60: Obstetric Analgesia and Anesthesia

CHAPTER 60 Obstetric Analgesia and Anesthesia

6 What are the characteristics of the ideal local anesthetic for use in labor? Discuss the three most common local anesthetics used in obstetric anesthesia. How does epinephrine affect the action of local anesthetics?

The ideal local anesthetic for labor would have rapid onset of action, minimal risk of toxicity, minimal motor blockade with effective sensory blockade, and a minor effect on uterine activity and placental perfusion. Bupivacaine and ropivacaine are most commonly used for obstetric epidural analgesia. Lidocaine and chloroprocaine are most commonly used for obstetric surgical anesthesia.

Bupivacaine, an amide, is the most commonly used local anesthetic for obstetric analgesia. Pain relief after epidural injection is first noted by the patient after 10 minutes; 20 minutes is required to achieve peak effect. Analgesia usually lasts approximately 2 hours. Dilute solutions provide excellent sensory analgesia with minimal motor blockade. During early labor 0.125% bupivacaine or even lower concentrations is often adequate, whereas a 0.25% concentration may be required during the active phase of labor. Because bupivacaine is highly protein bound, its transplacental transfer is limited. Addition of epinephrine (1:200,000) to bupivacaine speeds its onset and lengthens its duration of action but also increases the intensity of motor blockade (which is not desirable in laboring patients).

Lidocaine is also an amide local anesthetic used in concentrations of 0.75% to 1.5% for sensory analgesia, but it crosses the placenta more readily than bupivacaine and produces more motor block than bupivacaine; thus it is rarely used outside the operating room. Analgesia lasts approximately 45 to 90 minutes and is usually apparent within 10 minutes.

2-Chloroprocaine is an ester local anesthetic. Onset of analgesia is rapid and lasts approximately 40 minutes; this short duration limits its usefulness in labor. Chloroprocaine 3% is frequently used to increase the anesthetic level quickly for cesarean section or instrumental vaginal delivery. Chloroprocaine has a very short half-life in maternal and fetal blood because it is metabolized by plasma esterase; thus it may be the safest of the commonly used local anesthetics.

May 31, 2016 | Posted by in ANESTHESIA | Comments Off on 60: Obstetric Analgesia and Anesthesia
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