Utility of numerical and visual analog scales for evaluating the post-operative pain in rural patients

BACKGROUND: Visual analog scales (VAS) and numeric analog scales (NAS) are used to assess post-operative pain, but few studies indicate their usefulness in rural illiterate population in India. AIMS: This study was designed to 1) Compare the impact of literacy on the ability to indicate pain rating on VAS and NAS in post-operative rural patients. 2) Assess the level of agreement between the pain scales. SETTING AND DESIGN: Cross sectional, hospital based study. METHODS: Informed consent was obtained from patients prior to undergoing surgical procedures in a teaching hospital. Post surgery, patients who were conscious and coherent, were asked to rate pain on both VAS and NAS. The pain ratings were obtained within 24 hours of surgery and within 5 minutes of each other. STATISTICAL METHODS: Percentages, chi square test, regression analysis. RESULTS: A total of 105 patients participated in the study. 43 (41%) of the sample was illiterate. 82 (78.1%) were able to rate pain on VAS while 81 (77.1%) were able to rate pain on NAS. There was no significant association between pain ratings and type of surgery, duration of surgery and nature of anaesthesia. In multivariate analysis, age, sex and literacy had no significant association with the ability to rate pain on VAS (P value 0.652, 0.967, 0.328 respectively). Similarly, no significant association was obtained between age, sex and literacy and ability to rate pain on NAS (P value 0.713, 0.405, 0.875 respectively). Correlation coefficient between the scales was 0.693. CONCLUSION: VAS and NAS can be used interchangeably in Indian rural population as post-operative pain assessment tools irrespective of literacy status.