BASIC KETAMINE INFUSION ANAESTHESIA

We’ve previously mentioned total ketamine anaesthesia in our post on war surgery, using a simple i.v. drip. Today, I talked to a friend and colleague of mine with extensive experience from MSF (Médecins sans frontières – Doctors without borders). Here’s his handy tips on ketamine infusion anaesthesia in the developing world.

Ketamine i.v. drip infusion
Mix 500mg of Ketamine in a bag of 500 mL saline, to get ketamine 1 mg/ml. Get the patient’s weight in kilograms. Let the starting point for your maintanence dose of ketamine i.v. drip infusion be [the patient’s weight i kg] drops per minute. This will equal around 4 mg/kg/hr. Adjust to effect.

Ketamine induction cocktail
You will still need an induction dose of ketamine 1-2 mg/kg i.v. For children (or grown-ups) where you can’t easily get i.v. access while they’re awake, you can use a dose of ketamine 5-8 mg/kg i.m. for induction. You can also mix in atropin and a little midazolam in the same i.m. syringe to give them the full cocktail i.m. induction.

Remember, while ketamine is probably the most stable among any of the quick acting induction agents we have, ketamine still needs to be dose adjusted for bled-out, unstable patients. And, obviously, tips like these are not medical advice, but a tip to be used at your own discretion and with your own clinical judgement. Anyway, thanks for the tips, Jonas!

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8 Responses to BASIC KETAMINE INFUSION ANAESTHESIA

  1. Minh Le Cong says:

    Thomas, I love you! This is great. An American paramedic was asking me about how to do ketamine sedation in the helicopter without an infusion pump and I wrote back about my time in Africa, using ketamine drips like what your friend here has mentioned.
    I did not describe it so nicely like you have here so have sent him a link to your article. keep up the great blogging, Sir Viking!

  2. minh le cong says:

    can you check that dosing rate with your friend, Thomas.
    4mg/kg/min seems a bit high

    • Thomas D says:

      Glad you liked it, Minh! I really enjoyed Jonas’ tips as well. Handy bush tips!

      Sorry about the dosing rate. I didn’t check back with him, as this was a simple case of me thinking one thing and writing another. It’s mg/kg/hr not mg/kg/min. My bad.

      Thanks for pointing that out – and with an almost British sense of understatement! I set it straight in the post as well. I’m glad someone’s vigilant around here.

      About the rate, I found this paper listing ketamine 2 mg/kg/hr, whereas anaesthetists at my hospital advocate 5-6 mg/kg/hr. So 4 mg/kg/hr sounds like a decent starting rate for your maintanence dose. Season to taste.

  3. Alex says:

    Apologize for the late reply:
    Considering pharmacodynamics with main effect wearing off in 15-20 mins,
    and with induction of 1mg/kg faster than slower I’d
    go with the 4 mg/kg/hr dosis and adjust it.
    2mg/kg/hr really seems to small a dose.
    3-4 to start and 5-6 if necessary…

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  6. Dr Daniel Albert says:

    Computer modelling indicates that an infusion of about 1.4 times the induction dose, per hour will keep the analgesia and sedation at a constant level for about one hour (thereafter, the infusion rate needs reducing a little as more protected spaces start to fill up with the drug).

    This relies on giving the induction dose slowly — say 10mg/min in an adult. It will then take about 3 minutes to get analgesia and up to 10 minutes to get anaesthesia. There should be no rush, since you will not be going through an unprotected airway stage (as with e.g. propofol).

    Say you achieved good anaesthesia with 140mg in a 70kg man, you would then give 1.4 x140=196 mg/hour (2.8 mg/kg/hour). If it took 210mg to put the same patient to sleep, he would need 1.4x240mg= 336 mg (4.8 mg/kg/hour).

    Which, I think, means that your estimates are about right.

    • Thomas D says:

      Thanks to both Alex and Dr. Albert for looking into the dosing and commenting on it here! It’s just another proof that social media in medicine/FOAM works. Great to get a confirmation on the dosage and rate of infusion.

      As said earlier – season to taste: Adjust up if the patient seems light, hold back if he seems too deep. It’s one of the great things about working with quick-acting and quickly metabolising drugs – the patient’s clinical response is your feedback loop.

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