Passive leg raising (PLR) is a technique I am going to cover extensively as I am writing a lecture where this will be a hot subtopic. I’ve covered it before on my blog and instagram. It’s all in the effort to NOT drown our patients in IV fluids when they’re hypotensive. Turns out that performing a passive leg raise and looking to see if the blood pressure goes up does not work for assessing fluid responsiveness.
When I was a younger whipper snapper in training, I thought I could perform the passive leg raise assessments by picking up some legs, looking at the BP increase and call it a day. Boy, was I wrong. I learned some further principles behind why I was wrong but today (8/28/20) I found the data as to how wrong I was. Needless to say, I was very wrong. Did I mention I was wrong? Glad we’re clear. I wasn’t born knowing everything and still have a ton to learn.
In this paper they placed a swan in their patients and did some other stuff that I will cover at a later date. As some background and to define certain principles, a person who is fluid responsive is one who receives an amount of fluid, in this case PLR is approximately 300cc, is one who has an increase in their stroke volume or cardiac index/output. It is NOT someone who’s blood pressure goes up just because they got fluids. Looking at the sensitivity and specificity of looking at the arterial blood pressure versus the measures generated via thermodilution, you can see how looking at the BP is absolute poop and should not be used.
The authors found that the area under the curve of PLR-induced changes in arterial pulse pressure was 0.65. That is not good at all. As a point of reference, when they looked at changes in cardiac index and changes in end-tidal CO2 (EtCO2) the area under the curve was 0.98 and 0.93 respectively. Both of those are considered to be outstanding. Looking at the pulse pressure, not so much.
I altered a copyrighted photo to help illustrate the area under the curve. I’ll take it down if I upset anyone. At the end of the day I’m just trying to save lives. Haney Mallemat @criticalcarenow has done some great coverage on End-tidal CO2 so check out his work on the matter. Hope this helps so that you do not perform a passive leg raise test and call it positive because the blood pressure goes up.
Learn more about Resuscitation and Fluid Responsiveness HERE.
Monnet X, Bataille A, Magalhaes E, et al. End-tidal carbon dioxide is better than arterial pressure for predicting volume responsiveness by the passive leg raising test. Intensive Care Med. 2013;39(1):93–100. doi:10.1007/s00134-012-2693-y
Link to Abstract