Pulmonary over-inflation syndromes are a group of disorders caused by over expansion of the lung. These syndromes generally occur secondary to ascent without exhaling. This group of disorders includes: pneumothorax, mediastinal emphysema, subcutaneous emphysema, and air gas embolism.
Pulmonary overinflation is most commonly seen in the context of inadvertant breatholding during an uncontrolled ascent by an inexperienced or poorly trained diver. Following Boyles Law, the air volume of a diver who has taken a breath at depth exceeds the divers lung capacity causing overpressurization. As little as a 90 cm H2O overpressurization may cause the alveoli in the lung to rupture, potentially allowing release of air into body spaces including the mediastinum, the neck, the chest cavity, or the pulmonary vasculature (discussed below).
Overinflation is most likely to occur near the surface as the greatest pressure and volume changes occur in this zone. Constant exhalation is therefore necessary any time a diver is surfacing, as failure to exhale may result in overinflation and consequent alveolar rupture.
Pneumothorax – is caused by air outside the lung that is trapped in the chest cavity
Mediastinal and Subcutaneous Emphysema – are caused by air which is trapped behind the breast bone in the mediastinaum (mediastinal emphysema), or air which has dissected into the neck (subcutaneous emphysema)
Air Gas Embolism – is caused by air which has entered the pulmonary capillaries (lung blood vessels) and enters the left side of the heart. After leaving the left ventricle, these air bubbles may either travel to the coronary arteries (heart blood vessels), or the cerebral arteries which may cause symptoms similar in many respects to a heart attack or stroke. The diagram below illustrates this process.
Symptoms: Symptoms associated with pulmonary overinflation syndromes range from shortness of breath seen with pneumothorax, to changes in voice and substernal air trapping seen with mediastinal and subcutaneous emphysema, to air gas embolism symptoms which may include mental status changes and loss of consciousness.
Any time a diver losing consciousness within 10 minutes of surfacing or upon surfacing, should be assumed to have an air gas embolism until proven otherwise. Symptoms generally occur within minutes of an uncontrolled ascent, and should be referred to a medical professional immediately.
Prevention: Prevention of pulmonary over-inflation syndrome should first focus on a medical selection process eliminating those with evidence of active lung disease or a history of spontaneous pneumothorax. Those with respiratory disease including (but not limited to) asthma, lung surgery, and traumatic pneumothorax should undergo a full medical examination before diving. Second, training in diving physics/physiology and correct use of diving equipment is essential. Third, An emergency contigency plan should exist for treatment of diving injuries including: location and contact numbers for the nearest recompression facility (contact DAN for recognized chambers).
Treatment: Treatment of pulmonary overinflation syndromes differs according to severity of symptoms, but whenever suspected should be referred to a medical professional familiar with diving medicine.
Pneumothorax – a mild pneumothorax may be treated with 100% oxygen by face mask, however, more severe cases may require placement of a chest tube, a procedure which should only be performed by experienced medical personnel. A pneumothorax seen in combination with suspected air gas embolism should not prevent emergent recompression.
Mediastinal and Subcutaneous Emphysema – minor mediastinal or subcutaneous emphysema treatment may be accomplished through 100% oxygen therapy; however, more severe cases may require recompression therapy. The injured diver should be immediately transfered to an emergency room facility for evaluation by a medical professional familiar with diving medicine. Chest xrays should be taken to rule out pneumothorax.
Air Gas Embolism – divers suffering from air gas embolism may require immediate basic life support/CPR upon surfacing so remember your ABC’s (Airway, Breathing, Circulation). Be sure the diver has a patent airway (free of vomit, debris), check breathing and circulation, and begin CPR if indicated. Alert the emergency transport team immediately and alert the receiving medical/recompression center so recompression therapy may be utilized as early as possible.
If 100 percent oxygen is available, it should be administered by face mask. Oxygen should only be discontinued if convulsions consistent with oxygen related seizure occur. Cover the diver with blankets and transport the patient to the nearest emergency room in preparation for transfer to the nearest recompression chamber. In route monitor for and treat cardiac dysrhythmias per ACLS protocals. Hydration is recommended when possible.