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Meng Cai,1,&ast; Jie Liu,2,&ast; Xiao-Feng Lei,1 Yun-Long Li,3 Jin Yu1 1Department of Anesthesiology, Women and Children’s Hospital of Chongqing Medical University, Chongqing Health Center for Women and Children, Chongqing, People’s Republic of China; 2Department of Respiratory, The Affiliated Banan Hospital of Chongqing Medical University, People’s Hospital of Chongqing Banan District, Chongqing, People’s Republic of China; 3Department of Obstetrics and Gynecology, Women and Children’s Hospital of Chongqing Medical University, Chongqing Health Center for Women and Children, Chongqing, People’s Republic of China&ast;These authors contributed equally to this workCorrespondence: Jin Yu, Department of Anesthesiology, Women and Children’s Hospital of Chongqing Medical University, Chongqing Health Center for Women and Children, No. 120, Longshan Road, Yubei District, Chongqing, 401147, People’s Republic of China, Tel +86-18623117820, Fax +86-23-63702844, Email dodoes@qq.comBackground: Intravenous labor analgesia is recommended as an alternative for parturients who have contraindications to epidural analgesia. There are several opioid analgesics and different administering regimens used in the clinic. This study aimed to compare the effectiveness and safety of two intravenous remifentanil dosage regimens in the first labor stage.Patients and Methods: One hundred and fifteen parturients with a contraindication to epidural analgesia but were willing to receive systemic labor analgesia were randomized into group A received a fixed dose of remifentanil throughout the first stage of labor, and group B received an elevated dose of remifentanil during the active phase of the first stage both by patient-controlled analgesia (PCA). Maternal numerical rating scale (NRS) pain score and oxygen desaturation, sedation efficacy, satisfaction, as well as maternal and fetal adverse reactions were recorded and compared.Results: The mean NRS pain scores before analgesia and in the latent phase showed no statistically significant difference between the two groups (P > 0.05). However, during the active phase, group B demonstrated significantly lower mean NRS pain scores and lowest pain score compared to group A (P < 0.05). Furthermore, group B exhibited higher overall sedation scores and satisfaction scores in comparison to group A (P < 0.05). The incidence of adverse reactions between the two groups was similar (P > 0.05).Conclusion: Relatively elevated intravenous dosage of remifentanil with PCA during the active phase in the first stage of labor is safe and more effective than a fixed-dosage regimen for labor analgesia.Trial Registration: This study was registered with ChiCTR on 24/08/2021 with trial identification number: ChiCTR2100050247. First participant was recruited on 31/08/2021. The last patient was recruited on 12/08/2022.Graphical Abstract: Keywords: patient-controlled analgesia, PCA, remifentanil, labor analgesia, intravenous administration, opioids

Meng Cai,1 Hao Liu,2 Yong Peng,2 Jing-Kun Miao,2 Xiao-Feng Lei,1 Jin Yu1 1Department of Anesthesiology, Chongqing Health Center for Women and Children, Women and Children’s Hospital of Chongqing Medical University, Chongqing, People’s Republic of China; 2Department of Pediatrics, Chongqing Health Center for Women and Children, Women and Children’s Hospital of Chongqing Medical University, Chongqing, People’s Republic of ChinaCorrespondence: Jin Yu, Department of Anesthesiology, Chongqing Health Center for Women and Children, Women and Children’s Hospital of Chongqing Medical University, No. 120, Longshan Road, Yubei District, Chongqing, 401147, People’s Republic of China, Tel +86-18623117820, Email dodoes@qq.comObjective: Remifentanil, in combination with etomidate and sevoflurane, is commonly used in clinics for general anesthesia induction in cesarean section (CS). This study aimed to evaluate the correlation between the induction to delivery (I-D) time and neonatal plasma drug concentration and anesthesia, as well as its effects on neonates.Methods: Fifty-two parturients in whom general anesthesia was induced for CS were divided into group A (I-D< 8 min) and group B (I-D≥ 8 min). Maternal arterial (MA), umbilical venous (UV), and umbilical arterial (UA) blood samples were collected at delivery to analyze the remifentanil and etomidate concentrations using liquid chromatography-tandem mass spectrometry.Results: There were no statistically significant differences between the two groups in terms of plasma concentrations of remifentanil in the MA, UA, and UV blood (P > 0.05). The plasma concentration of etomidate in MA and UV was higher in group A than that in group B (P< 0.05), whereas the UA/UV ratio of etomidate was higher in group B than that in group A (P< 0.05). The Spearman rank correlation test showed no correlation between the I-D time and plasma remifentanil concentration in the MA, UA, and UV plasma (P> 0.05). The concentrations of etomidate in the MA and UV were negatively correlated with the I-D time (P < 0.05).Conclusion: Prolonged I-D time did not significantly influence the maternal or neonatal plasma concentration of remifentanil. It is safe to administer remifentanil target-controlled infusion in combination with etomidate and sevoflurane for general anesthesia induction during CS.Keywords: cesarean section, placental transport, general anesthesia, remifentanil, etomidate, drug concentration