Single Compartment Dialysis

Question 1

What is single compartment dialysis?

Answer 1

• removal of urea by haemodialysis

- urea comes from protein intake at a hypothetically uniform rate

Question 2

Function of kidneys

Answer 2

• clear many soluble wastes including urea (breakdown product of protein metabolism)

Question 3

What is urea used for

Answer 3

• indicator of effectiveness of renal function (and of dialysis)

Question 4

How is the [urea] in the blood measured

Answer 4

• mmol/l

* BUN (blood urea nitrogen) measured on mg/dL

Question 5

Assumption about urea

Answer 5

1. Produced in direct proportion to protein intake
2. Traverses membranes easily & establishes equilibrium rapidly -> considered to exist in a single compartment of TBW (total body water) which is assumed to be 42l in an adult
3. Urea can be assumed to be distributed uniformly (as it well mixed throughout the body)

Question 6

Single compartment urea kinetics assumptions

Answer 6

• no residual renal function
• dialyzer clearance 200ml/min
• dialysis every mon, wed, fri starting at 10am for 4 hours
• no water is removed

Question 7

Urea elimination rate for Monday

Answer 7

Dialysis clearance”[urea] PULSE TRAIN(0+10, 4, 7*24, 600)

Question 8

Urea elimination rate for wed

Answer 8

Dialysis clearance ”[urea]”PULSE TRAIN(48+10, 4, 7*24,600)

Question 9

Urea elimination rate for Friday

Answer 9

Dialysis clearance “[urea]”PULSE TRAIN (96+10, 4, 7*24,600)

Question 10

Total urea elimination rate

Answer 10

UERmon+ UERwed + UERfri mmol/hour

Question 11

Level of urea

Answer 11

INT(urea production rate- urea elimination rate) mmol

Initial value:
42 x 30 mmol
- I.e. (TBW) x [urea]

Question 12

What suggests the need for a two compartment model

Answer 12

The urea rises sharply after dialysis session before resuming linear increase