ABC of oxygen: Hyperbaric oxygen therapy

Over the past 40 years hyperbaric oxygen therapy has been recommended and used in a wide kind of aesculapian conditions, often without adequate scientific establishment of efficacy or base hit. consequently a high degree of aesculapian agnosticism has developed regarding its use. The Undersea and Hyperbaric Medical Society approves use of hyperbaric oxygen for a few conditions for which there is thought to be fair scientific tell or well validate clinical experience. In these conditions early referral is all-important .

Therapeutic uses of hyperbaric oxygen

Strong scientific evidence

Main treatment

adjunctive discussion

  • prevention and discussion of osteoradionecrosis
  • Improved skin graft and beat mend
  • Clostridial myonecrosis

Suggestive scientific evidence

adjunctive treatment

  • Refractory osteomyelitis
  • radiation induced wound
  • Acute traumatic ischemic injury
  • prolong failure of wreathe healing
  • exceptional anemia from blood loss

Hyperbaric oxygen has been shown ineffective in diseases such as multiple sclerosis and dementia, but it continues to be used despite the risks of the treatment. For conditions where its use remains unproved—for case, rheumatoid arthritis, cirrhosis, and gastroduodenal ulcer—hyperbaric oxygen should be used merely in the context of well controlled clinical trials .

Biochemical and physiological effects

At sea level the plasma oxygen assiduity is 3 ml/l. Tissues at rest command about 60 ml of oxygen per liter of rake flow ( assuming normal perfusion ) to maintain normal cellular metamorphosis, although requirements vary between tissues. At a press of 3 atmospheres ( 304 kPa ) dissolved oxygen approaches 60 ml/l of plasma, which is about sufficient to supply the rest full oxygen requirement of many tissues without a contribution from oxygen restrict to haemoglobin. This has advantages in situations such as carbon monoxide poison or in severe anemia where unmanageable crossmatching or religious belief prevents rake transfusion .

Cellular and biochemical benefits of hyperbaric oxygen

  • Promotes angiogenesis and hurt bring around
  • Kills certain anaerobes
  • Prevents growth of species such as Pseudomonas
  • Prevents production of clostridial alpha toxin
  • Restores neutrophil mediated bacterial kill in previously hypoxic tissues
  • Reduces leukocyte attachment in reperfusion injury, preventing release of proteases and exempt radicals which cause vasoconstriction and cellular damage

oxygen at 300 kPa increases oxygen tension in arterial blood to about 270 kPa and in weave to about 53 kPa. This improves the cellular oxygen provide by raising the tissue-cellular diffusion gradient. The hyperoxia has likely benefits including improved angiogenesis. The formation of collagen matrix is substantive for angiogenesis and is inhibited by hypoxia. In irradiate tissue hyperbaric oxygen is more effective than normobaric oxygen at raising tissue partial derivative pressure of oxygen and promoting angiogenesis and wound heal. The healing process may besides be helped in non-irradiated tissues with compromise perfusion, but this requires farther establishment. Advice on the nearest suitable UK unit and help to coordinate the management can be obtained from the Institute of Naval Medicine, Gosport (24 hour emergency number 0831 151523, daytime inquiries 01705 768026) The value of hyperbaric oxygen therapy in decompression illness and arterial gasoline embolism depends on the forcible properties of gases. The volume of a gas in an enclosed distance is inversely proportional to the pressure exerted on it ( Boyle ’ s law ). At 300 kPa bubble volume is reduced by about two thirds. Any intravascular bubbles causing obstruction move to smaller vessels, which reduces extravascular tissue price. profligacy of the natural gas bubble is enhanced by replacing the inert gasoline in the bubble with oxygen, which is then quickly metabolised by the tissues .

Availability and administration

Multiplace chambers are available in a few NHS hospitals ( Aberdeen, Craigavon, Newcastle upon Tyne ), Royal Navy centres, private units, police diving units, professional diver educate schools, and sites associated with the North Sea petroleum industry. The United States has over 250 facilities.

Comparison of monoplace and multiplace hyperbaric oxygen chambers

Monoplace

  • Claustrophobic environment ; specify access to patient
  • whole chamber containshyperbaric oxygen, increasing fire risk
  • Lower cost
  • portable

Multiplace

  • More room ; assistant canenter to deal with acuteproblems such aspneumothorax
  • Hyperbaric oxygen via tightfitting mask—chamber gascan be air ( decreased displace risk )
  • risk of cross infection whenused for ulcers etc

often early discussion is essential for maximum profit. This poses appreciable practical problems as badly ill patients may have to be transported long distances and may require intensifier aesculapian support, including mechanical breathing, between treatment sessions. It is important to discuss the potential benefits and risks for each patient with the regional hyperbaric oxygen facilities. Multioccupancy chambers are required for critically ill patients who require an attendant within the chamber and are normally used for acute problems. Monoplace chambers can be used to treat patients with chronic medical conditions. Hyperbaric oxygen is inhaled through masks, fast fitting hoods, or endotracheal tubes. Inside the chambers pressure is normally increased to about 250-280 kPa, equivalent to a depth of 15-18 m of urine. The duration of discussion varies from 45 to 300 min and patients may receive up to 40 sessions. Appropriate monitor is essential during treatment, and facilities for resuscitation and immediate mechanical ventilation should be available .

Dangers of hyperbaric oxygen

The potential risks and risk-benefit ratio of hyperbaric oxygen have often been underemphasised in curative trials. The side effects are much mild and reversible but can be severe and life heavy. In general, if pressures do not exceed 300 kPa and the length of treatment is less than 120 minutes, hyperbaric oxygen therapy is safe. overall, dangerous cardinal nervous system symptoms occur in 1-2 % of treat patients, symptomatic reversible barotrauma in 15-20 %, pneumonic symptoms in 15-20 %, and reversible ocular symptoms in up to 20 % of patients. reversible myopia, due to oxygen toxicity on the lens, is the common side effect and can death for weeks or months. epileptic fits are rare and normally cause no permanent damage. A suggest carcinogenic consequence of hyperbaric oxygen has not been substantiated in extensive studies.

Risks of hyperbaric oxygen

Fire hazard

Most common black complication

General features

  • claustrophobia
  • reversible myopia
  • fatigue
  • concern
  • Vomiting

Barotrauma

Oxygen toxicity

  • brain
    • Convulsions
    • psychological
    • • Lung
    • Pulmonary edema, bleeding
    • pneumonic perniciousness
    • respiratory failure ( may beirreversible when due topulmonary fibrosis )

Decompression illness

  • Decompression illness
  • pneumothorax
  • Gas embolus

Pneumothoraces must be adequately drained before treatment with hyperbaric oxygen. Pulmonary oxygen perniciousness with thorax tightness, cough, and reversible falls in pneumonic routine may occur with repeat treatment, peculiarly in patients exposed to high oxygen levels before treatment. Oxygen toxicity can be prevented in most tissues by using tune in the chamber for 5 minutes every 30 minutes. This allows antioxidants to deal with loose oxygen radicals formed during the hyperoxic period .

Therapeutic uses

Decompression sickness and arterial gas embolism

When divers surface besides quickly the partial press of nitrogen dissolved in the tissues may exceed the ambient atmospheric imperativeness sufficiently to form gas bubbles in the blood and the tissues. Although less common, rapid rise to over 5500 m can result in senior high school altitude decompression nausea. Decompression nausea may produce mild problems such as foolhardy or joint pain or be more serious with paralysis, confusion, convulsions, and ultimately death junior-grade to blockage of vital lineage vessels. Hyperbaric oxygen is the main treatment, and its efficacy has been validated by across-the-board clinical know and scientific studies. Recompression quickly alleviates the symptoms, and tables are available to determine safe periods for subsequent decompression. treatment should be started arsenic soon as potential and given in sessions of 2-5 hours until the symptoms have resolved. Air may besides enter the circulation during placement of arterial and venous catheters, cardiothoracic operating room, hemodialysis, or mechanical ventilation. Although no conventional trials support the use of hyperbaric oxygen in air out embolism, the well established physical properties of gases and extensive clinical have apologize its use as the primary treatment. Treatment should begin immediately at pressures of 250-300 kPa for 2-5 hours. profit is reported when hyperbaric oxygen therapy begins several hours after the attack of air embolism but further trials are required to establish the stay after which hyperbaric oxygen is no longer of respect .

Carbon monoxide poisoning

Carbon monoxide poison is an crucial lawsuit of death from poisoning, peculiarly in the United States. Carbon monoxide binds to haemoglobin with an affinity 240 times that of oxygen. This reduces the oxygen carrying capacity of the blood. Unoccupied hemoglobin binding sites have an increased affinity for oxygen, further reducing the handiness of oxygen to the tissues. In summation, carbon monoxide binds to the large pool of myoglobin increasing tissue hypoxia. Hyperbaric oxygen provides an alternate informant of weave oxygenation through oxygen dissolved in the plasma. It besides facilitates dissociation of carbon monoxide from the hemoglobin and myoglobin ; the carboxyhaemoglobin half life is 240-320 min breathing air travel, 80-100 min breathing 100 % oxygen, and about 20 min with hyperbaric oxygen. In accession, hyperbaric oxygen dissociates carbon monoxide from cytochrome hundred oxidase, improving electron transportation and cellular department of energy state .

Symptoms of carbon monoxide poisoning

  • Loss of consciousness
  • neurological abnormalities
  • myocardial ischemia
  • Pulmonary edema
  • metabolic acidosis
  • concern
  • nausea
  • Delayed neuropsychological features ( much permanent )

Controlled studies comparing hyperbaric oxygen and normobaric 100 % oxygen in the acuate and delayed effects of carbon paper monoxide poisoning have produced conflict results, although some benefit was seen in patients who experienced loss of consciousness or neurological abnormality. The clinical severity of carbon monoxide poisoning does not correlate well with carboxyhaemoglobin concentrations If carbon monoxide poisoning results in unconsciousness, convulsions, neurological deterioration ( including abnormal pace or mental state of matter test results ) or austere metabolic acidosis the font should be discussed with the nearest regional center. A one school term of hyperbaric oxygen therapy will normally reverse the acute, potentially life sentence threatening effects of carbon monoxide poison, but extra treatments may be needed to reduce the delay neuropsychological sequela. Patients with less severe poisoning should be treated with 100 % oxygen .

Necrotising infections and osteomyelitis

The primary treatment of myonecrosis and gasoline necrose of soft tissues resulting from clostridial infection and alpha toxin output is surgical debridement and antibiotics. however, experimental attest and clinical feel suggest that adjunctive treatment with hyperbaric oxygen improves systemic illness and decreases tissue loss by demarcating the margin between devitalised and healthy tissue. This reduces the extent of surgical amputation or debridement. Controlled trials of hyperbaric oxygen and normobaric 100 % oxygen are not available. In necrotising fasciitis ( quickly progressive skin infection without muscle disease ) retrospective studies suggest that hyperbaric oxygen is beneficial in combination with surgical debridement but prospective controlled trials are lacking. Hyperbaric oxygen is besides claimed to be helpful in refractory osteomyelitis. animal experiments show improved mend of osteomyelitis compared with no discussion, but the impression is no better than that with antibiotics alone and the two treatments have no synergistic effect. Uncontrolled trials of operation and antibiotics combined with hyperbaric oxygen in furnace lining osteomyelitis have reported success rates of ampere high as 85 %, but controlled trials are needed .

Post radiation damage

soft tissue radionecrosis and osteonecrosis after surgery on irradiate mandibles are reduced by hyperbaric oxygen. In a controlled cogitation comparing osteoradionecrosis at six months postoperatively, the incidence was 5 % in patients receiving 30 preoperative hyperbaric oxygen treatments compared with 30 % in patients who received only preoperative antibiotics. A exchangeable improvement in weave heal after operating room has been shown in patients with irradiate tissue who receive preoperative hyperbaric oxygen therapy. Normobaric 100 % oxygen does not seem to confer the same benefits. The higher partial derivative pressures achieved with hyperbaric oxygen may stimulate new vessel growth and healing in damaged enlighten weave which has lost the capacity for recuperative cellular proliferation. To prevent mandibular osteonecrosis after surgery on irradiated facial and neck tissue 30 preoperative 90 minute sessions and 10 postoperative sessions are recommended

Skin grafts, flaps, and wound healing

In ailing vascularised tissue hyperbaric oxygen improves both bribery and flap survival compared with act postoperative surgical care alone. The effect of normobaric 100 % oxygen was not examined in these studies. In the United States problem wounds are the commonest indication for a trial of adjunctive hyperbaric oxygen therapy and include diabetic and other little vessel ischemic foot ulcers. several studies have shown improved curative and a lower incidence of amputation with 4-30 sessions. Hyperbaric oxygen should be considered for problem wounds if the facility is readily available

Other indications

Hyperbaric oxygen has been used successfully to treat hemorrhagic shock in patients who refuse blood on religious grounds or for whom suitable rake was not available. similarly, there is evidence for benefit in acuate traumatic ischemic injuries including compartmental syndromes and oppress injuries .

Conditions which do not benefit

Hyperbaric oxygen has been tried in numerous conditions and is often reported to be beneficial. however, in many of these situations the scientific evidence is flimsy and use should be restricted to randomised controlled trials. Hyperbaric oxygen has been intelligibly shown not to be beneficial in several diseases including multiple sclerosis and senility.

Summary

  • lack of randomised manipulate trials makes it unmanageable to assess the efficacy of hyperbaric oxygen in many diseases
  • side effects are normally meek but can be animation threatening
  • absolved evidence of benefit has been found in decompression sickness and a few early conditions
  • much work remains to be done to establish the time, indications, and therapeutic regimens required to obtain the best clinical and cost effective results
  • The cellular, biochemical, and physiologic mechanisms by which hyperbaric oxygen achieves beneficial results are not amply established

The suggestion that hyperbaric oxygen may be beneficial in multiple sclerosis rise from animal work suggesting that it improved experimental allergic encephalomyelitis and several uncontrolled studies suggesting disease remission in humans with multiple sclerosis. In 1983, a humble controlled test reported meaning benefit, and boastfully numbers of patients with multiple sclerosis were treated with hyperbaric oxygen. Since this initial trial at least 14 trials, of which eight are high quality randomised master studies, have been published. In the eight high quality studies the patients had chronic stable or chronic progressive multiple sclerosis, had at least 20 sessions of therapy for 90 minutes over four weeks, and were adequately assessed with elicited potentials and for functional and disability state. only one study showed a benefit from hyperbaric oxygen. No convert tell exists for using hyperbaric oxygen in thermal burns. In the only randomised controlled trial of hyperbaric oxygen and usual burn care the distance of hospital stay, need for autografting, and deathrate were about identical with both treatments .

Footnotes

P Wilmshurst is adviser cardiologist at Royal Shrewsbury Hospital, Shrewsbury.

The ABC of Oxygen is edited by Richard M Leach, adviser doctor, department of intensive care, and P John Rees, adviser doctor, department of respiratory medicine, Guy ’ second and St Thomas ’ sulfur Hospitals Trust, London. The pictures of the hyperbaric chamber and necrotic heel of diabetic patient were downloaded from the internet with license from Proteus Hyperbaric Systems. The visualize of gas gangrene was downloaded with license from St Joseph Medical Center, Fort Wayne, Indiana, USA

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