The goal of labor analgesia is to effectively alleviate pain, while potentially improving uterine blood flow and reducing adverse effects caused by maternal hyperventilation. Labor analgesia can be used throughout labor, from its onset to the second stage of labor.
Causes of Pain
Pain during the first stage of labor largely originates from uterine muscle ischemia and hypoxia during contractions, as well as muscle tension caused by cervical dilation. These pain signals are transmitted to the spinal cord via the sympathetic nerves (thoracic nerves T10–T12).
Pain during the second stage of labor additionally arises from compression of the fetal head on the pelvic floor, vagina, and perineum, which is transmitted to the spinal cord through sensory fibers of the sacral nerves S2–S4.
Maternal tension and anxiety may exacerbate pain by triggering the fear-tension-pain syndrome.
Basic Principles of Labor Analgesia
These include:
- Minimal interference with labor progression.
- Safety and minimal adverse effects on both the mother and the fetus.
- Rapid onset, reliable effect, and simple methods of administration.
- Invasive analgesia should be administered by anesthesiologists who provide continuous monitoring.
Types of Labor Analgesia
Non-Pharmacological Analgesia
Pain during labor is closely related to psychological tension. Prenatal education is important for emphasizing that childbirth is a natural physiological process. Adequate psychological support is considered helpful in obtaining maternal cooperation. Non-pharmacological methods include breathing techniques, whole-body massage, continuous presence and emotional support from family members or doulas, as well as acupuncture or acupoint electrical stimulation. These methods can be used alone or in combination with pharmacological approaches.
Systemic Opioid Analgesia
Opioids can be administered intermittently via intravenous or intramuscular injection or through patient-controlled analgesia (PCA). However, the analgesic effect of opioids on contraction pain varies significantly among individuals, and the overall efficacy is limited. Potential adverse effects include maternal oversedation, nausea, respiratory depression, delayed gastrointestinal emptying, reduced fetal heart rate variability, and neonatal respiratory depression. Commonly used opioids include pethidine, fentanyl, remifentanil, and nalbuphine.
Neuraxial Analgesia for Labor
This method involves inducing sensory blockade in specific regions of the body through the use of local anesthetics. Techniques include spinal anesthesia, epidural anesthesia, or combined spinal-epidural anesthesia. Neuraxial analgesia offers several advantages, such as a precise level of pain relief, minimal motor blockade, ease of drug dose adjustment, and a prolonged duration of analgesic effect. However, excessively high anesthesia levels may result in severe respiratory depression. Other potential complications include hypotension, toxic reactions to local anesthetics, allergic reactions, post-dural puncture headache, nerve injuries, intrapartum fever, and prolonged second-stage labor. Given these potential side effects and complications, anesthesiologists are responsible not only for mastering the technical aspects of anesthesia and adhering to standard operational protocols but also for being well-prepared to manage emergencies related to complications.