A backpacker weighs 220 pounds. Assume his blood weight is about 7% of his body

Question

A backpacker weighs 220 pounds. Assume his blood weight is about 7% of his body weight. His hematocrit at rest is 40% and total plasma proteins is 6 g%. After hiking on a hot day, the backpacker loses a net 4 L of body fluid by sweating and drinking, where the drinking is insufficient to match his sweating. Assume that the plasma makes up 8% of his total body water and that the fluid lost from each compartment is in proportion to the size of each fluid compartment.

A. Assuming no loss of blood, what is his hematocrit after his hot hike?

B. What is his total plasma protein concentration after hiking?

C. What affect would these changes have on his blood viscosity?

Explanation / Answer

A)

The blood weight = 7%

Weight of the backpacker = 220lb

The blood volume is = 0.07 x 220 lb / 2.2 lb kg-1= 7 kg.

The volume is = 7 kg /1.055 g cm-3= 6.63 L.

Hematocrit ratio at rest = 40%

Therefore, hematocrit ratio before the hike = 0.40.

During the hike, he lost 4 L of fluid, of which 8% was from the plasma, or (8 x 4/100 =0.32) 0.32 L.

Therefore, the blood volume is = 6g + 0.32 = 6.32L.

The packed cell volume does not change when the fluid lost was isoosmotic but this is unlikely.

The packed cell volume = 0.40 x 6.63 L = 2.65L.

This packed cell volume is now in 6.32L of blood,

So, new hematocrit ratio = 2.65 / 6.320 = 0.42.

If fluid lost is 8% and it may came from the intracellular fluid in the red blood cells.

Then, the packed cell volume is decreased from 2.65 to 0.92 x 2.65 = 2.44

The new hematocrit ratio = 2.44 / 6.32 =0.39

B)

The plasma proteins are conserved in the blood.

The total protein content before the hike = 6 g dL-1x 6.63L x (1 - 0.40)= 238.7 g.

This is the same before as after the hike. But, distributed volume is small and is 3.658L instead of 3.978 L.

Then, the new protein concentration in plasma is = 238.7 g / 3.658 L =6.67g%.

C)

The increased hemaytocrit ratio and concentration of plasma protein should result in increase of the blood viscosity. However, the changes in hematocrit after hike and plasma protein concentration after hike are very less and therefore, the viscosity should not be greatly different.

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