Chronic obstructive pulmonary disease is increasingly recognised as a systemic disorder. Muscle wasting and deconditioning and vascular dyfunction are present in this condition (the latter the subject of a previous blog). How should we measure and discuss disease severity in such a systemic condition?
I chewed over this question a little when giving a talk to GPs in Warrnambool last year, and again on the ward round with the registrar this morning (prompted by the sort of patient represented by the attached CXR - how's the hyperexpansion!?). I also tried to skewer our radiologist yesterday because I am irritated by radiological comments on 'severity' ('there is evidence of severe emphysema', for example, on interpretation of a CT) when I think that 'extent' is what is meant ('There is evidence of extensive generalised emphysema').
I'd hate to be guilty of the same crime myself. In particular, I need to ask myself the following question; 'Is severe obstruction on spirometry equivalent to severe COPD?"
Our guidelines (for example, the global initiative in obstructive lung disease - 'GOLD' ) do provide neat summary tables of how spirometry correlates with severity in COPD. These are easier to remember than the wordier paragraphs that outline how a range of other factors should also be taken into consideration when we wish to evaluate the real disease 'severity'. As a consequence we may tend to become over-reliant on spirometry alone. It is certainly not the only, nor perhaps even the most, meaningful measure of severity of disease.
As befits a systemic condition, there are multi-component indices which provide measures of disease severity. In 2004 the BODE (Body mass index (B), degree of airflow Obstruction (O), dyspnoea (D) and exercise capacity (E)) index was validated as a measure of severity which proved predictive of mortality. The initial paper was printed in the New England Journal of Medicine. In this scale, dyspnoea was measured with a modified Medical Research Council dyspnoea scale, and exercise capacity with a 6 minute walk test. The latter of these is difficult to employ extensively in clinical practice, and partly for this reason further efforts to define a clinically useful scale have been ongoing.
In December a paper promoting a new, and simple scale, was published in the blue journal. The DOSE (dyspnoea (MRC dyspnoea scale), obstruction (FEV1 % predicted), smoking status, exacerbation frequency) index was derived froma dataset of patients with COPD in Devon, and then validated in Devon, London, Tokyo and Holland datasets. The four components were selected from a range of proposed markers as being most consitently associated with health status measured using the Clinical COPD Questionnaire. (Interestingly, current smoking status was predictive of poor health status, where overall tobacco consumption measured by packet years was not).
A numerical score between zero and four was assigned for each of the four indices, and the four scores were added together to give the 'DOSE' Index score.
The score derived from this approach was found reproducibly to correlate significantly with health status meaures obtained by the more complicated COPD clinical questionnaire. A DOSE index score of more than four was also found to correlate with hospital admissions, respiratory failure and exercise capacity (negative correlation) when 6MWT was measured (in the Japanese cohort only). DOSE index results were found to increase over time throught the 8 years of the study, suggesting disease progression. Although MRC dyspnoea scale score and FEV1% measures on their own also correlated with hospital admissions, the correlation was weaker than the composite index.
How is this relevant to our practice? An index such as this, which is easy to administer, and which identifies patients with more severe disease - specifically those most likely to need hospitalisation - will help us target the more intensive of our interventions in clinical practice. It may even provide a useful way for us to monitor the effectiveness of our interventions. Sometimes the stuff we should all be doing regularly with our patients with COPD (quantifying breathlessness, reviewing smoking history, checking spirometry) happens best if it is proceduralised and done by practice staff (rather than the consultant physician - did I really just say that?). This DOSE index could be a very useful tool to facilitate just such a procedure in this practice....
I chewed over this question a little when giving a talk to GPs in Warrnambool last year, and again on the ward round with the registrar this morning (prompted by the sort of patient represented by the attached CXR - how's the hyperexpansion!?). I also tried to skewer our radiologist yesterday because I am irritated by radiological comments on 'severity' ('there is evidence of severe emphysema', for example, on interpretation of a CT) when I think that 'extent' is what is meant ('There is evidence of extensive generalised emphysema').
I'd hate to be guilty of the same crime myself. In particular, I need to ask myself the following question; 'Is severe obstruction on spirometry equivalent to severe COPD?"
Our guidelines (for example, the global initiative in obstructive lung disease - 'GOLD' ) do provide neat summary tables of how spirometry correlates with severity in COPD. These are easier to remember than the wordier paragraphs that outline how a range of other factors should also be taken into consideration when we wish to evaluate the real disease 'severity'. As a consequence we may tend to become over-reliant on spirometry alone. It is certainly not the only, nor perhaps even the most, meaningful measure of severity of disease.
As befits a systemic condition, there are multi-component indices which provide measures of disease severity. In 2004 the BODE (Body mass index (B), degree of airflow Obstruction (O), dyspnoea (D) and exercise capacity (E)) index was validated as a measure of severity which proved predictive of mortality. The initial paper was printed in the New England Journal of Medicine. In this scale, dyspnoea was measured with a modified Medical Research Council dyspnoea scale, and exercise capacity with a 6 minute walk test. The latter of these is difficult to employ extensively in clinical practice, and partly for this reason further efforts to define a clinically useful scale have been ongoing.
In December a paper promoting a new, and simple scale, was published in the blue journal. The DOSE (dyspnoea (MRC dyspnoea scale), obstruction (FEV1 % predicted), smoking status, exacerbation frequency) index was derived froma dataset of patients with COPD in Devon, and then validated in Devon, London, Tokyo and Holland datasets. The four components were selected from a range of proposed markers as being most consitently associated with health status measured using the Clinical COPD Questionnaire. (Interestingly, current smoking status was predictive of poor health status, where overall tobacco consumption measured by packet years was not).
A numerical score between zero and four was assigned for each of the four indices, and the four scores were added together to give the 'DOSE' Index score.
The score derived from this approach was found reproducibly to correlate significantly with health status meaures obtained by the more complicated COPD clinical questionnaire. A DOSE index score of more than four was also found to correlate with hospital admissions, respiratory failure and exercise capacity (negative correlation) when 6MWT was measured (in the Japanese cohort only). DOSE index results were found to increase over time throught the 8 years of the study, suggesting disease progression. Although MRC dyspnoea scale score and FEV1% measures on their own also correlated with hospital admissions, the correlation was weaker than the composite index.
How is this relevant to our practice? An index such as this, which is easy to administer, and which identifies patients with more severe disease - specifically those most likely to need hospitalisation - will help us target the more intensive of our interventions in clinical practice. It may even provide a useful way for us to monitor the effectiveness of our interventions. Sometimes the stuff we should all be doing regularly with our patients with COPD (quantifying breathlessness, reviewing smoking history, checking spirometry) happens best if it is proceduralised and done by practice staff (rather than the consultant physician - did I really just say that?). This DOSE index could be a very useful tool to facilitate just such a procedure in this practice....
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