Pulmonary Overinflation Syndromes

Pulmonary overinflation syndromes are disorders that are caused by gas expanding within the lung. The disorders encountered in diving are arterial gas embolism, mediastinal and subcutaneous emphysema, and pneumothorax. Normally, only arterial gas embolism (AGE) requires recompression therapy (Chapter 20, paragraph 20-2).

19-3.1 Mediastinal and Subcutaneous Emphysema. Mediastinal emphysema is caused by gas expanding in the tissues behind the breast bone. Symptoms include mild to moderate pain under the breast bone, often described as a dull ache or feeling of tightness. Deep inspiration, coughing, or swallowing makes the pain worse, and the pain may radiate to the shoulder, neck or back.

19-3.1.1 Causes of Subcutaneous Emphysema. Subcutaneous emphysema results from movement of the gas from the mediastinum to the region under the skin of the neck and lower face. Mild cases are often unnoticed by the diver. In more severe cases, the diver may experience a feeling of fullness around the neck and may have difficulty in swallowing. The diver's voice may change in pitch. An observer may note a swelling or apparent inflation of the diver's neck. Movement of the skin near the windpipe or about the collar bone may produce a cracking or crunching sound (crepitation).

19-3.1.2 Treatment of Mediastinal and Subcutaneous Emphysema. Suspicion of medias-tinal or subcutaneous emphysema warrants prompt referral to medical personnel to rule out pneumothorax. Treatment of mediastinal or subcutaneous emphysema with mild symptoms consists of breathing 100 percent oxygen at the surface. If symptoms are severe, shallow recompression may be beneficial. Recompression should only be carried out upon the recommendation of a Diving Medical Officer who has ruled out the occurrence of pneumothorax. Recompression is performed with the diver breathing 100 percent oxygen and using the shallowest depth of relief (usually 5 or 10 feet). An hour of breathing oxygen should be sufficient for resolution, but longer stays may be necessary. Decompression will be dictated by the tender's decompression obligation. The appropriate air table should be used, but the ascent rate should not exceed 1 foot per minute. In this specific case, the delay in ascent should be included in bottom time when choosing the proper decompression table.

19-3.2 Pneumothorax. A pneumothorax is air outside the lung that is trapped in the chest cavity. This condition can result from a severe blow to the chest or a rupture of lung tissue due to overpressurization.

19-3.2.1 Symptoms of Pneumothorax. Pneumothorax is usually accompanied by a sharp unilateral (one side) pain in the chest, shoulder, or upper back that is aggravated by deep breathing. To minimize the pain, the victim will often breathe in a shallow, rapid manner. The victim may appear pale and exhibit a tendency to bend the chest toward the involved side. A collapsed lung may be detected by listening to both sides of the chest with the ear or a stethoscope. A completely collapsed lung will not produce audible sounds of breathing. In cases of partial pneumothorax, however, breath sounds may be present and the condition must be suspected on the basis of history and symptoms. In some instances, the damaged lung tissue acts as a one-way valve, allowing gas to enter the chest cavity but not to leave. Under these circumstances, the size of the pneumothorax increases with each breath. This condition is called tension pneumothorax. In simple pneumothorax, the respiratory distress usually does not get worse after the initial gas leakage out of the lung. In tension pneumothorax, however, the respiratory distress worsens with each breath and can progress rapidly to shock and death if the trapped gas is not vented by inserting a catheter, chest tube, or other device designed to remove gas from the chest cavity.

19-3.2.2 Treating Pneumothorax. Mild pneumothorax can be treated by breathing 100 percent oxygen. Cases of pneumothorax that demonstrate cardiorespiratory compromise may require the insertion of a chest tube, large-bore intravenous (IV) catheter, or other device designed to remove intrathoracic gas (gas around the lung). These devices should only be inserted by personnel trained in their use and the use of other accessory devices (one-way valves, underwater suction, etc.) necessary to safely decompress the thoracic cavity. Divers recompressed for treatment of arterial gas embolism or decompression sickness, who also have a pneumothorax, will experience relief upon recompression. A chest tube or other device and a one-way relief valve may need to be inserted at depth to prevent expansion of the trapped gas during subsequent ascent. If a diver's condition deteriorates rapidly during ascent, especially if the symptoms are respiratory, tension pneumothorax should always be suspected. If a tension pneumothorax is found, recompression to depth of relief is warranted to relieve symptoms until the thoracic cavity can be properly vented. Pneumothorax, if present in combination with arterial gas embolism or decompression sickness, should not prevent immediate recompression therapy. However, a pneumothorax may need to be vented as described before ascent from treatment depth.

19-3.3 Prevention of Pulmonary Overinflation Syndrome. The potential hazard of the pulmonary overinflation syndromes may be prevented or substantially reduced by careful attention to the following:

■ Medical selection of diving personnel, with particular attention to eliminating those who show evidence of lung disease or who have a past history of respiratory disorders. Divers who have had a spontaneous pneumothorax have a high incidence of recurrence and should not dive. Divers who have had pneumothorax from other reasons (e.g., surgery, trauma, etc.) should have their fitness for continued diving reviewed by an experienced Diving Medical Officer, in consultation with appropriate respiratory specialists.

■ Evaluation of the diver's physical condition immediately before a dive. Any impairment of respiration, such as a cold, bronchitis, etc., may be considered as a temporary restriction from diving.

■ Proper, intensive training in diving physics and physiology for every diver, as well as instruction in the correct use of various diving equipment.

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