A randomized sequential allocation study to determine the ED90 values of initial ropivacaine dose under different temperatures using dural puncture epidural technique for epidural labor analgesia

INTERVENTION: 23? group:All patients received an initial dose of ropivacaine at 23?. The first patient received an initial bolus of ropivacaine (10 mg [0.1%]) combined with sufentanil 0.3 µg/mL in a 10 mL volume;37? group:All patients received an initial dose of ropivacaine at 37?. The first patient received an initial bolus of ropivacaine (10 mg [0.1%]) combined with sufentanil 0.3 µg/mL in a 10 mL volume; CONDITION: Pain during laboring PRIMARY OUTCOME: The ED90s of the initial ropivacaine bolus required for effective analgesia (VAS score <3 within 30 minutes) under dural puncture epidural ; SECONDARY OUTCOME: Visual analogue scale (VAS) score;Bromage score;Apgar score;Adverse event;Delivery related indicators; INCLUSION CRITERIA: 1.Patients aged between 18 and 40 years, experiencing a single full ‐ term pregnancy (including primiparas and multiparas), who are scheduled to receive epidural labor analgesia; 2. Cervical dilation less than 5 cm; Visual Analog Scale (VAS) score greater than 5; 3. American Society of Anesthesiologists (ASA) physical status classification grade II.