Dysbaric injuries may be the result of several distinct events that expose an individual to a change in barometric pressure. The first possible etiology is an altitude-related event, which can be illustrated by the rapid ascent or descent during airplane transport or sudden cabin decompression at an altitude of 25,000 ft. The second type of dysbaric injury results from an underwater diving accident. A third dysbarism is caused by a blast injury that produces an overpressurization effect. This chapter covers dysbaric diving injuries, and to a lesser degree, aviation-related dysbarisms. Blast injuries are outside the scope of this chapter.

Scuba (self-contained underwater breathing apparatus) diving currently allows the recreational diver to descend to depths >100 ft. There are a number of recreational diving organizations that have minimum age requirements for certifications. In general, candidates must be 15 or 16 years old for full certification. Pool-based divers may be certified at the age of 8 years, and some organizations will certify 10-year-olds for ocean diving to 40 ft (12 m). However, certification is not required to dive and it is the untrained or poorly trained individual who is at greater risk for injury.

Serious diving-related injuries and fatalities are rare and are often associated with human error, unsafe behaviors, or hazardous conditions. From 2010 to 2014, the Divers Alert Network averaged almost 13,000 scuba-related phone and email correspondences per year, with over 4000 emergency calls. In 2014 in the United States, there were 1220 emergency room admissions for scuba-related injuries—and providers were often inexperienced with the presentation and management of these injuries.¹ From 2004 to 2014, there has been an average of 65 diving fatalities annually in the United States and Canada,^1,2 with a steady decline from 75 in 2011² to 54 in 2014.¹ The most common cause of death is from drowning.^1–3 On average, there were 16 diving injuries requiring hyperbaric recompression therapy in scuba divers aged 19 years and younger in North America between 1988 and 2002.⁴ During this time period, the youngest diving fatality was 14 years old and the youngest injured diver was 11.⁴

Several terms are often used when discussing this topic. Dysbarism represents the general topic of pressure-related injuries. Barotrauma, the most common diving injury, refers to the injuries that are a direct result of the mechanical effects of a pressure differential. The complications related to the partial pressure of gases and dissolved gases are called decompression sickness.

Dysbarisms can best be explained by the physical gas laws and through an understanding of pressure equivalents that cause these injuries. The amount of pressure exerted by air at sea level and at different altitudes or depths can be described in several different ways, as shown in Table 142-1.

Individuals and objects under water are exposed to progressively greater pressure due to the weight of the water. Small changes in underwater depth result in large atmospheric pressure and volume changes. This is significantly different from the pressure and volume variation noted in air above sea level. Boyle’s law explains this relationship. Under water, the largest proportionate change in the volume of a gas is seen near the water surface. An air-filled cavity that is 33 ft below the water surface will double when it reaches the surface. In comparison, a volume of gas at sea level will need to rise to an altitude of 18,000 ft to double in volume.

Dalton’s law of partial pressure describes the pressure exerted by gases at various depths or altitudes. Each gas will exert a pressure equal to its proportion of the total gaseous mixture. Figure 142-1 depicts the gaseous composition of the atmosphere at sea level and the corresponding partial pressures.

Henry’s law states that the quantity of gas dissolved in a liquid is proportional to the partial pressure of the gas in contact with the liquid. The partial pressure of a gas and the solubility of the gas determine the amount of gas that will dissolve into a liquid. This law will help explain the increased absorption of nitrogen during underwater descent.

The clinical findings of dysbaric injuries may be immediate or delayed in onset up to 36 hours or more. Most will occur during descent or in close proximity to ascent. A delayed presentation is possible, however, which may make diagnosis difficult.

Barotrauma is the direct result of a pressure difference between the body’s air-filled cavities, which are subject to the effects of Boyle’s law, and the surrounding environment. While scuba diving, barotrauma can occur during ascent or descent, with most symptoms developing during a descent. On descent, a negative pressure develops within enclosed air spaces relative to the ambient surrounding pressure. If air is unable to enter these structures, equalization does not take place, and the air-filled cavities collapse. If the cavity is a rigid structure and unable to collapse, the negative pressure may result in fluid being displaced from the blood vessels of the surrounding mucosa into the intravascular space. The resulting injury pattern can include pain, hemorrhage, edema, vascular engorgement, and tissue damage.

If air is unable to escape on ascent, an expansion of gas within enclosed air spaces causes a positive pressure to develop. This may result in the rupture of these spaces or the compression of adjacent structures. Many of the symptoms of barotrauma in the human body result in a “squeeze” phenomenon. These trapped gas disorders are differentiated by the gas-filled part of the body that is affected.

BAROTITIS

Barometric pressure changes can result in disorders of the external, middle and inner ear. The tympanic membrane (TM) separates the middle ear from the outer ear, and the eustachian tube functions as a valve allowing air pressure to equalize between the middle ear and ambient environment.

Barotitis media, also referred to as middle ear squeeze or ear block, is the most common diving-related barotrauma and involves the middle ear. Equalization via the eustachian tube will occur when there is a pressure differential of approximately 15 to 20 mmHg. The diver becomes symptomatic if equalization is unsuccessful and the pressure differential reaches or approaches 100 mmHg.

Middle ear squeeze commonly develops on descent between 10 and 20 ft below the surface. The symptoms include a fullness in the ears, severe pain, tinnitus, vertigo, nausea, disorientation, and transient conductive hearing loss. Up to 10% of divers may have no pain during descent but will become symptomatic after the dive. If the diver is unable to equalize the pressure and continues to descend, symptoms may be exacerbated and the TM may rupture and bleed. With perforation, the caloric stimulation of cold water entering the middle ear can cause vertigo, nausea, and disorientation. Physical examination may reveal erythema or retraction of the TM, blood behind the TM, a ruptured TM, or a bloody nasal discharge.

Treatment for middle ear squeeze should be directed toward its prevention before pain develops. Scuba divers should attempt to clear their ears every 2 to 3 ft during descent. Under normal situations, pressure in the middle ear is equalized without incidence by actively opening the eustachian tube, which opens and exposes the middle ear to ambient pressures. Divers must learn to open the eustachian tube through various maneuvers such as blowing the nose against pinched nostrils or repositioning the jaw (false yawning), while keeping a regulator in their mouth. Another suggested treatment for barotitis is the Frenzel maneuver. This is performed by pinching the nose closed, placing the tongue on the roof of the mouth, then moving the tongue backward and upward as when starting to swallow. This is repeated as many times as necessary until equalization occurs.

Equalization may be compromised if the eustachian tube is obstructed by swelling of the mucosa, the presence of polyps, previous trauma, allergies, upper respiratory infection, a sinus problem, or smoking. To decrease the incidence of ear discomfort and injury to the TM, a pre-dive treatment of a topical vasoconstrictor nasal spray (oxymetazoline hydrochloride, 0.05%) may be beneficial when used approximately 15 minutes before beginning a dive. The recommended pediatric dosage for ages ≥6 years is two to three sprays in each nostril. Oxymetazoline hydrochloride is not recommended for children younger than 6 years. Pseudoephedrine may also be considered as a pre-dive treatment. For ages 6 to 12, the recommended dose is 30 mg PO. For children older than 12 years, the adult dose of 60 mg PO may be used. If pain persists after the dive, analgesics may be used. If a pre-dive decongestant was not used, it may be considered at this time.

Any patient with barotitis media is to be instructed to refrain from diving until all signs and symptoms have resolved. Erythema generally resolves within 1 to 3 days, whereas it will take 2 to 4 weeks when there is blood behind the TM. A perforated TM must heal before any further diving is attempted. A 10-day course of oral antibiotics and otic suspension is indicated if there is a perforation of the TM. Ear, nose, throat (ENT) follow-up is given upon discharge from the emergency department.

Barotrauma can occur during either descent or ascent. If air is unable to escape the middle ear through the eustachian tube during ascent, a diver may develop symptoms of reverse ear squeeze.