Systemic Opioids During Labor
25. Should M.T. be given a systemic analgesic rather than epidural analgesia?
If possible, CNS depressants should be avoided during labor because they can compromise fetal vital functions.100,101 Nevertheless, if an analgesic is deemed necessary, then an agent that meets the following criteria should be chosen: (a) provides adequate pain relief; (b) has little effect on the course or duration of labor; and (c) affects fetal vital signs minimally during labor, delivery, and postpartum phases. Meperidine and fentanyl meet most of these criteria and, therefore, are frequently preferred over other opioids in obstetrics when given in small, frequent parenteral injections or through a PCA.102,103 As with all opioid analgesic use, close monitoring of the patient for analgesia and untoward effects is essential.
Although meperidine and fentanyl seem to have only minimal residual effects on the neonate at analgesic doses, adverse effects, such as respiratory depression, can still occur.104,105 According to an early neonatal neurobehavioral scale, meperidine broadly depressed most measured neonatal activities on the first and second days of life.106 Nevertheless, if the contractions are very strong, erratic, and prolonged early in the course of labor (as with M.T.), a short-acting analgesic (e.g., meperidine) could be useful to blunt the labor pain and calm the mother, so that she can regain control over her contractions and conserve her energy for the actual delivery.
Butorphanol (Stadol) also has minimal effects on fetal and neonatal function and is a reasonable alternative to meperidine or fentanyl in this situation.107 All potent analgesics should be administered IM or subcutaneously because IV administration is associated with more neonatal and fetal depression because of the high peak serum concentration achieved by this route.108,109 Pentazocine has similar effects as butorphanol, but is seldom used because of local tissue reactions at the site of IM or subcutaneous injections. Pentazocine and butorphanol are mixed opiate-agonists/antagonists and can precipitate acute withdrawal reactions in some opiate-dependent individuals. As a result, these drugs need to be used cautiously, if at all, in the opiate-addicted population (see Question 27).
If neonatal respiratory difficulties are manifested as a result of opioid analgesics administered during labor, they can be reversed with naloxone (Narcan). For M.T., meperidine 50 mg IM was given with good clinical response. As with all opioid analgesics, the dose has to be adjusted after an evaluation of the patient's history and clinical findings. Analgesic doses always should be individualized for the specific patient.
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