Morphine is not used routinely for labor epidurals because it is characterized by which of the following?

Morphine is not used routinely for labor epidurals because it is characterized by which of the following?

• A. Increases Uterine Tone
• B. Causes Excessive Neonatal Respiratory Depression
• C. Has A Slow Onset
• D. Decreases Uterine Blood Flow

Answer: (C)

The key idea is how neuraxial opioids differ in onset due to their chemistry. Morphine is hydrophilic and diffuses slowly from the epidural or intrathecal space into the CSF and systemic circulation, so the analgesic effect takes longer to develop compared with lipophilic opioids like fentanyl. In labor, where rapid and predictable pain relief is important, this slow onset makes morphine less desirable as a routine epidural analgesic. It does provide prolonged relief, but the delay in onset plus potential for longer-lasting opioid effects on mother and baby are drawbacks. While neonatal respiratory depression is a concern with neuraxial morphine due to placental transfer, the defining practical limitation for routine use during labor is its slow onset.

The key idea is how neuraxial opioids differ in onset due to their chemistry. Morphine is hydrophilic and diffuses slowly from the epidural or intrathecal space into the CSF and systemic circulation, so the analgesic effect takes longer to develop compared with lipophilic opioids like fentanyl. In labor, where rapid and predictable pain relief is important, this slow onset makes morphine less desirable as a routine epidural analgesic. It does provide prolonged relief, but the delay in onset plus potential for longer-lasting opioid effects on mother and baby are drawbacks. While neonatal respiratory depression is a concern with neuraxial morphine due to placental transfer, the defining practical limitation for routine use during labor is its slow onset.