Background: Assessment of postoperative nausea intensity is difficult because nausea is a subjective and unpleasant sensation. We propose using the Visual Analogue Scale (VAS) device to increase the efficiency and precision in the assessment of nausea. We carried out a pilot study on postoperative patients suffering from nausea to measure the degree of agreement between the VAS scores and those given on a 4-point verbal descriptive scale (VDS).
Methods: Postoperative nausea was evaluated by means of a classical VAS (0-10 cm) device and a 4-point VDS (0=no nausea, 1=mild, 2=moderate, 3=severe) in 128 surgical spontaneously complaining patients. Evaluation was repeated 45 min after rescue medication given if nausea was intractable, lasted more than 10 min or at the request of the patient. Ordinal logistic regression was used to measure the association between VAS and VDS and to determine cut-off points on the VAS.
Results: The VAS device was easily understood and used by patients. VAS scores decreased significantly from 5.5+/-2.3 to 1.4+/-1.8 after rescue medication (P=0.002). Application of ordinal logistic regression to pre- and post-medication data combined yielded an agreement of 86% between VAS and VDS and the cut-off points on the VAS were estimated as follows: 0-1 (no nausea), 1+/-4 (mild), 4+/-7 (moderate) and 7+/-10 (severe).
Conclusion: The VAS method proved to be useful for assessing quantitative nausea intensity and for testing the efficacy of rescue medication. It was found that a cut-off value of 4 on the VAS may be considered as a critical threshold triggering anaesthesiologists or nurses to administer rescue medication.