Comparison of opioid-free and opioid-inclusive propofol anaesthesia for thyroid and parathyroid surgery: a reply

We thank Chen et al. [1] for their interest in our study [2], in which we found that opioid-free versus opioid-inclusive propofol anaesthesia reduced the incidence of postoperative nausea and vomiting (PONV) during the first 48-h postoperatively (5% vs. 24%; odds ratio 0.17, 95%CI 0.08–0.35; number needed to treat 5.3; p < 0.001). Opioid-free anaesthesia was also associated with a reduced need for rescue anti-emetics, lower incidences of hypotension and oxygen desaturation after tracheal extubation, and improved patient satisfaction.

Chen et al. suggest that nausea, retching and vomiting episodes should be documented and analysed separately. We defined PONV as a composite outcome including any episodes of nausea, retching or vomiting based on the literature [3]. This definition was also used in our recent study conducted in patients undergoing thoracoscopic lung surgery [4]. Few studies specified an individual occurrence of nausea, retching or vomiting as the primary outcome. We did not report the individual occurrences of PONV in our patients; however, among the secondary outcomes, the reduced PONV severity and need for rescue anti-emetics suggests that opioid-free anaesthesia alleviated PONV in patients undergoing thyroid and parathyroid surgery.

To assess the severity of PONV, we applied the PONV impact scale [3]. For opioid-free versus opioid-inclusive anaesthesia, the incidences of mild, moderate and severe PONV episodes were 5% versus 16% (p < 0.001), 1% versus 4% (p = 0.037) and 0% versus 3% (p = 0.030), respectively. The between-group differences were all statistically significant before multiple comparison corrections. In a post hoc analysis of combining moderate and severe PONV categories, we found a reduced incidence of moderate-to-severe PONV (1% vs. 7%, p < 0.001) in the opioid-free group, which remains significant even after correction for multiple comparison. Based on these data, we respectfully disagree that opioid-free propofol anaesthesia reduced only mild PONV in our patients. Moreover, we showed that patient satisfaction was higher in the opioid-free group. It is clinically meaningful that opioid-free anaesthesia improved patient comfort after thyroid and parathyroid surgery.

In terms of adverse effects, the incidence of nightmares or hallucination was 4% in the opioid-free group versus 2% in the opioid-inclusive group (odds ratio 1.78, 95%CI 0.56–5.50, p = 0.617), without a significant between-group difference. We cannot assume that more patients in the opioid-free group would experience nightmares or hallucinations. The tracheal extubation time was slightly longer (median 5 min) in the opioid-free group, while the duration of post-anaesthesia care unit stay was comparable between groups. The median dose of intra-operative propofol was 740 mg and 690 mg in the opioid-free group and opioid-inclusive group, respectively. This is a clinically insignificant difference. Hence, these results suggested that opioid-free propofol anaesthesia did not prolong recovery or increase resource utilisation in our patients. The median dose of sufentanil used in the opioid-inclusive group was 40 μg (approximately 0.6 μg.kg^-1) as per our clinical practice. This provides sufficient analgesia and is in line with doses reported in the literature [5, 6].