RINGER’S A LOUSY VOLUME EXPANDER

With colloids being miscredited by Cochrane and synthetic colloids being hammered by RCTs, it might seem we’re left with crystalloids. So how good is our standard crystalloid, Ringer’s Lactate, at volume replacing a volume depleted patient? This study withdrew blood and replaced it with 3 times the volume of Ringer’s Lactate. Very little of it stayed in the blood stream.

Introduction
From the study: “Recent data were interpreted to indicate a comparable intravascular volume effect for crystalloids and colloids, challenging the occasionally suggested advantage of using colloids to treat hypovolemia. General physiological knowledge and clinical experience, however, suggest otherwise”.

We also know most of the crystalloid volume from solutions like Ringer’s Lactate/Hartmann’s and Normal Saline will go interstitial. But how much? And can colloids bring it back inside the vessels?

The study
In this study, in healthy test subjects, less than 20% of the RL stayed in the blood stream. 80% ends up as interstitial fluid – and eventually edema. So for every litre of Ringer’s Lactate, the patient only receives around 200ml of intravascular fluid! Now, what to do with all that interstitial fluid? luckily, colloids can bring much of that back into the blood stream, as shown in this trial.

The volume effect was measured with a fancy method involving dye ICG and measuring its concentration to reflect plasma volume, and some fluorescent labeling to red blood cells to measure these. Plasma and red blood cells, this is the total intravascular volume. So it seems this project had pretty good track of both the red blood cells and total intravascular volume, and could say something meaningful about the patient’s volume changes during this trial.

Results
Infusion of Ringer’s Lactate gave a modest 17% increase in intravascular volume, while infusion of albumin 200mg/ml gave a much more impressive 184% increase in volume per volume infused – providing you have interstitial fluid to draw into the circulation. I guess that’s why they call colloids volume expanders…

Of course, this is all in healthy subjects, with an intact vascular wall, where we assume large colloids stay in the blood stream to keep the oncotic pressure up. Other real life studies with sick patients have observed a much smaller difference between the volume effects of crystalloids and colloids, possibly reflecting an altered vascular barrier that also leaks colloids.

It’s an interesting study. It points out that general physiology still holds true – but it also probably shows how really sick patients will mess up your basic physiology.

The intravascular volume effect of Ringer’s lactate is below 20%: a prospective study in humans, Crit Care, 2012.

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5 Responses to RINGER’S A LOUSY VOLUME EXPANDER

  1. BF says:

    So the question is Normal Saline a better resus fluid?

    • Thomas D says:

      Thanks for your comment!

      No, normal saline would be similar. Maybe I should write something about it in the post, the distribution follows the different volume ‘compartments’ in the body. It’s very natural from a physiological stand that crystalloids like NS or RL spread themselves in the way mentioned above, often said to have a 75/25 or 80/20 relation between extra- and intravascular space.

      The exception is glucose mixtures, that will distribute themselves as pure water after the sugar is absorbed by the body’s cells. So glucose/dextrose mixes are not useful for volume loading at all.

      Try following this link – it explains this much better than I can:
      http://www.anaesthesiamcq.com/FluidBook/fl8_1.php

      Update: I just put in a mention of normal saline in the post above to clarify.

  2. nfkb says:

    hi !

    thank you for this post !

    In our ICU we use a lot Ringer Lactate (i think it’s better than saline looking at the chloride issue) and albumin @ 200 mg/ml because we have a lot of malnourished patients with deep hypoalbuminemia.

    Despite good evidence we are pretty happy with this combo (the pharmacist is not hapy with the cost of albumin) so i think there’s something to dig with the association of a balanced crystalloid and albumin. The middle way 😉

    • Thomas D says:

      I agree with you totally! This post is not against the use of Ringer’s Lactate, it’s just to remind us how it works physiologically when you infuse it, and to keep that in mind when treating patients.

      We do the same in our ICU: RL (mainly to avoid chloride overload) and albumin 200 mg/ml or plasma as volume expanders. The middle way. Still, I sometimes wonder how much volume expansion colloids provide in critically ill patients with leaking vascular walls…

      In the OT and also in the ICU HES and other colloids are still used as volume expanders for low risk, not so sick, patients.

      • nfkb says:

        hi Thomas !

        Actually when the patient is leaking and shocked i’ve got a preference toward low concentration albumine (40g/l) and ringer/saline.

        Of course i keep in mind that everythink leaks and one important point is to teach resident to titrate the volume expansion and not prescribing it like sore throat pills

        In the OR i mainly use RL (90% of the fluid i use) If the patient bleeds we have the blood and plasma really quick in our universitary hospital so i do not use HES or gelatine anymore. We also do a lot of hepatic and oncologic surgery so albumin take its place in the operating theatre too

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