Opiods Essay

Opiods are the most popular class of drugs used for post-cesarean analgesia. They are most useful in treatment of somatic pain. Use of morphine, diamorphine, fentanyl, sufentanil, meperidine, nalbuphine and buprenorphine is well documented. The various opiods differ in their potency and severity of side effects. A discussion of the merits and de-merits of each is beyond the scope of this article. The common minor side effects include nausea, vomiting, pruritus, shivering and urinary retention. Respiratory depression, especially late-onset, is a more dreaded complication.

ROUTES OF OPIOD ADMINSTRATION

CENTRAL NEURAXIAL – INTRATHECAL / EPIDURAL

Intrathecal opiods exert analgesic action by acting on the μ-receptors of the spinal cord. The onset and duration of action are dependent on lipid solubility. Lipid soluble opiods like fentanyl and sufentanil diffuse more from the cerebrospinal fluid into the neural tissue. This translates to faster onset and shorter duration of action when compared to less lipid soluble opiods like morphine, diamorphine and buprenorphine. However, sufentanil has a longer duration of action than fentanyl due to its higher μ-receptors affinity. Very small amounts of opiods are required via the central neuraxial route as compared to the larger doses required systemically. Hence secretion into breast milk is not a cause for concern5.

Intrathecal morphine is the gold standard for post-cesarean analgesia. Palmer et al.6 found a ceiling analgesic effect with intrathecal doses of morphine above 75 μg. Higher doses increased the severity of pruritus, while other common opioid-related side effects, such as nausea and vomiting, did not have any dose-dependent relationship. They suggest an intrathecal dose of 0.1 mg...

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...e epidural space contains an extensive venous plexus which is engorged in pregnancy. Therefore, the intravascular reabsorption of opioids following epidural administration is extensive. Though the epidural doses of opiods are higher than that given intrathecally, they are, nevertheless, safe in breastfeeding12.

Data from a dose-response study by Palmer et al13 data indicate that the degree and duration of analgesia of epidural morphine increase in a dose-related manner from 0 to 3.75 mg. A single bolus dose provides good analgesia for the first 24 hours. An extended release formulation EREM (extended release epidural morphine) is also available.

Shorter acting opiods like fentanyl (2 mcg / ml) and sufentanil (0.8 mcg / ml) are used in nurse-controlled or Patient Controlled Epidural Analgesia (PCEA) techniques in combination with low-dose local anesthetic agents.