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The visual analog scale in the immediate postoperative period: intrasubject variability and correlation with a
L J DeLoach1, M S Higgins, A B Caplan
1Department of Anesthesiology, Johns Hopkins Bayview Medical Center, Baltimore, MD 21224, USA.
Anesthesia and Analgesia
|January 16, 1998
Summary
The visual analog scale (VAS) shows good correlation with numeric pain scales but has significant imprecision. Postoperative pain assessments using VAS should account for a margin of error of +/- 20 mm.
Area of Science:
- Pain Management
- Clinical Assessment
- Medical Statistics
Background:
- The Visual Analog Scale (VAS) is frequently employed to evaluate pain management effectiveness in acute postoperative pain.
- However, its reliability and precision in postoperative pain studies remain unconfirmed.
Purpose of the Study:
- To assess the utility of the VAS in measuring acute postoperative pain.
- To evaluate the correlation between VAS scores and an 11-point numeric pain scale.
- To determine the repeatability and consistency of VAS scores in the immediate postoperative period.
Main Methods:
- Sixty subjects in the immediate postoperative period were studied.
- Data collected included VAS scores, 11-point numeric pain scale scores, VAS repeatability over short intervals, and changes in VAS scores versus verbal pain reports.
- Statistical analysis involved calculating correlation and repeatability coefficients.
Main Results:
- VAS scores demonstrated strong correlations with the 11-point numeric pain scale (coefficients ranging from 0.91 to 0.95).
- Repeatability coefficients for VAS scores varied (13.5 to 23.0 mm), with only 29% of patients showing consistency within 5 mm across all assessments.
- While 92% of VAS score changes were within 20 mm of reported pain changes, 31% showed changes in the opposite direction of verbal reports.
Conclusions:
- The VAS correlates well with a verbal 11-point pain scale for postoperative pain assessment.
- However, individual VAS determinations in the immediate postoperative period possess a significant imprecision of approximately +/- 20 mm.
- This imprecision necessitates careful interpretation of single VAS measurements in clinical practice and research.