Advantages and disadvantages of the main outcome measures

MortalityWidely accepted; consistently defined, universally available in trials, observational studies and registriesInsensitive to small or medium treatment effects, those improving symptoms or accelerating recovery
Clinical treatment success or failureFrequently evaluated and reported in AECOPD trials
A crude measure of treatment effect
Significant variability in the definition that limits comparability
Improvement in health status or symptomsEasy to complete questionnaires, frequently self-administered
Some are designed to evaluate multiple features of an AECOPD
Significant variability in the utilised measures, which are of untested and doubtful validity
Often have complex results that are challenging to interpret
Length of hospitalisationEasy to define and widely accepted outcome
Universally available in trials, observational studies and registries
Cannot be used for moderate (non-hospitalised) AECOPD
Also, its accuracy is limited by:
 1) the availability and extent of community COPD care
 2) non-medical delays in discharge as well as social care
 3) the lack of consistent criteria to guide timing of hospital discharge
Time-to-treatment successMay be more sensitive to small or medium treatment effects, especially acceleration of recoveryInfrequently reported
May be limited by the subjectivity of patient-reported outcomes
Microbiological responseEasily and consistently definedLack of sensitivity and specificity of sputum cultures in COPD exacerbations
SpirometryConsistently defined and universally available testA substantial proportion of patients are unable to perform acceptable spirometry during AECOPD
Lack of repeatability during AECOPD

AECOPD: acute exacerbation of chronic obstructive pulmonary disease; COPD: chronic obstructive pulmonary disease.