher altitudes can exacerbate chest pain or cause a heart attack in passengers with active angina. Gas expands when ascending, which could lead to post-surgery complications.

Vacation activities on land and in the sea can also result in medical emergencies in the air. For example, scuba divers who do not wait at least 24 hours before flying can come down with the bends, or decompression sickness. Hikers or bikers who broke a rib and punctured a lung during a hard tumble may be prone to tension pneumothorax, a potentially fatal condition.

“Don’t just show up,” Cowl said. “Think of what potential health risks are there.”

You can also take precautions while flying. To avoid blood clots and other possible medical crises, hydrate with water (not caffeinated, sugary or alcoholic beverages) and stand up to stretch your legs and wiggle your toes every few hours. And don’t forget to pack your medications in your carry-on bag, not your checked luggage.

What a flight attendant can do in an emergency

If you start to feel unwell, immediately alert a flight attendant. Your condition could resolve itself - or quickly deteriorate.

The flight attendants will assess the situation by asking the passenger to describe their symptoms, assuming they are lucid and conscious. Depending on the case, they will administer care themselves or consult with a medical professional onboard or on the ground.

Cowl has provided assistance above and below the clouds. One of his most memorable cases occurred about 20 years ago, when he was a member of the Mayo Clinic team that provided counsel from the ground. A passenger had smuggled a monkey on a New York-bound flight. The wild animal escaped and scratched several passengers, possibly infecting them. Health authorities eventually determined that the monkey was not rabid, though for several harrowing hours, the travelers hung in medical limbo.

On board, licensed medical practitioners who respond to the crew’s request for help are permitted to treat the patient and prescribe medications. The Good Samaritans are protected by the Aviation Medical Assistance Act of 1998.

Flight attendants may also contact physicians through a medical advisory service such as MedAire or MedLink. The flight crew can dispense prescription medications approved by these physicians, who provide advice by such communication devices as satellite phone, radio or app. The team of medical and aviation experts will also determine whether the pilot should reroute the plane to the closest hospital or stay the course, according to Alves.

“They are diverting less and less without taking risk,” he said.