Hyperbaric Oxygenation Treatment (HBOT) is a type of non-invasive therapy that consists of administering oxygen (O2) at a pressure greater than the atmospheric for therapeutic purposes. It has a set of physiological effects that affect every person subjected to the hyperbaric environment. The therapeutic effects are based on the increase of oxygen in plasma that improves tissue availability. Its side effects are well defined and are rare if the treatment is indicated by specialists.
1) Physiological effects of HBOT: they depend on the increase of the environmental pressure per se, and on the elevation of the partial pressure of oxygen.
2) Volumetric effects: based on the Boyle-Mariotte law, the elevation of the environmental pressure decreases the volume of all the aerial organic cavities that are not in contact with the respiratory tract (urinary bladder, digestive tract, paranasal sinuses) in proportionally inverse function. This effect is reversible by restoring the value of the atmospheric pressure. All hollow objects, or that contain air inside, experience the same volume variations.
3) Solometric effects: according to Henry’s law, breathing a pure oxygen in a hyperbaric environment produces a progressive increase in arterial oxygen pressure. The volume of oxygen dissolved and transported by the plasma increases more than 22 times.
4) Therapeutic effects:
Direct effects: arterial, venous and tissue hyperoxia, and especially the great increase in transport and availability of plasma oxygen, provide a possible therapeutic effect in those diseases in which there is a general or local tissue hypoxia phenomenon, as an etiopathogenic factor. Hyperbaric oxygenation provides an additional supply of oxygen transported by the plasma. It is oxygen in physical form, dissolved in plasma, oblivious to the rheological limitations or metabolic constraints that limit the transfer or use of erythrocyte oxygen; it is an oxygen that accedes by capillarity, for example, to terminal ischemic territories and that is transferred in favor of gradient by simple diffusion.
Indirect effects: depending on certain pathophysiological states, specific therapeutic actions are produced in some diseases:
- a) Decrease in the volume of bubbles in case of gas embolism
- b) Robin-Hood effect: when there is a state of local hypoxia (peripheral vasculopathies, compartmental syndromes, malignant edema), this territory benefits from the deprived plasma volume at the expense of healthy territories.
- c) Stimulation of microneovascularization and neocolagenization. Angiogenesis.
- d) Reactivation of oxygen-dependent phagocytic capacity of polymorphonuclear granulocytes (PMN).
- e) Bactericidal action on some anaerobic sporulated germs.
- f) Blocking the formation of clostridial toxins.
- g) Fast elimination of carboxyhemoglobin (HbCO).
The increased pressure may cause barotraumatic lesions on the eardrum, sinuses, hollow cavities and lungs if adequate preventive measures are not taken.
Hyperoxia increases the formation of enzymatic antioxidants that try to stop the increase of free radicals. If this compensating mechanism is insufficient, oxidative stress occurs.
As in any therapeutic modality, careful approaches are required. The presence of pneumothorax with valvular mechanism, the existence of thoracotomies, the history of spontaneous pneumothorax, or hypersusceptibility to convulsive episodes, as well as infectious and catarrhal diseases of the upper respiratory tract, flatulent dyspepsia and acute or chronic septal syncope force to increase caution.
Lilliam Arteaga Monge, Gerald Schmitz and Xiomara Arias González; Hyperbaric oxygen therapy; Medical Journal of Costa Rica and Central America LXVIII (599) 393-399 2011.
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