CHAPTER 141 - Scuba Diving and Dysbarism

Abstract

Underwater free diving to salvage wrecks and to harvest seafood, sponges, coral, and mother-of-pearl has been practiced for more than 5000 years. Historically, divers also used breathing tubes, such as hollow reeds; however, it is nearly impossible to use these at depths of more than 3 feet because of the restriction of inspiration by underwater pressure. Subsequent inventions from the 16th to the 19th centuries, including diving dresses, allowed divers to remain underwater for prolonged periods at depths of up to 12 fathoms (72 feet). The first diving dress (1715) was a reinforced, leather-covered barrel with watertight armholes and a viewing porthole. With the advent of these technologies, the symptoms of divingrelated illness began to be recognized. Colonel William Pasley, the officer in charge of a unit of the British Royal Engineers that salvaged the sunken warship HMS Royal George in 1840, observed symptoms in his divers. At approximately the same time, similar symptoms and even fatalities were observed among caisson workers.* The ailment became known as caisson disease, but the construction workers on the Brooklyn Bridge (built from 1870 to 1883) attached the name “the bends,” characterizing the symptoms that often caused the victim to bend forward in pain. The first clinical description of caisson disease was by Paul Bert in 1878. He correctly attributed the disease to nitrogen gas coming out of solution in the tissues during decompression. This led to the recommendation of slow ascents for pressurized workers and the development of the first recompression chambers. The significant breakthrough allowing diving at depth was the invention of the aqua-lung by Jacques-Yves Cousteau and Emile Gagnan in 1943. The lighter and less expensive equipment, widely known by its acronym SCUBA (self-contained underwater breathing apparatus), does not require a surface supply of air or the support personnel that are necessary for helmet diving. This innovation allowed widespread deep-sea diving, and millions of divers have become certified to date. Most amateur divers use compressed air, open-circuit scuba equipment at depths of less than 130 feet of seawater (fsw). Systems with artificial mixtures of various gases, however, are used to extend the depths to which divers can descend. Some of these are used in sport diving, but their use is uncommon and is primarily limited to commercial applications (Table 143-1). Other variations of supplying air for divers are closed-circuit and semiclosed-circuit diving apparati (“rebreathers”) that use calcium hydroxide to absorb expired carbon dioxide. Oxygen is then added to the decarboxylated gas before rebreathing. The advantages of rebreathers over compressed air scuba are that they are more efficient (less gas is used for a given time), allow deeper dives and longer bottom times, and generate few if any bubbles. The total number of diving-related injuries is unknown, but the absolute numbers of patients with decompression-related illnesses, one of the most serious dive-related injuries, continue to climb as the number of divers has increased despite the rate per 10,000 dives remaining relatively constant since 2001. This rate varies somewhat on the basis of the type of diver: 0.015% for scientific divers, 0.01 to 0.019% for recreational divers, 0.030% for U.S. Navy divers, and 0.095% for commercial divers. The rate of mortality in diving varies between 1.5 and 9 per 100,000 dives. With the popularity of diving and the relative ease of rapid travel from distant destinations, it behooves even the land-locked emergency physician to be aware of diving-related illnesses.