Friday, January 24, 2014

Ignore This Fixed-Dose Philosophy For Morphine

Emergency physicians are legendary for poor control of pain in the Emergency Department, with many factors challenging optimal care.  One solution – and one I’ve taught in the ED – is to use a weight-based approach to dosing.  This works out to 0.1-0.15 mg/kg of morphine or equivalent as an initial starting dose.

These authors gather 300 patients – 100 non-obese, 100 obese, and 100 morbidly obese – who all received a 4mg intravenous dose of morphine for median initial pain levels of ~8 on a scale to 10.  Upon reassessment a median of ~1 hour after administration, the median pain level in all groups had fallen to 2 or 3.  This somewhat tailors along with other work, which observed substantial numbers of patients with adequate response following even doses of morphine of less than 4mg.  The authors therefore conclude:
“BMI does not predict the analgesic response to a single dose of intravenous morphine in the ED. This is true even for patients who are morbidly obese. We suggest using fixed doses rather than weight-based doses of morphine for acute pain in obese patients.”
However, this retrospective study fails to capture and control for many of the other factors associated with opiate response, including age, substance abuse history, pre-hospital pain control – along with all the other contextual factors lost through chart abstraction.  Additionally, patients at Maricopa Medical Center in Phoenix are not hardly generalizable to, well, nearly anywhere in the world.

Ultimately, this limited study leads to an erroneous, and potentially harmful conclusion that weight-based doses are unnecessary.  Aggressive, titrated or weight-based, pain control is not in any fashion refuted by this work.

“Analgesic response to morphine in obese and morbidly obese patients in the emergency department.”


  1. Unfortunately it is often difficult -- for any number of reasons -- to give appropriate doses of morphine. Hydromorphone is a bit easier to dose properly. 4mg of morphine is a fine dose, so long as it's given early & often. I love the work done on pain protocols -- nurse-driven administration based on need, not intermittent dosing. Takes us out of the equation, empowers and engages the nurse. I frequently tell the nurse to give 4mg as often as the patient needs it, or do the hydromorphone 1+1 -- which is brilliant, because nurses hate the hassle of "wasting" meds.

  2. I think the best conclusion from this study is that a near placebo dose of morphine gives a near placebo response to pain regardless of BMI. I imagine acetaminophen (paracetamol) arm or even a true blinded placebo would have given the same response.

    A fixed dose of analgesia is a bit silly. Patients regardless of BMI have different responses and it is always best to titrate to effect. Forget the pain score... just ask if they need more analgesia.

    Brian Doyle, MD FACEM FACEP

  3. Great point re: placebo effects. I agree – a non-narcotic dose of analgesia would probably have similar scores in a properly controlled and blinded trial.

    I agree with Seth, taking the physician out of the loop so nurses can use a handful of repeated doses is an excellent solution – whether 4 or 8mg of morphine or 1mg of hydromorphone.

    1. I'm not sure that simply writing a PRN order is the solution. Unfortunately, a number of studies from the nursing literature (e.g. Link Nurses' personal opinions about patients' pain and their effect on recorded assessments and titration of opioid doses. ) have suggested that RNs may respond variably to PRN orders, owing to both confusion about how to interpret such orders, as well as (like physicians) personal biases.

      The EMS literature certainly suggests that simply writing a PRN order (i.e. a standing morphine administration protocol) doesn't necessarily lead to large increases in provision of opiods. In our study ( Link Paramedic attitudes regarding prehospital analgesia. ), we found that even in systems where medics could give 0.1 mg/kg of morphine without talking to "med control," many preferred to administer smaller doses, in part due to outdated education, culture, and various other disincentives.

    2. I agree -- I don't think we should be "simply writing a PRN order." And it doesn't work with every nurse. For the nurses I have a good relationship with -- trust in both directions -- I order a first round, and talk to the nurse. Explain that I ordered the first dose of meds, and then give a "verbal PRN" -- so we work together with them driving the pain control. I can always add more pain meds on top.

  4. Also I agree with Seth, I tell the nurse to give 4 mg morphine as often the patient needs, young, older, adult, obese or not. we haven't registered any problem!. We love this!!!

  5. I find the weight based dosing extremely effective allowing to get on top of the pain two-three times quicker than using homeopathic doses as used to be the case in our department. Another advantage of this approach, I find that the total dose of morphine required to control pain is half that would be needed using homeopathic dosing and often it wouldn't control pain at all. The result is happier patient, happier nurse and everyone can get on with their business. I'm yet to see the patient who was not happy with with weight based approach. I've been using weight based dosing for some three years and initially, yes there was some apprehension about sometimes seemingly large dose, however it was always easy to get nurse on your side once you explained the rationale.
    I too often give "verbal PRN" instructions and vast majority of nurses are comfortable with that once they feel your support. Alternatively I enter PRN orders on the chart and explain/comment how to use it - works just as great.
    I also often get the patient involved and explain thatfif they tell us they need analgesia it makes our job easier and their pain easier to manage.
    So, strategies mentioned by Seth and Bryan put together along with weight based dosing work fantastic.



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