Although most dogs travel by air without problems, some need sedation, which increases the risk of complications. When your dog rides in a plane's cargo hold, no one can monitor the effects of sedatives.

Sedation affects a dog's equilibrium, says Patricia Olson, DVM, director of veterinary affairs and studies for the Englewood, Colo.-based American Humane Association. This can impair its ability to steady itself against sudden movements, which can result in injury. High altitudes can create respiratory or cardiovascular problems in sedated dogs.

The Schaumburg, Ill.-based American Veterinary Medical Association agrees. Excessive sedation is the most frequent cause of animal death during air travel, according to a study published in the Journal of AVMA. Over-sedation can occur when owners who observe their dog in an excitable state before ravel administer a little more sedative. After the initial excitement of the trip to the airport and handling during loading, the dog might revert to a quiet resting state in the dark cargo hold. The sedatives then have an excessive effect.

Use conditioning - not chemicals - for safe travel, says Victoria Lukasik, DVM, a board-certified veterinary anesthesiologist. "Tranquilizers, the most popular being acepromazine, interfere with cardiac function and promote heat loss," Lukasik says. "This makes animals more susceptible to stress and cold, both of which are in abundance in the air cargo holds. I ask the [owners] consider carefully if their pet needs a tranquilizer or if they are conditioned to being in their crate and are comfortable there."

Preconditioned animals usually have no need for drugs, Lukasik says. Instead, they do well with a big blanket and some moisture-absorbing pads (provided the dog is not the type that will try to eat the pads during the trip). If owners don't' have time to condition their dogs to a crate before flying, Lukasik recommends they try diphenhydramine (Benadryl), an over-the-counter antihistamine. Give the dog a dose at home first to see if it makes the dog sleepy. (Dosage depends on your dog's weight. Consult your veterinarian before giving any medication to your dog.) If acepromazine is absolutely necessary, try a few test doses at home before travel.