Epidural opioid analgesia

Epidural opioid analgesia is a technique to reduce pain from labour. Opioids act by interacting with specific receptors in the dorsal horn and dorsal roots of the spinal cord. Most often, it is given in combination with bupivacaine as opioids alone are not able to provide adequate pain-relief. In combination with local anaesthetics, pain relief is rapid, shivering is decreased and motor blockade is more dense.The common side effects are urinary retention and pruritus.[1]

Mechanism of action

Pain is transmitted in the dorsal horn of spinal cord via C fiber neurons. At the pre-synapse of these neurons, neuropeptides are released. Tachykinin, a neuropeptide, binds to the post-synaptic neurokinin receptors and cause depolarization and changes in second messengers. In the spinal cord, opioids act by reducing the release of neuropeptides at presynaptic level and by hyperpolarizing the membrane of dorsal horn neurons at the post-synaptic level.[2]

Properties of opioids in epidural space

Epidural opioids can produce analgesia without motor or sympathetic blockade. Lipid insoluble opioids stay in the cerebrospinal fluid for a long time and hence give a longer supply of analgesia. However, in this case, the onset of analgesia is delayed. The lipophilicity of an opioid is determined by its octanol-buffer partition coefficient. The concentration of an opioid in the spinal cord is determined by the net difference between its rate of uptake and distribution in the vascular and subarachinoid spaces.

gollark: (technically it also has some code to force it to respond to an instant-lose/instant-win situation)
gollark: It is funny that people keep losing to a fairly trivial piece of code which just decides how good a move is by playing 100 *entirely random games* starting from it and seeing how many it wins.
gollark: Okay, I am now decreasing my estimate of your programming competence.
gollark: I don't know if there's a general strategy. The main thing to exploit is that the AI can't really respond to two threats at once.
gollark: I don't think you saw the number I just posted.

References
  1. Cunningham, Gary F. William's Obstetrics (24 ed.). McGraw Hill. p. 517.
  2. OA, Leon-Casasola (October 1996). "Postoperative epidural analgesia: What are the choices?". Anaesthetic Analgesia. 63 (4): 863–74. PMID 8831337.
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