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Properties Of Gases A Case Study Of The Bends Symptoms

Clinical Manifestations and Diagnosis

Symptoms of decompression illness can occur within minutes and up to 24 hours or more after exposure to changes in ambient pressure associated with dives of 20 feet in depth or more. The severity of symptoms depends on the rate and the magnitude of the change of ambient pressure and can vary among individuals. Diagnosis is based on clinical manifestations, which can be classified according to whether they are caused by formation of inert nitrogen gas bubbles or the localized toxic effects of gas (associated with decompression sickness), barotrauma associated with descent (sinus or otic barotrauma), barotrauma associated with ascent (pulmonary barotrauma), or more severe arterial gas embolism syndromes.

Symptoms vary according to location of bubble formation. For example, type I decompression sickness, also known as the bends or caisson disease, is typically associated with pain in the joints, from mild to severe, and numbness of the extremities. Rashes and lymphedema may also occur. Symptoms of type II decompression sickness may be systemic (fatigue, hypovolemic shock), cardiopulmonary (cough, substernal chest pain, tachypnea, asphyxia), otic (vertigo, hearing loss), or neurologic (ataxia, aphasia, speech disturbances, incontinence, confusion, personality changes, depression, paralysis, and loss of consciousness).

Otic barotrauma, which typically occurs during descent, can affect the external, middle, or inner ear (Chapter 434). External ear symptoms, such as a sensation of ear fullness or otalgia, are caused by a blockage of the canal, for example, with the use of ear plugs or presence of cerumen. Middle ear symptoms of otalgia, vertigo, tinnitus, transient conductive hearing loss, and facial nerve palsy occur when inadequate equalization of pressures results from blocked eustachian tubes, typically in association with allergic rhinitis or upper respiratory infections. Inner ear barotrauma, which is a more serious form of otic barotrauma, is associated with elevated intracranial pressure and rupture of the inner ear membrane. Inner ear barotrauma causes symptoms of sensorineural deafness, tinnitus, vertigo, nausea, and vomiting. Sinus barotrauma typically occurs during descent, is associated with facial pain and epistaxis, and occurs more frequently in individuals with mucosal inflammation from allergies or infection.

Pulmonary barotrauma, which is the second leading cause of death among divers, should be suspected in postdive individuals, particularly at-risk individuals, with symptoms of sudden pleuritic pain, dyspnea, or coughing. Physical examination findings include tachypnea, subcutaneous emphysema, and dullness to percussion or decreased breath sounds over a pneumothorax. Development of tension pneumothorax (Chapter 99) or severe pneumomediastinum may lead to decreased venous return of systemic blood and reduced cardiac preload, a situation that is characterized by hypotension and may lead to refractory shock or cardiac arrest. Chest and neck radiographs are recommended for diagnosis, particularly because pneumothoraces must be treated with chest tube thoracostomy before recompression therapy.

Because arterial gas embolism syndromes are caused by pulmonary barotrauma, careful neurologic assessment is critical. The neurologic findings are similar to those of an acute stroke (Chapter 414), with manifestations of focal or unilateral motor deficits, visual disturbances, sensory deficits, speech difficulties, and cognitive disturbances, including loss of consciousness. Symptoms typically occur within 10 minutes after ascent. Delayed neurologic symptoms are more likely to be due to type II decompression sickness.

In 2012, Mike Prickett, a world-renowned underwater cinematographer, was working on a commercial photo shoot in Tahiti when he witnessed a fellow diver sinking and drowning. While saving the drowning victim, Mike fell victim to decompression sickness (the bends), which led to paralysis from the chest down. This interrupted case study uses Mike's story to explore the kinetic molecular theory of gases, gas laws (specifically Boyle's Law and Henry's Law), hyperbaric oxygen therapy, and partial pressures of gases in mixtures, including the human blood stream. Students investigate how SCUBA equipment works and use a sketching activity to visualize the pressure changes that affect divers as they travel underwater. In-class demonstrations are used to help students visualize the types of conditions that effect changes in gas behavior and to draw connections between them, theoretically and in real life. The case was originally designed for use in a lab setting for undergraduate introductory chemistry or General Organic and Biochemistry (GOB) course, or for an introductory level chemistry class for nursing students.