|Synonyms||Squeeze, Decompression illness, Lung overpressure injury|
|Mild barotrauma to a diver caused by mask squeeze|
|Classification and external resources|
Barotrauma is physical damage to body tissues caused by a difference in pressure between a gas space inside, or in contact with the body, and the surrounding gas or fluid. The initial damage is usually due to over-stretching the tissues in tension or shear, either directly by expansion of the gas in the closed space, or by pressure difference hydrostatically transmitted through the tissue. Tissue rupture may be complicated by the introduction of gas into the local tissue or circulation through the initial trauma site, which can cause blockage of circulation at distant sites, or interfere with normal function of an organ by its presence.
Barotrauma generally manifests as sinus or middle ear effects, decompression sickness (DCS), lung overpressure injuries, and injuries resulting from external squeezes.
Barotrauma typically occurs when the organism is exposed to a significant change in ambient pressure, such as when a scuba diver, a free-diver or an airplane passenger ascends or descends, or during uncontrolled decompression of a pressure vessel such as a diving chamber or pressurised aircraft, but can also be caused by a shock wave. Bats can be killed by lung barotrauma when flying in low pressure regions close to operating wind turbine blades.
- 1 Presentation
- 2 Causes
- 3 Diagnosis
- 4 Prevention
- 5 Treatment
- 6 Barotrauma in animals
- 7 See also
- 8 References
Examples of organs or tissues easily damaged by barotrauma are:
- Middle ear (barotitis or aerotitis)
- Paranasal sinuses (causing Aerosinusitis)
- Eyes (the under-pressure air space is inside the diving mask)
- Skin (when wearing a diving suit which creates an air space)
- Brain and cranium (temporal lobe injury secondary to temporal bone rupture)
- Teeth (causing Barodontalgia, i.e. barometric pressure related dental pain, or dental fractures)
- Genital (squeeze and associated complications of P-valve use)
Pressure differences while diving
When diving, the pressure differences which cause the barotrauma are changes in hydrostatic pressure: There are two components to the surrounding pressure acting on the diver: the atmospheric pressure and the water pressure. A descent of 10 metres (33 feet) in water increases the ambient pressure by an amount approximately equal to the pressure of the atmosphere at sea level. So, a descent from the surface to 10 metres (33 feet) underwater results in a doubling of the pressure on the diver. This pressure change will reduce the volume of a gas filled space by half. Boyle's law describes the relationship between the volume of the gas space and the pressure in the gas.
Barotraumas of descent are caused by preventing the free change of volume of the gas in a closed space in contact with the diver, resulting in a pressure difference between the tissues and the gas space, and the unbalanced force due to this pressure difference causes deformation of the tissues resulting in cell rupture.
Barotraumas of ascent are also caused when the free change of volume of the gas in a closed space in contact with the diver is prevented. In this case the pressure difference causes a resultant tension in the surrounding tissues which exceeds their tensile strength. Besides tissue rupture, the overpressure may cause ingress of gases into the tissues and further afield through the circulatory system. This pulmonary barotrauma (PBt) of ascent is also known as pulmonary over-inflation syndrome (POIS), lung over-pressure injury (LOP) and burst lung. Consequent injuries may include arterial gas embolism, pneumothorax, mediastinal, interstitial and subcutaneous emphysemas, not usually all at the same time.
Breathing gas at depth from underwater breathing apparatus results in the lungs containing gas at a higher pressure than atmospheric pressure. So a free-diver can dive to 10 metres (33 feet) and safely ascend without exhaling, because the gas in the lungs had been inhaled at atmospheric pressure, whereas a diver who inhales at 10 metres and ascends without exhaling has lungs containing twice the amount of gas at atmospheric pressure and is very likely to suffer life-threatening lung damage.
Explosive decompression of a hyperbaric environment can produce severe barotrauma, followed by severe decompression bubble formation and other related injury. The Byford Dolphin incident is an example.
An explosive blast and explosive decompression create a pressure wave that can induce barotrauma. The difference in pressure between internal organs and the outer surface of the body causes injuries to internal organs that contain gas, such as the lungs, gastrointestinal tract, and ear.
- absolute pressures used in order to ventilate non-compliant lungs.
- shearing forces, particularly associated with rapid changes in gas velocity.
Barotrauma is a recognised complication of mechanical ventilation that can occur in any patient receiving mechanical ventilation, but is most commonly associated with acute respiratory distress syndrome. It used to be the most common complication of mechanical ventilation but can usually be avoided by limiting tidal volume and plateau pressure to less than 30 to 50 cm water column (30 to 50 mb). As an indicator of transalveolar pressure, which predicts alveolar distention, plateau pressure or peak airway pressure (PAP) may be the most effective predictor of risk, but there is no generally accepted safe pressure at which there is no risk. Risk also appears to be increased by aspiration of stomach contents and pre-existing disease such as necrotising pneumonia and chronic lung disease. Status asthmaticus is a particular problem as it requires relatively high pressures to overcome bronchial obstruction.
Use of a hyperbaric chamber.
In terms of barotrauma the diagnostic workup for the affected individual would include the following: Laboratory:
- Creatine kinase (CPK) level: Increases in CPK levels indicate tissue damage associated with decompression sickness.
- Complete blood count (CBC)
- Arterial blood gas (ABG) determination
- Chest radiography can show pneumothorax, and is indicated if there is chest discomfort or breathing difficulty
- Computed tomography (CT) scans and magnetic resonance imaging (MRI) may be indicated when there is severe headache or severe back pain after diving.
- Spiral CT is the most sensitive method to evaluate for pneumothorax. It can be used where barotrauma-related pneumothorax is suspected and chest radiograph findings are negative.
- Echocardiography can be used to detect the number and size of gas bubbles in the right side of the heart.
Barotrauma can affect the external, middle, or inner ear. Middle ear barotrauma (MEBT) is the most common being experienced by between 10% and 30% of divers and is due to insufficient equilibration of the middle ear. External ear barotrauma may occur on ascent if high pressure air is trapped in the external auditory canal either by tight fitting diving equipment or ear wax. Inner ear barotrauma (IEBT), though much less common than MEBT, shares a similar mechanism. Mechanical trauma to the inner ear can lead to varying degrees of conductive and sensorineural hearing loss as well as vertigo. It is also common for conditions affecting the inner ear to result in auditory hypersensitivity.
A problem mostly of historical interest, but still relevant to surface supplied divers who dive with the helmet sealed to the dry suit. If the air supply hose is ruptured near or above the surface, the pressure difference between the water around the diver and the air in the hose can be several bar. The non-return valve at the connection to the helmet will prevent backflow if it is working correctly, but if absent, as in the early days of helmet diving, or if it fails, the pressure difference will tend to squeeze the diver into the rigid helmet, which can result in severe trauma. The same effect can result from a large and rapid increase in depth if the air supply is insufficient to keep up with the increase in ambient pressure.
Lung over-pressure injury in ambient pressure divers using underwater breathing apparatus is usually caused by breath-holding on ascent. The compressed gas in the lungs expands as the ambient pressure decreases causing the lungs to over-expand and rupture unless the diver allows the gas to escape by maintaining an open airway, as in normal breathing. The lungs do not sense pain when over-expanded giving the diver little warning to prevent the injury. This does not affect breath-hold divers as they bring a lungful of air with them from the surface, which merely re-expands safely to near its original volume on ascent. The problem only arises if a breath of ambient pressure gas is taken at depth, which may then expand on ascent to more than the lung volume. Pulmonary barotrauma may also be caused by explosive decompression of a pressurised aircraft.
Diving barotrauma can be avoided by eliminating any pressure differences acting on the tissue or organ by equalizing the pressure. There are a variety of techniques:
- The air spaces in the ears, and the sinuses. The risk is burst eardrum. Here, the diver can use a variety of methods, to let air into the middle ears via the Eustachian tubes. Sometimes swallowing will open the Eustachian tubes and equalise the ears.
- The lungs. The risk includes pneumothorax, arterial gas embolism, and mediastinal and subcutanous emphysemas. which are commonly called burst lung or lung overpressure injury by divers. To equalise, all that is necessary is not to hold the breath during ascent. This risk does not arise when snorkel diving from the surface, unless the snorkeller breathes from a high pressure gas source underwater, or from submerged air pockets. Some people have pathologies of the lung which prevent rapid flow of excess air through the passages, which can lead to lung barotrauma even if the breath is not held during rapid depressurisation. These people should not dive as the risk is unacceptably high. Most commercial or military diving medical examinations will look specifically for signs of this pathology.
- The air inside the diving mask enclosing the eyes and nose (also known as a half mask). The main risk is bleeding from the capillaries of the eyes from the negative pressure or orbital emphysema from higher pressures. This can be avoided by allowing air into the mask through the nose. Goggles covering only the eyes are not suitable for diving as they cannot be equalised.
- Air spaces inside a dry suit. The main risk is skin getting pinched by folds of the dry suit. Most dry suits have a hose connection with a manually operated valve to feed intermediate pressure air in from the cylinder. Air must be manually injected on the descent and is usually automatically vented on the ascent.
Professional divers are screened for risk factors during initial and periodical medical examination for fitness to dive. In most cases recreational divers are not medically screened, but are required to provide a medical statement before acceptance for training, in which some of the most common and easy to identify risk factors must be declared. If these factors are declared, the diver may be required to be examined by a medical practitioner, and may be disqualified from diving if the conditions indicate.
Asthma, Marfan syndrome, and COPD have very high risk of pneumothorax. In some countries these may be considered absolute contraindications, while in others the severity may be taken into consideration. Asthmatics with a mild and well controlled condition may be permitted to dive under restricted circumstances.
A significant part of entry level diver training is focused on understanding the risks and procedural avoidance of barotrauma. Professional divers and recreational divers with rescue training are trained in the basic skills of recognizing and first aid management of diving barotrauma.
Treatment of diving barotrauma depends on the symptoms. Lung over-pressure injury may require a chest drain to remove air from the pleura or mediastinum. Recompression with hyperbaric oxygen therapy is the definitive treatment for arterial gas embolism, as the raised pressure reduces bubble size, low inert gas partial pressure accelerates inert gas solution and high oxygen partial pressure helps oxygenate tissues compromised by the emboli. Care must be taken when recompressing to avoid a tension pneumothorax.
Pre-hospital care includes basic life support of maintaining adequate oxygenation and perfusion, assessment of airway, breathing and circulation, neurological assessment, and managing any immediate life-threatening conditions. High-flow oxygen up to 100% is considered appropriate for diving accidents. Large-bore venous access with isotonic fluid infusion is recommended to maintain blood pressure and pulse.
- Endotracheal intubation may be required if the airway is unstable or hypoxia persists when breathing 100% oxygen.
- Needle decompression or tube thoracostomy may be necessary to drain a pneumothorax or haemothorax
- Foley catheterization may be necessary for spinal cord AGE if the person is unable to urinate.
- Intravenous hydration may be required to maintain adequate blood pressure.
- Therapeutic recompression is indicated for severe AGE. The diving medical practitioner will need to know the vital signs and relevant symptoms, along with the recent pressure exposure and breathing gas history of the patient. Air transfer should be below 1,000 feet (300 m) if possible, or in a pressurized aircraft which should be pressurised to as low an altitude as reaonably possible.
Sinus squeeze and middle ear squeeze are generally treated with decongestants to reduce the pressure differential, with anti-inflammatory medications to treat the pain. For severe pain, narcotic analgesics may be appropriate.
Suit, helmet and mask squeeze are treated as trauma according to symptoms and severity.
Following barotrauma of the ears or lungs from diving the diver should not dive again until cleared by a diving doctor.
- After ear injury examination will include a hearing test and a demonstration that the middle ear can be autoinflated. Recovery can take weeks to months.
Barotrauma in animals
Whales and dolphins suffer severely disabling barotrauma when exposed to excessive pressure changes induced by navy sonar, oil industry airguns, explosives, undersea earthquakes and volcanic eruptions.
Injury and mortality of fish, marine mammals, including sea otters, seals, dolphins and whales, and birds by underwater explosions has been recorded in several studies. Bats can suffer fatal barotrauma in the low pressure zones behind the blades of wind turbines due to their more fragile mammalian lung structure in comparison with the more robust Avian lungs, which are less affected by pressure change.
Swim bladder overexpansion
Fish with isolated swim bladders are susceptible to barotrauma of ascent when brought to the surface by fishing. The swim bladder is an organ of buoyancy control which is filled with gas extracted from solution in the blood, and which is normally removed by the reverse process. If the fish is brought upwards in the water column faster than the gas can be resorbed, the gas will expand until the bladder is stretched to its elastic limit, and may rupture. Barotrauma can be directly fatal or disable the fish rendering it vulnerable to predation, but rockfish are able to recover if they are returned to depths similar to those they were pulled up from, shortly after surfacing. Scientists at NOAA developed the Seaqualizer to quickly return rockfish to depth. The device could increase survival in caught-and-released rockfish.
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