Re:Survey of non-invasive ventilation use in ALS in Britain: authors' response
I understand Dr Bourne's concerns regarding my criticism of the survey of NIV reported from Sheffield. My Editorial Commentary was prompted by the very evident shortcomings in the survey reported, relying as it does on unverified data. We have reached a stage in epidemiological work when accurate data are needed to assess the uptake of medical interventions and their outcomes. Surveys cannot provide this essential evidential database.
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Survey of non-invasive ventilation use in ALS in Britain: authors' response
We are concerned that the article by Professor Swash  misrepresents both the nature and findings of our recent UK national survey of the use of NIV in patients with MND/ALS. Although entitled an "editorial commentary", the article is essentially restricted to a critique of our study alone. In particular, he criticises the response rate to the survey (63%) and the lack of verification of the data in a sub -population; he grudgingly acknowledges that the study "contains some hints of changing practice" but concludes that "it would be unwise to place too much reliance on these suggestions." Most of the criticisms have already been refuted or acknowledged in our paper. In the light of recent evidence showing the benefits of NIV in this population,[2-4] the main aim of the survey was to compare present practice with that found in a virtually identical survey we performed 9 years earlier. To ensure comparability between the two surveys, we used the same methodology; questionnaires were posted to all practising neurologists in the UK, identified through the Association of British Neurologists, with a second mailing to non-respondents. In this respect, ours is a more complete survey of national practice than others, which have largely been limited to specific regions, specialist centres or neurologists who elected to participate. The number of new cases of MND diagnosed in the preceding year was virtually identical in our two surveys, reflecting the relatively stable incidence of MND, and in line with the expected incidence in the UK. This implies that most of the neurologists involved in the care of MND patients responded. In the paper, we acknowledged that, as with most such surveys, the data were not independently verified in a sub-group of neurologists; it should be noted that the survey was anonymous and most of the information collected reflects aspects of practice that could not have been gleaned from a database. Where specific numbers of patients were requested, the scope for error is much smaller than suggested by Swash as, in MND, NIV is initiated only after careful consideration, the number referred by individual neurologists is small and any individual errors are mitigated by the large number of responses. Our results showed a very large increase in the number of patients referred for, and successfully initiated on, NIV (2.6 and 3.4 fold respectively), as well as other improvements in respiratory care. These impressive increases over a short period are much greater than any potential reporting error by individual neurologists. With regard to data on quality of life (QoL), the author seems to have misunderstood the purpose of our study, which was a large-scale survey of national practice rather than a study of the benefits of treatment. We have previously shown that NIV improves the QoL of patients with MND; clearly, it was not our aim to show this again, nor would it have been feasible to gather QoL data on a representative cohort of patients in the practice of each neurologist. We acknowledge that we did not compare the practice of individual neurologists to national guidelines. We highlight that the National Institute of Clinical Excellence (NICE) guidelines, were in development, but they were not available over the time period to which the survey referred. Judging the practice of neurologists against these guidelines would clearly have been inappropriate. We would suggest that our approach provided much more worthwhile information: we assessed the actual practice of each neurologist, including whether referral for NIV was based on symptoms alone or in combination with physiological impairment, whether they consider early intervention (physiological impairment with no or only minimal symptoms) and, if respiratory function was assessed, which specific tests were applied, whether they were performed at presentation, routinely or only if symptomatic, and the specific threshold that triggered referral. We showed that, compared to the main body of neurologists, those with the highest rates of referral for NIV were more likely to monitor respiratory function routinely and (in addition to vital capacity) they were more likely to measure sniff nasal inspiratory pressure and arterial blood gases and to consider early intervention. Assessment along these lines is supported by the recently published National Institute of Clinical Excellence guidelines. Swash interprets our analysis by practice size incorrectly. We ranked the size of neurologists' practice in quartiles according to the number of new patients seen. Compared to neurologists in the quartile with the largest practice, those with practices in the lowest quartile had a similar NIV referral rate (corrected for practice size), but the proportion of patients successfully established on NIV was lower (an outcome of importance to patients and their carers). Also, we found that neurologists within the lowest practice quartile were less likely to monitor respiratory function and less likely to rely on the combination of symptoms and respiratory function, both factors likely to influence appropriate selection of patients for NIV.
With regard to oxygen therapy, the potential for varying interpretation of the commonly used phrase "end of life" is covered in our paper. Neurologists were asked about their use of oxygen 1) at the end of life, 2) prior to the end of life, NIV not tolerated / inappropriate and 3) prior to the end of life, before a trial of NIV. We think this is clear. We only highlighted the use of oxygen in the latter group (26% of responding neurologists). The humane and reasonable use of oxygen to which Swash refers applies to the former two groups (full data shown in our paper, Table 6). Whilst it is well documented that patients with hypercapnia due to respiratory muscle weakness share the propensity of others with hypercapnia to develop more severe and potentially life- threatening carbon dioxide retention when breathing uncontrolled oxygen, our experience, and now the results of our survey, suggest that this is not widely recognised by clinicians.
1. Swash M. Survey of non-invasive ventilation use in ALS in Britain. J Neurol Neurosurg Psychiatry Published Online First: 2 September 2011. doi:10.1136/jnnp-2011-300990.
2. Mustfa N, Walsh E, Bryant V et al. The effect of noninvasive ventilation on ALS patients and their caregivers. Neurology 2006;66:1211- 17. 3. Bourke SC, Tomlinson M, Williams TL et al. Effects of non-invasive ventilation on survival and quality of life in patients with amyotrophic lateral sclerosis: A randomised controlled trial. Lancet Neurology 2006;5:140-47.
4. Farrero E, Prats E, Povedano M et al. Survival in amyotrophic lateral sclerosis with home mechanical ventilation: The impact of systematic respiratory assessment and bulbar involvement. Chest 2005;127:2132-38.
5. Bourke SC, Williams TL, Bullock RE et al. Non-invasive ventilation in motor neuron disease: Current UK practice. Amotroph Lateral Scler Other Motor Neuron Disord 2002;3:145-49.
6. National Institute for Health and Clinical Excellence. Motor neurone disease - non-invasive ventilation. London: (CG105) National Institute for Health and Clinical excellence, 2010.
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