Effect of aromatherapy on postoperative pain relief: A systematic review and meta-analysis of randomized controlled trials

Postoperative pain is very common in patients. Aromatherapy has been used to relieve postoperative pain. This systematic review and meta-analysis evaluated the effect of aromatherapy on postoperative pain and relevant physical and psychological outcomes in adults. Eight databases were searched up to November 28, 2022 for randomized controlled trials (RCTs) on postoperative pain in adults, that compared aromatherapy with routine care (RC) or placebo on relieve postoperative pain. Pain score was the primary outcome, while secondary outcome included heart rate, blood pressure and anxiety level. For meta-analysis, if homogeneity was found to be absent, a random-effect model was applied; otherwise, a fixed-effect model was applied. Subgroup analyses were performed to investigate the origin of the heterogeneity. Cochrane risk of bias tool and the Grading of Recommendations Assessments, Development and Evaluation (GRADE) approach were applied. The publication bias of studies was measured using Begg's and Egger's test as well as the funnel plot. A total of 19 studies with 1768 cases were included. All RCTs had a moderate or high risk of bias. The addition of aromatherapy to RC significantly reduced postoperative pain severity on a scale of 0 to 10 compared to RC with or without a placebo (17 RCTs, 22 comparisons, 1308 participants, MD VAS (0-10)= -1.22, 95% CI [-1.65, -0.79], P < 0.00001; I2: 85%, P < 0.00001). In subgroup analysis, the effects of aromatherapy may be different among type of essential oil (test for subgroup differences: P = 0.004, I2: 68%) and patients from different countries (test for subgroup differences: P <0.00001, I2: 95%). However, aromatherapy does not appear to significantly reduce anxiety scores, systolic blood pressure or diastolic blood pressure or heart rate. No significant publication bias was found. The quality of evidence was “very low” according to GRADE methodology. The risk of adverse events is unknown due to non-reporting. As the quality of much of the evidence was deemed “very low”, it is uncertain if aromatherapy can relieve postoperative pain. Higher quality RCTs will be required to further explore the analgesic effects of aromatherapy and specific safe interventions. PROSPERO registration: CRD42021276211; Funding: none.