TAMPA, Fla. — The verdict is still out on what caused the death of an 8-year-old Pomeranian that seemed fine, only to be found unresponsive two hours later when it was checked on while in a cargo facility during a layover.

Delta Airlines said it was conducting a "thorough review" of the matter after the dog was discovered dead during a layover in Detroit on a flight from Phoenix to Newark, N.J.

MORE: 8-year-old dog dies on Delta layover from Phoenix to Newark

Dr. Walter Woolf, a veterinarian with Air Animal in Tampa which specializes in preparing pets for shipment across the globe, says there are several factors that could cause a pet's sudden death on a plane that might have nothing to do with the airline itself.

"I've seen a lot of scenarios and 99 percent of these situations have a pre-existing condition that will unfold itself at an inappropriate time during a flight," Woolf said.

RELATED: The cost and other complexities to consider before flying with your pets

The extreme conditions of flying, Woolf says, like the changes in oxygen levels, pressure and temperature, coupled with the anxiety it can cause in an animal can also lead to an unexpected death.

But there are a few things he recommends before you put your pet on a plane:

  • A routine check-up from a vet, especially for a pet traveling for the first time. Woolf says you can even get a signed health certificate stating the pet is fit to fly.
  • Get your pet used to being in its crate in an unknown, loud environment.

"Put the dog in its container and take them through the carwash," he said. "It goes dark, there's shaking, noises the dog has never heard before... and what that will do is pre-flight condition the dog."

  • Do not feed your pet 4-5 hours before a flight and cut back food by half the day prior to travel
  • Never sedate you pet. It slows their breathing which can be the difference between life and death, Woolf says, when there are changes in oxygen and pressure levels during a flight.

But bottom line, Woolf cautions that while you can take steps to prepare putting your pet as much as possible for the rigors of air travel, it still can be a risky proposition even if the airline does everything right.

"I wish the dog could turn around and say 'oh by the way, I've haven't been feeling good the last several days,' but they don't do that," he said.

"There are certain inherent risks we cannot predict."

Petfriendlytravel.com has compiled an extensive list of global airlines and their policies on pets.

Keep in mind, of the more than half a million animals that flew on commercial flights in the U.S. last year, 24 died in transit, according to the Department of Transportation. Of those deaths, 18 occurred on United, which up until May remained one of the few major U.S. air carries still accepting breeds deemed to be "high risk," like boxers, pugs and Boston terriers, due to their short or snubbed noses which can lead to respiratory issues.

MORE: More pets died on United than Delta, American

As for the case involving the 8-year-old Pomeranian, the dog's owner told CBS New York he has arranged a necropsy. The owner's attorney claims the dog's crate was returned with a bloodstained blanket inside.

Make it easy to keep up-to-date with more stories like this. Download the 10News app now.

Have a news tip? Email desk@wtsp.com, or visit our Facebook page or Twitter feed.