Question

As a dialysis patient, Michelle has a 4-h dialysis treatment three times a week. When she arrives at the dialysis clinic, her weight, temperature, and blood pressure are taken and blood tests are done to determine the level of electrolytes and urea in her blood. In the dialysis center, tubes to the dialyzer are connected to the catheter she has had implanted. Blood is then pumped out of her body, through the dialyzer where it is filtered, and returned to her body. As Michelle's blood flows through the dialyzer, electrolytes from the dialysate move into her blood, and waste products in her blood move into the dialysate, which is continually renewed. To achieve normal serum electrolyte levels, dialysate fluid contains sodium, chloride, and magnesium levels that are equal to serum concentrations. These electrolytes are removed from the blood only if their concentrations are higher than normal. Typically, in dialysis patients, the potassium ion level is higher than normal. Therefore, initial dialysis may start with a low concentration of potassium ion in the dialysate. During dialysis, excess fluid is removed by osmosis. A 4-h dialysis session requires at least 120 L of dialysis fluid. During dialysis, the electrolytes in the dialysate are adjusted until the electrolytes have the same levels as normal serum. Initially the dialysate solution prepared for Michelle's pre-dialysis blood tests shows that the electrolyte levels in her blood are as follows:

HCO3− 24 mEq/L, K+ 6.0 mEq/L, Na+ 148 mEq/L, Ca2+ 3.0 mEq/L, Mg2+ 1.0 mEq/L, Cl− 111.0 mEq/L.

A dialysis solution is prepared for Michelle that contains the following:

HCO3− 30.0 mEq/L , K+ 2.0 mEq/L , Na+ 120.0 mEq/L , Ca2+ 5.0 mEq/L , Mg2+ 3.5 mEq/L , Cl− 100.5, glucose 5.0% (m/v).

What is the osmolarity of the dialysate fluid?
Express your answer using two decimal places.

Answer 1

Given:

concentration of dialysate fluid:

The osmolarity of a solution is the osmotic concentration.

For ions with single charge one osmole is 1 mol.

For ions with 2 charges, one osmole is half that of the mol.

HCO3^- = 24 + 30 = 54 mmol/L = 54 osmol/L

K⁺    = 6 + 2 = 8 mmol/L= 8 osmol/L

Na⁺ = 148 + 120 = 168 mmol/L= 168 osmol/L

Ca²⁺ = 3 + 5 = 8 mmol/L= 8 osmol/L

Mg²⁺   = 1 + 3.5 = 4.5 mol/L= 4.5 osmol/L

Cl^-   = 111.0 + 100.5 = 211.5 mmol/L= 211.5 osmol/L

Glucose = 5% m/v = 5g/Lsolution = 5/180.2 = 0.0277 mol/L = 0.0277 osmol/L

Osmolarity of the dialysate is the addition of the osmolarities of Blood and dialysis

Osmolarity of Solution = 54 + 8 + 168 + 8 + 4.5 + 211.5 + 0.0277 osmol/L = 0.47545 osmol/L

The Solution has not considered osmosis because no data has been provided about the osmotic pressures.