r/pharmacology • u/nowlistenhereboy • Jun 14 '21
What is the reason why intravenous epinephrine must be diluted more than intramuscular in the setting of cardiac arrest?
Just curious what the physiological reason is that 1:1000 epinephrine is not to be used for cardiac arrest/active CPR.
3
u/Mediocre_Doctor Jun 14 '21
I don't like this proportion nomenclature. It's better to state the concentration.
The 1 mg/mL epi has led to fatal med errors:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2826951/
During a day surgery ENT procedure, the surgeon requested local anesthetic for injection (specifically lidocaine 1% with epinephrine 1:100,000) and was handed a pre-drawn syringe. The surgeon injected the medication into the surgical site. Immediately afterward, the patient experienced a cardiac arrhythmia leading to cardiac arrest. Despite full resuscitation measures, the patient died.
Information gathered after the incident indicated that the syringe contained epinephrine 1 mg/mL (1:1,000) intended for topical use, rather than the local anesthetic for injection that was requested.
IIRC the patient recieved up to 30 mg of epinephrine.
1
u/nowlistenhereboy Jun 14 '21
Yes but my question is specifically regarding patients who are already in cardiac arrest. It is explicitly stated in protocols that the more concentrated epi cannot be substituted for use in ACLS resuscitation.
My question is if there is an actual physiological reason why the higher concentrated epi would be contraindicated in a patient who already has no heartbeat and you are doing active CPR?
2
u/pking8786 Jun 14 '21 edited Jun 14 '21
So for IM injection you need a better circulation to get it into the blood stream. Even giving IV Adrenaline (epi) you generally need to follow it with a 50ml bolus of saline to push it in during CPR (especially if using lower limb cannula).
Just read you didn't specifically mention IM, and I get that 1mg is 1mg, but dropping 1ml IV of 1 in 1000 can be damaging to blood vessels, and there's less room for error when it's concentrated, which is why our guidelines recommend an "IV expert" give IV Adrenaline in the UK resuscitation guidelines
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1
u/hockeystar357 Jun 14 '21
It's so the full dose makes it to circulation. A few years ago there was a shortage of the premixed epinephrine syringes used during codes. Many hospitals ended up simply giving the regular concentration followed immediately by 10 mL NS. So the dilution has nothing to do with the physical aspects of the drug but rather making sure the body receives a full dose.
11
u/[deleted] Jun 14 '21
A more concentrate formulation allows for a smaller volume in muscle which is easier to administer.
A long slower infusion is required IV to reduce fatal hypertension, pulmonary and cerebral edema. For example 0.5ml of 1:10,000 IV for anaphylaxis is easier to administer safely than 0.05ml 1:1000. For cardiac events approx 10ml 1:10,000 is infused slowly which is safer and easier than 1ml 1:1000, especially when dose volume isn't a concern.