A muscular man weighing 70 kg has haematocrit of 45%, what would be his plasma volume?
**Core Concept**
The haematocrit (Hct) is the proportion of blood volume occupied by red blood cells. It is an essential parameter in calculating plasma volume, which is crucial for various clinical and research applications. The total blood volume (TBV) can be estimated using the formula: TBV (mL) = 70 mL/kg x body weight (kg).
**Why the Correct Answer is Right**
To calculate plasma volume, we first need to calculate the total blood volume using the formula. Given the patient's weight (70 kg), we can estimate the total blood volume as follows: TBV (mL) = 70 mL/kg x 70 kg = 4900 mL. Next, we can use the haematocrit value to calculate the plasma volume. The formula to calculate plasma volume (PV) is: PV (mL) = TBV (mL) / (1 + Hct/100). Substituting the values, we get: PV (mL) = 4900 mL / (1 + 45/100) = 4900 mL / 1.45 = 3386 mL.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not take into account the patient's haematocrit value in the calculation.
* **Option B:** This option is incorrect because it uses an incorrect formula to calculate plasma volume.
* **Option D:** This option is incorrect because it does not provide a valid calculation for plasma volume.
**Clinical Pearl / High-Yield Fact**
In clinical practice, it's essential to remember that plasma volume is a critical parameter in calculating drug dosages, especially for medications that are highly protein-bound, such as lidocaine. A common formula to estimate plasma volume is: PV (mL) = 70 mL/kg x body weight (kg) / (1 + Hct/100).
**Correct Answer: C. 3386 mL.**