Skip to Main Content

++

FLUID COMPARTMENTS

++

Fluid in the body is distributed between intracellular and extracellular compartments. Total body water (TBW) is the sum of the intracellular and extracellular compartments. In a 70-kg adult male, it comprises 60% of body weight or about 42 L. This value can vary with age, gender, and with the amount of adipose tissue versus lean muscle present in the body, as the latter has higher water content.

++

The extracellular fluid compartment (EFC) is equal to approximately one-third of the TBW or about 14 L in a 70-kg adult male. The extracellular compartment is subdivided into vascular, interstitial fluid, and transcellular compartments. The vascular compartment accounts for about 5% of total body weight or 3.5 L. The interstitial fluid compartment accounts for about 15% of total body weight or 9 L. The interstitial fluid tends to be low in protein and thus has a low oncotic pressure as compared to the vascular compartment. The intracellular fluid compartment accounts for two-third of TBW or about 28 L in a 60-kg adult male.

++

ELECTROLYTES

++

Sodium

++

Sodium is the major cation found in the ECF. Its normal concentration in serum is 135-145 mmol/L. Sodium concentration plays a large role in governing the ECF volume through osmotic forces. Additionally, sodium plays an important role in the ability of neuronal and cardiac tissue to generate an action potential.

++

The main factors that control sodium balance in the body are renal function (glomerular filtration rate), renin-angiotensin-aldosterone system, antidiuretic hormone (ADH), and atrial natriuretic peptide. Changes in serum sodium concentration largely have to do more with imbalances of TBW rather than sodium itself.

++

Hyponatremia is largely due to an excess of water relative to sodium in the setting of increased ADH secretion, either due to hypovolemia, decreased effective atrial volume, or inappropriate secretion of ADH (SIADH). Hyponatremic patients can present with symptoms, including vomiting, weakness, mental status changes, seizures, and coma. The severity of these symptoms is related to acuity of the changes in serum sodium concentration. In asymptomatic patients, sodium concentration should be corrected slowly with a rate of no greater than 0.5 mEq/L/h using isotonic fluids such as normal saline or lactated ringers. Correcting at too rapid a rate can cause fluid shifts from the intracellular compartment to the extracellular compartment, potentially leading to central pontine myelinolysis. In symptomatic patients, the rate of sodium correction should be faster, with a goal of 2 mEq/L/h for the first 2-3 hours, until symptoms begin to improve. Treatment for hyponatremia can vary depending on the etiology. In patients with hypovolemic hyponatremia, normal saline infusion will provide volume resuscitation, removing the stimulus for ADH secretion and allowing the kidneys to remove excess free water. In patients with SIADH, fluid restriction and treatment of the underlying cause is most effective. With hypervolemic hyponatremic, patients require loop diuretics to mobilize excess water and ...

Want remote access to your institution's subscription?

Sign in to your MyAccess profile while you are actively authenticated on this site via your institution (you will be able to verify this by looking at the top right corner of the screen - if you see your institution's name, you are authenticated). Once logged in to your MyAccess profile, you will be able to access your institution's subscription for 90 days from any location. You must be logged in while authenticated at least once every 90 days to maintain this remote access.

Ok

About MyAccess

If your institution subscribes to this resource, and you don't have a MyAccess profile, please contact your library's reference desk for information on how to gain access to this resource from off-campus.

Subscription Options

AccessAnesthesiology Full Site: One-Year Subscription

Connect to the full suite of AccessAnesthesiology content and resources including procedural videos, interactive self-assessment, real-life cases, 20+ textbooks, and more

$995 USD
Buy Now

Pay Per View: Timed Access to all of AccessAnesthesiology

24 Hour Subscription $34.95

Buy Now

48 Hour Subscription $54.95

Buy Now

Pop-up div Successfully Displayed

This div only appears when the trigger link is hovered over. Otherwise it is hidden from view.