Some people have pathology 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. Diving mask squeeze enclosing the eyes and nose: The main risk is rupture of the capillaries of the eyes and facial skin because of the negative pressure difference between the gas space and blood pressure, or orbital emphysema from higher pressures. This can be avoided by breathing air into the mask through the nose. Goggles covering only the eyes are not suitable for deep diving as they cannot be equalised. Dry suit squeeze. The main risk is skin getting pinched and bruised by folds of the dry suit when squeezed on descent. Most dry suits can be equalised against squeeze via a manually operated valve fed from a low pressure gas supply. Air must be manually injected during the descent to avoid squeeze and is manually or automatically vented on the ascent to maintain buoyancy control. Diving helmet squeeze: Helmet squeeze will occur if the gas supply hose is severed above the diver and the non-return valve at the helmet gas inlet fails or is not fitted. Severity will depend on the hydrostatic pressure difference.
Rapid change of altitude
A rapid change of altitude can cause barotrauma when internal air spaces cannot be equalised. Self inflicted barotrauma
Excessively strenuous efforts to equalise the ears using the Valsalva manoeuvre can overpressurise the middle ear, and can cause middle ear and/or inner ear barotrauma. Blast-induced barotrauma
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.Lung injuries can also occur during rapid decompression, although the risk of injury is lower than with explosive decompression. Ventilator-induced barotrauma
Mechanical ventilation can lead to barotrauma of the lungs. This can be due to either:
absolute pressures used in order to ventilate non-compliant lungs. shearing forces, particularly associated with rapid changes in gas velocity.The resultant alveolar rupture can lead to pneumothorax, pulmonary interstitial emphysema (PIE) and pneumomediastinum.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.