OK! As promised, here’s my very first #Tweetorial on #ketamine. It comes to you in 6 parts:
1 Mechanism
2 Intermittent bolus dosing
3 Procedural sedation
4 Low dose IV infusion
5 High dose IV infusion
6 Contraindications/warnings
#medtwitter #pharmacy #FOAMed #FOAMcc
Because I’m a hospital pharmacist, we’re going to focus on IV ketamine. Ketamine has other modes of administration (looking at you nasal-spray-for-depression) so feel free to add your own experiences below!
When an injury occurs, the dorsal horn releases glutamate which binds to the NMDA receptor. In some patients, this signals a cascade which eventually leads to the nervous system being stuck in a state of “high reactivity."
This can lead to opioid tolerance, opioid-induced hyperalgesia, and basically everything that makes chronic pain hard to treat.
Ketamine is an NMDA antagonist which means it can intervene in this pathway. It also has effects on mu receptors, muscarinic receptors, and others which is why it can also be used for acute pain and sedation. It’s a jack of all trades!
Dose: up to 0.35 mg/kg every 30 minutes or so
Good for: status asthmaticus causing confusion (pt is agitated and won’t keep the BiPAP on), severe pain not responding to opioids (to get a patient out of that spiral/crisis), painful dressing changes in opioid tolerant patients
Dose: 1-2 mg/kg
With propofol: 0.5-0.75 mg/kg ketamine + 0.5-0.75 mg/kg propofol = “ketofol”
Works GREAT in kids (>3 months). Oh, and turn off the TV in the room before giving it. Especially if it's turned to creepy cartoons.
Before we jump into IV infusions, let’s talk about units.
Ketamine for infusion can be dosed in 2 ways: mcg/kg/min or mg/kg/hr. Both are seen in the literature. Make sure you know which one your EMR recognizes and make sure it matches the pump entry.
If you don’t, you might end up accidentally running 0.5 mcg/kg/min which is….. homeopathic.
1 mg/kg/hr = 16.6 mcg/kg/min
The interesting and challenging thing about ketamine is that there are 3 distinct levels of patient experience that are dose-dependent:
If you titrate your low-dose pain infusion too high, they start to dissociate and have hallucinations, nightmares, etc.
If you are starting an infusion for pain, it’s important to educate the patient so they can tell you if they start to experience *weirdness*
If emergence occurs, don’t panic! Turn off the infusion and the effects should go away in 10-20 minutes (think procedural sedation). If the patient is distressed, you can give a small dose of benzo which will take them out of it/forget what happened.
So who should get a sub-anesthetic ketamine drip? I’ve had the best experience in patients with high opioid tolerance who have acute-on-chronic pain (post-op or trauma patients with high opioid tolerance).
I have also had positive experiences in palliative/end of life care (especially in advanced cancer). If dosed correctly, the patient can be awake and interact with family while achieving adequate pain control.
So, what’s the dose?
Bolus: up to 0.35 mg/kg
Infusion: 0.05-1 mg/kg/hr (~1-16 mcg/kg/min)
Titration: 0.1-0.2 mg/kg/hr every 30 minutes to goal pain score
These numbers (and most of this thread) come from the consensus guidelines on ketamine use from the American Society of Regional Anesthesia and Pain Medicine, The American Academy of Pain Medicine and the American Society of Anesthesiologists (PMID: 29870457).
From my own experience, I have found that most patients end up in 0.3-0.6 mg/kg/hr (5-10 mcg/kg/min) range. Much higher usually leads to emergence and much lower usually does nothing. But each patient is different! Isn’t pain management fun??
OK let’s transition to sedation. I’m going to start off by saying that I am not an anesthesiologist. My experience comes from difficult-to-sedate vented patients in the MICU/SICU.
In my experience, ketamine is usually the 3rd or 4th medication being added to these patient’s regimens to keep them vent compliant or to keep them from pulling the tube or flinging themselves out of bed (or both).
This one is pretty simple. The dose for sedation 1-5 mcg/kg/hr (17-90 mcg/kg/min). The titration instructions are similar to the above: Increase by 0.25-0.5 mg/kg/hr every 20-30 minutes to goal RASS.
Oh, and all of these patients need to be on the vent.
The important thing to remember is how to get the patient OFF of the ketamine drip. For that, we need to go back to our handy picture:
If you titrate the ketamine drip off as you would a fentanyl or midazolam drip, you might end up leaving your patient in the “dissociation/emergence” area for some amount of time which is not pleasant for the patient.
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