Rattibha

Time for a #CriticalCare #Tweetorial!
‼️Basics of CRRT for the non-nephrologist‼️
Exiting my typical #Neurology wheelhouse as I tackle some #FOAMcc topics for my own learning. Please join in on teaching and address any mistakes!
#EmoryNCCTweetorials
@EmoryNephrology
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CRRT- What does it stand for?!
Continuous- Runs around the clock (sort of)
Renal- The beans!
Replacement- More of a rinse than a true replacement
Therapy- It helps!
@criticalbeansmd @EmoryNeuroCrit @caseyalbin @KrafteKraft4 @mallyaa @VijayanMD
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Why do we use CRRT instead of HD?
Patient’s with hemodynamic instability (ie blood pressure is so low they can’t tolerate HD)
Conditions where you need to avoid large fluid shifts (like cerebral edema)
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Goal of CRRT is to achieve clearance. Could be fluid, K, Urea, or Cr.
To understand how lets start with some chemistry by understanding the molecular weights of some common components in blood.
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So this gives us small, middle, and large molecules. To rid the blood of those different sizes we have a couple different options.
Ultrafiltration- generally takes care of large and middle sizes
Diffusion- generally takes care of small sizes
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Diffusion: Solute transport across a semipermeable membrane from a high to low concentration.
Ultrafiltration (convection): Solutes pass along a semi-permeable membrane with the solvent (“solvent drag”) due to a pressure exerted on them (like coffee through a filter)
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So what can CRRT accomplish based on size?
Typically it caps out around 50,000 daltons
But this includes important target molecules like Na, Urea, K, Cr, and Uric acid.
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Also important to consider the clearance of drugs. Thankfully our pharmacists are on top of this! @katskript @KeatonSmetana @CaseyMayPharmD @karenccrx
Vancomycin is about 1450 daltons, Keppra is 170 so both can be cleared by CRRT which affects your dose and admin time!
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Now that you have a basic understanding of the principles underlying CRRT, lets talk about different modes!
SCUF
CVVH
CVVHD
CVVHDF
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SCUF
(Slow Continuous UltraFiltration)
Uses ultrafiltration to remove volume. Less emphasis on clearance.
Blood passed over a filter and the effluent (urine) is filtered out with no pre or post replacement fluid.
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CVVH
(Continuous VenoVenous Hemofiltration)
Similar to SCUF, but with a pre- or post-replacement fluid.
Removes both fluid and solutes to achieve a clearance goal.
Figure: journal.chestnet.org
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journal.chestnet.org

CVVHD
(Continuous VenoVenous HemoDialysis)
Main difference is use of diffusion. Blood pumped in one direction, with a dialysate pumped in the opposite direction.
Achieves a diffusion gradient. No replacement fluids.
Figure: journal.chestnet.org
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journal.chestnet.org

CVVHDF
(Continuous VenoVenous HemoDiaFiltration)
What is used @EmoryNephrology most commonly.
I think of it as a combo of all the prior modes. Utilizes a dialysate and replacement fluid to maximize ultrafiltration and diffusion.
Figure: journal.chestnet.org
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journal.chestnet.org

So now that you have the modes down. What about the terrifying machine 😱
We mainly use the Prismaflex @EmoryNephrology @EmoryCCC
The machine generates your ability to achieve ultrafiltration and diffusion through a series of pumps and filters.
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So hop on board the #MagicSchoolBus and lets go for a ride through the CRRT circuit.
First stop is access. Most commonly this is achieved through a vascath or trialysis catheter.
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After leaving the body blood passes through a series of tools to measure pressure, pump, and potentially add anticoagulation or pre-filter fluids. All prior to entering the filter.
Great diagram showing this from @derangedphys
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As the blood enters the filter it interacts with the membrane and has a cross-current with the dialysate as it is pumped in.
Effluent is pumped out and blood exits the filter.
Diagram: @derangedphys
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After leaving the filter, post-filter replacement fluid can be added.
Blood then enters a bubble chamber/detector before it is returned back to the body.
Diagram: @derangedphys
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Dose, rates, alarms are all for a future #Tweetorial.
Hopefully next time you walk into an ICU room you have at least a general understanding of the CRRT machine!
@AvrahamCooperMD @LDCritCare @MedTweetorials @crit_caring_MD @colleenmfarrell @critcareguys @Capt_Ammonia
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