Opioids for Post Operative Pain Management
Mar 03, 2025
Blue pill or red pill? ๐๐ด
The use of opioids for the management of acute postoperative pain is a mainstay in the recovery room with well-documented evidence of their effectiveness. But what exactly do opioids do, and why would you choose one over the other? Let us break it down for you! ๐ง ๐ก
Firstly, it's important to establish that not all opioids are the same! Some are organic ๐ฑ, and some are synthetic ๐งช, and are differentiated by the name they are given. Opiates are naturally occurring products such as morphine and codeine (deriving from the opium poppy ๐ธ) and opioids are synthetic products such as oxycodone and fentanyl (they are made in a lab! ๐ญ)
The pharmacokinetics of opioids is quite complex, but at a basic level it's important to understand that the main receptor they act on is the Mu (μ) receptors. Mu are mainly involved in nociception โก, however they can affect stress ๐ฐ, temperature ๐ก๏ธ, respiration ๐ฌ๏ธ, endocrine activity ๐งฌ, gastrointestinal activity ๐ฝ๏ธ, memory ๐ง , mood ๐, and motivation ๐ช as well. You can see here how some of those opioid side effects come to be!
Opioids are Mu receptor agonists ๐ง๐ฌ and act as a neuromodulator - that is, they change the way the brain perceives and responds to noxious stimuli. The cause of the pain is still present, it’s just that the brain doesn’t care so much about it for the time being! ๐งโ๏ธ
There are a wide variety of opioids available these days, and many are used within anaesthesia ๐. For the purposes of pain management, the following are the main opioids used in acute pain management due to their potency โก, duration of action โณ, and clearance ๐งช.
Morphine ๐
Not so commonly used anymore, but still worth a mention! Morphine use has declined due to the common occurrence of side effects with its use. There are higher rates of nausea ๐คข and vomiting ๐คฎ, pruritus (itching) ๐ and constipation ๐ฝ with morphine use when compared with other opioids. Its onset time is also slower than that of other opioids, with an onset time of 5-10 minutes post-IV administration โฑ๏ธ. Morphine tends to be used in patients who have allergies or reactions to other opioid analgesics.
Oxycodone ๐
One of the most commonly used analgesic opioids these days. Oxycodone has an onset time of 2-3 minutes post-IV administration ๐ and a lengthy duration of action โณ. It is well-researched ๐, and well-tolerated by most patient cohorts. These days it is generally considered as “first line” when considering opioid analgesia.
Fentanyl ๐
Fentanyl has a rapid onset time of approximately 1 minute โฑ๏ธ, however, a much shorter duration of action when compared to oxycodone. Fentanyl tends to be used for elderly and/or frail patients ๐ต๐ด, and those with significant renal impairment ๐ง or who are particularly co-morbid โ ๏ธ, as well as those with an allergy or intolerance for oxycodone.
Naloxone ๐จ
Naloxone is a Mu receptor antagonist ๐, working to counteract the effects of opioid agonism in the case of overdose. For all patients receiving opioid analgesia, naloxone should be ordered on the medication chart ๐, and should be readily available in the recovery room/ward environment for immediate administration in the case of over sedation ๐ค and respiratory depression ๐ฌ๏ธ.
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References:
Ding, Z., Wang, K., Wang, B., Zhou, N., Li, H., & Yan, B. (2016). Efficacy and tolerability of oxycodone versus fentanyl for intravenous patient-controlled analgesia after gastrointestinal laparotomy: A prospective, randomized, double-blind study. Medicine, 95(39), e4943. https://doi.org/10.1097/MD.0000000000004943
Lambert, D.G. (2023). Opioids and opioid receptors; understanding pharmacological mechanisms as a key to therapeutic advances and mitigation of the misuse crisis. BJA open. V6. DOI: 10.1016/j.bjao.2023.100141
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