So, some of you may have seen one of my earlier posts about the myth of low-flow renal failure in CHF (http://wp.me/p1avUV-2J), and be aware of my growing conviction that elevated venous pressures – too often sought after – are actually fairly nefarious.

So a couple of recent and very interesting pieces to add to the puzzle. First, I listened to an awesome podcast about

ICP by Wilson (http://intensivecarenetwork.com/wilson-monro-kellie-2-0/) which is an absolute MUST LISTEN to anyone in acute care.  One of those moments where all of a sudden someone shines a light in a dark corner you’d never really paid much attention to. Really, really cool and game-changing, at least certainly in the physiology model I play with in my head every time I deal with a patient who is genuinely sick.  In a nutshell, just to make sure everyone actually goes to listen to it, Wilson explains how you can get venous hypertension simply from increased cerebral blood flow… And we happen to be faced with one of the most common causes of increased CBF almost every day: hypoxia.  So when you are dealing with neurological injury (CVA/SAH/post-arrest), the danger of hypoxia (remember the concept of avoiding secondary injury of hypoxia, hypotension and hyperthermia?) lies not only in the obvious cellular lack of oxygen, but also that it is the most potent stimulus for increased CBF, and the main issue being that our venous system is simply not designed to accommodate that kind of traffic, resulting in venous hypertension without (yet) truly elevated ICP.

I’m also faced with the recurrent problem of having to be somewhat “rude” when not following suggestions from nephrology consultants in some of  my ICU patients, when they advise fluids or holding diuretics in patients with renal failure AND elevated venous pressures (as assessed by a large, non-varying IVC – in the absence of reversible causes such as tamponade, tension pneumo, etc…).  It isn’t their fault. They aren’t looking at the venous system (not bedside sonographers yet – “looks dry” on exam/gestalt is as much as you’ll get), and they don’t hold venous hypertension in high (or any) regard (yet, hopefully).

So I was totally psyched when, during a really cool conference (#BMBTL) organized by @EGLS_JFandMax, my highly esteemed colleague and friend Andre Denault (not yet on twitter…working on him) gave a talk – here is a segment:

And here is the article he is referring to:

Fluid+balance+and+acute+kidney+injury

So it isn’t like this is unknown, it simply isn’t at the forefront of our clinical mind-set, for the most part. Congestive renal failure and congestive cerebral failure are simply not things we routinely diagnose, though they MUST be just as as prevalent as congestive heart failure, which we all clearly believe in…

So just another angle to keep in mind, both when resuscitating and when managing patients with organ dysfunction of almost any sort…

 

Love to hear your thoughts!

…and if you like this kind of stuff, if you are an acute care doc, you’ll want to come to CCUS2015! http://wp.me/p1avUV-bG

Philippe

 

Jon-Emile Kenny (of the awesome heart-lung.org fame) says:

This is a great topic for review Philippe!

I have come across this problem, certainly on more than one occasion. I was first introduced to the idea of renal venous pressure and renal hemodynamics as a house-officer at Bellevue Hospital in New York. Dr. Jerome Lowenstein published work on this phenomenon as it pertained to ‘Minimal Change Syndrome.” He used to ‘wedge’ the renal vein and measure renal interstitial pressure in these patients and measured the response to diuresis. It was very enlightening and made me feel more comfortable given more diuretics in such patients. [Am J Med. 1981 Feb;70(2):227-33. Renal failure in minimal change nephrotic syndrome].

I am also glad that you bring up the cranial vault in this discussion, because I have often wondered if the encapsulated kidneys behave in a similar way. That is, as renal interstitial volume increases from edema, if there is some point on their compliance curve [like the cranium] where there is a very marked increase in renal interstitial pressure? I have found a few articles which loosely address this idea, but would be interested if anyone else knew of some. In such a situation, there would be a ‘vascular waterfall’ effect within the kidneys whereby the interstitial pressure supersedes the renal venous pressure [like West Zone II in the lungs]; then, renal blood flow would be driven by a gradient between MAP and renal interstitial pressure [not renal venous pressure]. I know of one paper that addresses this physiology in dogs, and finds the vascular ‘choke point’ to be in the renal venous system and not Bowman’s space.

What’s even more interesting, is that when renal interstitial pressure is elevated is that the kidney behaves in a sodium avid state [i.e. urine electrolytes will appear ‘pre-renal’] and this physiology has been known for at least a century!

Lancet. 1988 May 7;1(8593):1033-5. Raised venous pressure: a direct cause of renal sodium retention in oedema?

There is no good explanation as to why this occurs, but one I read is that the high renal interstitial pressure tends to collapse the afferent arteriole and the decrease in afferent arteriole trans-mural pressure which facilitates renin secretion [just like low blood pressure would]; but that would require a fairly high renal interstitial pressure unless the MAP was concomitantly low.

Again, what I must caution [and I’ve been personally wrong about this] is the reflex to give diuretics when seeing a ‘plump IVC’. When I was treating a woman with mild collagen-vascular-related pulmonary arterial hypertension, community-acquired pneumonia with a parapneumonic effusion and new acute renal failure, I assessed her IVC with ultrasound. It was plump an unvarying. I lobbied the nephrologist to try diruesis based on the aforementioned reasoning, but was very wrong. Her kidneys took a hit with lasix. What got her kidneys better was rehydration. In the end, what happened was her mild PAH raised her venous pressure and the hypoxemic vaso-constrction from her new pnuemonia only made that worse. Her right heart pressures, venous pressure and probably renal venous pressure were undoubtedly high. But I didn’t take into consideration her whole picture. She had a bad infection, had large insensible losses and had not been eating and drinking. She was hypovolemic, no doubt, despite her high right heart pressures. Fortunately, her pneumonia resolved and fluids brought her kidneys back to baseline.

Thanks again for another thought-provoking topic

 

dr.uthaler says:

hi, i am an anaesthesist / intensivist from austria. very interesting topic. at the esicm meeting last month in barcelona there was a very good session about hemodynamic monitoring focusing on the right heart and the venous system. the lectures about the guyton approach to fluid management were a big eye opener and certainly changed my approach to patients in the real life icu world. what i always do now is to correlate the cvp with the morphology of the right heart. lets say i have a cvp of 5 with a large right ventricle then i don’t hesitate to give diuretics. i really can’t understand how recent guidelines (surviving sepsis campaign) can still state a cvp of 10-12 as a target value ! new german s3 guidelines on fluid management at least advise not to use cvp for hemodynamic monitoring. guess who was against it? the german sepsis society, probably because they didn’t like to upset their friends from the surviving sepsis campaign group 🙂 let me send you a link to a very good article: Understanding venous return: Intensive Care Med. 2014 Oct;40(10):1564-6. doi: 10.1007/s00134-014-3379-4. Epub 2014 Jun 26. i went through some of the cited articles – awesome information! thanks for the interesting discussion and keep on posting !

Sounds like a good session!  I cannot understand why CVP remains in guidelines when there is clear, irrefutable evidence that it does not work to estimate either volume status or responsiveness.   As you say, other, more physiological information renders CVP irrelevant.  I have not used CVP in years. Thanks for the reference, will make sure to check it out!

thanks for reading!

Philippe