Hyperbaric oxygen therapy (HBO 2) is a type of treatment in which a person inhales 100% O 2 under increased atmospheric pressure. HBO 2 treatment can be done in a single-person (single patient) or multi-place (typically between 2 and 14 patients). The chamber is subject to pressures of 2 to 3 atmospheres absolute (ATA). This is the sum of the atmospheric pressure (1 ATA) and the hydrostatic pressure equivalent of one or two atmospheres (1 atm = 14.7 pounds per square inch, or 101 kPa). Treatments can take between 1.5 and 2 hours depending on the indication. They may be repeated up to three times per day. Monoplace chambers are typically compressed with pure O 2. Multiplace chambers are usually pressurized with pure Osub>2/sub>. Patients in multiplace chambers inhale pure O 2 through tight-fitting masks, hoods, or endotracheal tubes. Tissues can develop a level of 200 to 400 millimeters Hg, and arterial O 2 tension can often exceed 2000 mmHg during treatment.
The first effect of pressurizing the body is obvious. An increase in hydrostatic pressure causes partial pressure to rise and a decrease in the volume of gas-filled spaces. Boyle's law states that this results in a reduction of the volume of gas-filled space. Gas volume reduction is directly relevant to the treatment of pathological conditions where gas bubbles are present, such as arterial gas embolism or decompression sickness. Most patients who receive HBO 2 therapy do not have to be treated for any bubble-induced injuries. Therefore, therapeutic mechanisms are based on an elevated O 2 partial pressure.
It is widely accepted that an increase in the production of reactive oxygen substances (ROS) can be caused by breathing more than 1 ATAO 2. This is crucial because it provides the molecular basis of many therapeutic mechanisms. Signaling molecules such as ROS and reactive nitrogen species (RNS) are used in transduction pathways or cascades for many growth factors, hormones, and cytokines. ROS can be defined as both O 2-derived radicals and O 2-derived nonradical species like hydrogen peroxide or hypochlorous acid. ROS are part of normal metabolism and can be produced by mitochondria, endoplasmic retina, peroxisomes as well as various oxidase enzymes. ROS interact with many redox systems, including glutathione and thioredoxin, and play central roles for cell signaling coordination and anti-oxidant, protected pathways. This is the central point of the discussion: oxidative stress does not necessarily mean oxygen toxicity.
RNS includes nitric dioxide (*NO), and agents that are formed by reactions between *NO or its oxidation products and ROS. Myeloperoxidase, an enzyme that is peroxide-dependent, can catalyze reactions between *NO (or its oxidation products) and hydrogen peroxide, or hypochlorous acids to produce oxidants like nitryl chloride, and nitrogen dioxide, which is capable of nitration, S-nitrosylation, and nitration reactions. There are three types of nitric oxide syntheticase. The apparent Michaelis-Menten constant O 2, which is the value for catalytic activity in hyperoxia, is different for each of the three NOS forms. This is partly because enzyme activity is limited by ferric-ferrous transformation at the active site. Hyperoxia, however, increases RNS production.
This review will discuss the most relevant HBO 2 indications to Plastic and Reconstructive surgery. Recent texts provide a general discussion of HBO 2 indications. For the general surgeon, it is important that advice and consultation on HBO 2 can be obtained through the Undersea and Hyperbaric Medical Society and locally with board-certified doctors. The American Board of Medical Specialists is authorized to sub-specialty certificate in Undersea or Hyperbaric Medicine.
HBO 2 can be used to treat diabetic lower extremity injuries and delayed radiation injuries. Although the pathophysiology for each disorder is different, they all share some elements. These include chronic inflammation, depletion of epithelial or stromal cells, and fibrosis. They also have an imbalance or abnormalities of extracellular matrix components and remodeling process, as well as impaired keratinocyte function. Reduced growth factor production in diabetic wound healing can also be a problem. However, post-radiation tissue appears to have an imbalance between factors that mediate fibrosis and normal tissue healing. For more information on pathophysiology, the reader can refer to several recent reviews.
The Wound Healing HBO 2 Protocols involve daily treatments lasting 1.5 to 2 hours and last for 20 to 40 consecutive days. It is possible to evaluate the effectiveness of HBO 2 as an adjuvant treatment for diabetic lower extremity urticaria. This can be viewed from the perspective that it hastened to heal and reduce the risk of major amputations. These two perspectives are related but not identical. Current diabetic wound care often includes partial or full foot amputations as an acceptable approach for wound closure and prompt rehabilitation.
Meta-analysis is now a common method of evaluating the effectiveness of interventions. The most recent evaluation found that HBO 2 reduces the risk of major amputations with an odds ratio (OR) of 0.326) [95% confidence interval, (CI), 0.133 - 0.4418]. The odds ratio for diabetic wound care that includes HBO 2 adjunctively is 11.64 [95% confidence interval (CI) 0.133 - 0.418]. This analysis was based upon clinical trials which were conducted from 2007 to 2007. These results show that HBO 2 significantly improves outcomes. A meta-analysis found that HBO 2 was sufficient to treat only four patients to prevent one amputation. Two additional groups reported the benefits of HBO 2 since publication. One was a double-blinded, randomized trial. These results show that HBO 2 has a positive effect on outcomes. Double-blinded trials were conducted in single centers to enroll individuals with foot ulcers. The individuals were randomly assigned to receive HBO 2 (100% oxygen, 2.5 ATA, for 85 minutes five times per week for eight weeks) or control (room, 2.5ATA, for 85 minutes five times per week for eight weeks) along with good wound care. After 12 months, the wound was healed. 99 people were examined. 38 received HBO therapy and 37 received control therapy. After one year, 52% of patients who received HBO 2 were healed, and 29% of those who received control therapy (p=0.03).
In randomized trials, HBO 2 has also been proven to be beneficial for radiation injury. Independent evidence-based reviews have also supported its use. HBO 2 can be used for both radiation-related wounds and diabetic wounds. This was the protocol used in clinical trials. It is easy to understand based on its mechanisms of action. HBO 2 should not be used in the post-operative period or when there is no appropriate surgical care.
While this review highlighted the positive aspects of HBO -induced reactive substances, there are potential negative effects. O 2 toxicities depend on the intracellular concentration and localization of reactive substances. Studies have shown that hyperoxia exposure in clinical HBO protocol protocols is very short. This means that antioxidant defenses are sufficient to reverse biochemical stress related to an increase in reactive species. Air breaks are a type of treatment that allows patients to only inhale air for five minutes each time they receive treatment. It has been shown that this intervention can increase pulmonary O 2 tolerance. Grand mal seizures are a sign of CNS O 2 toxicity. It occurs in approximately one to four cases per 10,000 patients treated. Studies with rabbits, guinea pigs, and humans have not shown any pathological changes associated with isolated O -2-mediated seizures. Patients who receive prolonged daily therapy have been known to develop progressive myopia. However, this usually resolves within six weeks. Excessive treatments exceeding 150 to 200 hours have been linked to the development of nuclear cataracts. The change doesn't occur by itself.
This short review highlighted the benefits of HBO 2 as well as the data that suggests hyperoxia, which can cause oxidative stress. This summary outlines the mechanisms that all appear to be influenced by elevated reactive species. Although there have been significant advances in the field over the past few years, it is still necessary to determine the role of HBO 2 in 21st-century medicine. Still, fundamental mechanisms need to be investigated and more patient selection criteria could improve cost-efficiency. Recent texts include extensive discussion of other indications for HBO 2.
Sources:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3058327/
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