When divers surface too rapidly the partial pressure of nitrogen dissolved in the tissues may exceed the ambient atmospheric pressure sufficiently to form gas bubbles in the blood and the tissues. Although less common, rapid ascent to over 5500m can result in high altitude decompression sickness.
Decompression sickness may produce mild problems such as rash or joint pain or be more serious with paralysis, confusion, convulsions, and ultimately death secondary to blockage of vital blood vessels. Hyperbaric oxygen Therapy Chambers is the main treatment, and its efficacy has been validated by extensive clinical experience and scientific studies. Hyperbaric oxygen therapy chambers make Recompression rapidly alleviates the symptoms, and tables are available to determine safe periods for subsequent decompression. Treatment should be started as soon as possible and given in sessions of 2-5 hours until the symptoms have resolved.
Air may also enter the circulation during placement of arterial and venous catheters, cardiothoracic surgery, haemodialysis, or mechanical ventilation. Although no formal trials support the use of hyperbaric oxygen therapy chambers in air embolism, the well established physical properties of gases and extensive clinical experience justify its use as the primary treatment. Treatment should begin immediately at pressures of 250-300kPa for 2-5 hours in a multiplace hyperbaric oxygen therapy chamber . Benefit is reported when hyperbaric oxygen therapy chambers begins several hours after the onset of air embolism but further trials are required to establish the delay after which hyperbaric oxygen therapy chambers is no longer of value.
2- Carbon monoxide poisoning
Carbon monoxide poisoning is an important cause of death from poisoning, particularly 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 haemoglobin binding sites have an increased affinity for oxygen, further reducing the availability of oxygen to the tissues. In addition, carbon monoxide binds to the large pool of myoglobin increasing tissue hypoxia. Hyperbaric oxygen therapy chambers provides an alternative source of tissue oxygenation through oxygen dissolved in the plasma. It also facilitates dissociation of carbon monoxide from the haemoglobin and myoglobin; the carboxyhaemoglobin half life is 240-320 min breathing air, 80-100 min breathing 100% oxygen, and about 20 min with hyperbaric oxygen. In addition, hyperbaric oxygen therapy chamber dissociates carbon monoxide from cytochrome c oxidase, improving electron transport and cellular energy state.
3-Symptoms of carbon monoxide poisoning
- Loss of consciousness
- Neurological abnormalities
- Myocardial ischaemia
- Pulmonary oedema
- Metabolic acidosis
- Delayed neuropsychological features (often permanent)
Controlled studies comparing hyperbaric oxygen theapy chamber and normobaric 100% oxygen in the acute and delayed effects of carbon monoxide poisoning have produced conflicting 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 impairment (including abnormal gait or mental state test results) or severe metabolic acidosis the case should be discussed with the nearest regional centre. A single session of hyperbaric oxygen therapy will usually reverse the acute, potentially life threatening effects of carbon monoxide poisoning, but additional treatments may be needed to reduce the delayed neuropsychological sequelae. Patients with less severe poisoning should be treated with 100% oxygen.
4-Necrotising infections and osteomyelitis
The primary treatment of myonecrosis and gas gangrene of soft tissues resulting from clostridial infection and alpha toxin production is surgical debridement and antibiotics. However, experimental evidence and clinical experience suggest that adjunctive treatment with hyperbaric oxygen therapy chamber improves systemic illness and decreases tissue loss by demarcating the border between devitalised and healthy tissue. This reduces the extent of surgical amputation or debridement. Controlled trials of hyperbaric oxygen therapy chamber and normobaric 100% oxygen are not available. In necrotising fasciitis (rapidly progressive skin infection without muscle disease) retrospective studies suggest that hyperbaric oxygen therapy chamber is beneficial in combination with surgical debridement but prospective controlled trials are lacking.
Hyperbaric oxygen therapy chamber is also claimed to be helpful in refractory osteomyelitis. Animal experiments show improved healing of osteomyelitis compared with no treatment, but the effect is no better than that with antibiotics alone and the two treatments have no synergistic effect. Uncontrolled trials of surgery and antibiotics combined with hyperbaric oxygen therapy chamber in refractory osteomyelitis have reported success rates of as high as 85%, but controlled trials are needed.
5-Post radiation damage
Soft tissue radionecrosis and osteonecrosis after surgery on irradiated mandibles are reduced by hyperbaric oxygen therapy chamber . In a controlled study comparing osteoradionecrosis at six months postoperatively, the incidence was 5% in patients receiving 30 preoperative hyperbaric oxygen treatments by multiplace hyperbaric oxygen therapy chamber compared with 30% in patients who received only preoperative antibiotics. A similar improvement in wound healing after surgery has been shown in patients with irradiated tissue who receive preoperative hyperbaric oxygen therapy by multiplace hyperbaric oxygen therapy chamber . Normobaric 100% oxygen does not seem to confer the same benefits. The higher partial pressures achieved with hyperbaric oxygen therapy chamber may stimulate new vessel growth and healing in damaged irradiated tissue which has lost the capacity for restorative 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
6-Skin grafts, flaps, and wound healing
In poorly vascularised tissue hyperbaric oxygen therapy chamber improves both graft and flap survival compared with routine 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 small vessel ischaemic foot ulcers. Several studies have shown improved healing and a lower incidence of amputation with 4-30 sessions.
Hyperbaric oxygen therapy chamber should be considered for problem wounds if the facility is readily available
Hyperbaric oxygen therapy chamber has been used successfully to treat haemorrhagic shock in patients who refuse blood on religious grounds or for whom suitable blood was not available. Similarly, there is evidence for benefit in acute traumatic ischaemic injuries including compartmental syndromes and crush injuries.