Determining the Optimal Dose of Intrathecal Morphine for Post-Cesarean Analgesia

Using spinal or epidural anesthesia (known as neuraxial blocks) is the gold standard for pain control during childbirth, especially in cesarean sections (C-sections). However, many women experience moderate to severe pain after a C-section, which can affect both their physical and emotional well-being, and even impact their ability to care for their newborn. Unfortunately, this pain is often not treated effectively, which can lead to increased sensitivity to pain or even chronic postoperative pain. One effective way to manage this pain is by giving opioids directly into the spinal fluid (subarachnoid space). This method allows doctors to use much smaller doses than would be needed if the same medication were given through a vein, which also helps avoid many of the common side effects of opioids like respiratory depression, nausea, pruritus, and constipation. Common opioids used in this setting include fentanyl, sufentanil, and morphine. These drugs behave differently depending on their chemical properties. For example, drugs that are more fat-soluble work faster, while those that are less fat-soluble tend to last longer. Morphine, which is less fat-soluble than the others, provides strong and long-lasting pain relief. When injected spinally, its effect can last 18-24 hours, with the pain relief starting 1-2 hours after the injection. Its performance is comparable to that of epidural anesthesia or nerve blocks. Researchers have studied a wide range of spinal morphine doses (from 20 to 500 micrograms) to find the most effective and safest dose. Most of these studies are small or use set doses without clear reasoning. Recently, a method called sequential allocation has become popular for finding the best dose more accurately. About the Study This research aims to find the ideal dose of spinal morphine when it's given with a fixed amount of fentanyl and varying doses of ropivacaine (a local anesthetic) during spinal anesthesia for C-section in healthy full-term part