OSCE - Equipment - HF Flashcards

1
Q

What is ultrafiltration

A

Movement of water across a semipermeable membrane

Because of a hydrostatic pressure gradient

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2
Q

What is convection

A

When there is ultrafiltration of large volumes of water across of semi permeable membrane, there is a convective current that drags additional molecules.

This is convection and removes small/mid size molecules

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3
Q

Define HF

A

Process where ultrafiltration and convection are used to remove fluid and solutes in blood

Requires pressure gradient across a semi-permeable membrane

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4
Q

Define HD

A

Uses a COUNTER CURRENT flow

Diasylate in one direction across the membrane, blood on the other

Enhances diffusion across the semi permeable membrane due to concentration gradients

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5
Q

How do we remove fluid from a patient in HF

A

Ultrafiltration removes fluid from plasma

We then replace it with less fluid to create a net loss

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6
Q

What is pre-dilution

A

Replacement fluid can either be added pre or post filter.

Pre - dilutes blood and prolongs the lifespan of the filter by reducing tendency to clot

Therefore less anti-coag

BUT

Post dilution concentrates blood in the filter - greater clearance

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7
Q

Factors influencing clearance of substances from plasma

A
Membrane - 
Surface area
Hydraulic permeability
Pore sore 
Charge

Pressure gradient - hydrostatic, colloid, osmotic

Solute properties - size, charge, concentration

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8
Q

Methods of anti-coag

A

Heparin - binds antithrombin III, inhibits activated factor X

LMWH - Factor Xa inhibitor

Citrate - binds ionised calcium

Prostacyclin- antiplatelet action

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9
Q

Who would you avoid citrate in

A

Hepatic dysfunction

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10
Q

Causes of the filter clotting, and how to manage

A

Impaired vascular access - adequate flow and positioning

High intra-abdo pressures and high intra-thoracic pressures impede flow

Ineffective anti-coagulation - consider pre-dilution

Ensure optimal haemofilter settings

OR - consider taking a break and assess renal recovery

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11
Q

Other things to consider while on HF

A
Drug dose corrections
Correct electrolytes
Fluid balance
Maintain normothermia
Haemodynamic stability
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12
Q

Indications for RRT

A
Metabolic acidaemia
Hyperkalaemia
Symptomatic uraemia
Fluid overload
Overdose - Lithium, salicylates
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13
Q

CVVHF

A

Convection
Bulk flow
Hydrostatic pressure gradient
Rate of removal proportional to blood flow rate, pressure gradient and membrane area

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14
Q

CVVHD

A

Diffusion
Countercurrent blood and diasylate
Concentration gradient

High diasylate flow and blood flow, sets up maintained pressure gradient

Apply pressure difference- fluid out

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15
Q

What is the dose of RRT

A

Defines how much effluent is produced

25-35ml/kg/hour

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16
Q

Prescription factors

A
Intermittant or continuous
HF or HD
Dose (higher flow rates do nothing)
Pre and post fluid (usually as a ratio)
Fluid balance
Anti-coagulation
Flow rates up to 250ml/min