An Ascent to Altitude After Diving Causes Complications

By Dan Kinkade, DAN Medical Information Specialist

The Diver: He is a 48-year-old man, 6 feet, 1 inch (185cm), who weighs 225 pounds (101kg). At the time of his dives, he had no medical problems and used no medication. He has been a certified diver since 1999, with 78 dives. The Dives: He spent four days diving in Mexico. During that time, he made eight dives, with a maximum depth of 82 feet (25 msw). His last dive went to a maximum depth of 53 fsw (16 msw) and ended at 9:20 p.m. All dives lasted 48 minutes, with an hour surface interval between dives. He made all his dives on air, using a computer as his dive planner. He had no problems with any of his dives and felt fine after his last dive, which had to be rescheduled from the previous night. The Complications: The next day, 12 hours after his last dive, he flew a short hop in an unpressurized aircraft at 3,000 feet (904 meters). After a three-hour layover, he then flew on a pressurized charter flight home. He made the flight home without incident, and felt no different than when he left for his vacation. The next morning he woke up feeling fatigued. During the day, he experienced problems with short-term memory. A DAN Member, he contacted the DAN Diving Emergency Hotline; he was advised to go to a hospital for evaluation. The medical facility closest to him did not have a hyperbaric facility. The Diagnosis: He arrived at the local hospital and, after an evaluation of his symptoms, he was placed on 100 percent oxygen via non-rebreather face mask. After one hour of oxygen, he said his fatigue and confusion had not resolved. He was advised to go to the university medical center hyperbaric facility for further evaluation. He drove himself there the next day, another 24-hour delay.After further evaluation, he was diagnosed with DCS-II and placed in the hyperbaric chamber for treatment. He was treated with a U.S. Navy Treatment Table 6 (see sidebar), which resulted in full resolution of all symptoms. Without any further problems, he was released. The physician at the treatment facility gave him no limitations on returning to dive or fly. Since then he has returned to diving, without any problems. The Discussion: Altitude exposure after diving is a very common occurrence. That might include driving over a pass or flying in a pressurized or unpressurized aircraft. Commercial aircraft pressurize to 8,000 feet (2,411 meters) cabin altitude. Experts in the dive medicine community have recognized such exposure to altitude after diving to be a contributing risk of DCI. Data collected by DAN has shown that about one fifth of the injured divers reported some form of altitude exposure after diving. Nearly 60 percent of those involved air travel. Ongoing studies examine the surface interval time for flying after diving. The current recommended minimum waiting time for flying after diving is 12 hours for a single, low-stress dive and 24 hours for multiple or deco dives. These guidelines allow the offgassing of nitrogen in the body. After a dive, residual nitrogen takes several hours to dissipate and return the body to a pre-dive level. When the diver is exposed to altitude soon after a dive, then it is tantamount to doing another ascent. An ascent to altitude exposes the body to a pressure of less than 1 atmosphere. This exposure negates the offgassing that is taking place. And based on the standard dive tables, this exposure may exceed acceptable limits of residual nitrogen. This puts the diver at a higher risk of getting DCI. About The Treatment Table 6 The most commonly used treatment protocol for divers with decompression illness, a U.S. Navy Treatment Table 6 is comprised of alternating short periods of breathing normal air with long periods of breathing 100 percent oxygen. This treatment, developed by the U.S. Navy for its own divers, is a highly effective, decompression or slow "ascent" to ambient pressure which allows the body time to gradually offgas. Additionally, breathing high concentrations of oxygen under pressure increases the partial-pressure gradient of inert gas and thus, increases the rate of resolution of inert gas from tissue. The treatment spans four hours, 45 minutes at two main "depths" of pressurization in a hyperbaric chamber: 60 feet (18 meters) for one hour, 15 minutes; a 30-minute "ascent" to 30 feet (9 meters) while breathing oxygen; then alternating air with oxygen for another two and a half hours. While breathing oxygen for the entire final 30 minutes, the patient is returned to ambient pressure. When necessary, the treatment may be extended to provide greater oxygen exposure for stubborn or persistent symptoms. However, there are limits to which the lungs and nervous system may be safely exposed to high concentrations of oxygen in a single treatment. Provisional Flying After Diving Guidelines These recommendations, which apply to recreational divers, represent the consensus reached by attendees at the 2002 Flying After Diving Workshop. The recommendations are based on earlier published work and recent experimental trials as described in the Workshop Proceedings. Recommendations apply to air dives followed by flights at cabin altitudes of 610 to 2,438 meters for divers who do not have symptoms of decompression sickness (DCS). The consensus recommendations should reduce DCS risk during flying after diving but do not guarantee avoidance of DCS. Preflight surface intervals longer than the recommendations will reduce DCS risk further. Dives within the No-Decompression Limits ¥ A Single No-Decompression Dive: A minimum preflight surface interval of 12 hours is suggested. ¥ Multiple Dives per Day or Multiple Days of Diving: A minimum preflight surface interval of 18 hours is suggested. Dives Requiring Decompression Stops ¥ There is little experimental or published evidence on which to base a recommendation for decompression dives. A preflight surface interval substantially longer than 18 hours appears prudent.