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INTRODUCTION

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For cesarean delivery, neuraxial (epidural, spinal, and combined spinal/epidural) techniques are preferred to and are more greatly used than general anesthesia (GA) for cesarean delivery. This is attributed to appreciation of the risks of airway complications during GA in pregnant patients, the limited neonatal drug transfer, and the ability of the mother to be awake to experience childbirth. The lower maternal morbidity and mortality with the use of neuraxial anesthesia than with GA has also been a primary motivator for that transition toward greater use of neuraxial anesthesia for cesarean delivery.

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NEURAXIAL ANESTHESIA

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Because afferent nerves supplying abdominal and pelvic organs accompany sympathetic fibers that travel in the sympathetic trunk (T5 to L1), a sensory block that extends from the sacral dermatomes to T4 is needed for cesarean delivery. Assessing the level of sensory blockade using pinprick identifies a level of blockade that is several segments higher than that identified by light touch. Of equal importance to the extent of the block is the density of the block which is drug concentration and dose dependent. Because the undersurface of the diaphragm (C3 to C5) and the vagus nerve may be stimulated by surgical manipulation during cesarean delivery, maternal discomfort such as shoulder pain, nausea, and vomiting may occur despite a T4 level of blockade. Neuraxial opioids help minimize these symptoms.

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Spinal Anesthesia

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Spinal anesthesia is the most commonly used anesthetic technique for cesarean delivery since it provides rapid onset of dense neural blockade that is more profound and more predictable than that provided with an epidural technique. The small amount of local anesthetic utilized during spinal anesthesia results in minimal drug transfer to the fetus and in negligible maternal risk for systemic local anesthetic toxicity.

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The continuous spinal anesthetic technique utilizing microcatheters (27–32 gauge) is no longer used in the United States because of concern about cauda equina syndrome and catheter breakage. The technique is used occasionally in the setting of an intentional or unintentional dural puncture with an epidural needle.

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Bupivacaine is the agent of choice for spinal anesthesia for cesarean delivery because it produces a dense block of long duration. In the United States, spinal (hyperbaric) bupivacaine formulated as a 0.75% solution in dextrose 8.25% is the most widely used formulation. Plain (isobaric/hypobaric) bupivacaine 0.5% is less frequently used. The anesthesia characteristics and hemodynamic changes are similar when plain or hyperbaric bupivacaine is used. The baricity of the local anesthetic can, on the other hand, affect the spread of the blockade. Head-down patient tilt can result in cephalad spread of hyperbaric local anesthetic.

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The dose of intrathecal bupivacaine that has been successfully used for cesarean delivery ranges from 4.5 mg to 15 mg. In general, pregnant patients require smaller doses of spinal local anesthetic than nonpregnant patients as a result of the smaller cerebrospinal fluid (CSF) volume ...

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