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Editors

JariSuvilehto
AnneRäisänen-Sokolowski

Diving Medicine

Principles

  • Diving is a popular leisure activity, and doctors should therefore be aware of diving-related medical problems and treatable conditions.
  • A self-assessment for fitness to dive must be carried out before recreational diving is started and regularly thereafter. The diver confirms that he/she has understood the risks caused by the listed health factors and that he/she has obtained an appropriate medical assessment if any such risk factor was possibly observed.
  • The frequency of a medical assessment carried out by a physician is dependent on the patient's health, age and the nature of the diving.
  • The medical assessment of a professional diver can only be carried out by a physician with expertise in diving and hyperbaric medicine.
  • In this article, diving refers to diving under water (not, for example, smoke diving by firemen).

Health requirements imposed by diving

  • The diving environment, i.e. the water pressure and temperature as well as the inhaled gas mixture, set certain requirements on the diver's health.
  • Moreover, the sensory environment changes under water; the diver floats in a ”weightless” space with limited visibility, and it becomes more difficult to estimate the size and distance of objects. As the sense of direction deteriorates, auditory perception also changes thus hindering orientation to surrounding objects. The determination of height, depth and direction of movement is usually based on meter readings and not on the diver's own tactile or sensory perception.
  • The diver's physical fitness level and body systems must be able to match the increased demands, i.e. adapt to the surrounding environment.
  • The failure of any body system under water may, at worst, lead to drowning.
  • Immersion in water triggers a ”diving reflex” in the human body. The reflex evokes bradycardia, alters the regulation of both ventilation and the autonomic system as well as redistributes the blood volume. These changes are not always beneficial for an ordinary diver.

Contraindications to diving

  • Contraindications include all conditions where the diver may suddenly lose consciousness, or where he/she may no longer be able to breathe efficiently or adapt to the increased physical demand, i.e. the diver will not be able to complete the task.
  • Neurological causes include
    • epilepsy
    • other sudden disturbance to the level of consciousness.
  • Psychiatric causes include
    • panic disorder (panic is one of the most common causes of serious diving accidents)
    • claustrophobia or agoraphobia
    • serious mental health problems (impaired sense of reality, suicidal tendencies / severe depression, paranoia)
    • use of antipsychotic medication (except SSRIs in mild depression)
    • alcohol abuse or illegal drugs.
  • Respiratory causes include
    • acute or exercise-induced asthma (in mild asthma, spirometric examination and exercise testing should be carried out; if exercise does not induce asthma, diving is allowed, but with more frequent check-ups), cold-induced asthma
    • upper respiratory tract infections
    • other conditions predisposing the diver to pneumothorax or air embolism when exposed to increased pressure
    • spontaneous pneumothorax
    • diminished respiratory function.
  • Cardiovascular causes include
    • arrhythmias; immersion increases the incidence of arrhythmias in any case
    • heart failure
    • coronary heart disease
    • recent infarction or
    • high, uncontrolled blood pressure.
  • Musculoskeletal system
    • The diving equipment alone weighs many kilos (10 kg, may weigh over 30 kg) and the equipment hinders normal movements.
    • Poor physical fitness is a relative contraindication. If the diver's fitness fails, the tendency to panic increases.
    • Considerable obesity (BMI > 30) increases the risk of decompression sickness.
  • Diabetes
    • Insulin-dependent diabetes poses a significant risk when diving with equipment. A medical assessment performed by a physician well experienced in diving and hyperbaric medicine is absolutely necessary.
    • Diet-controlled or tablet-controlled diabetes is not always a contraindication, but a second opinion should be sought from a specialist in diving medicine in order to evaluate potential associated conditions.
  • Haematological conditions
    • Anticoagulant treatment is a relative contraindication to diving (it worsens barotrauma and increases the risk of bleeding after injury); an assessment by a specialist in diving medicine should be sought.
  • Otological problems
    • Problems with pressure equalization within the middle ear cause pain, damage to the tympanic membrane or the inner ear, rotatory vertigo and an increased risk of drowning.
    • Paranasal sinus problems, usually caused by an infection, may become complicated, and may also prevent diving in the long run.
    • Inner ear problems are usually not compatible with diving.
  • If the medical assessment gives rise to suspect a diving related risk, it is recommended that a specialist in diving medicine be consulted in order to prevent future problems.

Diving accidents

  • The most common causes of diving accidents are causes other than medical.
  • Pure equipment failure is also rare.
  • In as many as 80% of diving accidents the cause can be traced to a human error: safety procedures have not been followed, either deliberately or inadvertently.

Barotrauma

  • Barotrauma occurs when the volume of gas changes inversely in relation to the pressure (Boyle's law). During diving, the volume of gas contained in the air-filled cavities (lungs, middle ears, sinuses, intestines) changes, unless pressure equalization is carried out. In scuba diving, a regulator provides the diver's lungs with breathing gas using pressure that matches ambient pressure. It is therefore not necessary to take care about the equalization of the lung pressure. The equalization of the pressure takes place spontaneously in the sinuses as well, unless there is mucosal swelling. A diver must, however, him-/herself actively equalize the pressure of the middle ears by applying different pressure balancing techniques.
  • The most common health hazard during diving, and during hyperbaric chamber treatment, is pressure-induced damage to the middle ear.
  • The descent during a dive, or the increased pressure in the chamber, causes an inward bulge in the tympanic membrane. The diver must actively correct this change by equalizing the pressure of the middle ear via the pharynx and Eustachian tube.
    • If the equalization fails, the tympanic membrane will stretch and eventually perforate. This will lead to pain and a blocked ear. Perforation of the tympanic membrane may cause caloric vertigo and nystagmus, nausea and disorientation. In severe cases, there is even a possible risk of drowning if the diver remains immersed in water.
    • A mild disturbance will correct itself once the pressure has equalized.
    • This is the most common injury encountered by divers, and the management includes stopping diving and allowing the tympanic membrane time to heal.
    • Before pressure is reintroduced to the ear after the injury, a medical check-up is recommended.
  • The same problem may occur the other way round during ascent, i.e. during pressure decrease. However, this phenomenon is more common in the paranasal sinuses. The underlying cause is often the same, i.e. an untreated upper respiratory tract infection or allergy.
    • Treatment follows the usual protocols, and diving should be forbidden during the treatment period.
  • If the pressure equalization fails, barotrauma may also occur in all other body cavities where gas is present, such as in temporary fillings and in the intestines. A face mask and dry suit may also cause barotrauma on the skin and eyes.

Pulmonary barotrauma

  • Pulmonary barotrauma is the most severe form of barotrauma. It occurs if a person holds his/her breath during rapid ascent underwater, when the ambient pressure decreases. The expanding gas may break a pulmonary alveolus whereby so-called pulmonary laceration develops. It may also develop in depths common in swimming pools or while escaping from a submerged car.
  • The clinical picture depends on where the gas leaks into. Gas in the thoracic cavity causes a pneumothorax Pneumothorax and gas in the mediastinum causes mediastinal emphysema. The most dangerous, however, is air entering the blood circulation (arterial gas embolism, AGE), which nearly always leads to death if it develops whilst diving.
    • The initial symptoms is usually unconsciousness, occurring almost immediately after surfacing. At this stage, the amount of gas in the cerebral arteries and the heart is already excessive for any resuscitative measures or hyperbaric chamber treatment to succeed.
    • As the diagnosis is not clinically apparent straight away, advanced life support should be attempted. The diver may ”only” be suffering from pneumothorax or mediastinal emphysema or from any combination involving some of the above-mentioned conditions and severe decompression sickness (DCS).
    • Pneumothorax is treated with thoracocentesis Pneumothorax, which should preferably be done before entering the hyperbaric chamber. Mediastinal emphysema resolves spontaneously or during hyperbaric treatment. Untreated tension pneumothorax may, however, prove to be fatal.
    • Common symptoms in all patients who have survived have been e.g. the following:
      • respiratory distress
      • cyanosis and/or bloody sputum and
      • acute neurological symptoms of varying degree.
    • Prevention is the only effective treatment of pulmonary barotrauma; healthy lungs as well as expiration and avoidance of breath holding during ascent, or pressure decrease. Several pulmonary diseases may predispose to pulmonary laceration, such as asthma, fibrosing or inflammatory pulmonary diseases, emphysema or surgical scars.

Decompression sickness (DCS)

  • According to the laws of physics, water pressure increases by 1 bar (atmosphere) for each 10 meters of water. Decompression sickness (DCS) develops when an inert gas, i.e. gas that is not involved in metabolism (nitrogen or helium) is dissolved in the tissues while the pressure increases. Blood circulation transports the gas from lungs to the tissues. The deeper one dives, the faster the dissolving takes place and the larger amounts of gas are capable of dissolving. The tissues seek saturation of gas, i.e. the gas aims at reaching the same partial pressure in the breathing gas and in the tissue in each surrounding pressure, i.e. diving depth. When the pressure decreases during ascent from depth, the inert gas starts to form bubbles if it is not removed by exhaling in an adequate amount and speed.
  • The lowest pressure after which DCS has been noted is approximately 60-80 kPa = 0.6-0.8 bar abs, which equals to a water depth of approximately 6-8 m.
    • In practice, the diving depth needs to exceed 10 m before the risk of DCS becomes real. This is because during shallow dives there is not enough time for an inert gas (nitrogen) to dissolve in tissues in amounts that would be sufficient for bubble formation.
  • The most common breathing gas is compressed air with 78% of nitrogen and 21% of oxygen. In order to lengthen the diving times, to increase the diving depths, and to avoid nitrogen narcosis, divers may also use oxygen-enriched compressed air (nitrox) , or helium is added to the breathing gas (heliox and trimix). The use of the latter ones is referred to as technical diving.
  • If the pressure decrease is faster than the elimination of gases, bubbles will form in the blood circulation and in tissues. Because nitrogen is particularly soluble in fat, tissues containing fat pose a particular problem during long and deep diving. When the released amount of gas, whether it is nitrogen, helium or another gas, becomes excessive, the diver develops DCS.
  • The bubbles on their own will cause physical and biochemical problems. The perfusion of peripheral tissues will be mechanically obstructed and, moreover, a protein film may form on their surface leading to platelet aggregation. Blood coagulation will be activated throughout the body, not only locally. Endothelial damage activates mediators of inflammation, which for their part worsen the mechanical damage caused by the bubbles. Lungs are the most important filter before the blood moves from the venous side to the arterial and systemic circulation.
  • DCS develops with the same mechanism independent of the gas mixture used, and the modern computers attached to the wrist or to the diving equipment are quite good in preventing DCS by calculating the saturation level of gases in tissues and safe decompression when surfacing.

Classification and symptoms of DCS

  • The old divisionto type I and type II DCS bears no relevance to the pathophysiology of the condition, and therefore it should not be used anymore. The new classification helps to understand the urgency and pathophysiology of the disease. After all, the ultimate management always consists of recompression and hyperbaric oxygen treatment in a pressure chamber.
  • Mild DCS
    • Musculoskeletal pain, particularly in big joints
    • Sensory disturbances (tingling, numbness) that do not follow dermatomes, often in alternating positions
    • General symptoms, such as tiredness that is not in normal relation to the diving performed and an overall feeling of being sick.
    • Itching or erythematous rash (NB: no actual marbling)
  • Severe DCS
    • Cardiopulmonary DCS
      • Cough, dyspnoea, retrosternal pain
      • Sometimes rapid development of disturbances of consciousness and a dramatic drop in blood pressure
    • Cutaneous DCS
      • Cutis marmorata (livedo reticularis, marbling of the skin): bluish-red patches, paleness and tenderness of the skin
      • Often a prodromal symptom of severe DCS, such as spinal cord DCS
    • Spinal cord DCS
      • Bilateral neurological symptoms or back pain
      • Atony of the bladder or anus
      • Para- or tetraplegia
      • Rapid recompression: if untreated or treated with delay, permanent injuries are possible
    • Inner ear DCS
      • Vestibular symptoms: vertigo, nausea, vomiting, ataxia
      • Cochlear symptoms: tinnitus, deafness
      • Occurs particularly in diving with gas mixtures (helium) and during change of breathing gases when ascending from the depth.
      • Important differential diagnosis is barotrauma of the inner ear, in which case no recompression.
    • Cerebral DCS
      • As late symptoms (after days or weeks) concentration difficulties, memory problems, changes in mood and character
    • Lymphatic DCS
      • Subcutaneous oedema, particularly in the upper parts of the thorax
      • Disappears completely by treatment and time.

Treatment Recompression and Adjunctive Therapy for Decompression Illness (Dci)

  • The aim of treatment is the removal of excessive inert gas from the body, restoration of peripheral oxygenation and repair of possible ischaemic damage.
  • First aid in diving accidents is always pure oxygen. As high oxygen concentration as possible is aimed at, and often 100% O2 is delivered via a tight fitting mask with an oxygen dispenser or a reservoir bag mask. Divers often bring such devices with them for delivering first aid oxygen at diving sites and many divers are trained to use them. If nasal cannulae are the only device available for oxygen delivery, even they are better than no oxygen. High oxygen concentration in the breathing air replaces the maximum amount of inert gas from the inspired air and therefore hastens the removal of nitrogen or helium from the tissues.
  • If the hyperbaric treatment is initiated early enough, the nitrogen bubbles dissolve back into the circulation. In such a case, the prognosis of even severe central nervous system symptoms is good.
  • If the hyperbaric oxygen treatment (see also Hyperbaric Oxygen Therapy (HBOT)) is initiated with a delay of hours or even days, the treatment aims to improve peripheral hypoxic injury. A great majority of the cells at the periphery of circulation do not die immediately when faced with oxygen starvation. Instead, when hypoxia and acidosis are corrected the normal function of the cells may be restored.
  • The transfer to a hyperbaric chamber should take place using the most suitable and speediest method taking into account the patient's condition and symptoms. If a helicopter is used, the flight should be performed as a so called low-altitude flight, at an altitude not exceeding 300 meters.
  • In practice, HBOT involves the patient sitting or lying inside a treatment chamber where the pressure is increased to correspond to pressure at depth of 18 m (2.8 bar abs, 280 kPa). The patient breathes in 100% oxygen via a mask or hood. This will ensure the highest possible pressure gradient between the oxygen in the blood and the tissue fluids enabling the maximum diffusion of oxygen into the cells. At the same time the removal speed of nitrogen or other inert gas is increased. The hyperbaric oxygen also begins to repair possible ischaemic damage.
    • The first standard session usually lasts for about 2.5 or 4.5 hours (US navy table 5 or 6). The symptoms start to improve usually as early as during the first twenty minutes. HBOT sessions are continued daily with the pressure at 2.4-2.5 bar abs for 90 minutes as necessary, until all symptoms have resolved or no further improvement takes place between consecutive treatment sessions.
    • Diving emergencies are treated in exactly the same manner whether the diver has used a gas mixture or compressed air as the breathing gas. Treatment schemes that utilize higher pressure than that corresponding to the depth of 18 m exist, in which case a mixture of helium and oxygen is used in the treatment. These schemes are not available in all countries.
  • Find out about the local instructions and policies regarding the treatment locations in different situations.
  • A patient who presents with changes in vital functions must be transferred to the nearest treatment centre as quickly as possible (e.g. with an ambulance or a low-flying helicopter Transport of Patients with Decompression Illness).

Prognosis

  • If treatment is started soon after surfacing, the prognosis is very good, even in severe cases.
  • Cases of DCS where mild joint pain emerges later on, or where treatment has been delayed (hours/days) for some reason, are in most cases treatable with hyperbaric oxygen therapy without major late complications, but may need several treatment sessions.
  • Late complications of untreated DCS, or DCS that was treated insufficiently or too late, include central nervous system symptoms and aseptic bone necrosis, the latter being nevertheless quite rare. Its typical locations include areas close the articular surfaces of long bones (hip, upper arm). No specific treatment exists for the necrosis.

References

  • Vann RD, Butler FK, Mitchell SJ et al. Decompression illness. Lancet 2011;377(9760):153-64. [PubMed]
  • Edmonds C, Bennett M, Lippmann J, Mitchell SJ. Diving and subaquatic medicine. Fifth edition 2016®. CRC Press, Boca Raton, FL, USA

Evidence Summaries ⬆