Question

Michelle suffers from kidney disease because of severe strep throat she contracted as a child. When her kidneys stopped functioning, Michelle was placed on 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. Michelle’s blood tests prior to dialysis show that the electrolyte levels in her blood are:

HCO−3 21.0 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 dialysate solution is prepared for Michelle that contains the following:

HCO−3 35.0 mEq/L, K+ 2.0 mEq/L, Na+ 130 mEq/L , Ca2+ 5.0 mEq/L, Mg2+ 3.0 mEq/L, Cl− 105.0 mEq/L, glucose 5.0% (m/v).

1.

After dialysis, the level of magnesium in Michelle's blood was 0.0017 g/dL . What is this value in milliequivalents per liter?

Express the concentration in milliequivalents per liter to two significant figures.

Answer 1

This is conversion question of g/dL to (milli equivalents) / litre , up to two significant figures.

The Mg⁺² ion (Magnesium) concentration is given in units of Grams Per Decilitre (g/dL)

Note the conversion factor: 1 dL = 0.1 Liter

milli equivalents = milli moles / n

where n = charge on the metal ion = 2

Now, the given value = 0.0017 g/dL

That is 0.0017 g of Mg⁺² is present = (0.0017g)/ (24.03 g/mol) = 0.0000707 moles = 0. 07074 milli moles

Or, milli equivalents = 0. 0707 milli moles/ 2   = 0.03537   is present in 1 dL or 0.1 liter

Therefore,

milliequivalents per liter = (0.03537 milli equivalents) / (0.1 liter)    = 0.3537

Or, up to significant figures = 0.35 milliequivalents per liter         ....Answer