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Christian, S. D. (2001) A Study to identify the incidence in the United Kingdom of long-term sequelae following exposure to carbon monoxide, www.fitting-in.com/christian A Study to identify the incidence in the United
Kingdom
of long-term sequelae following exposure
to carbon monoxide. Professor SD
Christian
University of Ulster. |
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Summary There can be little doubt that carbon monoxide in a domestic situation represents one of the greatest hazards to man. Exposure to this gas is insidious in its effects whether it is through long-term exposure to low levels due to poorly maintained gas heating appliances or through a single, high level exposure following a fire in a dwelling. The study of the effects of carbon monoxide has a long history, eminent researchers over 100 years ago elucidated the theory of how carbon monoxide entered the blood through inhalation and the effect this had on the principal organs of the human body. This research activity continues today and an extensive revision of some of the early theory has been necessary as a result of this subsequent work. A visit to any of the major technical literature sources shows this a dynamic area of research with more learned publications being produced on a monthly basis. The early research, such as that carried out by Douglas and the Haldanes [1] at the beginning of the last Century suggested simply that the haemoglobin in the blood had a greater affinity (over 200 times) for carbon monoxide than it did for oxygen. In the circumstances where both carbon monoxide and oxygen were present, the haemoglobin would preferentially bind with the carbon monoxide. This would saturate the blood with carboxyhaemoglobin rather than oxyhaemoglobin. This, in turn, would reduce the amount of oxygen carried around the body by the blood and thereby reduce the available oxygen to the body. By not having oxygen to release, the haemoglobin could not collect the carbon dioxide and so transport it away from the organs, back to the lung where it could be replaced with oxygen and thereby repeat the process. However, it is now known that this traditional view explains the mechanism of carbon monoxide toxicity in only a few of the people exposed to it. Research has expanded these original hypotheses. |
Introduction
Carbon monoxide (CO) is a colourless, odourless, non-irritating gas created when fossil fuels (such as petroleum, wood, and coal) burn incompletely. It has been known to be poisonous since the mid-1800s.
Persistent symptoms following acute carbon monoxide exposure is now well recognised, on the other hand there appears to be less information about persistent symptoms in persons exposed chronically (greater than one week) to carbon monoxide.
In one recent study symptoms of more than three months duration following exposure were identified. The research team evaluated 94 patients with carbon monoxide poisoning and persistent symptoms reported included headache, fatigue, irritability, and difficulty concentrating and impaired memory. The initial levels of carbon monoxide measured in the blood as carboxyhaemoglobin ranged from 0.4% to 5.8%. Fifteen of the 23 patients were followed up for at least 12 months. All 15 were still experiencing symptoms one-year post exposure.
Discussion in the medical literature clearly identifies that a problem exists in the clinical treatment of patients who have been exposed to carbon monoxide. The problems identified are profound and long lasting, as such the patients and their family is often devastated. The additional burden of the costs of subsequent health care, taken together with loss of earnings, perhaps over an extended period, is also significant.
The medical literature identifies the following as the likely problems that can follow exposure – headache; irritability; personality changes; confusion and loss of memory. Specific psychiatric changes include depressed/elated moods; apathy; disorientation; amnesia and bizarre behaviour.
However, most significant, is the presence of one or more symptoms of dementia – such as loss of intellectual ability of sufficient severity to interfere with social or occupational functioning, memory impairment of thinking and judgement.
Research Objectives and Methodology
The objective of the study reported here, conducted on behalf of the United Kingdom Department of Trade and Industry (Consumer Affairs and Competition Directorate), was to examine the incidence of a delayed response in persons who are known to have been exposed to carbon monoxide in the United Kingdom.
According to the available data [2], it is quite clear that an exposure to any level of carbon monoxide can lead to complicated conditions or symptoms (sequelae) following the exposure, which may be long lasting or even permanent, if not correctly identified and treated.
The study involved a detailed examination of victims who had experienced an exposure to carbon monoxide and was undertaken to ascertain the level of incidence of long term sequelae within the United Kingdom, using the latest available data. The study addressed both single, acute exposures, such as domestic fire, as well as chronic exposures resulting from damaged flues or faulty domestic heaters.
The casualties were requested to compete a formal, generally accepted questionnaire (GHQ-60) and this was reinforced with a number of face-to-face interviews. Where these follow-up interviews were held with the casualties, the opportunity was taken, were appropriate, to extend the interview to the immediate families of the casualties. This was intended to ascertain whether they had noticed any change in the casualty’s behaviour and to provide a control.
The casualties examined were either as the result of a chronic exposure following problems in domestic dwellings with faulty carbon monoxide producing equipment, i.e. faulty flues or appliances; or in the form of a single acute exposure following an unwanted fire in a dwelling. This study did not include any deliberate exposure such as attempted suicide.
The report prepared, builds upon and complements three other recent reports prepared for the Department of Trade and Industry (Consumer Affairs and Competition Directorate):
Carbon Monoxide Poisoning (Europe), January 1995.
A study of the occurrence of poisonings from carbon monoxide heating appliances in the European Community. August 1995.
Poisonings by carbon monoxide from domestic heating appliances.
In preparing the background to the current research project, discussions were held with a large number of individuals and organisations. This project was not intended to provide information to individuals who were intending to embark on any legal action in respect of responsibility for any injuries. All of the people, who agreed to participate, did so on the basis that they were providing information to the research team to assist in the understanding of the problem.
Research Methodology
Two main sources of data were used to identify potential contributors to the study. In addition supporting ancillary databases were used. The Home Accident Surveillance Scheme operated on behalf of the Department of Trade and Industry augmented by data from two specific hospitals providing specialist treatment. The Home Office Fire Statistics augmented by individual fire brigade statistics.
The Home Accident Surveillance Scheme
This scheme established by the Department of Trade and Industry, record injuries resulting from accidents in domestic dwellings. Dedicated staff working on behalf of the Department is located in eighteen selected hospital casualty departments. These staff record data following presentation by individuals who have suffered an injury, howsoever caused, in their home. The data generated provides a detailed record of the cause and nature of the injury. The data collected from the eighteen hospitals represents approximately 5% of all cases.
This database was interrogated to identify casualties who had attended any of the participating hospitals as suffering from exposure to carbon monoxide. If the casualty was reported as resulting from an unwanted fire then no effort was made to follow-up as it was assumed they would be listed as a fire brigade casualty.
This database therefore provided details of casualties who were exposed in other (i.e. non-fire) situations. By this means, casualties who had been exposed in chronic conditions such as faulty flues or heating appliances were identified.
As a supplement to this data, two hospitals were also contacted as these provided a specialist service (Hyperbaric Oxygen Therapy) to persons exposed to carbon monoxide. One hospital in North London (Whipps Cross) and the other at Peterborough provided facilities to contact all their patients who had receive treatment over the past two years.
The Home Office Fire Statistics
This data is collected by The Home Office, Fire and Emergency Planning Directorate and published annually. It comprises data generated by local authority fire brigades following their attendance at fires.
By far the largest data source, it provided the bulk of the data for the study.
The Home Office data allows for the number of casualties by nature of injury, over any given period, to be identified. This data showed that over recent years (1992 – 1998) the total number of fire related casualties had risen from 13, 462 in 1992, to 17,492 in 1998.
The manner in which the data is collated allows for a further degree of refinement in that a specific sub-classification of overcome by gas or smoke is provided.
With the permission of the Home Office, Fire and Emergency Planning Directorate, all fire authorities in the United Kingdom were contacted and invited to provide the names and address of the casualties on their records, who were known to have been exposed to fire gases (carbon monoxide). Whilst some brigades were content to pass the names to the researchers, the majority were not.
On this basis, copies of a letter introducing the study and an invitation to participate were provided to brigades who then sent out the correspondence under a cover letter explaining that confidences had not been breached and inviting the casualty to return a preliminary proforma to the researchers.
By doing this, the casualties were providing the research team with their personal details thereby enabling direct contact to be made.
By this means attempts were made to contact over 4,000 casualties.
Tracking the victims proved to be difficult due to the fact that many of the victims appear to have moved house following the fire, particularly when the fire has been serious enough to result in the individual to have been hospitalised. Compounding this, a higher proportion of domestic fires was found (confirming other data) to be occurring in low-income groups. Where council (local authority) owned property is effected, it is common practice for the tenants to be re-housed. The accommodation will then normally be re-furbished and let to someone else. The further back in time the study goes, the less likely that people are still going to be living at the address of the fire.
Consequently, a number of the questionnaires appear not to have reached the individual involved, a large number being returned as ‘unknown or gone away’. A small number were returned with a note that the addressee had ‘passed away’. This was unfortunate, but given the time scale and the probable age of the victims, it is not unsurprising that some would have died in the intervening period. This could not be avoided and a polite letter was sent to the person who returned the questionnaire documentation apologising for any distress caused.
A very large number of the returns declined to participate in the study and in a minority of cases, the returns had been defaced with abusive remarks which was surprising in light of the careful construction of the cover letter and the detailed explanation given.
Given the importance of the project and the detailed explanation given, it is disappointing that a larger database was not generated. However, the available database identified was adequate, within statistical terms, to provide a meaningful sample.
In the first instance, the casualties who agreed to participate were sent a questionnaire (GHQ60) prepared by the Institute of Psychiatry. This was accompanied by a short additional questionnaire produced by the research team, intended to gather information on the conditions of the actual exposure to carbon monoxide.
Use of Hyperbaric Oxygen Therapy
Hyperbaric oxygen therapy uses specialised equipment and experienced personnel to deliver oxygen at higher than atmospheric pressures. The safe and rational use of this therapy is increasing, as medical and paramedical staffs become more familiar with its potential benefits. It is used for a number of other conditions that have been demonstrated to benefit by well-established research.
Oxygen delivered at a pressure of two atmospheres causes carboxyhaemoglobin dissociation to occur at a rate greater than that achievable by breathing pure oxygen at normal pressure. In addition, Hyperbaric oxygen, but not ambient pressure oxygen, has several actions which have been demonstrated in animal models to be beneficial in ameliorating pathophysiological events associated with central nervous system injuries mediated by carbon monoxide.
The literature in support of providing routine treatment by Hyperbaric oxygen for all exposures to carbon monoxide is now extensive and it is now widely accepted as a valid position. The number of such facilities in the United Kingdom and their geographical location – usually dependant on their ‘prime’ purpose of providing emergency treatment for divers – means that delays of several hours, occur between exposure and treatment. When taken with the degree of knowledge of medical staffs in casualty departments of hospitals of the availability of such treatment, the problem is compounded.
Although there remains controversy over the use of hyperbaric oxygen, there is little argument that 100% normabaric oxygen should be administered as soon as possible once the casualty has been removed from the contaminated atmosphere.
It has been shown that important data has emerged suggesting that hyperbaric oxygen reduce the incidence of late sequelae. On the simple basis that the available data is considered to be weighted in favour of such treatment, its use would seem to be expedient.
From the register of hyperbaric chambers operated by hospitals in the United Kingdom. Two of these were contacted as part of this study, they were:
Peterborough Hospitals NHS Trust Peterborough District Hospital
(Director Dr Paul N Reed); and
Forest Healthcare NHS Trust, Whipps Cross Hospital (Director Dr MR Hamilton-Farrell),
These two facilities are generally regarded as being the busiest facilities in the United Kingdom. A total of 575 patients reported as having been exposed to carbon monoxide over a three-year period (1993-96) were referred to British Hyperbaric facilities. The proportion of accidental and non-accidental exposures was 1:1.05. Of the accidental exposures, central heating faults were responsible for 71.5% of cases (n=206). Smoke inhalation from fires was responsible for a further 13.5% (n=39).
The Directors` of both these units agreed to assist in the study by contacting previous patients and inviting them to participate in the study. As with the local authority fire brigades, copies of letters from the University of Ulster were provided and these were sent out by the two hospitals. Both Dr Reed and Dr Hamilton-Farrell discussed the research proposals with the University of Ulster Research Assistant and provided invaluable information on their individual experiences.
Dr. Hamilton-Farrell is the co-author of a recent paper published in the Journal of Accident Emergency Medicine (J Accid Emerg Med 1999; 16; 92-96) in which he reports that carbon monoxide is the major cause of death from poisoning in the United Kingdom.
Dr. Hamilton-Farrell has also examined the British Hyperbaric Association carbon monoxide database, 1993-96 (J Accid Emerg Med 1999; 16; 98-102). This study examined the referral pattern of patients poisoned with carbon monoxide and subsequently transferred to British Hyperbaric oxygen facilities. Hamilton-Farrell reports that the mean time delay to arrival in a hyperbaric oxygen facility was 9 hours and 15 minutes after removal from exposure. He concluded that smoke inhalation victims were often not referred for hyperbaric treatment.
Other, later data for the number of patients treated in Hyperbaric chambers shows that of 1,374 receiving treatment in 1997, 352 (25.6%) were for carbon monoxide poisoning. This is the largest single category of patients and when you consider the predominant use of the chamber was intended to provide treatment for decompression illness related to diving or working in pressurised atmospheres, it is indicative of the acceptability of this particular treatment for this problem.
The cost of hyperbaric treatment is understood to be modest, since it is a primary mode of therapy. In addition, prevention of morbidity from delayed neurologic sequelae represents a substantial cost saving to the health care system and society in general.
Hamilton-Farrell, the Director of the Hyperbaric Unit at Whipps Cross has discussed his experiences in another Paper published in 1999 (J Accid Emerg Med 1999; 16; 98-103).
In the Paper, Hamilton-Farrell reports that all the patients who present at Whipps Cross Hospital Hyperbaric Unit are invited to return between 8 and 12 weeks after their treatment for follow-up assessment. Of the 50 patients (26%) who did so during the period of his study, 37 complained of further symptoms after discharge, including memory loss, headaches and fatigue. While 44 were found to be normal on neurological examination, six were found to have persistent short-term memory loss. He further reports that post-treatment symptomatology was not significantly different between acutely and chronically exposed patients.
Hamilton-Farrell offers an interesting conclusion in his Paper in that the outcome analysis, as far as it has been conducted, reveals a common pattern of continuing head-ache and general ill-health for several days after Hyperbaric oxygen treatment. The persistence of memory loss in particular suggests that the removal of the carbon monoxide from blood and central nervous system at the time of treatment does not resolve the pathology of the poisoning. He acknowledges that the attendance rate for follow-up was low and that it is possible that patients would wish to attend specifically because they had continuing symptoms.
If the