A reply

Abstract

Thank you for the opportunity of replying to the letter from Dr Bell, who has raised some interesting issues concerning mechanism of action and possible side-effects of hyperbaric oxygen (HBO), and also the ethics of undertaking this treatment. Clinical experience leads us to feel that the mechanism of action for pulsed HBO in severe blood loss anaemia is largely related to paying back the established oxygen debt. Between treatments, lactate production occurs during anaerobic metabolism in tissues due to the diminished blood oxygen content caused by severe anaemia. Hence lactic acidosis worsens, the oxygen debt arises again at which point further HBO is administered. Without these pulsed HBO exposures, there is the potential for the acidosis to continue worsening, resulting eventually in multi-organ failure. The assertion that HBO was responsible for the slower increase in the haemoglobin level is unfounded as there is certainly evidence that HBO actually exerts a favourable stimulus on erythropoiesis following massive blood loss [1]. Furthermore, we demonstrated a good reticulocyte response. It is well known that sepsis causes potent suppression of bone marrow, and once the infection in our patient was treated the haemoglobin level increased. Dr Bell's statement ‘it must be accepted that a cerebellar infarction occurred as a possible adverse consequence of decompression’ is totally implausible. Firstly, the patient was not subject to any inert gas load as she was breathing 100% oxygen, and as such the development of decompression illness is impossible. Second, at no time was the patient or attendant subject to episodes of rapid decompression capable of producing arterial gas emboli. Thus the only plausible explanation for the infarction was that of local tissue hypoxia. Unfortunately, the limited space available for the case report did not allow a full discussion regarding the decision to embark on this treatment. HBO was commenced after all acceptable conventional modes of treatment had been exhausted and then only after discussions between the Obstetric and Intensive Care consultants locally. Advice was taken from other major hyperbaric centres within the UK and also in the USA. These included the Institute of Naval Medicine (Gosport), the National Hyperbaric Centre (Aberdeen) and the hyperbaric unit in Long Beach, California. This unit has extensive experience in the field, having published a series of 26 similar patients treated with HBO with a mortality rate of only 5% (if you exclude those patients arriving late with no cerebral function) [2]. All were in total agreement that this treatment was acceptable. The comment that the treatment is unproven is inaccurate. It may be that this treatment has been logistically unavailable in the UK until recently, but severe blood loss anaemia is one of the 13 accepted conditions for treatment with HBO by the Undersea and Hyperbaric Medical Society in the USA [3], and both the Report on Confidential Enquiries into Maternal Deaths in the UK 1991–93 and the Management of Anaesthesia for Jehovah's Witnesses (March 1999) also acknowledge its use. There are now seven hyperbaric units in the UK capable of supporting critically ill patients. All provide hyperbaric and diving support for the NHS, all are members of the British Hyperbaric Association and have accepted the recommendations of the Cox report of the Faculty of Occupational Medicine published in May 1994 under the auspices of the Royal College of Physicians [4]. We agree that transfusion of blood is a relatively safe and specific treatment for haemorrhage. However, there are certain individuals who for religious or other reasons refuse blood transfusions, as is their right. The question then arises whether we should embark upon more costly interventions because of their refusal to accept transfusion. An analogy might be withholding treatment of respiratory disease from a smoker, or management of a severe head injury in a boxer. The argument is a moral one about the individual's right to choice and to still receive good medical care. In certain states in the USA (such as Texas), the Justice of the Peace can give an immediate, legally enforced order for blood replacement. This mechanism does not exist in the UK for consenting adults. As a result, we will very occasionally see these patients, and we feel that there is enough evidence to support the use of HBO if all else fails.