D20 (Deuterium oxide) is used to measure volume of
**Core Concept**
Deuterium oxide, also known as heavy water, is a compound of deuterium (a heavy isotope of hydrogen) and oxygen. It is used as a tracer in various medical and scientific applications due to its unique properties. In the context of this question, deuterium oxide is used in a specific medical application to measure a particular volume.
**Why the Correct Answer is Right**
Deuterium oxide is used to measure total body water (TBW) and its distribution in the body. The principle behind this measurement is based on the dilution principle, where a known amount of deuterium oxide is administered to the patient, and its concentration is measured in a blood or urine sample at a later time. The dilution of deuterium oxide is directly proportional to the volume of total body water. This method is particularly useful in assessing hydration status, particularly in patients with fluid or electrolyte imbalances.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because deuterium oxide is not primarily used to measure blood volume.
**Option B:** This option is incorrect because while deuterium oxide can be used to measure extracellular fluid volume, it is not the primary application of this tracer.
**Option C:** This option is incorrect because deuterium oxide is not used to measure muscle volume specifically.
**Clinical Pearl / High-Yield Fact**
Deuterium oxide is a useful tool in assessing hydration status, particularly in patients with fluid or electrolyte imbalances. It is essential to note that this method should be used in conjunction with other clinical assessments and diagnostic tests to ensure accurate results.
**Correct Answer: D. Total body water**