Intravenous Remifentanil for Labor Analgesia (IRELAN)

• Rate of cesarean delivery [ Time Frame: Analgesia initiation (0 min) to successful vaginal delivery (this time period underwent changing in different individuals) ] [ Designated as safety issue: Yes ]
• Rate of instrument-assisted delivery [ Time Frame: Analgesia initiation (0 min) to successful vaginal delivery (this time period underwent changing in different individuals) ] [ Designated as safety issue: Yes ]
• Indications of cesarean delivery [ Time Frame: Analgesia initiation (0 min) to cesarean section (this time period underwent changing in different individuals) ] [ Designated as safety issue: Yes ]
• Duration of analgesia [ Time Frame: Initiation of analgesia (0 min) to the disappearance of sensory block (this time period underwent changing in different individuals) ] [ Designated as safety issue: Yes ]
• Maternal satisfaction with analgesia [ Time Frame: At the end of the vaginal delivery (this time period underwent changing in different individuals) ] [ Designated as safety issue: No ]
• Maternal oral temperature [ Time Frame: Analgesia initiation (0 min) to successful vaginal delivery (this time period underwent changing in different individuals) ] [ Designated as safety issue: Yes ]
• Use of oxytocin after analgesia [ Time Frame: Analgesia initiation (0 min) to successful vaginal delivery (this time period underwent changing in different individuals) ] [ Designated as safety issue: Yes ]
• Maximal oxytocin dose [ Time Frame: At the end of vaginal delivery (this time period underwent changing in different individuals) ] [ Designated as safety issue: No ]
• Breastfeeding success at 6 weeks after vaginal delivery [ Time Frame: At the sixth week after successful delivery ] [ Designated as safety issue: Yes ]
• Neonatal one-minute Apgar scale [ Time Frame: At the first minute of baby was born ] [ Designated as safety issue: Yes ]
• Neonatal five-minute Apgar scale [ Time Frame: At the fifth minute of baby was born ] [ Designated as safety issue: Yes ]
• Umbilical-cord gases analysis [ Time Frame: At the time baby was born (0 min) ] [ Designated as safety issue: Yes ]
• Neonatal sepsis evaluation [ Time Frame: After the baby was born (15 min after delivery) ] [ Designated as safety issue: Yes ]
• Neonatal antibiotic treatment [ Time Frame: After the baby was born (one day after delivery) ] [ Designated as safety issue: Yes ]
• Incidence of maternal side effects [ Time Frame: Analgesia initiation (0 min) to successful vaginal delivery (this time period underwent changing in different individuals) ] [ Designated as safety issue: Yes ]

• Rate of cesarean delivery [ Time Frame: Analgesia initiation to successful vaginal delivery ] [ Designated as safety issue: Yes ]
• Rate of instrument-assisted delivery [ Time Frame: Analgesia initiation to successful vaginal delivery ] [ Designated as safety issue: Yes ]
• Indications of cesarean delivery [ Time Frame: Analgesia initiation to cesarean section ] [ Designated as safety issue: Yes ]
• Duration of analgesia [ Time Frame: Initiation of analgesia to the disappearance of sensory block ] [ Designated as safety issue: Yes ]
• Maternal satisfaction with analgesia [ Time Frame: At the end of the vaginal delivery ] [ Designated as safety issue: No ]
• Maternal oral temperature [ Time Frame: Analgesia initiation to successful vaginal delivery ] [ Designated as safety issue: Yes ]
• Use of oxytocin after analgesia [ Time Frame: After analgesia to vaginal delivery ] [ Designated as safety issue: Yes ]
• Maximal oxytocin dose [ Time Frame: At the end of vaginal delivery ] [ Designated as safety issue: No ]
• Breastfeeding success at 6 weeks after vaginal delivery [ Time Frame: At the sixth week after successful delivery ] [ Designated as safety issue: Yes ]
• Neonatal one-minute Apgar scale [ Time Frame: At the first minute of baby was born ] [ Designated as safety issue: Yes ]
• Neonatal five-minute Apgar scale [ Time Frame: At the fifth minute of baby was born ] [ Designated as safety issue: Yes ]
• Umbilical-cord gases analysis [ Time Frame: At the time baby was born ] [ Designated as safety issue: Yes ]
• Neonatal sepsis evaluation [ Time Frame: After the baby was born ] [ Designated as safety issue: Yes ]
• Neonatal antibiotic treatment [ Time Frame: After the baby was born ] [ Designated as safety issue: Yes ]
• Incidence of maternal side effects [ Time Frame: Analgesia initiation to successful vaginal delivery ] [ Designated as safety issue: Yes ]

Labor analgesia is an essential health caring procedure for women. However, epidural analgesia cannot be performed on all subjects for different contraindications, such as lower platelet counter, back infection at the puncture site, and fear of epidural injection etc. Therefore, intravenous analgesia is an alternative for such conditions. Given the influence of intravenous administration of drugs on fetus, the drug selection is very important. Remifentanil, a super-short efficacious opioid, can last for 3-4 minutes after injection, which is similar in both maternal and fetal environment. Thus the fetus-associated side effects would be less than other drugs. The investigators hypothesized that remifentanil would be a superior intravenous drug used with patient-controlled technique for labor analgesia.

• Drug: Hydromorphone
  Intravenous administration of hydromorphone 1mg at the patient's request if they felt uterine contraction pain
• Drug: Remifentanil
  Remifentanil intravenous PCA: 0.2μg/kg, lockout time interval 2 minutes, continuous infusion rate 0.2-0.8μg/kg/min.
  Other Name: ReiFen

• Active Comparator: 1
  Intravenous administration of hydromorphone intermittently
  Intervention: Drug: Hydromorphone
• Experimental: 2
  Remifentanil intravenous patient-controlled analgesia
  Intervention: Drug: Remifentanil

Inclusion Criteria:

1. Nulliparous women
2. > 18 years and < 45 years
3. Spontaneous labor
4. Analgesia request
5. Epidural puncture contraindications
6. Tendency of bleeding

Exclusion Criteria:

1. Allergy to opioids, a history of the use of centrally-acting drugs of any sort, chronic pain and psychiatric diseases records
2. Participants younger than 18 years or older than 45 years
3. Those who were not willing to or could not finish the whole study at any time
4. Using or used in the past 14 days of the monoamine oxidase inhibitors
5. Alcohol addictive or narcotic dependent patients were excluded for their influence on the analgesic efficacy of the epidural analgesics
6. Subjects with a nonvertex presentation or scheduled induction of labor
7. Cervical dilation was 5.0cm or greater before performing epidural puncture and catheterization
8. Diagnosed diabetes mellitus and pregnancy-induced hypertension
9. Twin gestation and breech presentation