Pain Management in Patients: When to use Fentanyl, Morphine, or Ketamine

We have all had patients who are in pain and as a provider we need to treat them as appropriately as possible. We have many types of medications at our disposal to help us with this feat but when is the most appropriate times to use each of them? Well we have the 7 rights of medication administration:

  1. Right patient
  2. Right drug
  3. Right dose
  4. Right time
  5. Right route
  6. Right reason
  7. Right documentation

You can see one of the medication rights is “right drug” so that means we need to know what we are pushing and how it works in the body. We are going to go over two opiates and one dissociative anesthetic medication.

Fentanyl

Fentanyl is an analgesic medication (relieves pain) and is a synthetic opioid. Opioids act on three main opioid receptors: Mu, Kappa, and Delta.

Mu1: Responsible for analgesia effects, sedation, and bradycardia.

Mu2: Responsible for euphoria and respiratory depression.

Delta: Spinal analgesia and respiratory depression.

Kappa: Spinal analgesia, sedation, and respiratory depression.

Fentanyl is a short acting opioid agonist medication that primarily focuses on the Mu receptors but can still work on the Delta and Kappa receptors. It is highly lipid soluble which means it takes effect a lot quicker than other opioid medications, like morphine. Fentanyl is 80-100 times more potent than morphine and is dosed in micrograms (mcg).

Loading dose: 1-2 mcg/kg (25-100 mcg) IV

Duration of action- 30-60 minutes

Half life- 2-4 hours

As with all opioids, you have chances of sending the patient into respiratory depression, causing bradycardia, and dropping BP. These effects are not as common in comparison to other opioid narcotics. Fentanyl is reported to release less histamine than morphine which decreases the probability of the patient’s BP to drop.

Morphine

Morphine is an analgesic medication and a natural opioid and is not man made like fentanyl is. Like fentanyl, morphine has a higher affinity to interact with the Mu receptors. Morphine also binds to post synaptic receptors on neurons and causes them to be overstimulated which reduces the amount of pain signals sent to the central nervous system. As mentioned in the Fentanyl section, morphine causes histamine release. Histamine acts on the vasculature of the body and causes dilation which subsequently drops BP.

Loading dose: 0.1-0.15 mg/kg with a maximum dose of 10 mg IV

Duration of action: 4-5 hours IV

Half life: 2-4 hours

Now for both fentanyl and morphine, we can use Narcan if too much is given. Narcan works on blocking the opioid receptors and making it so the medication can’t bind to them.

But there is issues with giving Narcan to patients as they can develop non-cardiogenic pulmonary edema (which we have a post on).

Ketamine

 Ketamine is considered a dissociative anesthetic drug. This drug makes the patient detach from themselves and from the environment. This drug disrupts the neurotransmitter (brain chemical) glutamate. Glutamate is involved with learning, memory, emotion, pain recognition. It can exhibit sympathomimetic activity which can lead to rapid heart rate and elevated blood pressure. The drug was originally produced as a fast acting general anesthesia but now in today’s world, the drug is being introduced for pain control, depression management, veterinary practices, EMS ambulances, psychiatric patients with excited delirium syndrome, septic shock patients, hypotension patients, and even burn patients. 

Dose: 0.1 mg/kg IV

Dose IN Pediatrics: 1mg/kg IN (do not administer more than 0.5 mL into each nare)

Duration: 15-30 minutes IV

Half life: 45 minutes

When to Use Them

Now that we know more about the medications, we need to know the best time to use them. Fentanyl has shown to be more effective and more superior than morphine in many studies. Fentanyl also has a lower chance to drop BP in comparison to morphine as stated earlier. Fentanyl and morphine can be used for most traumatic injuries but if you have an option to use one over another in an emergency setting and you are worried about hypotension, opt for fentanyl over morphine. Fentanyl has a lower duration than morphine so it can be used for short durations with the patient but you will need to give it more frequently. Morphine has a longer duration and subsequently doesn’t need to be given as often. We also have heard of the term MONA for treatment of patients experiencing a STEMI. As times have progressed, we have a new acronym, FONA which replaces morphine with fentanyl. We give pain medications to not just be nice to the patient and allow them to be in less pain, but to help the body with the infarction. When the patient relaxes, there is a drop in catecholamine release (such as epinephrine and norepinephrine) which decreases stimulation of the alpha-1 receptors which in turn drops the heart’s overall workload. As discussed previously, morphine has a higher probability to dropping the patient’s BP which then causes a decrease in venous blood return to the heart and consequently a worse preload. This decreases cardiac output which is a no-no especially in patients with an inferior STEMI with RVI. Fentanyl usually does not cause as much of a drop in BP or bradycardia in comparison to morphine but it still has a possibility. So you need to use it cautiously if the patient has an inferior STEMI with RVI and ensure their systolic BP is well above 90 mmHg. You can help reduce the chances of hypotension and bradycardia by mixing the fentanyl in saline to dilute it and SLOWLY pushing it if needed but still use caution. If you are very keen on still administering fentanyl in a patient with an inferior STEMI with RVI, it may be a decent idea to have fluids going to offset any vasodilation that may occur. Now if you live in the USA, you have heard of the opioid crisis and many people have a resistance to opioids, so now we can talk about our friend ketamine. This is the preferred medication for extreme burns or crush injuries and for moderate to high levels of pain. Ketamine will actually increase your blood pressure and heart rate which can be very beneficial. A lot of this comes down to personal preference and medications available.

Image result for ketamine for everything meme

This site is meant to be used for educational use only. We strive to push evidence based medicine with no bias to help you obtain all the important information. You should always follow your protocols that have been set in place. 

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References

Chen, A., & Ashburn, M. (2015, October 13). Cardiac Effects of Opioid Therapy. Retrieved February 07, 2021, from https://academic.oup.com/painmedicine/article/16/suppl_1/S27/2472479

Fentanyl – Drug Summary. (n.d.). Retrieved February 07, 2021, from https://www.pdr.net/drug-summary/Abstral-fentanyl-1395

Pandharipande P, McGrane S. Pain control in the critically ill adult patient. Post TW, ed. UpToDate. Waltham, MA: UpToDate Inc. http://www.uptodate.com. Accessed July 11, 2019.

Pasternak, G., & Pan, Y. (2013, September 27). Mu opioids and their receptors: Evolution of a concept. Retrieved February 07, 2021, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3799236/

Ramos-Matos, C. (2020, April 13). Fentanyl. Retrieved February 07, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK459275/

Rosenbaum, S. (2020, October 05). Ketamine. Retrieved February 07, 2021, from https://www.ncbi.nlm.nih.gov/books/NBK470357/

Vahedi, H., Hajebi, H., Vahidi, E., Nejati, A., & Saeedi, M. (2019). Comparison between intravenous morphine versus fentanyl in acute pain relief in drug abusers with acute limb traumatic injury. Retrieved February 07, 2021, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6264977/

3 thoughts on “Pain Management in Patients: When to use Fentanyl, Morphine, or Ketamine

  1. jbailxy says:

    Thanks a lot for this. Unfortunately, we’re somewhat behind in the UK and do not have access to ketamine or fentanyl. Would have been interesting had you included specific circumstances where fentanyl may be more beneficial than morphine, e.g. inferior MI. Additionally, intranasal ketamine- opinions, especially for rapid paediatric analgesia (burns, etc). Take care mate!

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