1) DIFFUSION
 Movement of molecules from a region of
higher concentration to a region of lower
concentration until the equilibrium is
reached.

Types of Diffusion
1. Simple Diffusion : Substance moves
through a semi permeable membrane or In
a solution without the help of transport
proteins
2. Facilitate Diffusion : Substance move
through a semi permeable membrane or in
a solution with the help of transport
proteins

In Dialysis, Diffusion can be defined as
transport of solute across the
semipermeable membrane through a
concentration gradient.
Solutes ex: Na+, K+, Ca+, Urea,
Glucose, Cl-

Diffusion is bi directional
From Blood to Dialysate => Diffusion
From Dialysate to Blood => Back Diffusion

Factors affecting rate of diffusion
1. Temperature: Higher the temperature
faster the diffusion (Reason; higher the
temperature the particles will be having
more kinetic energy.)
2. Surface area: larger surface area of
membrane = faster diffusion
3. Concentration: if concentration gradient
is higher diffusion will be faster

Counter current mechanism will help for
faster diffusion

2) Osmosis
• During osmosis, fluid moves from areas of
high water concentration to lower water
concentration across a semi-permeable
membrane until equilibrium is reached.
• In dialysis, excess fluid moves from blood to
the dialysate through a membrane until the
fluid level is same between blood and
dialysate.

3) Transmembrane pressure(TMP)
Difference in hydrostatic pressure
between the Blood compartment and
the Dialysate compartment across
the dialysis membrane this is called
the Transmembrane pressure (TMP).

TMP alarm in Dialysis machine
Causes:
1. Clamped line
2. Clotted Dialyzer
3. Kink Dialysate line
4. Poor vascular access
5. High UFR
6. Measurement error
7. Ruptured membrane
8. Protein deposit in membrane

Management
1. Check the line for kink
2.Check the shunt connection with dialyzer
3.Flush the dialyser to check clot in dialyzer
4.Check Transducer protector(TP) whether
it is dry or wet
5. If TMP is lower increase UF or Increase
blood flow

4) Venous Pressure
Normal range of venous pressure is 100-
200mmHg.
Maximum pressure is 300mmHg.

High Venous pressure

Low Venous Pressure

5) Ultrafiltration
• Ultrafiltration is the removal of fluid
from a patient.
• Ultrafiltration occurs when fluid
passes across a semipermeable
membrane (a membrane that allows
some substances to pass through but
not others) due to a driving
pressure.

• Ultrafiltration removes excess plasma volume
without causing a significant change in
electrolytes
• In majority of patients we do need
ultrafiltration needs. Some units mention a
minimum UF rate, such as of 10ml/hr or 500
ml (200 ml for a drink + 300 ml for
restitution of the blood at end of a session).
• The limit of ultrafiltration rate (UFR)
monitored by the Centers for Medicare or
Hospitals is 13 ml/kg per hour.

THANK YOU