• asthma
• COPD mechanisms
• COPD epidemiology
• COPD exacerbations
• COPD pharmacology
• exercise
• lung physiology
• sleep apnoea
• asthma mechanisms
• cough/mechanisms/pharmacology
• assisted ventilation
• emphysema
• pulmonary rehabilitation
• tobacco and the lung

We thank the correspondents for these kind and helpful comments.1 In adopting the Global Initiative on Obstructive Lung Disease (GOLD) classification of severity of airflow obstruction, the National Institute for Health and Clinical Excellence (NICE) guideline update has introduced consistency with international guidelines including those of the American Thoracic Society and the European Respiratory Society. The NICE guidelines note that this classification relates specifically to degrees of airflow obstruction which are arbitrary and may not be closely related to degrees of clinical severity in chronic obstructive pulmonary disease (COPD).2 The current use of the term ‘severe’ for airflow obstruction with forced expiratory volume in 1 s (FEV₁)<50% in place of ‘moderate’ (NICE 2004) may also help to underline the potentially serious nature of the lung function impairment and encourage smoking cessation and more active management.

The NICE guidelines stress the overriding importance of clinical criteria to assess COPD severity, and promote multidimensional assessment using a range of tools to assess breathlessness and functional capacity, ranging from the simple Medical Research Council (MRC) scale to the BODE Index, which includes breathlessness, BMI and exercise capacity as well as lung function.3 Outcomes in COPD are known to be related to clinical factors, including severity of symptoms and exacerbation frequency, as well as lung function. These should be taken into account, together with comorbidities, in assessing patients admitted to hospital with acute exacerbation of COPD and in whom intensive care and use of mechanical ventilation is to be considered.4–6

It is acknowledged that there is variation in intensive care unit criteria for admission to manage COPD. This suggests a need for clear evidence-based criteria for intensive care support and intermittent mandatory ventilation (IMV) based on valid prognostic indicators rather than on a diagnostic classification of severity of airflow obstruction which is not intended for this purpose. Evidence-based guidance for the use of non-invasive ventilation (NIV) uses criteria other than severity of airflow obstruction. Failure of NIV leading to the need for IMV is predicted not by lung function but by the Acute Physiology and Chronic Health Evaluation II (APACHE II) score, pH, respiratory rate, and Glasgow coma score.7 8

The authors acknowledge the National COPD Resources and Outcome Project (NCROP) evidence of low use of IMV in patients with COPD, and agree that the data suggest a variable degree of nihilism for which there is no clear justification. The NICE guidelines note that the decision on which patients with exacerbations of COPD will benefit from intubation is difficult, and involves balancing health status with an estimate of expectation of survival. Factors that are likely to influence this decision are prior functional status, BMI, requirement for oxygen when stable, comorbidities and previous intensive treatment unit (ITU) admissions. Physiological thresholds for use of IMV have not been subjected to systematic evaluation and decisions are currently based on clinical judgement rather than objective data.9 The severity of the acute illness (APACHE II), associated comorbidity and malignancy are predictors of in-hospital mortality in patients with COPD and acute respiratory failure.10 There is clearly a need for further evidence-based assessment of predictors of outcome from IMV rather than inappropriate reliance on diagnostic stratification of FEV₁.

The authors agree that there is a need to explain the reclassification and its meaning to patients and colleagues responsible for acutely ill patients with COPD. In keeping with the NICE guidelines, COPD severity should be described in terms of functional status using at least the modified MRC score, as well as previous severity of lung function impairment. It should be made clear that the severity of lung function impairment in COPD does not necessarily correlate with clinical severity or outcome of inpatient care, which may include ITU and IMV management.