Relationship between intensity and relief in patients with acute severe pain.

OBJECTIVE: To test whether a single-category improvement on a Likert pain relief scale equals the minimum clinically significant difference of 1.3 units in pain intensity reduction on a 10-unit numerical rating scale (NRS).
METHODS: Prospective cohort of adults with acute severe pain receiving standardized analgesia. Patients rated pain intensity via NRS before receiving morphine and 30 minutes later. Patients described pain relief as "none," "a little," "moderate," "a lot," or "complete." The primary outcome was the difference in NRS scores between each contiguous pair of pain relief categories over 30 minutes.
RESULTS: One hundred thirty-one patients, age range 21 to 65 years, median baseline NRS pain score 10 (interquartile range, 9-10). Patients whose relief was "complete," "a lot," "moderate," "mild," and "none" had the following NRS unit reductions in pain, respectively: 9, 5.7, 3.9, 2.1, and -0.1. The difference between each pair of relief categories was 3.3, 1.8, 1.8, and 2.2 units.
CONCLUSION: Each single-category improvement on a pain relief scale exceeds the minimum clinically significant difference in pain intensity as measured on an NRS.