1/
As kidney replacement therapies (KRT) have become a strained and limited resource during the #COVID19 pandemic, here is a quick #tweetorial on how these treatments work:
What is the main mechanism by which clearance is achieved during intermittent #hemodialysis?
As kidney replacement therapies (KRT) have become a strained and limited resource during the #COVID19 pandemic, here is a quick #tweetorial on how these treatments work:
What is the main mechanism by which clearance is achieved during intermittent #hemodialysis?
2/
KRT has 2 powers:
Clearance (removal of solutes, like potassium
)
Volume removal 
...and it comes in 2 flavors:
Intermittent
Continuous
KRT has 2 powers:




...and it comes in 2 flavors:


3/ How does the potassium go from 7.2 meq/L to 4 after an intermittent #hemodialysis (iHD) session?
Chemistry 101: DIFFUSION!
Solutes are cleared via diffusion as they move
their concentration gradient across a SEMIPERMEABLE membrane
DOI: 10.1056/NEJMc1301071
Chemistry 101: DIFFUSION!
Solutes are cleared via diffusion as they move

DOI: 10.1056/NEJMc1301071
4/ A closer look at that dialysis filter...
Blood runs through the filter "straws", while the dialysate runs in the opposite direction
around them & does not come in direct contact with the 
Larger filters with bigger pores can be used to further optimize clearance.
Blood runs through the filter "straws", while the dialysate runs in the opposite direction


Larger filters with bigger pores can be used to further optimize clearance.
5/ Strategies to maximize clearance (particularly relevant now given the #COVID19-related strain on KRT):
Bigger filter size
Higher dialysis blood flow rates (usually, these are 300-400 cc/min)
Widen the concentration gradient and try a potassium-free dialysate



6/ So that's how we remove solute. What about the fluid?
Ultrafiltration (UF), or ISOTONIC fluid removal, is achieved via pressure that is exerted across the membrane that drives fluid out.
DOI: 10.1056/NEJMct1206045 @luck_urine
Ultrafiltration (UF), or ISOTONIC fluid removal, is achieved via pressure that is exerted across the membrane that drives fluid out.
DOI: 10.1056/NEJMct1206045 @luck_urine
7/ Here's what goes into the iHD order:
Access, blood flow, + dialysate flow rates (standard 800 cc/min)
Dialysate composition
Ultrafiltration volume
Filter size
Duration (standard 3.5hrs - though #COVID19 has forced shorter treatment times, affecting clearance)





8/ What about SLED? (sustained low efficiency dialysis)
It's just like iHD, but...not as efficient...and should be done for longer durations (e.g. 8 hours) to obtain similar clearance to iHD
It's just like iHD, but...not as efficient...and should be done for longer durations (e.g. 8 hours) to obtain similar clearance to iHD
9/ Let's move on to the CONTINUOUS KRTs
The Players: CVVH, CVVHD, & CVVHDF
CVVH = continuous venovenous hemofiltration
CVVH is the only continuous modality that does NOT use a dialysate. So how do we get clearance?
REPLACEMENT FLUID
The Players: CVVH, CVVHD, & CVVHDF
CVVH = continuous venovenous hemofiltration
CVVH is the only continuous modality that does NOT use a dialysate. So how do we get clearance?


10/ If you've seen a pt connected to a #CVVH machine, you remember the huge bags hanging in the room - these are bags of replacement fluid that achieve clearance & are infused into the patient via the filter.
Hospitals can purchase pre-made replacement fluid (example below)
Hospitals can purchase pre-made replacement fluid (example below)

11/ Remember that replacement fluid is essentially infused unchanged into the pt, so use caution in those with hypoNa to avoid overcorrection
Of note: Therapy fluid can be infused either before or after the CVVH filter. If you do it before, may lose some solute (via convection)
Of note: Therapy fluid can be infused either before or after the CVVH filter. If you do it before, may lose some solute (via convection)
12/ The graphic below illustrates the differences between #CVVH, #CVVHD, and #CVVHDF
CVVH:
Convection + replacement fluid;
dialysate
CVVHD
Dialysate + convection;
replacement fluid
CVVHDF:
Dialysate + convection + replacement fluid
@RenalFellowNtwk #FOAMed
CVVH:


CVVHD


CVVHDF:

@RenalFellowNtwk #FOAMed
13/ Say you only need volume removal, but no clearance:
Use your resources wisely and opt for a pure- #convection therapy:
Slow continuous ultrafiltration ( #SCUF) AKA aquapheresis or "CHF Solutions"
Don't waste dialysate or replacement fluid if you don't need it!
#COVID19
Use your resources wisely and opt for a pure- #convection therapy:
Slow continuous ultrafiltration ( #SCUF) AKA aquapheresis or "CHF Solutions"
Don't waste dialysate or replacement fluid if you don't need it!
#COVID19
14/ Compared to iHD, continuous KRT will achieve slower clearance & volume removal
(e.g. 100 cc/hr vs 1L/hr)
PIRRT = "middle ground" and uses higher RF rates to lower tx times & has been used during #COVID19 pandemic to maximize CKRT machine use
https://www.nxstage.com/hcp/therapies/pirrt/

PIRRT = "middle ground" and uses higher RF rates to lower tx times & has been used during #COVID19 pandemic to maximize CKRT machine use

https://www.nxstage.com/hcp/therapies/pirrt/
15/ In summary:
KRT = continuous/intermittent
Solute clearance: diffusion; UF: convection
Modality choice: Volume/solute removal needs + what's available
Optimize treatments that may be shorter by
blood/RF flow rates, using larger filters, & tailoring your dialysate





16/
And did not cover this above - but acute #PeritonealDialysis is another innovative and effective way to relieve some of the strain on resources like iHD & CVVH
Will let @osamaelshamy88 tackle that #tweetorial...
And did not cover this above - but acute #PeritonealDialysis is another innovative and effective way to relieve some of the strain on resources like iHD & CVVH
Will let @osamaelshamy88 tackle that #tweetorial...