Monday, February 9, 2015

Assess the pipes, Carotid VTI and fluid responsiveness

Clinical Scenario:

You are working in the ED when a 75 yo F hx of CHF, DM presents with fever, cough, and hypoxia and hypotension. You are concerned for sepsis with presumed pneumonia as the source. You initiate volume resuscitation and start broad spectrum antibiotics.  Your  patient's BP initially responds to fluids, but now after your 3L your patient is still hypotensive. You perform bedside US of the inferior vena cava (IVC) with equivocal findings. You wonder, is there another way to perform rapid bedside ultrasound for volume responsiveness?  You remember a recent paper about carotid velocity time integral (VTI) , and begin to investigate

Literature review:
It seems that predicting volume responsiveness is the never-ending tale in critical care medicine, as numerous methods have been proposed over the past several years with varying degrees of success. With the expansion of ultrasound, measuring IVC collapsibility has been one of the more popular methods utilized in the emergency department. However, measuring the IVC can often be limited by body habitus, excessive intra-abdominal gas, respiratory variation, and operator experience. (1) Measuring IVC collapsibility at greater than 50% has been shown to correlate with a CVP of less than 8mmhg, and a lower CVP has been associated with volume responsiveness, but a higher CVP does not exclude volume responsiveness. (1) A recent paper by Marik et al described the novel use of Carotid VTI and passive leg raise (PLR) as a marker of volume responsiveness in hemodynamically unstable patients.  The benefit of  PLR is that it produces a hemodynamic response similar to a 200-300ml bolus, is relatively easy to perform, and is rapidly reversible.
 Courtesy Ultrasound Podcast
 By combining PLR with dynamic ultrasound, Marik et al sought to create the ideal non-invasive method of determining volume responsiveness.  They demonstrated that a 20% increase in carotid VTI had a sensitivity and specificity of 94% and 86% respectively for predicting volume responsiveness (a patient with a stroke volume increase of greater than 10% was considered volume responsiveness). 
This study was limited in that it was nonrandomized, nor blinded, and complete data was available for only 34 patient. (2)  Mike and Matt from the Ultrasound podcast provide an excellent review and explanation on how perform VTI that you can find here @ Ultrasound podcast

Take home points:
Studies have shown that only 50% of hemodynamically unstable patients are volume responders. Appropriate fluid resuscitation in sepsis is associated with improved outcomes, while excessive fluid administration is associated with increased ICU LOS and mortality. Determining fluid responsiveness is difficult but VTI combined with PLR appears to have both a high specificity and sensitivity for predicting volume responsiveness.  More studies will be needed to demonstrate validity of this method. 

Submitted by Louis Jamtgaard, PGY-3 @Lgaard
Faculty Reviewed by Deb Kane 


1)Nagdev A et al . Emergency department bedside ultrasonographic measurement of the caval index for noninvasive determination of low central venous pressure. Ann Emerg Med. 2010 Mar;55(3):290-5. doi: 10.1016/j.annemergmed.2009.04.021. Epub 2009 Jun 25.

2) Marik P et al. The use of bioreactance and carotid Doppler to determine volume responsiveness and blood flow redistribution following passive leg raising in hemodynamically unstable patients.
Chest. 2013 Feb 1;143(2):364-70.

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