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Analgesia is the loss or modulation of pain perception. It can be (1) local and affect only a small area of the body, (2) regional and affect a larger portion of the body, or (3) systemic. Analgesia is achieved by the use of hypnosis (suggestion), systemic medication, regional agents, or inhalational agents.

Anesthesia is the total loss of sensory perception and may include loss of consciousness. It is induced by various agents and techniques. In obstetrics, regional anesthesia is accomplished with local anesthetic techniques (epidural, spinal) and general anesthesia with systemic medication and endotracheal intubation.

The terms analgesia and anesthesia are sometimes confused in common usage. Analgesia denotes those states in which only modulation of pain perception is involved. Anesthesia denotes those states in which mental awareness and perception of other sensations are lost. Attempts have been made to divide anesthesia into various components, including analgesia, amnesia, relaxation, and loss of reflex response to pain. Analgesia can be regarded as a component of anesthesia if viewed in this way.

The use of techniques and medications to provide pain relief in obstetrics requires an expert understanding of their effects to ensure the safety of both mother and fetus.

It may be academic to argue that pain should be defined as the parturient's response to the stimuli of labor, because agreement on a definition of pain has eluded scholars for centuries.

Nevertheless, it should be appreciated that the “pain response” is a response of the total personality and cannot be dissected systematically and scientifically. Physicians are obligated to provide a comfortable or at least a tolerable labor and delivery. Many patients are tense and apprehensive at the onset of labor, although they may have little or no discomfort. The physician must be knowledgeable of the options for pain relief and respond to the patient's needs and wishes.

The evolution of pain in the first stage of labor originally was described as involving spinal segments T11 and T12. Subsequent research has determined that segments T10–L1 are involved. Discomfort is associated with ischemia of the uterus during contraction as well as dilatation and effacement of the cervix. Sensory pathways that convey nociceptive impulses of the first stage of labor include the uterine plexus, the inferior hypogastric plexus, the middle hypogastric plexus, the superior hypogastric plexus, the lumbar and lower thoracic sympathetic chain, and the T10–L1 spinal segments.

Pain in the second stage of labor also is produced by distention of the vagina and perineum. Sensory pathways from these areas are conveyed by branches of the pudendal nerve via the dorsal nerve of the clitoris, the labial nerves, and the inferior hemorrhoidal nerves. These are the major sensory branches to the perineum and are conveyed along nerve roots S2, S3, and S4. Nevertheless, other nerves, such as the ilioinguinal nerves, the genital branches of the genitofemoral nerves, and the perineal branches ...

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