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Dysbarism - Barotrauma DYSBARISM - BAROTRAUMA Introduction Dysbarism is the term given to medical complications of exposure to gases at higher than normal atmospheric pressure. It includes barotrauma, decompression illness and nitrogen narcosis. Barotrauma occurs as a consequence of excessive expansion or contraction of gas within enclosed body cavities. Barotrauma principally affects the: 1. Lungs (most importantly): Lung barotrauma may result in: ● Gas embolism ● Pneumomediastinum ● Pneumothorax. 2. Eyes 3. Middle / Inner ear 4. Sinuses 5. Teeth / mandible 6. GIT (rarely) Any illness that develops during or post div.ing must be considered to be diving- related until proven otherwise. Any patient with neurological symptoms in particular needs urgent referral to a specialist in hyperbaric medicine. See also separate document on Dysbarism - Decompression Illness (in Environmental folder). Terminology The term dysbarism encompasses: ● Decompression illness And ● Barotrauma And ● Nitrogen narcosis Decompression illness (DCI) includes: 1. Decompression sickness (DCS) (or in lay terms, the “bends”): ● Type I DCS: ♥ Involves the joints or skin only ● Type II DCS: ♥ Involves all other pain, neurological injury, vestibular and pulmonary symptoms. 2. Arterial gas embolism (AGE): ● Due to pulmonary barotrauma releasing air into the circulation. Epidemiology Diving is generally a safe undertaking. Serious decompression incidents occur approximately only in 1 in 10,000 dives. However, because of high participation rates, there are about 200 - 300 cases of significant decompression illness requiring treatment in Australia each year. It is estimated that 10 times this number of divers experience less severe illness after diving. Physics Boyle’s Law: The air pressure at sea level is 1 atmosphere absolute (ATA). Alternative units used for 1 ATA include: ● 101.3 kPa (SI units) ● 1.013 Bar ● 10 meters of sea water (MSW) ● 760 mm of mercury (mm Hg) ● 14.7 pounds per square inch (PSI) For every 10 meters a diver descends in seawater, the pressure increases by 1 ATA. This pressure change impacts on gas spaces within the body according to Boyle’s law. The absolute pressure exerted by a given mass of an ideal gas is inversely proportional to the volume it occupies if the temperature and amount of gas remain unchanged within a closed system Mathematically, Boyle’s law can be stated as: ● P is proportional to 1/V Or ● PV = k Where P is the pressure of the gas, V is the volume of the gas, and k is a constant. For comparing the same substance under two different sets of conditions, the law can be usefully expressed as: ● P 1.V 1 = P 2.V2 Depth vs pressure and gas volume (from Boyle’s law): Depth Absolute Pressure Gas volume % (ATA) 0 1 100 10 2 50 20 3 33 30 4 25 40 5 20 Pathophysiology Boyle’s Law states that for a particular quantity of gas the volume is inversely proportional to the pressure. The effect of the column of water above a diver means that 1 atmosphere of pressure is added for every 10 metres of seawater descended. Barotrauma occurs when the pressure of an air-filled space within the body does not equilibrate with changes in ambient pressure of the environment, and can occur either on descent or ascent. Injury can occur during both descent (“squeeze” injuries) or during ascent. Sinus: Mucosal swelling and haemorrhage occur if the communication of the sinuses with the nasopharynx is blocked and equalization of sinus pressure is not possible during descent. The frontal sinuses are most commonly involved. Middle-ear barotrauma: Middle-ear barotrauma is the most common medical disorder of diving,. It usually occurs during descent. Increased ambient pressure results in a reduction of middle-ear volume. If equalization of the volume via the eustachian tube is inadequate, then the following may result: ● The tympanic membrane is deformed inwards and may rupture. ● Inflammation and haemorrhage ● Mucosal oedema and vascular engorgement Pulmonary: Breathing compressed air at depth, means that the diver’s lungs contain greater amounts and density of gas than on the surface. Pulmonary barotrauma results when a diver ascends without exhaling adequately and the expanding gas in the lungs exceeds the lung’s elasticity, tearing alveoli. This occurs most commonly when a diver runs out of air, panics and ascends too rapidly. Even a change in pressure over 1 meter near the surface is sufficient to cause lung barotrauma. It can also occur with a normal ascent if there is a localized area of lung that does not empty properly, as is possible in divers with asthma, reduced pulmonary compliance or air trapping. Clinical features Barotrauma can occur after even very short and shallow dives. The onset of symptoms is usually within 30 minutes of ascent to the surface. A history establishing the onset of symptoms in relation to the dive phase (ascent or descent) helps to delineate syndromes. Ocular: Ocular injury is essentially the result of “Facemask squeeze”. If divers fail to exhale air into their masks on descent, the reduced volume inside the mask can cause pain, petechiae and conjunctival haemorrhage. In assessing these divers, it is important to confirm that they have normal visual acuity and fundi are normal. The condition is usually self-limiting. Sinuses: Sinus pain usually develops during descent. “Sinus squeeze” can result in: 1. Pain / tenderness ● Frontal sinus pain is the most common Maxillary sinus involvement can refer pain to the upper teeth or cheek. ● There may be resolution of the pain at depth, due to mucosal oedema and blood filling the volume deficit left by gas compression. Pain and epistaxis m a y occur as the diver ascends. 3. Epistaxis ● This may occur as the diver ascends. Dental: “Dental squeeze” can result in: 1. Toothache ● Severe tooth pain may occur with descent or ascent if air is trapped under a decaying tooth or recent filling. ● Percussion of the involved tooth is painful. 2. Jaw pain 3. Dislodged dental fillings may occur. Ear: “Ear squeeze” develops on descent, resulting in pain and hearing loss due to damage to the middle and/ or inner ear. Middle ear: There may be sudden relief of pain if the tympanic membrane ruptures. Unilateral tympanic membrane rupture can result in: 1. Bleeding from the ear canal 2. Vertigo 3. Nausea 4. Disorientation due to caloric stimulation of cold water in the middle ear. Middle ear barotrauma severity can be graded as follows: SEVERITY CLINICAL FEATURES Grade 0 Symptoms without signs Grade 1 Injection of TM along handle of malleus Grade 2 Slight haemorrhage within the TM Grade 3 Gross haemorrhage within the TM Grade 4 Free blood in middle ear Grade 5 Perforation of TM Inner ear: Inner ear damage is suggested by: 1. Tinnitus 2. Severe vertigo 3. Significant sensorineural hearing loss Sudden pressure changes between the middle and inner ears can cause rupture of the round or oval windows or a tear of Reissner’s membrane. This usually occurs during rapid descent without equalizing or forceful Valsalva manoeuvres. The main differential diagnosis is decompression illness (DCI) involving the inner ear or vestibular apparatus. Frequently it is difficult to distinguish between inner ear barotrauma and vestibular DCI, although the latter is frequently accompanied by other symptoms or signs of DCI. Because of this overlap in clinical syndromes, early specialist advice should be sought. Pulmonary: The resultant clinical syndromes depend on the sites at which the air escapes and include 1. Pneumothorax: ● Pneumothorax is fairly uncommon, although it becomes more likely in the presence of underlying lung disease or previous pneumothorax. 2. Pneumomediastinum: ● Pneumomediastinum may present with: ♥ Pleuritic chest pain radiating to the shoulders ♥ Dyspnoea ♥ Coughing ♥ Dysphagia ♥ Palpable crepitation due to subcutaneous emphysema Tension pneumomediastinum is a rare entity, presenting with all of the above symptoms and progressing rapidly to severe respiratory distress and cardiovascular collapse due to generalized increased intrathoracic pressure obstructing venous return to the heart. 3. Arterial gas embolism (AGE): ● Barotrauma of the lungs can also result in arterial gas embolism with bubbles of gas being forced from the alveoli, through a breech in a vessel w a l l into pulmonary capillaries, and then on to the systemic circulation. Gas bubbles can then distribute to the cerebral circulation; myocardial circulation with serious ischemic type complications. Neurological symptoms (which can be subtle) suggest AGE The exact symptom complex will depends on the size and location of the gas embolus Essentially any organ system may be also involved, but less commonly. If divers present with a pneumomediastinum or pneumothorax, then they may have up to 50% chance of associated AGE. Gastrointestinal: Expansion of gas within the gastrointestinal tract on ascent can occasionally cause colicky abdominal pain. Rupture of the stomach is rare but has occurred where panic or equipment failure has led to air swallowing and rapid ascent. The affected diver presents with abdominal pain and distension. Shoulder pain may be due to diaphragmatic irritation or coexisting DCI. Subdiaphragmatic free air may be visible on an erect chest x-ray. The differential diagnosis includes pulmonary barotrauma, because air can enter the peritoneum via the mediastinum and oesophageal or aortic openings in the diaphragm. The diagnosis is confirmed with endoscopy and surgical repair is necessary. Investigations ECG; If cardiac complications are suspected Myocardial infarction and arrhythmias may be seen. CXR: For: 1. Pneumothorax 2. Pneumomediastinum CT scan: A cerebral CT scan should be done for patients with an altered conscious state. CT scan can confirm evidence of sinus injury. Note however that investigations should not unduly delay, definitive hyperbaric treatment when this is urgently warranted. Management Any illness that develops during or post diving must be considered to be diving-related until proven otherwise. Any patient with neurological symptoms in particular needs urgent referral to a specialist in hyperbaric medicine.
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