Essential Guide to Analgesics: How They Work and Their Side Effects in the OR and Ward
Introduction
To everyone currently rotating through the Department of Anesthesiology,
thank you for your hard work.
When rotating through anesthesiology, the sheer number of analgesics can be
overwhelming, can't it?
To put it simply,
there are only two types of analgesics: narcotic (opioid) and non-narcotic.
Even without the added stress of an unfamiliar anesthesiology rotation,
trying to memorize them one by one blindly
is likely to be difficult.
In this article,
let's organize our thoughts
regarding the analgesics used in clinical practice!
Narcotic (Opioid) Analgesics: Powerful Analgesia and Side Effects
Opioids act on opioid receptors in the brain to
exert a powerful analgesic effect.
Because they are highly effective,
caution is required regarding side effects such as respiratory depression and nausea.
1. The Adjuster During Surgery
-
Remifentanil
Characteristics: A drug with an extremely short duration of action (about a few minutes).
When the infusion is stopped, the effect wears off immediately.
Usage: Ideal for fine-tuning the level of analgesia via continuous infusion.
Points to note: Because the effect wears off quickly, be sure to have a plan for postoperative pain management.
-
Fentanyl
Characteristics: A very potent opioid, approximately 100 times stronger than morphine.
It has a rapid onset of action, and blood concentration increases with multiple doses, making it effective for postoperative pain management.
Usage: Used during anesthesia induction, for sudden stimuli during surgery, and for postoperative pain relief.
Precautions: Respiratory depression is common. Please monitor breathing closely even after the patient has awakened.
2. Postoperative and Ward Pain Management
-
Morphine
Characteristics: This is the standard opioid medication.
Its effects are relatively long-lasting, persisting for about 4 hours.
Usage: Used for postoperative pain management (PCA) and in hospital wards.
Precautions: Side effects such as respiratory depression, nausea, vomiting, and pruritus are common.
Caution is required for patients with poor renal function, as the drug tends to remain in the body.
-
Buprenorphine
Features: It has a potent effect.
It comes in various forms, such as sublingual tablets and patches.
Usage: Used for the management of postoperative and chronic pain.
Precautions: The duration of the effect varies significantly depending on the type.
-
Tramadol
Features: Its effect is milder than morphine.
It is a drug that has both opioid and non-opioid effects.
Usage: Used as an oral medication for moderate to mild pain and chronic pain.
Precautions: Concomitant use with other drugs may increase the risk of serotonin syndrome.
3. Opioid Antagonists: The "Emergency Stop Button" for When Things Go Wrong
These are drugs used when side effects from opioids,
especially respiratory depression, become too severe.
-
Naloxone
Characteristics: A drug that antagonizes the effects of opioids.
It binds strongly to opioid receptors and blocks the effectiveness of pain relievers.
Usage: It is administered in emergencies when narcotic analgesics have been overused or when a patient experiences respiratory depression.
Precautions: Because it also cancels out the analgesic effect, the patient may suddenly feel intense pain.
Even if respiratory status improves after administration, you must be careful of re-sedation, where respiratory depression recurs once the drug's effect wears off.
Since naloxone is a short-acting agent, continuous observation is required even after administration.
Non-narcotic (non-opioid) analgesics: Supporting opioids
Used in combination to reduce opioid side effects and
safely enhance analgesic efficacy
(multimodal analgesia).
3. [Non-opioid] Essential drugs to increase safety
-
Acelio (Acetaminophen)
Features: It has analgesic and antipyretic effects, and is a highly safe drug with few side effects.
Usage: It is widely used as a regular pain reliever before and after surgery.
Precautions: It is processed by the liver.
Overdose can cause liver dysfunction, so please be careful.
Strict adherence to dosage and intervals (4-6 hours) is required.
-
Ropion / Diclofenac
Features: A type of NSAID (anti-inflammatory pain reliever).
Particularly effective for pain accompanied by inflammation.
Usage: Frequently used for postoperative pain management.
Precautions: Gastrointestinal bleeding and renal function are at risk of being affected.
In principle, it should not be used for patients with bleeding risks or poor renal function.
Summary for Today
It is easier to understand analgesics by dividing them into narcotic and non-narcotic categories.
Acelio and Ropion are essential when used in combination with opioids to enhance efficacy while reducing side effects.
Understand the characteristics of each drug and side effects to watch out for to ensure safe pain management.
I have posted the "Anesthesiology Residency Notebook" below, which is easy to carry and allows you to review essential anesthesiology knowledge. I found it very useful during my residency, so please give it a try.
References
・Anesthesiology Residency Check Notebook, 7th Revised Edition
・"Pharmaceutical Guidelines: Analgesics, Antagonists, and Pain," Japanese Society of Anesthesiologists
・"Clinical Anesthesiology Textbook," Kiyoshi Morita, Nakayama Shoten
Disclaimer
This article is for general educational purposes only and does not recommend specific medical procedures or judgments. Always follow your institution's policies and the guidance of senior physicians when managing actual patients.
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