Altitude Affects Anesthesia

High altitudes can affect an animal's blood pressure; it's the reason athletes must acclimate themselves to high altitude conditions long before they compete in them. University of California (UC), Davis, researchers were concerned that this could pose risks to equine patients undergoing surgical procedures in the field setting that required anesthesia, which is dependant upon the blood pressure. In the field supplemental oxygen isn't readily available.

Researcher Eugene Steffey, VMD, PhD, Dipl. ACVA, ECVA, a professor in the Department of Surgical and Radiological Sciences at UC Davis, explained, "At altitude, the oxygen is a lot thinner, there's less pressure in the air, and that translates to increased risk in any species, and it's particularly important to horses where short-term anesthesia is used more often.

"On top of that, no matter the altitude, the efficiency of oxygen decreases with any type of anesthesia," he stated. "Your margin of error for that patient (being anesthetized at altitude) is a lot less. Under operating room circumstances (in an equine hospital), we can address that to some extent. We can supplement the inspiriting breaths with supplemental oxygen."

Steffey suggested that veterinarians need to be more aware of altitude's affects on anesthesia. If the patient's health is already compromised, there should be added consideration.

To help reduce risk, he suggests shortening the procedure. "The longer they are down, the more chance there is for a problem to occur," he explained. Taking the patient into the hospital is another solution to high-risk situations. However, Steffey said, "Economics plays a role here."

If a horse is not yet acclimated to the higher altitudes would he be at greater risk? "It would make a small difference, but the amount of risk is already there," he said. "The margin for error is just cut a little bit more. Animals compensate in certain ways, but there are limits to how much they can do.

"Remember, the percentage of oxygen in the air is the same, what decreases is the total amount of pressure driving that oxygen," he said. For instance, the total air pressure at UC Davis, which is  100 feet above sea level, is a considerably higher than the air pressure in Denver, Colo., which is 5,280 feet above sea level.

Steffey said, "The higher one goes (above sea level), the more these concerns become apparent, and the more the veterinarian must pay attention to the horse's vital signs."

Researchers for the study, which was published in March 2006 issue of Veterinary Anaesthesia and Analgesia, included Steffey; Alma A Garcia Lascurain, MVZ, MC; Hector Sumano Lopez, MVZ, PhD; Patricio Santillán Doherty, MD; and Enrique Núñez Hernandez, MVZ, MC.

About the Author

Chad Mendell

Chad Mendell is the former Managing Editor for TheHorse.com .

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