Hyperbaric oxygen therapy involves of high concentrations of oxygen in a pressurized chamber. With this process, oxygen dissolved in the plasma may reach levels greater than 20 times that of breathing air at normal atmospheric pressure. This way, oxygenated plasma can reach hypoxic or ischemic tissue to promote angiogenesis, reduce edema, and even modulate the immune system response.
Hyperbaric oxygen therapy (HBOT) has been applied in clinical practice for many years. Initially HBOT was used to treat decompression sickness; additional indications like carbon monoxide poisoning, clostridial infections and wound healing followed soon after. Later, conditions such as compartment syndrome were added. While burns and frostbite, and even sensorineural hearing loss are being treated, these may not necessarily be reimbursed.
HBOT basically has two types of effects, physiologic and pharmacologic, as well as a combination of both. Oxygen occurs naturally and is essential for life. In emergency medical and clinical applications, it is considered drug which changes disease pathology. Since HBOT uses oxygen as a drug, proper dosing protocols have been established for the various indications.
Oxygen is considered a drug in the treatment of diseases and conditions through a variety of pharmacologic mechanisms. The most common use of HBOT today is for enhanced wound healing. Problem wounds from diabetic complications, delayed radiation injury, or skin grafts are seen in wound care center. Compromised healing often stems from tissue hypoxia and inadequate collagen synthesis. HBOT facilitates modulation of growth factors, promotes angiogenesis and improves immune system response, which facilitates enhanced healing.
Hyperbaric oxygen helps upregulate the production of vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF). This stimulates capillary budding and wound granulation due to altering signaling pathways leading to cell proliferation and migration. FGF plays a similar role in angiogenesis, but also induces neural development, keratinocyte organization, and fibroblast proliferation at wound sites leading to granulation and epithelialization.
Wound sites benefit directly from the antibacterial effect of HBOT on a cellular level. The reactive oxygen species (ROS) are able to kill bacteria both inside and outside the cells.
The basis of hyperbaric oxygen therapy is due to the increase in oxygen supply and arterial oxygen tension.
Air at sea level has about 21% oxygen. This results in an alveolar oxygen pressure (PAO2) of about 100 mmHg, with plasma hemoglobin is almost entirely saturated and minimal dissolved plasma oxygen meaning the combined blood oxygen content in whole blood is about 16.2 mL O2/dL.
Under hyperbaric conditions, while breathing 100% oxygen at 3 atmospheres absolute (ATA), the PAO2 value increases to around 2280 mmHg. According to gas laws (specifically Henry’s Law), the combined O2 in whole blood then increases to 23.0 mL O2/dL. That is an amazing 42% increase from sea level ambient breathing, and it is almost completely due to an increase in oxygen dissolved in plasma.
- HBOT facilitates oxygen delivery to hypoxic tissues, generating hyperoxia for increased healing.
- Hyperoxia has a bactericidal effect and improves the body’s immune system.
- Treatment protocols are established to maximize intervals of hyperoxia and hypoxia, which stimulates neovascularization.
- Hyperoxia diminishes tissue inflammation and reduces the negative consequences of reperfusion injury.
Vasoconstriction is another physiological effect, brought on through a decrease in local nitric oxide (NO) production by endothelial cells. Increased levels of carbon dioxide as a byproduct of respiration, on the other hand, promote NO production and vasodilation. Since short term hyperoxia causes cerebral vasoconstriction with reduced blood flow, this would be an important factor in cerebral blood flow, except the brain is hyperoxygenated under hyperbaric conditions. This hyperoxia has also been shown to decrease cerebral edema, and the mechanisms behind this are being researched for potential future applications.
On a cellular level, oxygen is primarily used by the body for making ATP (adenosine triphosphate), the molecule that makes energy transfer between cells possible. This process is called cellular respiration, and HBOT facilitates this through plasma oxygen, giving the body the potential to overcome massive hemorrhagic anemia.
Potential side effects
As with most medical treatments, certain precautions are indicated- in patient selection as well as during application of the hyperbaric oxygen therapy. Side effects range from temporary vision changes, potential drops in blood glucose in diabetic patients, to – though relatively rare – oxygen toxicity. Thought to be due to natural byproducts of cellular respiration called reactive oxygen species (ROS), it can damage cell structures like cellular membranes and cause oxidative stress.
Untreated pneumothorax (gas emboli, tension pneumo), Bleomycin (pneumonitis), Cisplatin and Sulfamylon (slowed wound healing), Disulfiram (increased susceptibility of oxygen toxicity), Doxirubicin (potential cardiotoxicity)
Asthma (potential for trapped air on ascent), COPD (reduced hypoxic drive), impaired Eustachian tubes or URI (barotrauma), uncontrolled fever, or seizure history (increased risk for seizures), implanted devices like pacemakers, insulin pumps, epidural pain management (check with manufacturer for compatibility with hyperbaric pressures), pregnancy (evaluate in emergencies like CO poisoning), claustrophobia/anxiety (low compliance with therapy).
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