Decompression Illness in Scuba Divers What You Need to Know The initial compression and subsequent expansion of air during a dive can have serious adverse effects on a wide range of body systems. As the popularity of the sport has increased in recent times, so has the likelihood that an emergency physician will see novice divers with decompression sickness, arterial gas embolism, and even pulmonary barotrauma. The authors explain how to be prepared. By Mark Merlin, DO, EMT-P, FACEP, Amy Ondeyka, BA, EMT-B, and Andreia Marques-Baptista, MD ecreational scuba diving has become in- grown, so has the incidence of diving-related inju- creasingly popular since the 1980s, with ries—in particular, decompression sickness (DCS) more than 500,000 new certifications and arterial gas embolism (AGE), which are collec- awarded each year. As the sport has tively referred to as decompression illness. R Decompression sickness results from gas bubbles Dr. Merlin is an assistant professor of emergency that form in the venous circulation and tissues as the medicine and pediatrics and medical director of the New ambient pressure decreases when a diver ascends to Jersey EMS/Disaster Medicine Fellowship at University of Medicine and Dentistry-Robert Wood Johnson Medical the surface. Arterial gas embolism occurs when gas School and EMS/critical care transport medical director bubbles causing circulatory and inflammatory de- at Robert Wood Johnson University Hospital in New rangements enter the arterial circulation, obstruct- Brunswick, New Jersey. He is also medical director of the New Jersey EMS Task Force and chair of the New Jersey ing blood flow to various organs. Emergency physi- MICU Advisory Board for the Department of Health cians need to be prepared to recognize and manage and Senior Services. Ms. Ondeyka, a medical student the effects that decompression illness can have on a at University of Medicine and Dentistry-Robert Wood Johnson Medical School, has been involved in emergency wide range of body systems. medical services for over five years, as both a paid and volunteer EMT in New Jersey and Pennsylvania, and is a HAZARDS OF CHANGING PRESSURE certified open water diver. Dr. Marques-Baptista is the In recreational scuba diving, divers typically do not New Jersey EMS/Disaster Medicine Fellow at University of Medicine and Dentistry-Robert Wood Johnson Medical exceed a depth of 130 feet sea water (fsw). As div- School. ers descend, the ambient pressure exerted on them © 2009 Argosy 18 EMERGENCY MEDICINE | JUNE 2009 www.emedmag.com DECOMPRESSION ILLNESS increases. At a depth of only 33 fsw, the ambient pressure on a diver has TABLE 1. Symptoms of Decompression Sickness already doubled.1 As stated in Boyle’s Type 1 Type 2 law, when a gas is subject to increas- ing pressure, its volume will decrease. • skin rashes CNS Increased pressure is felt not only in • joint pain • headache the air-filled spaces of a diver’s body, • musculoskeletal pain • paraplegia mainly the middle ear and sinuses, but • ataxia also in the lungs and intestines. Proper • unconsciousness equalization techniques are stressed in diver education to avoid pain and Pulmonary (chokes) damage to these spaces. • hemoptysis During ascent, the ambient pres- • cough sure decreases back toward that of • substernal chest pain the atmosphere and the volume of gas expands. If air becomes trapped • dyspnea in the lungs from disease or because a diver does not exhale during ascent, expanding air can cause the lungs to overinflate and safety stop should allow ample time for the excess burst, a condition called pulmonary barotrauma. nitrogen to leave the tissues, enter the low-pres- Scuba divers usually breathe a mixture of oxygen sure venous circulation, move into the pulmonary and nitrogen, which becomes compressed due to capillary bed, and be exhaled and eliminated in the the increased pressure during descent. Compressed normal manner. air contains more molecules at depth, and thus a descending diver receives more air molecules with SEVERAL TYPES OF ILLNESS each breath. This causes larger amounts of gas to If divers ascend too rapidly, they may not allow become dissolved in the blood and tissues. Oxygen enough time for excess gas to leave the tissues and is continually used by the body and does not ac- blood. Rapid ascent can cause gas to come out of cumulate, but the excess nitrogen molecules are not solution and form bubbles, which remain in tis- readily used, and the diver is left with greater residual sues or in the blood. With continued ascent, the amounts at increased depths. gas bubbles will expand as pressure decreases. The The Professional Association of Diving Instruc- expanded bubbles can obstruct blood flow directly tors, one of the largest diver training organizations, or cause tissue ischemia indirectly by activating recommends that scuba divers ascend slowly, no platelets and the coagulation cascade. Gas bubbles faster than 60 fsw per minute.1 Recreational divers can also lead to vascular en- are encouraged to perform a safety stop for dives dothelial dysfunction with >>FAST TRACK<< deeper than 60 fsw. A safety stop is merely a recom- capillary leakage, resulting The central nervous mended precautionary stop performed during ascent in complement activation system is especially at a depth of 15 to 20 fsw for 3 to 5 minutes. This and pathogenic interaction susceptible to recommended stop is different from a required de- between leukocytes and decompression illness compression stop, which is necessary for divers who endothelial tissues. These because nitrogen descend to depths greater than 130 fsw or who ex- changes provoke swelling dissolves so readily in its ceed the maximum time limit at a given depth. These that leads to pain in mus- fatty tissues. divers, depending on how deep they go, may be re- cles, joints, and tendons.3 quired to make multiple decompression stops.2 DCS types 1 and 2. Two distinct forms of DCS The purpose of a safety stop is to compensate are recognized (Table 1). Type 1 DCS, also called for variation in ascent rate and individual differ- the bends, results from the rapid formation and ex- ences in nitrogen absorption and elimination. A pansion of gas bubbles in the musculoskeletal, cu- slow ascent time combined with a recommended taneous, and lymphatic systems. Possible symptoms www.emedmag.com JUNE 2009 | EMERGENCY MEDICINE 19 DECOMPRESSION ILLNESS FIGURE. Pulmonary Barotrauma and Subsequent Complications PULMONARY BAROTRAUMA overinflation and rupture of alveoli leakage of air bubbles vessels surrounding tissue pleural cavity arterial gas embolism pneumothorax subcutaneous pneumomediastinum emphysema altered mental status, pleuritic chest pain, coma, seizures, chest pain, shortness of dyspnea, tachypnea, motor/sensory breath, hemoptysis deficits, visual decreased breath sounds disturbances, chest pain include arthralgia, myalgia, and skin rash. Type 1 outflow from the cord. This prevents the dissolved DCS usually presents within hours of surfacing but nitrogen already in the cord from leaving, which can occur up to 48 hours later. can result in the formation of in-situ bubbles that Type 2 DCS is diagnosed when gas bubbles have cause severe damage to the spinal cord. Type 2 DCS induced local ischemia in the central nervous, car- symptoms include severe headache, altered mental diovascular, pulmonary, and digestive systems.4 The status, paraplegia, motor weakness, ataxia, and loss central nervous system is especially susceptible to of consciousness.4 decompression illness because nitrogen dissolves Pulmonary DCS (the chokes) is caused by a large so readily in its fatty tissues. Spinal cord involve- number of gas bubbles entering the pulmonary artery. ment is usually the result of gas bubbles in the ve- Symptoms range from cough, hemoptysis, dyspnea, nous plexus system that eventually occlude venous and substernal chest pain to cardiovascular collapse. 20 EMERGENCY MEDICINE | JUNE 2009 www.emedmag.com DECOMPRESSION ILLNESS Pulmonary barotrauma. A very serious possible air emergency ascent, or cardiopulmonary or other consequence when a diver holds his or her breath symptoms of pulmonary barotrauma, including pneu- on ascent, causing air-trapping in the lung, is pulmo- mothorax and subcutaneous emphysema. In the case nary barotrauma. As pressure decreases, the trapped of suspected cerebral AGE, brain imaging can show air expands, which can lead to rupture of the alveolar intravascular cerebral air bubbles. Usually, however, lining, allowing air to leak into the interstitium of the imaging is normal even in the face of severe neurologic lungs. The intermediate consequence of this is pul- abnormalities. monary interstitial emphysema, usually asymptomatic unless further damage and air leakage occur. From WHAT TIPS THE SCALES? the interstitium, air can travel and cause three main Deep and repetitive dives, rapid ascent, cold water complications (Figure): mediastinal and subcutane- dives, and air travel after diving are all significant ous emphysema from accumulated air in the medias- risk factors for decompression illness. The deeper tinum, AGE from air bubbles in the arterial system, the dive, the more excess nitrogen is dissolved into and pneumothorax from accumulated air between the the body tissues and the greater the likelihood that lung and chest wall. Continuing, unrelieved accumu- bubbles will form. Repetitive dives (two or more lation of air may result in tension pneumothorax. 5 dives in one day) also result in excess nitrogen in Arterial gas embolism. In AGE secondary to the body, because residual nitrogen remains dis- DCS, the pulmonary capillary beds become over- solved in body tissues for at least 12 hours after whelmed with bubbles. If this occurs, some bubbles every dive. Air travel also heightens risk because may pass into the left side of the heart and subse- of the reduced ambient pressure inside the aircraft, quently into the arterial circulation. Gas bubbles can which increases the possibility of bubble formation. also directly enter the left side of the heart if the It is recommended that divers wait a minimum of 12 patient has a septal defect or patent foramen ovale.