Impacts of Cerebral Oxygen Metabolism on Postoperative Nausea and Vomiting in Patients following Thyroid Surgery

Background: Postoperative nausea and vomiting (PONV) is a common side effect after thyroidectomy, which can affect the recovery of patients who underwent thyroid surgery. It has been reported that cerebral oxygen metabolism may affect the occurrence of postoperative adverse reactions. Therefore, this study aimed to investigate the relationship between cerebral oxygen metabolism and PONV incidence in patients after thyroidectomy. Methods: This study retrospectively analyzed the clinical data of 100 female patients who underwent thyroid surgery in a tertiary hospital between May 2022 and September 2023. The study participants were categorized into two groups: the Mannitol group (n = 50), patients who received an intravenous infusion of 0.5 g/kg mannitol at a rate of 150 drops/minute before the operation, and the Control group (n = 50), patients who intravenously received the equivalent volume of normal saline. All participants received the same anesthesia induction and maintenance treatment. During the surgery, we recorded their heart rate (HR), mean arterial pressure (MAP), urine volume, cerebral oxygen metabolism index (cerebral oxygen extraction ratio (CERO2) and difference in arteriovenous oxygen (Da-jvO(2))) at each time point, including T0, 5 minutes after entering into the operating room; T1, 5 minutes after tracheal intubation; T2, immediately after cervical hyperextension; T3, immediately after the operation; T4, 50 minutes after the operation; T5, immediately at the operation stopped. Moreover, the incidence of PONV was assessed within 48 hours post-surgery. Results: There were no statistical differences in HR and MAP between the two groups at each time point (p > 0.05). Compared to the Control group, urine output in the Mannitol group showed no significant changes at T0, T1, T2, and T3 (p > 0.05) but significantly increased at T4 and T5 time points (p < 0.05). Da-jvO(2) and CERO2 in T1, T2, T3, T4 and T5 time points were significantly reduced compared to T0 (p < 0.05). Compared to T2 and T3, Da-jvO(2) and CERO2 at T4 and T5 were significantly reduced in the Mannitol group (p < 0.05), but they showed no substantial changes in the Control group (p > 0.05). Furthermore, Da-jvO(2) and CERO2 were significantly decreased at T4 and T5 time points in the Mannitol group compared to the Control group (p < 0.05). Additionally, PONV incidence was significantly lower (26.0%) in the Mannitol group compared to the Control group (50.0%) within 48 hours post-surgery (p < 0.05). The severity of PONV in the Control group was substantially higher than in the Mannitol group. Conclusion: The preoperative intravenous infusion of mannitol can affect cerebral oxygen metabolism, thereby reducing the incidence and severity of PONV in patients who underwent thyroid surgery.