Wilderness and Rescue Medicine 7th Edition Jeffrey Isaac, PA-C and David E. Johnson, MD

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Section V: Environmental Medicine

In a setting remote from advanced medical care, an attempt at resuscitation following prolonged submersion of up to an hour should be made only if it does not place rescuers at risk. Patients who do not respond quickly to basic life support (BLS) will not survive. Resuscitation efforts beyond the 30-minute cardiopulmonary resuscitation (CPR) or automated external defibrillator (AED) proto- cols are not justified. SCUBA Diving Injuries Hyperbaric injury (associated with an increase or decrease in air pressure) was seen before the invention of SCUBA from the use of diving bells and in workers from pressurized bridge construc- tion caissons. It became more common with the emergence of military and sport diving in the 1940s. It took many years and casualties before the problems associated with breathing gas under pressure were properly identified and understood. Certified sport and commercial divers are now well trained in the prevention and recognition of hyperbaric injury. However, because SCUBA has become popular as a tool for both recreation and rescue, it is important for all medical personnel working in water rescue and marine environ- ments to be able to recognize and treat diving injuries. This section will serve as a basic overview for practitioners who have not had the benefit of SCUBA training. Pulmonary Overpressure Syndromes and Decompression Sickness Dive-related injuries are caused by the behavior of air under pressure. As described by Boyle’s Law, an air-filled balloon forced underwater would be compressed to one half of its original volume at 10 meters below the surface, where the ambient pressure is double the surface air pressure. At 20 meters underwater, the balloon will be reduced to a third of its original volume. The same number of air molecules will be present, but they will occupy less space. If the balloon is allowed to return to the surface, it will expand back to its normal size

without damage. This is exactly what happens to the lungs of a free-diver not using pressurized air. To breathe underwater, a diver must be able to expand his or her lungs against the massive force of water pressure. Doing this more than a half of a meter below the surface requires the assistance of pressurized air. The pressure regulator in the SCUBA system provides just enough air pressure on inhalation to overcome water pressure and allow the diver to expand his or her lungs to full volume. The result is that at 10 meters below the surface, the diver’s lungs contain twice as many air molecules as they would on the surface. (The diver could also use a SCUBA tank to pressurize our example balloon to its original volume, even though it is also 10 meters underwater.) As the diver swims back toward the surface, our balloon begins to expand as the water pressure decreases. The diver’s lungs also begin to expand, but because the diver continues to exhale while ascending, the excess volume of air is vented through the regulator. Since the balloon has no ability to vent, it continues to expand until it ruptures in a cloud of bubbles. This is also what would happen to the lungs of the SCUBA diver if she were to ascend too fast for the expanding air to escape.

General Principles

Pulmonary Overpressure Syndromes

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Mechanism: • Uncontrolled rapid ascent from depth • Underwater blast • Hyperexpansion and rupture of lungs • Arterial gas embolus

Signs and Symptoms: • Altered mental status • Pneumothorax • Respiratory distress • Bloody sputum • Shock

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Pulmonary overpressure is the most dramatic and serious hyperbaric injury. The usual cause is a panicked rush for the surface while forgetting to breathe. Expanding air ruptures the lungs, air- ways, and blood vessels, allowing air to enter the chest cavity, subcutaneous tissue, and circulatory system. Large bubbles of air can cause an arterial