A man weighing 70 kg has a hematocrit of 45%. What would he his approximate plasma volume?
**Core Concept**
The hematocrit is the proportion of blood volume occupied by red blood cells. To estimate plasma volume, we need to use the formula for blood volume distribution, which is roughly 70% for blood cells and 30% for plasma. However, the exact calculation involves knowing the total blood volume.
**Why the Correct Answer is Right**
To estimate plasma volume, we can use the formula: Total Blood Volume (TBV) = [Hematocrit (Hct) / 1 - Hct] x Body Weight (BW). Given a hematocrit of 45% and a body weight of 70 kg, we can plug these values into the formula. TBV = [0.45 / (1 - 0.45)] x 70 kg = 85.71 liters. Since plasma volume is approximately 30% of TBV, the plasma volume would be 0.3 x 85.71 liters = 25.71 liters.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is likely a distractor, and without the correct formula, we cannot confirm its accuracy.
**Option B:** This option is incorrect because it does not account for the hematocrit value correctly in the formula.
**Option C:** This option is also incorrect as it incorrectly calculates the blood volume using the hematocrit value directly.
**Option D:** This option is likely incorrect and does not follow the correct formula for estimating plasma volume.
**Clinical Pearl / High-Yield Fact**
For estimating blood and plasma volumes, remember the formula TBV = [Hct / (1 - Hct)] x BW and that plasma volume is approximately 30% of TBV.
**Correct Answer:** **C.** 25.71 liters