Diving Medicine

Barotrauma refers to trauma or damage caused to body tissues by the mechanical effects of a pressure differential (between a body cavity and the hydrostatic pressure surrounding the body). For barotrauma to occur in a body area, the following five conditions must be met.

i) There must be a gas filled space

ii) The space must have rigid walls

iii) The space must be enclosed

iv) The space must have vascular penetration

v) A change in ambient pressure must occur.

A diver descending in the water column must “equalize” to prevent a middle ear squeeze from occurring as the outside pressure exceeds that inside the middle ear. This scenario commonly occurs in the context of eustachian tube dysfunction (due to anatomy or congestion) or secondary to inadequate equalization during descent. If pressure continues to increase without equalization, the ear drum will eventually burst as the pressure differential increases.

Barotrauma is must frequently seen during descent in the water column (referred to as a “squeeze”), but may also occur during ascent (“reverse squeeze”). Middle ear squeeze is the most common form of barotrauma; however, other types of barotrauma include: sinus, external ear, thoracic, face mask, gastrointestinal, and tooth squeezes.

Prevention: Proper equalization during diving prevents most sinus and ear squeeze from occurring. Given this fact, diving should not be attempted if the diver is unable to clear secondary to congestion. If decongestants are used, avoid those with a narcotic or sedative effect.

Treatment: To treat squeeze during descent: Stop descent. If efforts to equalize fail, ascend a few feet, and avoid clearing during ascent or forceful valsalva. If further efforts to equalize pressure fail – abort the dive. If the diver reports dizziness, abort the dive, and evaluate need to launch the stand-by diver. Follow-up with personnel trained in diving medicine.

To treat a reverse squeeze during ascent: Stop ascent and if clearing does not occur, descend 3 feet. Ascend slowly. Avoid forceful valsalva. Evaluate need to launch stand-by diver. Follow-up with personnel trained in diving medicine.

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.

Decompression sickness or “the bends” was first reported by Sir Robert Boyle in 1670 during animal pressure experimentation when Boyle reported, “… a viper furiously tortured in our exhausted receiver…that had manifestly a conspicuous bubble moving to and fro in the waterish humour of one of his eyes.” The pressure related disease acquired it’s nickname “the bends” after workers emerging from pressurized construction on the Brooklyn Bridge adopted a posture similar to fashionable ladies of the period (“the Grecian Bend” – below) because of symptoms of decompression sickness.

As a diver descends in the water column, the combination of increased pressure (Boyles Law) and consequent increased solubility of nitrogen in the body’s tissues (Henry’s Law) causes an increase in the “on-gassing” of nitrogen. Air is made up of approximately 79 percent nitrogen, which on the surface, is easily cleared from the body. However, as the diver goes deeper, the pressure increases, increasing the partial pressure of nitrogen, and the “on-gassing” of nitrogen exceeds the body’s ability to clear the gas. The deeper the diver goes, the faster this process occurs. A diver with a “nitrogen burden”, upon surfacing may allow nitrogen inside the body to come out of saturation (similar to removing the lid from a shaken/pressurized cola can) causing bubble formation. These bubbles may cause joint pain, sensory changes, limb weakness, and in severe cases paralysis and death, the symptoms being dependent upon location of bubble formation (joints, spinal nerves, spinal cord, etc.). This process is known as decompression sickness, or “the bends”. Onset of these symptoms generally occurs within 12 hours of surfacing from a dive (90% within 6 hours), however, a physician familiar with diving should be consulted anytime decompression sickness is a potential diagnosis.

History: Nitrogen burden and onset of symptoms within 12 hours of surfacing (90% within 6 hours)
Symptoms:

DCS Type 1
Pain – Periarticular (joint)

Mottling of the skin (cutis marmarota) – shown below

Swelling (lymphatic)
DCS Type 2
Pulmonary – cough, “chokes”

Spinal – sensory change, weakness

Inner ear – ringing, hearing change

Cerebral – mental status changes

Prevention: Decompression sickness may be prevented by following these basic steps: 1) Plan the dive prior to entering the water and stick to it. 2) Strictly adhere to no-decompression (No-D) limits as listed in available commercial dive tables. 3) Dive team members should be held to physical fitness standards. Adipose tissue (fat) readily absorbs nitrogen, increasing the potential for decompression sickness. 4) Train for diving often. When adverse conditions do occur, as is common in diving, the diver and the diving supervisor must know how to deal with the situation. 5) 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). 100% oxygen for treatment until recompression.

Treatment: Immediate transfer to a recompression chamber for evaluation by a physician familiar with diving medicine. In route, oral or iv hydration is recommended. If available, 100% oxygen should be administered by face mask.

As mentioned above, increases in pressure will increase body nitrogen saturation causing a progressive “intoxicating” nitrogen effect generally seen in divers at depths in excess of 100 feet. This effect is highly variable between individuals, but many divers refer to “the martini rule” which suggests that every 50 feet of sea water descended in excess of 100 feet has the effect of drinking a martini on an empty stomach. Most divers report symptoms similar to alcohol intoxication including decreased reasoning ability, increased reaction times, lightheadedness, and euphoria. Disorientation and poor judgement may result, placing the diver at risk in the unforgiving underwater environment.

Nitrogen narcosis generally resolves with ascent from depth and acclimatization may occur in divers with a history of exposure. Alternative breathing mixtures should be considered if nitrogen narcosis is regularly reported as symptoms may effect diving safety.