Minimally clinically important difference in chronic breathlessness: every little helps.

OBJECTIVES

The aim of the study was to determine the minimally clinically important difference (MCID) for breathlessness due to chronic heart failure (CHF).

BACKGROUND

The measurement of breathlessness is difficult because it is subjective and multifactorial. Statistically significant changes in assessment may not be clinically meaningful. This is the first determination of MCID in chronic breathlessness in CHF using patient-rated data.

METHODS

Measurements were made as part of a randomized, controlled, crossover trial of morphine, oxycodone, or placebo for breathlessness in CHF. Breathlessness intensity was assessed at baseline and at the end of each intervention (day 4) using 11-point numerical rating scales (NRS), modified Borg (mBorg) scales, and global impression of change (GC) in breathlessness at day 4. From these data, the change in NRS or mBorg associated with a 1-point change in GC was calculated.

RESULTS

Thirty-five patients completed all study interventions, resulting in 105 data sets. We defined MCID as a 1-point change in GC. Regression analysis found that the MCID, including 95% CIs, equaled change in average NRS breathlessness per 24 hours of 0.5 to 2.0 U (P < .001), change in worst NRS breathlessness per 24 hours of 0.4 to 2.9 (P < .001), change in average mBorg score of 0.2 to 2.0 (P < .001), and change in worst mBorg score as between 0.3 and 1.9 (P < .001). Corresponding effect size calculations lay within the 95% CIs for the regression analysis for each measure.

CONCLUSIONS

A 1-point change in NRS or mBorg score is a reasonable estimate of the MCID in average daily chronic breathlessness in CHF.