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

Wilderness and Rescue Medicine 166

gas embolus, producing ischemia in the heart and brain. Air in the chest cavity produces a tension pneumothorax. These are serious critical system injuries and death can be immediate. If the diver survives, emergent medical care is required. The other major diving injury is decompression sickness, otherwise known as the bends. This is caused by the tendency of air under pressure to dissolve into the blood and body tissues it is in contact with. As stated by Henry’s Law, the greater the pressure, the more air will be dissolved. As a diver descends, the air he or she is breath- ing is forced to dissolve into his or her blood and tissues in direct proportion to water depth. The deeper the diver goes and the longer he or she stays, the more air is forced into solution. This is why deeper dives are usually kept shorter in duration. If the diver returns to the surface too quickly, the gas (primarily nitrogen) will come out of solution to form bubbles in the blood. The best illustration of this is a carbonated beverage; when the bottle or can is opened, the pressure is released and the gas bubbles out. In a carbonated beverage, this is good; in the blood, this is bad. If the diver ascends slowly enough, the emerg- ing gas molecules are expired through his or her lungs without causing injury. Dive computers and decompression tables are used to determine a safe rate of ascent. This reduces the risk of decompres- sion sickness but does not eliminate it completely. Off-gassing actually continues for many hours after a dive. If a diver fails to decompress adequately for the depth and duration of the dive, small bubbles accumulate in the smaller vessels, causing micro- vascular ischemia and inflammation. The early symptoms of decompression sickness, such as skin itching, are caused by injury at the capillary level. These bubbles can cause more significant complications depending on their size and loca- tion. Larger bubbles tend to lodge at joints, caus- ing joint pain. Bubbles causing ischemia in the brain can elicit the symptoms of stroke. Bubbles in the spinal cord can cause paralysis. The onset of these various symptoms can be delayed by many

hours and are exacerbated by travel to high alti- tude or by the low cabin pressure in an aircraft. Treatment of Pulmonary Overpressure and Decompression Sickness BLS and advanced life support (ALS), including the administration of high-flow oxygen during rapid evacuation to a hyperbaric chamber, is the ideal treatment for both pulmonary overpressure and decompression sickness. If possible, include the patient’s dive computer (or the information on it) with your evacuation and communication. The Diver’s Alert Network (DAN) can help you find a hyperbaric chamber and is available by phone 24 hours a day by calling 1+919-684-9111. The chamber is the safest place to pressurize the patient to shrink the bubbles that are causing the problems.

General Principles

Decompression Sickness

6

Mechanism: • Prolonged exposure to pressure (eg. >20m > 60 minutes) or multiple dives • Insufficient time to decompress • Bubbles form in blood and tissue from slow dissolution of gas Signs and Symptoms: • Itching, tingling, joint pain • CNS: focal signs, AVPU changes, ataxia • Respiratory distress and shock in severe cases

©2018WMA

Ear Pain and Mask Squeeze Middle ear barotraumas can affect SCUBA and free divers alike. The tympanic membrane (ear drum) in the ear is particularly susceptible to injury from changes in water or air pressure. As the diver descends, he must force air into the mid- dle ear behind the ear drum to counter the water pressure pushing in from the outside. If the air pressure inside matches the water pressure out- side, the ear drumwill remain uninjured. If either becomes excessive, the membrane will rupture and allow water to enter the middle ear. Middle ear barotrauma is usually not an emer- gency, but it carries the anticipated problem of middle ear infection. The patient should not be