Percentage of pain intensity difference on an 11-point numerical rating scale underestimates acute pain resolution.
BACKGROUND
A 50% reduction in pain intensity difference (50%PID) between baseline and follow-up evaluation is commonly accepted as adequate pain relief in emergency departments (EDs). However, 50%PID seems to be problematic with the 11-point numerical rating scale (NRS) since even baseline values are more divisible by 2 (50% reduction) than odd baseline values. This study evaluated the impact of this bias and integrated time between baseline and follow-up measurements, hypothesizing that the slope of relative pain intensity difference (SRPID) is a more accurate gauge of pain relief that can decrease bias and incorporate the time component of pain relief.


METHODS
A post-hoc analysis of real-time data on an adult population from an urban ED identified 3199 consecutive patients who received an analgesic, had baseline NRS > 3 and a follow-up NRS within 2 h. Primary outcome was the percentage of patients with pain relieved from the 50%PID and the 50%SRPID criteria.


RESULTS
Results showed that with 50%PID, even pain intensity levels on baseline NRS comprised a higher percentage of patients [60.7%; 95% confidence interval (CI): 58.8-63.0] with pain relief compared to odd pain intensity levels (51.7%; 95% CI: 48.8-54.6; p < 0.001), underestimating pain-relieved patients by 9% [95% CI: 0.05-0.13; effect size (ES) = 0.09]. The percentage of pain-relieved subjects with the 50%SRPID criteria was not affected by baseline NRS values (59.7% for whole sample; 95% CI: 58.0-61.4; ES = 0.02).


CONCLUSIONS
The 50%PID method with an 11-point NRS for assessing adequate pain relief is significantly biased for specific baseline pain intensity level. In the particular context of ED acute pain, the SRPID seems less biased.
Department of Emergency Medicine, Research Centre, Sacré-Coeur Hospital of Montreal, Canada; Faculty of Medicine, Université de Montréal, Canada.
J-M
JM
Chauny
J
J
Paquet
G
G
Lavigne
R
R
Daoust
D059787:Acute Pain / Q000175:diagnosis* / Q000188:drug therapy; D000328:Adult; D000368:Aged; D000700:Analgesics / Q000627:therapeutic use*; D004636:Emergency Service, Hospital; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D059408:Pain Management; D010147:Pain Measurement / Q000379:methods*; D012720:Severity of Illness Index; D016896:Treatment Outcome
D000700:Analgesics