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ICU > Renal replacement therapy > Flashcards

Renal replacement therapy Flashcards

1
Q

What are the 3 layers of kidney

A

cortex
medulla
renal pelvis

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2
Q

What enters to form the glomerulus? Leaves?

What does this then become?

A

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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3
Q

Name the parts of the nephron in order

A 
(Bowmans capsule) 
Proximal tubule 
Loop of henle 
       - thin descending 
        - Thin ascending 
        - thick ascending 
Distal convoluted tubule 
collecting tubule 
collecting duct
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4
Q

Appox cardiac output to kidneys at rest

A

25%

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5
Q

Main function of short vs long nephrons in loop of henle

A

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

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

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6
Q

What happens in proximal tubule

A

reabsorb water, electrolytes, solutes

H+ ions passively secreted here

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7
Q

What happens in distal convoluted tubule

A

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

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8
Q

Key waste products secreted by kidneys

A

creatine
uric acid
urea

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9
Q

Indications for CRRT

A 
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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10
Q

Usual flow rate for CRRT

A

150-300ML per minute

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11
Q

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

A

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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12
Q

Which pressures are measured in CRRT

A

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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13
Q

4 main principles of CRRT

A

Diffusion
Ultrafiltration
Convection
Adsorbtion

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14
Q

Direction of blood / diasylate in filter

A

Blood bottom-> top
dialysate top->bottom

Ensures an adequate diffusion concentration gradient throughout

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15
Q

What size molecues can be filtered with diffusion

A

Depends on pore thickness

Small molecules only

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16
Q

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

A

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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17
Q

What 3 pressures can cause liquid to pass through a membrane

A

Osmotic
Oncotic
Hydrostatic

18
Q

Eg of hydrostatic pressure

A

Glomerulus

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

ULTRAFILTRATION

19
Q

What does ultrafiltration do

A

Uses hydrostatic pressure to mimic glomerulus

-> Removes fluid from patients blood

20
Q

What is convection

A

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

21
Q

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

A

Replace it - can use isotonic solution to do this

22
Q

When can replacement fluid be added to blood?

Advantage / disadvantage

A

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

23
Q

What is Adsorption? Key use?

A

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.

24
Q 
What is SCUF ? 
What is it?
When is it used?
Dialysate / replacement solution?
ph?
A

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

25
Q 
What is CVVH? 
What does it do?
When is it used?
Dialysate / replacement solution?
pH
A

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

26
Q 
What is CVVHD?
What does it do?
When is it used?
Dialysate / replacement solution?
pH
A

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

27
Q

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

A

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
28
Q

When would you not anticoagulate patients on crrt

A

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

29
Q

What 2 main issues with filter clotting

A

Increased downtime without filtration

May lose up to 1/2 unit of blood in filter
-> if frequent occurs will require blood transfusion

30
Q

Usual drug for systemic anticoagulation in CRRT?

When is a systemic method used?

A

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

31
Q

Reversal agent of heparin

A

protamine

32
Q

What do you need to monitor for patients on heparin infusion

A

HIIT - heparin induced idiopathic thrombocytopenia

If platelets falling->may need to change agent

33
Q

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

A

Direct thrombin inhibitors

No reversal -> use FFP / cryo / clotting factors

34
Q

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

A

Regional
Decreased risk of patient bleeding whilst increasing filter life

Requires closer monitoring

35
Q

Most common drug combo in regional anticoagulation

A

Heparin - pre-filter

Protamine - post filter

36
Q

Approx dose of heparin: protamine

A

100units heparin: 1g protamine

37
Q

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

A

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

38
Q

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

A

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

39
Q

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

A

Calcium levels

Post filter - Very low (if not then using insufficient citrate for filtration)

Patient - Normal levels

40
Q

As filters get clogged what changes ? What is this?

A

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

41
Q

What is pressure drop

A

The pressure of blood going through the filter

Ie pressure before - pressure after

42
Q

What causes pressure drop to increase

A

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

ICU (8 decks)

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