Pharmacologic Pain Relief during Labor
MECHANISM OF ACTION
Meperidine Hydrochloride is ideally used during labor because of the fact that it not only produces analgesic effect but at the same time it has additional sedative and antispasmodic actions. Thus, it is effective for pain relief, helps in cervical relaxation and provides a feeling of euphoria and well-being.
DOSE and ROUTE
Demerol can be given either intramuscularly or intravenously; 25 mg IV, 50-100 mg IM every 3 to 54 hours. It can also be given epidurally but this route is used less frequently.
- Demerol once given intramuscularly (IM) begins to act at about 30 minutes and about 5 minutes after intravenous (IV) administration. The drug’s duration of action is 2 to 3 hours.
- This medication crosses the placenta, thus, it can cause respiratory depression in a fetus. However, it takes about 2 to 3 hours after maternal administration, either IM or IV, before the fetal liver activates the drug into the fetal system. Thus, Demerol is given 3 hours away from birth to allow the peak action of the drug to have passed by the time of birth.
- If Demerol is given early it may slow labor contractions.
- When a narcotic is given to the mother, a narcotic antagonist should be available for administration of infant at birth. Naloxone Hydrochloride (Narcan) is a narcotic antagonist that counteracts the effect of narcotic analgesic.
When narcotics are administered by introducing a catheter into the spinal canal, intrathecal narcotics are used. Drug such as morphine when injected into the spinal canal provides excellent pain relief for labor. It takes effect as early as 15 to 30 minutes but these injections are not as effective in reducing the pain of the actual birth. Thus, they may be supplemented with a pudendal block in late labor.
Possible side effects of intrathecal morphine:
- Intense pruritus – can be treated with an IV of dipenhydramine (Benadryl) if it becomes too uncomfortable
- Nausea and vomiting
Regional anesthesia is the administration of a local anesthetic to block specific nerve pathways. This type of pharmacologic relief during labor is not introduced directly into maternal circulation, thus, minimal effects due to the uptake of these drugs by a fetus when compared to those of systemic agents. Aside from that, regional anesthesia administration allows a woman to be completely awake and aware of the labor and birthing process. If an infant is born with toxicity from a regional anesthesia, which seldom happens, an exchange transfusion at birth may be required. This is to remove the anesthetic from the infant’s bloodstream. Another way of managing this condition is through the performance of a gastric lavage to remove a great deal of anesthetic.