Managing Pain During Childbirth
In the past, the pain experienced during childbirth was thought to be comparable among women, gradually and predictably worsening as labor progresses. Today it's known that there is variability in the location, intensity, quality, and predictability of labor pain.
Described as severe to excruciating and intolerable by many women, labor pain is among the most agonizing of pain syndromes. In a classic 1984 study, Robert Melzack, PhD, found that only 9% of primiparae and 24% of multiparae rated their labor pain as mild to moderate, 30% of both groups rated it as severe, 38% of primiparae and 35% of multiparae reported having very severe labor pain, and 23% of primiparae and 11% of multiparae rated it as horrible or excruciating. Other research suggests that only 1% of women don't feel labor pain. Many controllable factors are believed to contribute to the suffering associated with labor pain, including insufficient analgesia, hunger, fatigue, lack of maternal self-confidence, absence of a support person, and inadequate childbirth preparation.
How effective are nondrug pain management options? Can IV opioids be safely used?
Since physiologic, emotional, and motivational differences among patients affect their analgesic needs, effective pain management during labor and delivery must be individualized. The use of nondrug methods, such as controlled breathing, imagery, effleurage, heat, and laboring in water are often promoted as the safest and most acceptable methods for controlling pain during childbirth. While these nondrug methods may be effective in helping the laboring patient relax and distract herself from the pain, there are few well-designed studies demonstrating that these methods actually reduce pain. The fact that a laboring woman maintains a controlled expression of pain or avoids analgesic use does not necessarily signify that she feels less pain. Many women report having experienced excruciating labor pain when nondrug measures were used exclusively.
Today, women have many safe pharmacologic choices for managing pain during childbirth, including some IV opioids, which may be used with or without nondrug methods. The mu-agonist opioid analgesics, such as fentanyl, morphine, and hydromorphone, are recommended for pain during labor.
Although commonly administered for labor pain, meperidine isn't recommended because it can produce dysphoria rather than analgesia in laboring women. Betty Kuhnert, PhD, and her colleagues have studied the adverse effects of meperidine and its metabolite, nonmeperidine, on the fetus and neonate. Normeperidine, which can produce CNS toxicity, has a half-life of 15 to 20 hours in adults. After multiple doses of meperidine during labor, maternal plasma levels indicate accumulation of both meperidine and normeperidine. Fetal accumulation of normeperidine occurs also, and since plasma protein binding doesn't approach adult levels until the first year of life, the mean half-life of normeperidine in neonatal tissues is up to 85 hours. When repeated doses of meperidine are given, uptake into fetal tissues is continuous-without time for clearance between doses. Fetal accumulation of normeperidine has been implicated in neonatal respiratory depression following meperidine use during labor.
Despite their widespread use for pain management during childbirth, agonist-antagonist opioids, such as nalbuphine and butorphanol, aren't recommended as first-line drugs for any type of pain. Some clinicians use agonist-antagonist opioid analgesics believing they cause less respiratory depression than the mu-agonist opioid analgesics. At equianalgesic doses, however, all opioids produce equal respiratory depression. Though agonist-antagonist opioids are limited in their ability to produce respiratory depression, they're limited in their ability to produce analgesia as well. When they reach their analgesic ceiling, dosage increases fail to produce any increased analgesia. That's why they're especially inappropriate for severe, escalating pain.