Divers hang on a line above the USCG Duane during a safety stop while ascending to avoid decompression sickness. Photo by Don Rhodes
Coming up the mooring line from a Dive on the U.S.C.G. Cutter Duane, intentionally sunk as an artificial reef in 120 feet of water on Nov. 26, 1987 off of Key Largo, I saw a group of divers hanging on the rope at about 50 deep.
They kept checking gages on their wrists or on instrument consoles hanging from their scuba regulators.
There was a current so, from a distance, the divers looked like a set of flags, one above the other. (Because of the current, diving on the Duane has been nicknamed “flag diving.”)
After about two minutes, they slowly ascended to a depth of 15 feet and waited three more minutes before moving up the line to the surface. Why did they do this? Did they want to take in the view? Or, were they just taking a break.
Scuba divers learn that air, including the air in scuba tanks, is made up of about 21 percent oxygen and 79 percent nitrogen. Oxygen is used in respiration. But, nitrogen is inert and dissolves into body tissues. Water exerts increasing pressure the deeper a diver descends. A scuba regulator supplies air to the diver at the pressure of the surrounding water to enable the diver to breathe. This means that the deeper a diver goes, the more nitrogen enters the diver’s body.
Normal blood circulation carries the excess nitrogen to the diver’s lungs, which then exits as the diver exhales. The problem comes when a diver comes up too quickly and nitrogen bubbles form leading to decompression sickness, which can damage blood vessels and block normal blood flow to different parts of the body. So, to state it simply, the divers on the line were performing safety stops to “vent off” the extra nitrogen they picked up on the dive to prevent it from forming bubbles and causing the bends.
Student divers are taught about the effects of nitrogen on the body and learn that there are both time and depth limits for first and repetitive dives to help reduce the potential of decompression sickness. (Diver’s with additional training can become certified to use enriched air or ‘nitrox” that contains higher fractions of oxygen to increase “bottom time” at certain depths.)
Divers also are taught recommended safety stops, and about mandatory decompression stops when time and depth limits have been exceeded. It is emphasized that recreational divers, except for those trained as technical divers, should avoid the necessity for mandatory decompression stops.
The first cases of decompression sickness in humans (experiments on animals date back to 1670) were documented in 1841 when two miners developed symptoms. The nickname “the bends” started to be used for the symptoms in 1873 after workers emerging from the pressurized construction on the Brooklyn Bridge took on a bent posture to in response to the pain. In 1878, Paris doctor Paul Bert determined that the symptoms were caused by nitrogen gas bubbles.
In the early 20th century, Scottish physiologist John Scott Haldane developed his Principles of Decompression based on experiments performed on goats using an end point of symptomatic DCS. These principles and corresponding tables formed the basis of current decompression theory including the development of the original U.S Navy Decompression Tables.
Over time, dive tables have become more sophisticated using updated mathematical models and Doppler ultrasound flowmeter testing of bubble formation. They have also been adapted to accommodate the diving patterns of recreational divers.
During the last two decades the formula used in tables have been incorporated into dive computers helping divers keep track of depth, time, breathing rates and absorption of gasses, especially repetitive and multi-level dives. Deep and long dives, cold water, hard exercise during or after a dive, rapid ascents and even a hot shower after a dive are can increase the chance of a diver getting DCS.
Other factors that increase the potential for DCS are age, illness, dehydration, poor fitness, high body fat, injuries, alcohol consumption, smoking and heart muscle birth defects.
The signs and symptoms of DCS, usually occur 15 minutes to 12 hours after a dive, and depend on where bubbles form in the body. They include dizziness, tingling, joint and limb pain, shock, numbness, difficulty breathing, weakness, prolonged fatigue, and, in isolated cases, paralysis or death. Sometimes DCS symptoms are mild and go away by themselves, but they may increase in severity until it is obvious to the diver that something is wrong and that help is needed.
A classification system used to classify DCS by severity is type I for symptoms involving only the skin, musculoskeletal system, or lymphatic system, and type II for symptoms where other organs like the central nervous system are involved. Most divers, including those with thousands of dives, never experience DCS. But, DCS can be random and divers shouldn’t gamble if they think they may need medical attention.
According to the Divers Alert Network (DAN), a non-profit 501(c) (3) organization, which provides dive safety information, emergency services, and insurance for the dive community, DCS is rare. The organization says estimates are between three and four cases for every 10,000 dives or approximately 1,000 cases per year. The majority of the DCS cases are minor and treatment results in complete resolution with no impact on future diving activity.
If a diver suspects DCS the first step is to breathe 100 percent oxygen while being transported to an emergency care facility. When you come to the hospital, the first step is an evaluation by a hyperbaric physician to determine if treatment in the chamber is appropriate.
There is a hyperbaric chamber available 24/7 at Mariners Hospital in Tavernier, which is staffed by three on-call hyperbaric physicians, a chamber supervisor, and highly trained technicians. Other chambers are located at Mercy Hospital in Miami and St. Mary’s Medical Center in West Palm Beach.
The chamber usually is pressurized with a high concentration of oxygen to an equivalent depth of 60 feet of sea water and later decreased to the pressure at 30 feet deep of sea water. In most cases treatment, based on US Navy Treatment Table 6, lasts approximately four hours and 45 minutes. A nurse or paramedic stays in the chamber and another person monitors a console located outside of the chamber during the entire procedure. Divers with severe problems may require multiple sessions and are kept at Mariners Hospital between treatments.
The cost of hyperbaric treatment can be expensive. Diving accident insurance is well worth the nominal cost.
If you dive, it is very important to stay in shape, keep your diving skills current, refresh your understanding of dive tables, and know how to use your dive computer. Know the time and depth limits for your planed dive and make sure to follow the plan. It is also a good idea to keep your CPR certification current, learn how to use emergency oxygen and to take a rescue diver course.
Mariners Hospital 24-hour Hyperbaric Evaluation Center can be reached at (305) 434-1600. The direct line for Hyperbaric Medicine is (305) 434-16003.
To become a member of DAN and to purchase diving accident insurance see:www.diversalertnetwork.org/ or call (800) 446-2671. The DAN diving emergency number is (919) 684-9111.
Don Rhodes, in addition to a career in government affairs, has taught scuba for 28 years. He and his wife retired to Tavernier five years ago, where he works as an instructor for Conch Republic Divers.
Source: Learn proper techniques to avoid the bends
