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Air travel safe for patients with pneumatic retinopexy, surgeon and expert pilot says
More risks are involved in the case of different altitude levels between hospital and patient destination.
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BARCELONA, Spain – Air travel in both pressurized airliners and nonpressurized airplanes is safe for patients with pneumatic retinopexy, experts say. Nevertheless, consideration should be given to differences between altitudes of the place where retinopexy is performed and the final destination of the patient after the procedure, according to Carlos Dante Heredia Garcìa, MD, PhD, head of the retina and vitreous department of the Centro de Oftalmología Bonafonte here.
Dr. Heredia Garcia is a private pilot and a clinical aviation medicine specialist, and he has personally carried out research on the behavior of gas tamponades at different altitudes.
“There are many physical laws that influence the behavior of expansive gases in the eye. We all know that these substances are insoluble in water, and can therefore remain in the vitreous cavity for a longer time than in the air. We also know that when a bubble of SF6 is injected, its volume becomes 1.5 times greater in 24 hours and reabsorbs in 14 days. The C3F8, on the other hand, increases in volume four times in 72 hours, and total reabsorption takes place in about 25 days. All this is under normal conditions,” he said.
Changes in altitude
However, there are modifications in the volume of gas bubbles in connection with changes in altitude.
Based on the Boyle-Mariotte law, an decrease in barometric pressure produces an increase in the volume of gas in the eye, which will eventually lead to higher IOP and possible adverse consequences.
“It is therefore very important to take into account the altitude of the place in which we perform pneumatic retinopexy, as well as the altitude of the place where the patient is going to stay for the period of prone positioning,” Dr. Heredia Garcìa said.
In Spain, where he practices, there is no risk for patients who undergo pneumatic retinopexy. Avila, the country’s highest city, is only 1,225 meters above sea level. However, there are many cities in the world at an altitude higher than 2,000 m, including Bogotà, Colombia, Tukucha, Nepal and Mexico City. La Paz, Bolivia, Cuzco, Peru and Leadville, Colorado are well over 3,000 m, and Gartok, Tibet, is more than 4,000 m above sea level.
Effects on gas volume
“A patient who is going to travel to one of these places after pneumatic retinopexy with expansive gases will have a 40% volumetric increase of the tamponade in the eye. This will produce a collapse of the chorioretinal circulation secondary to the increase in intraocular pressure and a consequent central retinal artery occlusion when IOP becomes higher than the maximum pressure of the central artery,” Dr. Heredia Garcìa said.
In his opinion, this could be another possible explanation of the “blackout syndrome,” with its irreversible loss of visual functions, which occurs in some patients after about 2 hours traveling in fast vehicles, like nonpressurized airplanes or helicopters, when sudden changes in altitude are involved.
“Traveling by land in mountain territories is safer in this respect, because the time of arrival is more protracted, and this allows the aqueous humor to drain, bringing IOP to normal levels,” he said.
When the procedure is performed at a high altitude and the patient then travels to a place near sea level, the inverse effect will occur. The volume of the gas diminishes by 40% in addition to the spontaneous reabsorption, resulting in very poor efficacy of the tamponade.
Traveling by air
Traveling by air carries no risk for patients with pneumatic retinopexy, according to Dr. Heredia Garcìa. Although commercial airplanes normally fly over 10,000 m, the presence of compressed air inside the cabin makes interior pressure equivalent to that of lower altitudes. Passengers therefore travel in an atmosphere that will not provoke hypoxic episodes or dysbaric effects, even on long-distance routes.
“We must consider two altitudes,” he explained. “First is the real altitude, also called highest flight altitude, which corresponds to the airplane altitude over the sea level, regulated by the altimeter. The other altitude, which is more important for our purposes, is the cabin, or artificial, altitude. The Concorde, the airliner that has the highest flight altitude at cruising speed, travels at 18,500 m. However, its cabin altitude is 1,855 m, which creates an optimal atmospheric environment for passengers inside. Similarly, the DC-9 has a maximum altitude of 10,650 m, with a cabin altitude of 2,440 m.”
Only an accidental decompression, due to a cabin break or a break III on the fuselage, may be a potential risk for patients with pneumatic retinopexy. The risk entity in such a case would be inversely proportional to decompression speed.
“Fortunately, such events are extremely rare thanks to the security systems of our airlines,” Dr. Heredia Garcìa said.
Small, private planes normally do not have pressurized cabins. For this reason they are only allowed by Visual Flight Regulations to fly below 3,000 m.
“Beyond those limits, the pilot would feel the effects of hypoxy from hypobary, better known as airsickness or aviator sickness,” he said.
Therefore, transport by private planes, which is usually carried out at an altitude of far less than the 3,000-meter limit, can be considered equally safe for patients with pneumatic retinopexy.
For Your Information:
- Carlos Dante Heredia Garcìa, MD, PhD, can be reached at Paseo Manuel Girona No. 15, Entresuelo, 08034 Barcelona, Spain; phone/fax: (34) 93-203-7486; e-mail: cheredia@telefonica.net; Web site: http://www.carlosheredia.com.