Development and validation of a postoperative nausea and vomiting intensity scale

Postoperative nausea and vomiting (PONV) is common and of concern to patients and clinicians. The effect of PONV can range from trivial and transient to major clinical importance, and it is unclear which of its characteristics lead to discomfort and distress. We first enrolled 180 participants (patients, family members, nurses, doctors) to identify the characteristics of clinically important PONV, and from these data developed a measurement scale. We then evaluated the scale in a further 163 patients reporting PONV. Validity, reliability, and responsiveness of the PONV Intensity Scale were tested using psychometric techniques. Most participants agreed that three or more vomits, and greater nausea severity and duration, were key factors in defining clinically important PONV. These data were used to derive a PONV Intensity Scale and a score to define clinically important PONV. The scale identified 29 patients (18%) as having clinically important PONV. Patients with clinically important PONV had a poorer quality of recovery (P < 0.0005) and needed twice as much antiemetic treatment (P < 0.0005). The scale was strongly associated with PONV consequences and complications, with odds ratios ranging from 6.0 to 31 (all P < 0.0005). The scale had excellent reproducibility (intraclass correlation 0.99, P < 0.0005). The scale could reliably reflect a clinically important change in health status (effect size 0.82, P < 0.0005). The PONV Intensity Scale is a valid, reliable, and responsive measure of clinically important PONV.