Effects of different intraoperative end-tidal carbon dioxide levels on postoperative nausea and vomiting in patients undergoing thyroidectomy

This study aimed to evaluate the effect of intraoperative end-tidal carbon dioxide (ETCO2) levels on the development of postoperative nausea and vomiting (PONV) in patients undergoing thyroidectomy. In this prospective observational study, 99 patients were allocated into a hypocapnia group (ETCO2 26–30 mmHg) or a normocapnia group (ETCO2 31–35 mmHg). Demographic data, ASA and Apfel scores, surgical and anaesthesia durations, intraoperative opioid consumption, postoperative analgesia, and haemodynamic variables were recorded. PONV incidence was assessed at 0–2, 2–6 and 6–24 h post-operatively. Overall PONV incidence was significantly higher in the hypocapnia group than in the normocapnia group (60.4 % vs 37.2 %, p = 0.035). During the early postoperative period (0–2 h), nausea (52.1 % vs 29.4 %, p = 0.022) and vomiting (47.9 % vs 27.5 %, p = 0.035) were also significantly more frequent with hypocapnia. Patients in the hypocapnia group had a higher proportion of females (83.3 %), higher Apfel scores (2.48 ± 0.71), lower smoking rates (20.8 %), and longer surgical times (p = 0.022). Age, body weight, intraoperative opioid dose and haemodynamic values were comparable between groups. Early-period nausea was more common in patients receiving postoperative tramadol (p = 0.044). Intraoperative hypocapnia is an important modifiable risk factor for PONV, with its effect most pronounced within the first two postoperative hours. Integrating ventilation strategies with Apfel-guided pharmacological prophylaxis may enhance multimodal PONV prevention in thyroidectomy patients. Keywords: Nausea and vomiting, ETCO2, PONV, Thyroidectomy