In the video I quoted a paper [1] which stated that “wide open” flow rate through an 18g IV was 20 – 30cc/min. Two different people reached out to me concerned that there is another paper [2] that quotes a “wide open” flow rate through an 18g IV as being 98.1cc/min. The concern was that if flow rate is higher, we would be giving a much higher dose of epinephrine per minute which could have some potential untoward outcomes.
The Dirty Epi Drip:
- 1mg of epinephrine placed into a 1L saline bag and run through an IV
- This is not perfect, but buys time until a pump or push dose epinephrine can be made
- It is called dirty epi drip for the simple reason that it is mixed at the bedside as opposed to getting it from the pharmacy
- In addition, it is not precise, and you don’t have an exact idea of how much medication you are giving
- Again, a more precise method would be through a pump or as push-dose
- Infusion rates will be dependent on height of the fluid bag above the patient, the size of the IV catheter, pressure placed on the IV bag, and micro- vs macro-drip set
- If needing this, I highly recommend using it with a micro drip setup
Micro vs Macro Drip Setup
- Both macro and micro drip setups connect the IV bag to a drip chamber
- Macro and micro drip refer to the diameter of the needle where the drop enters the drip chamber
Image From Mometrix (Link is HERE )
- This is then connected to the IV tubing which can either attach to an IV catheter directly or to a connecter attached to the IV catheter
- Macro-drip tubing delivers 10 to 20gtts/mL whereas micro-drip tubing delivers 60gtts/mL
- To calculate the drops per minute, the formula is total volume (mL) divided by time (min) multiplied by the drop factor (gtts/mL) which equals the IV flow rate in gtts/min
What IV Packaging Say for IV Flow Rates
Paper #1: Pierce et al (The one I quoted – Micro Drip Setup) [1]:
- Gravity-driven micro drip infusion sets are designed such that the number of drops per minute equals the milliliters/hr (i.e. A drip rate of 60drops/min delivers 60mL/hr)
- When the flow rate increases to the point that a continuous column of fluid replaces discrete drops in the chamber (“Wide-open”) it is no longer possible to visually quantify flow rate
Image from [1]
- In the “wide-open” state the rate of medication/volume delivery will vary depending on two factors:
- Height of the infusate bag relative to the patient
- IV catheter size
- What They Did: Used a micro-drip infusion set, plugged into a bag of normal saline, then connected to a high-flow stopcock at the distal end
- Looked at IV catheters ranging from 14 to 22g
- Fluid meniscus height of the normal saline was fixed at 60 to 120cm above the outflow point
- The roller clamp on the infusion set was in the fully open position (“wide open’) for all experiments
- Results:
Numbers Rounded to Closest Whole Number
- Bottom Line:
- Volume of fluid delivered by gravity-driven micro-drop infusion under “wide open” conditions is dependent on both the catheter size and the fluid column height
Paper #2: Reddick AD et al (Macro-Drip Setup)[2]:
- What They Did:
- Compare the flow rates of IV access catheters with different physical characteristics:
- Pressure bag
- Needle-free IV access connector
- 1L of 0.9% saline solution was connected to each cannula at a height of 130cm above the infusion point (This is higher than the previous study – Range of 60 to 120cm)
- Compare the flow rates of IV access catheters with different physical characteristics:
- Results:
- Bottom Line:
- The width of a peripheral IV cannula will have a predictable effect on the flow rate of fluids with 14g being the fastest and 22g being the slowest
- The addition of a connector to the IV will slow down the flow rate being given
Discussion:
- Flow through an IV will be dependent on your setup (For an 18g Peripheral IV):
- “Wide open” micro drip at 120cm above your patient, to gravity ≈ 30 to 35cc/min
- “Wide open” with macro drip with no connector at 130cm above your patient, to gravity ≈ 98.1cc/min
Original Video:
Follow Up Video:
Clinical Take Home Point
- The best way/most precise way to give vasoactive medications to a patient is through a pump. Giving as a push dose is an excellent secondary option if a pump is not immediately available
- It is not a great idea to do dirty epi drips, simply because there are just too many external factors that make it impossible to know how much epi you are exactly giving
- The only situation I can see using a dirty epi drip is if you can’t stay at the bedside and there are no infusion pumps available (i.e. this is really a suboptimal approach)
- If administering as a drip without an infusion pump, you must take into account a number of issues:
- It is not precise, hence the name “dirty”
- The measured height of the IV bag above the patient is also important and needs to be emphasized
- Use a micro-drip setup to gravity which will give you a flow rate of about 30 to 35cc/min “wide-open”
- Don’t use a macro-drip setup
- If using a macro-drip setup to gravity the flow rate is closer to 100cc/min without a connector “wide-open”
- If using a macro-drip setup to gravity the flow rate is closer to 80cc/min with a connector “wide-open”
References:
- Pierce ET et al. Medication and Volume Delivery by Gravity-Driven Micro0Drip Intravenous Infusion: Potential Variations During “Wide-Open” Flow. Anesth Analg 2013. PMID: 23400996
- Reddick AD et al. Intravenous Fluid Resuscitation: Was Poiseuille Right? EMJ 2011. PMID: 20581377
Post Peer Reviewed By: Anand Swaminathan, MD (Twitter: @EMSwami)
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