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Morphine, fentanyl, sufentanil, and epinephrine have been widely and safely used as adjuvants for labor analgesia and for cesarean delivery anesthesia. An introduction of alpha2-adrenergic agonist dexmedetomidine (DEX) in obstetric anesthesia could provide the unique analgesic benefit without side effects of opioids such as pruritus, urinary retention, hyperalgesia, and respiratory depression. The addition of DEX to neuraxial local anesthetics produces a significant prolongation in the duration of sensory and motor blockage and reduction in post cesarean opioid requirement.1 Various animal studies have been conducted using intrathecal DEX at a dose range of 2.5 to 100 μg without any neurotoxicity, similarly, without any postoperative neurological deficit in human studies.
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CONTROVERSY ON NEURAXIAL DEXMEDETOMIDINE
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Approval by the U.S. Food and Drug Administration (FDA) in 1999, DEX is indicated for sedation of ventilated patients in an intensive care setting and sedation for non-intubated patients prior to and/or during surgical procedures.2
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FDA defines DEX as pregnancy category C medication and suggests that it should be used during pregnancy ONLY if the potential benefits justify the potential risk to the fetus. Of note, although clonidine has been extensively investigated as an adjunct to neuraxial opioids, FDA placed a “black box” for using clonidine in pregnant women due to excessive hypotension and sedation. In the last decade, accumulating clinical data have demonstrated the profound analgesics and safety profile of DEX in obstetric anesthesia. Still, more data are needed to support the use of neuraxial DEX in obstetric anesthesia.
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PHARMACOLOGY AND APPLICATIONS
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Pharmacology and Applications2
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Highly selective alpha2-adrenergic agonist, the mediator for its analgesic effects.
Large dose of DEX can cause hypertensive episode due to stimulation of alpha2B receptor.
Some studies demonstrated neuroprotective effects of intrathecal DEX.3
Octanol: water partition coefficient 2.89, steady volume of distribution of 118 liters.
Protein binding 94%.
Maternal/fetal ratio 0.77,4 high placental retention with negligible placental transfer.
Preservative free.
For neuraxial route administration, the onset time for DEX is about 15 minutes; duration of action is about 6 to 8 hours.
Terminal elimination half-life: 2 hours when given intravenously.
Can be used for postoperative shivering, replacement of neuraxial opioids to stop pruritus, recurrent breakthrough labor pain, and postsurgical pain.
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CLINICAL PRACTICE AND INDICATIONS
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