From the Research
The estimated extracellular fluid (ECF) volume in a 60kg woman is approximately 12 liters, and her normal sodium level would be between 135-145 mEq/L. The ECF volume can be calculated as roughly 20% of total body weight, so for a 60kg individual, this equals about 12 liters (60kg × 0.2 = 12L) 1. The ECF includes plasma, interstitial fluid, and transcellular fluid, with sodium being the primary cation maintaining this fluid compartment's volume and osmolality.
Some key points to consider:
- The normal serum sodium concentration range is 135-145 mEq/L, with an average of about 140 mEq/L in healthy adults 2.
- This concentration is tightly regulated by the kidneys through various mechanisms including the renin-angiotensin-aldosterone system and antidiuretic hormone (ADH) 1.
- Understanding these values is important for assessing fluid and electrolyte status, particularly when managing conditions like dehydration, heart failure, or kidney disease where ECF volume and sodium levels may be altered 3, 4.
- It's also important to note that sodium levels can be affected by various factors, including traumatic brain injury, which can cause dysregulation of osmoregulation and affect neurological outcomes 1.
In terms of the options provided:
- A: The ECF is not always isotonic throughout the circulation, as its composition can vary depending on the location and the presence of certain conditions 5.
- B: The normal ECF sodium level is indeed between 135-145 mEq/L, which is consistent with the normal serum sodium concentration range 2.
- C: The estimated ECF volume is approximately 12 liters, which is consistent with the calculation based on total body weight 1.
- D: The protein content of the ECF is not similar to that of plasma, as the ECF includes interstitial fluid and transcellular fluid, which have different protein compositions 1.