Equilibration of Pulmonary Pressure

Areas of poor ventilation within the lung must also reach equilibration during compression and, more importantly, during decompression to prevent pulmonary barotrauma, which may result in pneumothorax, pneumomediastinum, or AGE. Patients with bullae evident on a chest radiograph could therefore be disqualified from hyperbaric therapy. Patients with obstructive pulmonary disease should have their bronchodilator therapy optimized before commencement of HBO. However, despite the relatively frequent occurrence of pulmonary barotrauma in scuba divers (≅100 cases per year from the continental United States reported to the Divers Alert Network^[126] ), pulmonary barotrauma during HBO therapy is extremely rare. We are aware of only two cases of AGE resulting from decompression of a patient inside a hyperbaric chamber. Such infrequency is perhaps surprising given that many patients of this type have been heavy smokers and therefore frequently have some degree of obstructive lung disease. Possibly the reason is that immersion in water elevates pulmonary closing volume. In some individuals, immersion is associated with airway closure at lung volumes above functional residual capacity,^[167] which implies that during immersion there may be areas of lung that are pneumatically isolated from the tracheobronchial tree and could rupture during decompression from a dive. In addition, rates of ascent in hyperbaric chambers can be much more accurately controlled and are generally slower (0.15 ATA/min as compared with up to 1.8 ATA/min in divers).

Although pneumothorax would be expected to diminish in size and be resorbed more quickly after compression, continued leakage of air from the lung might result in tension pneumothorax during decompression. Pneumothorax detected before treatment is usually treated by insertion of a chest tube and water seal or Heimlich-type valve. Caution must be exercised when using certain commercially available pleural suction regulators because they can exert high negative pleural pressure during chamber compression.^[168] Such excessive suction can be relieved by an attendant inside a multiplace chamber using the manual pressure relief valve.