Hyperbaric oxygen. A therapy in search of diseases

Characteristics and outcome of children with carbon monoxide poisoning with and without smoke exposure referred for hyperbaric oxygen therapy

OBJECTIVES

To describe the clinical characteristics and outcome of children with carbon monoxide (CO) poisoning with and without smoke exposure referred for hyperbaric oxygen therapy (HBOT), and to determine the association between any of these characteristics and death.

SETTING

Regional hyperbaric referral center.

PATIENTS

The medical records of 150 children with CO poisoning (COP) who were treated with HBOT between August 92 and September 95 were reviewed.

MEASUREMENTS/MAIN RESULTS

COP was defined as a history of probable exposure to CO, with either a carboxyhemoglobin level (COHb) > 25, or COHb < 25 with neurological, respiratory, or cardiac compromise. Major cutaneous burns were described as second degree burns over greater than 20% of the patient's total body surface area (TBSA), or third degree burns over greater than 10% of the patient's TBSA. Children extracted from a closed-space fire who had airway soot, singed facial hair/facial burns, or respiratory distress were defined as having smoke inhalation and carbon monoxide poisoning (CO/SI). CO/SI occurred in 40.1% of patients. Compared to children with COP alone, those with CO/SI were significantly more likely to have a depressed mental status upon arrival to an ED (76.3 % vs 13.6 %, P < 0.001), lower mean initial GCS (6.7 vs 14.7, P < 0.001), lower mean initial pH (7.2 vs 7.4, P < 0.001), respiratory arrest at the scene (68.5% vs 0%, P < 0.001), and cardiac arrest at the scene (25.9% vs 0%, P < 0.001). Children with CO/SI were significantly more likely to have a poor outcome (death) than children with COP alone (22.6% vs. 0%, P < 0.001). Comparing children with CO/SI who died versus survivors, there were significant differences in mean initial COHb (38.3 vs 24.3, P = 0.03), mean initial temperature upon arrival in an ED (94.9 degrees F vs 98.2 degrees, P < 0.006), respiratory arrest at the scene (92% vs 59.6%, P = 0.04), and cardiac arrest at the scene (66.7% vs 13.5%, P < 0.001). Sixty percent of children died who had a combination of risk factors of smoke inhalation, low temperature, high COHb level, and respiratory and cardiac arrest in the field.

CONCLUSIONS

These preliminary data suggest that children with COP alone who are treated with HBOT are at low risk for dying regardless of initial COHb level. Children with CO/SI have a significantly higher risk of dying than those children with COP alone. A combination of smoke inhalation, low temperature, high COHb level, respiratory arrest, and cardiac arrest is highly associated with death. Prospective studies are needed to confirm and further define these associations.

Effect of hyperbaric oxygen treatment on nitric oxide and oxygen free radicals in rat brain

Oxygen (O(2)) at high pressures acts as a neurotoxic agent leading to convulsions. The mechanism of this neurotoxicity is not known; however, oxygen free radicals and nitric oxide (NO) have been suggested as contributors. This study was designed to follow the formation of oxygen free radicals and NO in the rat brain under hyperbaric oxygen (HBO) conditions using in vivo microdialysis. Male Sprague-Dawley rats were exposed to 100% O(2) at a pressure of 3 atm absolute for 2 h. The formation of 2,3-dihydroxybenzoic acid (2, 3-DHBA) as a result of perfusing sodium salicylate was followed as an indicator for the formation of hydroxyl radicals. 2,3-DHBA levels in hippocampal and striatal dialysates of animals exposed to HBO conditions were not significantly different from controls. However, rats treated under the same conditions showed a six- and fourfold increase in nitrite/nitrate, break down products of NO decomposition, in hippocampal and striatal dialysates, respectively. This increase was completely blocked by the nitric oxide synthase (NOS) inhibitor L-nitroarginine methyl ester (L-NAME). Using neuronal NOS, we determined the NOS O(2) K(m) to be 158 +/- 28 (SD) mmHg, a value which suggests that production of NO by NOS would increase approximately four- to fivefold under hyperbaric O(2) conditions, closely matching the measured increase in vivo. The increase in NO levels may be partially responsible for some of the detrimental effects of HBO conditions.

Carbon monoxide poisoning

Carbon monoxide (CO) poisoning is common and frequently unrecognized since the signs and symptoms are relatively nonspecific. CO poisoning causes tissue hypoxia. Additionally, various animal studies have demonstrated that CO interferes with myoglobin, P450, and other enzyme function; causes lipid peroxidation through neutrophil activation; produces oxidative stress manifested by peroxynitrate deposition in endothelium; binds to cytochrome aa3, disrupting intracellular oxygen utilization; can cause neuroexcitotoxicity; and contributes to hippocampal cellular death through apoptosis. Emergency treatment for CO poisoning is 100% oxygen. Hyperbaric oxygen therapy (HBO2) is accepted in CO poisoning, although data from randomized clinical trials regarding the efficacy of HBO2 in CO poisoning is conflicting. CO poisoning, even when treated with supplemental oxygen can leave the patient with permanent neurocognitive or affective problems. Unfortunately, there appears to be no marker or constellation of signs or symptoms at presentation that predicts long-term outcome following CO poisoning. Given the neurocognitive sequelae following CO poisoning, increased awareness and prevention of CO poisoning is imperative.

Hyperbaric oxygenation, plasma exchange, and hemodialysis for treatment of acute liver failure in a 3-year-old child

A girl aged 3 years and 4 months weighing 16 kg was treated with plasma exchange (PE), hemodialysis (HD), and hyperbaric oxygenation (HBO) for acute hepatic failure and coma. She was given a total of 13 PEs, 13 HD sessions, and 9 HBO treatments over a period of 1 month. The initial 4 PEs were followed by HD sessions while the other 8 PE treatments were given simultaneously with HD. There was no renal failure; HD was instituted to improve ammonia elimination. In 1 HD session, 20% human albumin (370 ml) was used as the dialysate to enhance bilirubin elimination. Three volumes of plasma (2,000 ml) per PE were exchanged and replaced with fresh frozen plasma (FFP). The Bellco BL 791 plasmapheresis monitor and Gambro PF1000 and PF2000 plasma filters were used. Heparin was added to prevent clotting. A dual lumen pediatric HD catheter (7 Fr) placed percutaneously into the femoral vein was used as a blood access. The Fresenius 2008 C HD monitor and the Filtral 10 dialyzer were used for HD. PE and HD were instituted simultaneously to prevent the tetanic (hypocalcemic) cramps observed with 2 previous PEs due to citrate in the FFP. The extracorporeal circuit was primed with a mixture of concentrated red cells, human albumin, and saline solution and was discarded at the end of the procedure. The average blood flow rate in PE and/or HD circuits was 80 ml/min. During HBO, the girl breathed 100% oxygen at 2.5 atm for 90 min. Throughout the treatment, the patient was in good clinical, physical, and mental condition, but she was dependent on blood purification procedures. She was referred to a liver transplant center and successfully transplanted. The etiology of liver failure has not been clarified.

The effects of hyperbaric oxygen on normal and ischemic colon anastomoses

BACKGROUND

Leakage from colonic anastomoses is a major complication causing increased mortality and morbidity, and ischemia is a well-known cause of this event. Inadequate tissue oxygenation could be reversed by using hyperbaric oxygen. This study was designed to investigate the effects of hyperbaric oxygen on the healing of ischemic and normal colon anastomoses in the rat model.

METHODS

Standardized left colon resection 3 cm above the peritoneal reflection and colonic anastomosis were performed in 40 Wistar rats divided into four groups. The control group (I) received no further treatment. To mimic ischemia, 2 cm mesocolon was ligated on either site of the anastomosis in group II and IV rats. Hyperbaric oxygen therapy was started immediately after surgery in group III and IV rats (therapeutic groups). All animals were sacrificed on the fourth postoperative day. After careful relaparotomy, in situ bursting pressure was measured. The hydroxyproline contents of the anastomotic segments in equal length were determined.

RESULTS

The hydroxyproline assay revealed that rats in group II with ischemic colonic anastomosis have significantly lower levels (P <0.05). The highest levels are in the group III rats with normal colonic anastomosis treated by hyperbaric oxygen (P <0.05). There was no significant difference in hydroxyproline levels between group II and group IV animals (P >0.05). Group III animals had significantly higher bursting pressures than any other group (P <0.05). Group II rats had lowest bursting pressures (P <0.05). Group IV animals had significantly higher levels than group II (P <0.05). Mean bursting pressure values both in groups III and IV and hydroxyproline levels in group III were significantly increased by hyperbaric oxygen therapy (P <0.05).

CONCLUSIONS

Ischemia impairs anastomotic healing. Hyperbaric oxygen increases anastomotic healing of both normal and ischemic colonic anastomosis and reverses ischemic damage. This study demonstrated that hyperbaric oxygen improves anastomotic healing.

Hyperbaric oxygen therapy for intestinal obstruction in children: an exceptional experience in a compromised child

Intestinal obstruction in a 2-year-old girl with a histologically proven diagnosis of retroperitoneal yolk sac carcinoma developed after the second course of anticancer chemotherapy. Nonoperative treatment was not effective. Because the patient had fallen into a state of chemotherapy-induced myelosuppression, surgery was ruled out. Thus, hyperbaric oxygen therapy was the next treatment of choice. It was performed twice under hyperbaric oxygen conditions at 2.8 atmospheric pressure for 111 minutes. After the procedure, her general status recovered well. The air-fluid level disappeared on the radiograph, and no adverse effects were observed. Later, a surgical removal of the primary tumor was performed successfully, but an intestinal resection was not required. This is the first instance in which we performed hyperbaric oxygen therapy on a child in the management of an intestinal obstruction. Based on the successful outcome in this case, hyperbaric oxygen therapy is suggested to be a useful adjunct to nonoperative therapy for intestinal obstruction when a patient's overall state does not allow operative intervention.

Outcome of children with carbon monoxide poisoning treated with normobaric oxygen

OBJECTIVE

To evaluate the clinical characteristics and neurologic outcome of children with carbon monoxide poisoning treated with normobaric oxygen therapy.

METHODS

We reviewed the medical records of all children with a diagnosis of carbon monoxide exposure admitted during a 10-year period. Exposures were categorized as (1) severely toxic, carboxyhemoglobin level >25%; (2) toxic, carboxyhemoglobin level 10.1 to 25%; (3) suspected toxic, carboxyhemoglobin level < or = 10% with acute neurologic manifestations; or (4) nontoxic, carboxyhemoglobin < or = 10% without acute neurologic manifestations.

RESULTS

One hundred six patients (median age, 3.5 years; range, 0.1-14.9 years) were identified, 37 with severe toxic, 37 with toxic, 13 with suspected toxic, and 19 with nontoxic exposures. The most common presenting signs or symptoms included altered level of consciousness, metabolic acidosis, tachycardia, and hypertension. All patients received normobaric oxygen for 5.5 hours (range, 0.6-44 hours). Carboxyhemoglobin levels decreased to less than 3% in 3.6 hours (range, 0-15.5 hours). Fifteen patients died, three from massive burn injury, eight from hypoxic-ischemic encephalopathy after cardiopulmonary arrest at presentation, and four from late complications of burn injury. Seven survivors did not recover their premorbid neurologic state, four of whom had respiratory arrest when rescued. Two patients had initial neurologic recovery followed by transient deterioration at 4 and 14 days after exposure. One patient developed seizures and was found to have bilateral occipital lobe infarctions 51 days after exposure.

CONCLUSION

Acute neurologic manifestations after carbon monoxide exposure are common in children. These resolve rapidly with normobaric oxygen, however. Persistent sequelae are primarily related to asphyxia. Delayed neurologic syndromes are uncommon in children treated with normobaric oxygen.

Hyperbaric oxygen in the treatment of acute ischemic stroke: an unsettled issue

Therapy for acute ischemic stroke can be approached in two basic ways: first, by an attempt to restore or improve blood flow in an occluded vascular territory and, second, via therapy directed at the cellular and metabolic targets. As local anoxia and energy failure are the initiating cellular stage in ischemia, the inhalation of oxygen at increased atmospheric pressures might be effective. Treatment of acute focal cerebral ischemia with hyperbaric oxygen (HBO) has been reported in animals and humans. In general, the results of research in animals have suggested a promising role for the use of HBO. More than 400 cases of human ischemic stroke treated with HBO have been reported. In about half of the cases, improvement in status has been claimed on clinical or electroencephalographic grounds. In fact, the effectiveness of HBO in most disease processes other than carbon monoxide poisoning and decompression sickness is a subject of major ongoing debate. This short review will attempt: (1) to recall some early experiments involving HBO in the treatment of acute ischemia: (2) to point out some conflicting results regarding the role of HBO on cellular and metabolic disorders; and (3) to determine the possibility of a future role for HBO therapy in acute ischemic stroke.

Is hyperbaric oxygen a useful adjunct in the management of problem lower extremity wounds?

Hyperbaric oxygen (HBO) is currently being used in the treatment of nonhealing or "problem" wounds of the lower extremities. In an attempt to evaluate the efficacy of HBO in problem wounds, a retrospective study of the HBO experience at Orlando Regional Medical Center was conducted. From 1989 to 1994, fifty-four patients with nonhealing lower extremity wounds resulting from underlying peripheral vascular disease and/or diabetes mellitus were treated with HBO. Wounds were grouped into the following five categories: (1) diabetic ulcers (n = 17 [31%]); (2) arterial insufficiency (n = 8 [15%]); (3) gangrenous lesions (n = 6 [11%]); (4) nonhealing amputation stumps (n = 13 [24%]); and (5) nonhealing operative wounds (n = 10 [19%]). Each patient received an average of 30 treatments. Outcomes for all 54 patients treated with HBO in this study were dismal. None of the patients experienced complete healing, six (11%) showed some improvement, 43 (80%) showed no improvement, and in five cases (9%) results were inconclusive because these patients underwent concomitant revascularization or amputation. Thirty-eight of the 43 patients who showed no improvement (88%) ultimately required at least one surgical procedure to treat their wounds. Thirty-four patients (63%) developed complications, most commonly barotrauma to the ears, which occurred in 23 patients (43%). The average cost of 30 HBO treatments was $14,000 excluding daily inpatient charges. Based on the experience with HBO therapy at Orlando Regional Medical Center and the paucity of good supporting literature, it is difficult to justify such an expensive, ineffective complication-prone treatment modality for problem extremity wounds.

Hyperbaric oxygen treatment for haemorrhagic radiation cystitis

Radiation-induced severe haemorrhagic cystitis is difficult to treat. Conventional treatments may decrease haematuria but do not affect the radiocystitis itself. Hyperbaric oxygen treatment has been reported to do both. We report the results of a prospective study of hyperbaric oxygen (20 sessions of 100% oxygen inhalation at 3 bar for 90 min in a multiplace hyperbaric chamber) to 40 patients with biopsy-proven radiation cystitis and severe haematuria. Haematuria disappeared completely or improved in 37 patients after treatment. Mean follow-up was 23.1 months (range 1-74); and the recurrence rate was 0.12/year. There were no adverse effects. Hyperbaric oxygen treatment should be considered for patients with severe radiation-induced haematuria.

Hyperbaric oxygen after global cerebral ischemia in rabbits does not promote brain lipid peroxidation

OBJECTIVE

To determine whether hyperbaric oxygen administered immediately after global cerebral ischemia increases free radical generation and lipid peroxidation in the brain or alters neurophysiologic recovery.

DESIGN

Prospective, randomized, controlled trial.

SETTING

Animal research laboratory.

SUBJECTS

Adult male New Zealand white rabbits.

INTERVENTIONS

Anesthetized rabbits were subjected to 10 mins of global cerebral ischemia by infusing a mock cerebrospinal fluid into the subarachnoid space and increasing intracranial pressure equal to mean arterial pressure. Immediately upon reperfusion, one group of rabbits (n = 9) was treated with hyperbaric oxygen at 2.8 atmospheres absolute for 75 mins while the control group (n = 9) breathed room air for an equivalent period of time. At the end of the reperfusion period, oxyradical brain damage was determined by measuring brain levels of oxidized and total glutathione and free malondialdehyde. Neurophysiologic brain injury was assessed with cortical somatosensory evoked potentials.

MEASUREMENTS AND MAIN RESULTS

Both oxidized glutathione and the ratio of oxidized glutathione to reduced glutathione (total minus oxidized) were higher (p < .05) in the hyperbaric oxygen group, indicating that hyperbaric oxygen increased free radical generation. Nonetheless, brain malondialdehyde content, an index of lipid peroxidation, was similar (p > .05) in the two groups. Cortical somatosensory evoked potential recovery at the end of reperfusion was 50% higher (p < .05) in the hyperbaric oxygen-treated animals compared with controls.

CONCLUSIONS

Treatment with hyperbaric oxygen after ischemia increased the amount of oxygen free radicals in the brain. However, this increase in free radical generation was not associated with an increase in lipid peroxidation or a reduction in neurophysiologic recovery when measured after 75 mins of recirculation. These results suggest that hyperbaric oxygen administered immediately after global ischemia does not promote early brain injury.

Warehouse workers' headache: emergency evaluation and management of 30 patients with carbon monoxide poisoning

BACKGROUND

Carbon monoxide (CO) is the leading cause of fatal toxic inhalation in the United States, but the medical literature contains few reports of mass exposures. Warehouse workers' headache (WWH) is an infrequently reported form of CO poisoning due to industrial exposure.

METHODS

We describe 30 persons who developed WWH after inhaling exhaust from a propane-fueled forklift, their emergency medical management at a small community hospital, and their long-term courses.

RESULTS

Workers with more direct exposures to vented exhaust had significantly higher expired CO levels (21.1 +/- 0.7% versus 8.4 +/- 4.8%, P < 0.0001) and higher acute symptom scores (9.0 +/- 2.2 versus 4.7 +/- 3.3, P = 0.01) than persons with less direct exposures. Work location, expired CO levels, and acute symptom scores did not correlate with symptom scores 2 years after exposure. Workers experiencing acute difficulty concentrating or confusion had higher expired CO levels than persons with neither of these symptoms (16.3 +/- 6.7% versus 8.4 +/- 5.2%, P = 0.005) and developed higher chronic symptom scores (3.9 +/- 3.0 versus 1.1 +/- 1.5, P = 0.04), suggesting that this subgroup may require closer follow-up for long-term complications.

CONCLUSION

With earlier recognition of ongoing CO toxicity, this disaster would likely have been averted. Since CO exposures are more common than is often recognized, general internists must be familiar with the manifestations of CO toxicity, its timely evaluation, management, and prevention.

A multicenter review of the treatment of major truncal necrotizing infections with and without hyperbaric oxygen therapy

To examine the effectiveness of hyperbaric oxygen (HBO) therapy in the treatment of major truncal necrotizing infections, a retrospective (1980 to 1992) analysis of the medical records of 30 patients treated with HBO therapy and 24 patients treated without HBO therapy was undertaken. The two groups were similar; however, there was a selection bias towards more frequent clostridial infections in a younger population in the HBO group. There was no difference in length of hospital stay, intensive care unit (ICU) stay, or duration of antibiotic therapy between groups. The mortality rates were 9/30 (30%) in the HBO group versus 10/24 (42%) (nonsignificant difference) in the non-HBO group. The total number of operations was greater in the HBO-treated group. This study failed to show that the use of HBO in the treatment of major truncal necrotizing infections statistically reduced mortality or the number of débridements. We believe, however, that the apparent selection bias and the trend towards increased survival in the HBO-treated group (12%) justifies the continued use of and research with HBO therapy.

Hyperbaric oxygen therapy: Contraindications and complications

The literature is replete with references regarding the use of hyperbaric oxygen (HBO) therapy to treat various human maladies. However, the oral and maxillofacial surgery literature is lacking in information regarding patient selection criteria and possible contraindications to HBO therapy, as well as possible risks and/or complications of such therapy. This article details patient selection criteria, discusses relative and absolute contraindications to HBO therapy, and describes the potential risks and complications of this therapy.

Setting nursing standards in hyperbaric oxygen therapy

This articles focuses on work undertaken as part of a Standards of Care initiative in a Regional Hyperbaric Oxygen Unit in the North of England. The historical development of Hyperbaric Oxygen Therapy, possible clinical applications, and aspects of administration are reviewed. An example of one of the series of nursing standards derived is included together with the patient information sheet and evaluation questionnaire given to patients at the conclusion of the treatment. It is concluded that writing and monitoring Standards of Care can be a very effective quality assurance strategy at unit level.

Acute carbon monoxide intoxication and hyperbaric oxygen in pregnancy

Modalities of oxygen therapy for pregnant women intoxicated with carbon monoxide (CO) are ill defined. Hyperbaric oxygen (HBO) is presumed to be hazardous to the pregnancy. On the other hand CO entails anoxic injuries in the mother and fetus. We have entered 44 pregnant women who sustained an acute carbon monoxide poisoning at home, into a prospective study in order to assess HBO tolerance. They were treated within 5.3 +/- 3.7 h (range: 1-12) of the intoxication with a combination of 2 h of HBO at a pressure of 2 atmospheres absolute (ATA) and 4 h of normobaric oxygen, irrespective of the clinical severity of the intoxication and of the age of pregnancy. Six patients were lost to obstetric follow-up. Only 2 patients sustained a spontaneous abortion: 1 within 12 h and 1 within 15 days of the intoxication. Thirty-four women gave birth to normal newborns. Finally 1 elected to undergo abortion for reasons unrelated to the intoxication and 1 gave birth to a baby with Down's syndrome. There is no evidence that HBO was involved with either abortion of our study. We conclude that HBO may be carried out in pregnant women acutely intoxicated with carbon monoxide.

Closure of refractory perineal Crohn's lesion. Integration of hyperbaric oxygen into case management

A case is reported in which a comprehensive program of hyperbaric oxygen (HBO), surgical debridement and reconstruction, and continuing medical management resulted in complete and sustained closure of an extensive perineal Crohn's lesion refractory to conventional medical and surgical management. It is emphasized that in this case healing occurred in the setting of previous removal of all diseased intestinal tissue and only with the combined use of all three treatment modalities. HBO may be a useful adjunct in the therapy of large nonhealing perineal lesions post-proctocolectomy in patients who are unresponsive to metronidazole or to immunosuppressant therapy or who experience limiting side effects from continued medical therapy.

Hyperbaric oxygen increases survival following carotid ligation in gerbils

We studied the effects of graded exposure to hyperbaric (1,875 mm Hg) oxygen therapy in an acute stroke model prepared by unilateral carotid artery interruption in gerbils. Pentobarbital alone, superoxide dismutase alone, two periods of hyperbaric oxygen alone, and each agent combined with hyperbaric oxygen were administered to investigate possible mechanisms of protection from cerebral ischemia. Survival rates and neurologic deficit scores over 5 days in all treated groups were compared with those in a control group. Survival rates in the groups subjected to 2 (63.9 +/- 4.0%) and 4 hours (70.1 +/- 5.2%) of hyperbaric oxygen alone were significantly higher than in the control group (53.6 +/- 4.2%). The group treated with pentobarbital alone also demonstrated increased survival (69.8 +/- 7.0%), but the combination of therapeutic regimens offered no apparent additive protection. By 5 days there were no differences in the neurologic deficit scores of the survivors in the groups. The toxic pulmonary effects of hyperbaric oxygen were assessed in a pilot LD50 study. The pressure used caused no mortality during 4 hours of exposure, and the calculated LD50 was 7.26 hours. This investigation demonstrates that graded doses of hyperbaric oxygen given after the insult increase survival in a gerbil model of stroke.

Carbon dioxide embolism treated with hyperbaric oxygen

We report a case of suspected carbon dioxide embolism occurring during laparoscopy. Among the sequelae was neurological dysfunction felt to be secondary to paradoxical embolization. The patient was treated with hyperbaric oxygen therapy. Hyperbaric oxygen should be considered when confronted with a clinically important gas embolism.

Trial of normobaric and hyperbaric oxygen for acute carbon monoxide intoxication

The value of hyperbaric oxygen in the treatment of acute carbon monoxide intoxication was assessed in 629 adults who had been poisoned at home in the 12 h before admission to hospital. In patients without initial impairment of consciousness (group A) the effect of 6 h of normobaric oxygen (NBO) (group A0, n = 170) was compared with that of 2 h of hyperbaric oxygen (HBO) at 2 atmospheres absolute (ATA) plus 4 h NBO (group A1, n = 173). At the 1 month follow-up 66% of A0 and 68% of A1 patients had recovered. In patients with initial impairment of consciousness the effect of one session of HBO (group B1, n = 145) was compared with that of two sessions (group B2, n = 141); all group B patients also received 4 h of NBO. At 1 month of follow-up 54% group B1 and 52% group B2 patients had recovered. The 7 patients left with neuropsychiatric sequelae (3 B1, 4 B2) and the 4 who died (2 B1, 2 B2) had all presented with coma. HBO was not useful in patients who did not lose consciousness during carbon monoxide intoxication, irrespective of their carboxyhaemoglobin level, nor were two sessions of HBO in patients who sustained only a brief loss of consciousness. The prognosis is poorest for those presenting with coma; the trial needs to be pursued in this group of patients until the power of the study is sufficient to demonstrate the value or otherwise of HBO.

Preliminary observations on the effects of hyperbaric oxygen therapy on western diamondback rattlesnake (Crotalus atrox) venom poisoning in the rabbit model

Intermittent hyperbaric oxygen therapy has been shown to reduce skeletal muscle necrosis in a compartment syndrome animal model. To study whether intermittent exposure to hyperbaric oxygen augments antivenin therapy in reducing muscle necrosis, we injected sublethal doses of Western Diamondback rattlesnake (Crotalus atrox) venom intramuscularly into the hind legs of New Zealand White rabbits. In this pilot study, the animals were divided into three treatment groups. The first group received one vial of antivenin intravenously, the second group received one vial of antivenin intravenously plus three hyperbaric oxygen treatments, and the third group received no treatments. There were no statistically significant differences among the groups. These preliminary observations suggest that muscle necrosis secondary to Crotalus atrox venom poisoning is not significantly altered either by Antivenin [Crotalidae] Polyvalent at the dose level we used or in combination with intermittent hyperbaric oxygen treatments in this rabbit model.

Hyperbaric oxygen: primary treatment of radiation-induced hemorrhagic cystitis

Of 8 patients with symptoms of advanced cystitis due to pelvic radiation treated with hyperbaric oxygen 7 are persistently improved during followup. All 6 patients treated for gross hematuria requiring hospitalization have been free of symptoms for an average of 24 months (range 6 to 43 months). One patient treated for stress incontinence currently is dry despite little change in bladder capacity, implying salutary effect from hyperbaric oxygen on the sphincter mechanism. One patient with radiation-induced prostatitis failed to respond. This experience suggests that hyperbaric oxygen should be considered the primary treatment for patients with symptomatic radiation-induced hemorrhagic cystitis.