Can the Inferior Vena Cava Ultrasound guide our fluid administration in the ED? Of course it can!
So I was getting on the plane to Las Vegas for Essentials 2012, on my iphone was the latest from Mike and Matt of the Ultrasound Podcast. Up pops Mike “the Rock” Stone interviewing my buddy, Haney Mallemat; these two ultrasound gurus discuss some ultrasound soundbites, but then… They both state that IVC ultrasound is useless for determining fluid responsiveness. It is worth taking a listen to that episode if you have a moment. So how can two brilliant guys get it so wrong? They just had their focus knob turned all the way to the right. Lets optimize their settings with an EMCrit Podcast.
Mechanically Vented Patients
Now, most of the podcast bashed IVC in spont breathing patients, but there was some overflow disparaging of IVC in mech vented patients, so let's get that out of the way first. There is plenty of literature for these patients. Put them on a temporary, high tidal volume (10 ml/kg). Get an IVC shot and if it increases in size by 15-18% (depending on the study), the patient is fluid responsive.
- Intensive Care Med. 2004 Sep;30(9):1740
- Intensive Care Med. 2004 Sep;30(9):1834
- Neurocrit Care. 2010;13:3
- J Trauma. 2007;63:495
- J Intensive Care Med. 2011 Mar-Apr;26(2):116
Spontaneously Breathing Patients
Now as the two ultrasound masters allude to, there have been a few studies showing IVC ultrasound assessment merely correlates with CVP (it actually correlates with respirophasic CVP) and then use that fact to write off the IVC. Now we have maligned CVP as a marker of fluid responsiveness so IVC is crap as well, right?
There is evidence for the use of IVC as a marker of fluid status. In patients with ultrafiltration for congestive heart failure (Intensive Care Med. 2010 Apr;36(4):692-6) as well as fluid removal during hemodialysis (Clin J Am Soc Nephrol 2006;1:749 and Nephrol Dial Trans 1989;4:563). There was also a trauma study showing that fluid resuscitated patients with IVC collapse were more likely than those without to have recurrent hypotension (J Trauma. 2007 Dec;63(6):1245).
There was also a study just published in the Aussie EM Journal. This study was severely limited by the fact that none of these patients had any significant IVC collapse and the criterion standard is not a test any of us consider useful for cardiac index measurements; further, looking at the tables, some of the responder group did not seem to have any sig. increase in their CI in response to fluid. (Emerg Med Aust 2012;24:534).
And a meta-analysis study showing IVC's relation to fluid status (AJEM 2012;30:1414).
Luckily, there was also a recently published study with the table below (Crit Care 2012;16:R188).
Here is figure 1 from the study
Here is the area under the cure (AUC); you notice there are points with much higher specificity.
Hot off the presses, this study is more reassuring: (Shock 2013;39(2):155)
It lends additional credence to the use of dynamic IVC for fluid responsiveness.
It's not Fluid Responsiveness, It's Fluid Tolerance!
This is the crux of the matter. In the ED, we want to give a bunch of fluid, but not if we are going to cause pulmonary edema. The term, fluid tolerance, is a perfect description of this idea. Responsiveness is great, but all we want to make sure of is that we are not going to do harm with additional fluid. This term was introduced to me by an amazing ED Intensivist named Chad Meyers. His lecture on this stuff from the ALLNYCEM Conference will go up very soon. IVC ultrasound is the perfect guide to fluid tolerance. CVP is fine as well, but why expose the patient to a central line.
Mike discussed a study he was part of that showed where you measure the IVC matters (Acad Emerg Med. 2010 Jan;17(1):96-9). Make sure you don't measure at the diaphragm; measure distal to the hepatic veins or at least 3 cm past the diaphragm.
The Predicting Fluid Responsiveness Chapter at Crashingpatient.com has a bunch more info on all of this
Here is the video for how to perform the IVC ultrasound:
Now Mike is an amazing doc–he offhandedly mentions throughout the podcast, none of this crap matters until you have already given 6 liters of fluid or so. Amen brother. But a lot of folks are too scared to do that, hence the need for IVC ultrasound. Now there are unfortunately also references to the fluid depleted patient showing signs like cracked lips and a generally sere appearance; yeah, not so much. If we could assess volume status on vasodilated septic patients, that would be swell, but all of sepsis literature stands against our ability to do so.
Want to know why these studies may show results all over the map? It's probably b/c the IVC is tough to measure unless you are good as demonstrated here.
Passive Leg Raise
Instead of IVC, Mike and Haney recommend using the passive leg raise with echo assessment of cardiac output before and after. You only need to do this once to realize its utility exists merely on paper. Much better is simply…
Giving a Fluid Challenge
Check cardiac index using echo, give a liter of fluid, and then recheck cardiac index.
Up until this week, I would have advocated considering using NICOM bioreactance, but a study just published makes me a bit leery until more data are in.
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