At the Los Angeles County-University of Southern California Medical Center, we operate a hyperbaric chamber for the treatment of diving injuries. Our chamber is located on beautiful Santa Catalina Island off the coast of Los Angeles. When patients are triaged to the chamber via Baywatch (that’s right, our EMS providers out on the coast are actually referred to as Baywatch!), our faculty and residents fly out by helicopter from the Medical Center to meet them at the chamber. Once they arrive, physicians can “lock-in” to examine and treat one or more patients in our multiplace chamber. Our chamber medical director is Dr. Jeffrey Sipsey, a faculty member and veteran dive doctor whose experience spans several decades. One of the highlights of our residency program is the annual chamber course, when each class of residents gets to spend some quality time together learning about diving emergencies, doing test dives and managing sham cases in the chamber to test their new knowledge and skills.
We did a short review piece on diving emergencies last month and the audience response was impressive. It seems that many of us find this subject intimidating. An attempt to demystify diving injuries, listeners told us, is long overdue and much appreciated. Although diving emergencies are not something that we see everyday, they are important to emergency physicians for a couple of reasons. First, they are real emergencies involving patients that require resuscitation - unquestionably in our domain. Second, an understanding of the physiology involved in diving injuries cuts right to core concepts in our specialty: shock, oxygen delivery, tissue perfusion, arterial and venous occlusion, gaseous toxins and pulmonary mechanics. Whether you work near a body of water or not, knowing these concepts will enhance your appreciation of resuscitation in general.
When we talk about diving injuries, we are generally referring to injuries related to SCUBA diving - breathing compressed air at depth in an open system. What is the concept behind SCUBA? As a diver descends under the water’s surface it becomes increasingly difficult to generate the negative pressure required to inhale air that remains at atmospheric pressure. This is because of the tremendous pressure that the surrounding water exerts on the chest wall. In order to facilitate underwater breathing, the pressurized tank of the SCUBA diver releases air through a regulator that matches the pressure of the of the inspired air to the ambient pressure of the surrounding water at depth.
In addition to SCUBA related injuries, which as a category are referred to as dysbarism, divers are subject to injuries that are unrelated to breathing compressed air. These include simple drowning and near-drowning (submersion injury), trauma and marine envenomations – bites and stings, some or all of which may not be obvious on presentation. Of course, divers are also subject to all of the same medical events that can happen on land, such as acute coronary syndromes, asthma, stroke and seizures. But as a general rule, when a diver emerges from the water in a moribund state and we don’t yet know what has occurred, we often take them to the chamber for their resuscitation until certain types of dysbarism can be ruled out with a “trial of pressure”.
The figure above outlines the basic types of dysbarism, starting with the divers descent to depth and ending after their return to land. The most common injuries are a result of barotrauma and these occur either with descent (squeeze) or on ascent (reverse squeeze). In a nutshell, because the volume of gas in any of the body’s air-filled spaces shrinks with descent and expands with ascent, pressure gradients develop between these spaces and the outside world. These injuries tend to occur close to the surface where the relative volume changes are more marked and when divers have trouble equalizing the pressures between their air-filled spaces and the outside world. Examples of this include mask squeeze, when capillaries in the area enclosed by the diver’s mask burst (e.g. subconjunctival hemorrhage), middle ear squeeze, which results in ruptured and bleeding tympanic membranes, and sinus squeeze, which may result in damage to the sinuses and rupture of the blood vessels within them. As a rule, the treatment of these types of injuries does not involve the hyperbaric chamber. Some patients, however, may require referral to an ENT specialist, especially if there is a perforation of the tympanic membrane or if their symptoms persist despite conservative therapy with analgesics and decongestants.
When barotrauma involves the lungs, it can be life threatening. SCUBA divers that fail to maintain an open airway (e.g. by holding their breath), especially during the final stages of ascent, may develop the pulmonary over-pressure syndrome (POPS). In POPS, expanding gas that is unable to escape through the airway dissects out of the airspaces and into the mediastinum, resulting in pneumomediastinum, and occasionally into the pleural spaces, resulting in pneumothorax.
In the most serious instances, air escapes into the pulmonary arteries and veins, resulting in venous air embolus and arterial gas embolus, respectively. Pneumomediastinum and pneumothorax may be treated conservatively using high-flow oxygen and with drainage in the usual fashion using needle and chest thoracostomy as necessary. They do not require hyperbaric therapy.
Gas emboli, which mimic venous and arterial thromboembolic disease in their clinical presentation, require prompt transport and treatment in a hyperbaric chamber. The way that decompression in the hyperbaric chamber works is simple – it shrinks the gas emboli and relieves the vascular obstruction. Because these injuries occur during the final stages of ascent, they often present immediately upon surfacing. The typical picture is of a diver who loses control of his or her ascent, shoots to the surface with their breath held, and surfaces with symptoms suggestive of pulmonary embolus (chest pain, shortness of breath and hypoxia), stroke (aphasia, hemiparesis and hemianopsia), or myocardial infarction (chest pain and congestive failure). Many of these patients will be unconscious or in frank arrest upon surfacing. As they are being transported to a chamber for emergency decompression, they should be resuscitated and stabilized en route, administered fluid boluses as tolerated, and treated with a view that traumatic injuries and other medical conditions may also be present.
Dr. Swadron is Vice-Chair for Education and EM Residency Program Director at the LA County/USC Medical Center. EM:RAP (Emergency Medicine: Reviews and Perspectives) is a monthly audio program found at www.EMRAP.org
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