Renal replacement therapy Flashcards by Hamish Reed-Embleton

What are the 3 layers of kidney

cortex
medulla
renal pelvis

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What enters to form the glomerulus? Leaves?

What does this then become?

afferent arteriole
efferent arteriole - becomes peritubular capillaries of nephron

Afferrent is thicker -> high pressure in glomerulus allowing small molecules to pass through into nephron

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Name the parts of the nephron in order

(Bowmans capsule) 
Proximal tubule 
Loop of henle 
       - thin descending 
        - Thin ascending 
        - thick ascending 
Distal convoluted tubule 
collecting tubule 
collecting duct

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Appox cardiac output to kidneys at rest

25%

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Main function of short vs long nephrons in loop of henle

short - excretion / regulatory functions
- Acid base balance, electrolytes, waste,

Longer - concentrate / dilute urine - based on current physiological status

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What happens in proximal tubule

reabsorb water, electrolytes, solutes

H+ ions passively secreted here

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What happens in distal convoluted tubule

Regulate BP
Absorb / secrete solutes
ADH here
can resorb Bicarb / actively secrete H+ ions

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Key waste products secreted by kidneys

creatine
uric acid
urea

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Indications for CRRT

Critically ill  with severe AKI (ie too unstable for dialysis)
Fluid overload 
severe electrolyte imbalance 
Acid base imbalance 
sepsis + cytokine clearance 
rhabdomyolysis 
Heart failure

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Usual flow rate for CRRT

150-300ML per minute

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What 3 fluids in addition to blood in CRRT? When are they added

Pre blood pump
- Added just after blood out of body BEFORE the filter

Dialysate

Present IN filter
Not actually added to blood but on the other side of the filter membrane

Post filter pump
-Added AFTER filter, but before the de-aeration chamber

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Which pressures are measured in CRRT

Access pressure - (pre-filter)
-Always NEGATIVE

Pre-filter (after blood pump)
-Always POSITIVE

Return pressure (after the filter) 
-Always POSITIVE

Effluent pressure (pressure to pull plasma water from blood) 
-Usually negative (occasionally positive)

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4 main principles of CRRT

Diffusion
Ultrafiltration
Convection
Adsorbtion

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Direction of blood / diasylate in filter

Blood bottom-> top
dialysate top->bottom

Ensures an adequate diffusion concentration gradient throughout

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What size molecues can be filtered with diffusion

Depends on pore thickness

Small molecules only

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DIFFUSION in filtration
Which electrolytes are usually started at isotonic levels in dialysate?
Which are not isotonic?
What is not in dialysate?

Mg, Cl, Na

K - usually at lower levels because people tend to initially be hyperkalemic
->once normalised have to alter dialysate

Bicarb - Usually higher in dialysate initially
(renal failure tends to have low levels)

No urea/creatinine

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What 3 pressures can cause liquid to pass through a membrane

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Osmotic
Oncotic
Hydrostatic

Eg of hydrostatic pressure

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Glomerulus

Afferent bigger than efferent
Able to control this with contraction/relaxation of efferent arteriole

ULTRAFILTRATION

What does ultrafiltration do

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Uses hydrostatic pressure to mimic glomerulus

-> Removes fluid from patients blood

What is convection

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Movement of solutes through a semi permeable membrane with the flow of water
Also called SOLUTE DRAG

Ultrafiltration and convection mean large volume of fluid is taken from patients blood - what must you then do?

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Replace it - can use isotonic solution to do this

When can replacement fluid be added to blood?

Advantage / disadvantage

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BEFORE filter
-Dilutes blood -> less solute clearance
+Reduces clotting of blood in filter -> prolongs the life of the filter

AGFTER filter
+More conencreated blood in filter -> better solute clearance
-Increased clotting in filter -> filter shorter lifespan

Often use a MIX of both

What is Adsorption? Key use?

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Adherence of solutes/biological mater to the surface of the filtration membrane
->Eventually ‘clogs’ filter

Some filters are made to specifically adsorb cytokine for use in a cytokine storm.

What is SCUF ? 
What is it?
When is it used?
Dialysate / replacement solution?
ph?

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Slow continuous ultrafiltration
Slow filtration of fluid
Don’t get removal of solutes as slow ->less convection
pH NOT AFFECTED

In fluid overload

No dialysate / replacement fluid

``` What is CVVH? What does it do? When is it used? Dialysate / replacement solution? pH ```

Continuous veno-veno haemofiltration Removes fluid and solutes through ULTRAFILTRATION + CONVECTION ->Requires replacement solution (no dialysate) Uraemia Severe acid/base disturbance Large molecule clearance pH affected

``` What is CVVHD? What does it do? When is it used? Dialysate / replacement solution? pH ```

Continuous veno-veno haemodyalysis Removes waste products and solutes through DIFFUSION - Small / medium molecules Uraemia Severe acid/base disturbance ->pH affected Dialysate but not replacement fluid

What is CVVHDF What does it do? When is it used? Dialysate / replacement solution?

Continuous veno-veno haemoDiaFiltration Combination of Diffusion, Ultrafiltration + convection MOST common as used for everything and can turn down flow of various things as required without having to reset whole system Uses dialysate and replacement solution ``` ureamia Electrolye imbalance severe acid base disturbance removal of small-large molecules Fluid removal ```

When would you not anticoagulate patients on crrt

trauma / surgery Bleed on the brain Liver failure sepsis with coagulopathy

What 2 main issues with filter clotting

Increased downtime without filtration May lose up to 1/2 unit of blood in filter -> if frequent occurs will require blood transfusion

Usual drug for systemic anticoagulation in CRRT? | When is a systemic method used?

Heparin Used when need for systemic anticoagulation Eg DVT/PE, mechanical heart valve etc

Reversal agent of heparin

protamine

What do you need to monitor for patients on heparin infusion

HIIT - heparin induced idiopathic thrombocytopenia | If platelets falling->may need to change agent

Bar heparin what other agents can be used for systemic anticoagulation on crrt ? Reversal?

Direct thrombin inhibitors | No reversal -> use FFP / cryo / clotting factors

More common to use systemic or regional anticoagulation in CRRT? Why? What are the drawbacks

Regional Decreased risk of patient bleeding whilst increasing filter life Requires closer monitoring

Most common drug combo in regional anticoagulation

Heparin - pre-filter | Protamine - post filter

Approx dose of heparin: protamine

100units heparin: 1g protamine

An alternative drug combination of anticoagulation that is not heparin/protamine for regional anticoagulation

Citrate (pre-filter) / calcium (post filter)

How does citrate prevent clotting? What happens to citrate during filtration? What do you need to ensure when using citrate

binds to calcium (which is used in almost all parts of the clotting cascade ) Once bound to calcium becomes inactive Most citrate filtered out ->Need to give calcium to ensure adequate systemic levels returned

What do you monitor in when using citrate as an anticoagulant in CRRT? Values?

Calcium levels Post filter - Very low (if not then using insufficient citrate for filtration) Patient - Normal levels

As filters get clogged what changes ? What is this?

TMP (trans membrane pressure) goes up Pressure between blood and dialysate (hydrostatic pressure) -This is driving pressure for convection

What is pressure drop

The pressure of blood going through the filter | Ie pressure before - pressure after

What causes pressure drop to increase

Clotting - as the membranes clot off need more pressure to get blood through the filter

Renal replacement therapy Flashcards

(42 cards)