Water and Electrolyte Disorders Flashcards
What are the body fluid compartments?
ICF and ECF
ECF is subdivided into what components?
Interstitial, vascular
What is the major ECF cation?
Na
What is the major ICF cation?
K
What is the major ECF anion?
Cl
What is the major ICF cation?
Phosphate
Define plasma osmolality.
The number of solutes in plasma
POsm = ?
2(serum Na) + (serum glucose/18) + (BUN/2.8)
What is a normal POsm?
275-295 mOsm/kg
What is the major determinant of plasma osmolality?
Na
How does effective osmolality (EOsm) differ from plasma osmolality?
POsm - BUN/2.8 (urea diffuses between ICF and ECF and thus does not affect the osmotic gradient)
Detail the movement of water between ECF and ICF compartments of differing osmolalities.
Water from from low solute concentration to high solute concentration
What effect does hyponatremia have on the movement of water?
Water moves from ECF to ICF
What effect does hypernatremia/hyperglycemia have on the movement of water?
Water moves from ICF to ECF
Decreased TBNa presents with what clinical exam findings?
Signs of volume depletion- Decreased skin turgor, dry mucous membranes, decreased BP, increased pulse
The movement of fluid across a capillary into the interstitial space is driven by Starling forces. What changes result in the movement of fluid out of capillaries into the interstitial space?
Decrease in plasma oncotic pressure and/or increased hydrostatic pressure
Define isotonic fluid loss.
Net isotonic loss of Na + H2O
Give an example of isotonic fluid loss.
Secretory diarrhea (adults)
What clinical signs indicate isotonic fluid loss.
Signs of volume depletion
What are the expected values for POsm and serum sodium with isotonic fluid loss?
Normal- hypovolemic normonatremia
Detail the osmotic gradient between the ICF and ECF with isotonic loss of fluid.
No gradient or fluid shifts between compartments. ECF volume is contracted, but ICF volume remains the same.
Define isotonic gain of fluid.
Net isotonic gain of Na + H2O
What are the expected values for POsm and serum sodium with isotonic fluid gain?
Normal- hypervolemic normonatremia
Detail the osmotic gradient between the ICF and ECF with isotonic gain of fluid.
No gradient or fluid shifts between compartments. ECF volume is expanded, but ICF volume remains the same.
What is the composition of normal saline?
9g NaCl/L = 0.9%
How can you treat isotonic gain of fluid?
Restrict sodium and water. Loop diuretics
What physical exam finding may be present in a patient with an isotonic gain of fluid?
Pitting edema
What is always present with hypotonic fluid disorders?
Hyponatremia
Detail the osmotic gradient between the ECF and the ICF with hypotonic fluid disorders.
Fluid moves from ECF into ICF
What processes can lead to a hypotonic fluid disorder.
Loss of hypertonic solution, gain of pure water, or gain of hypotonic solution
Define hypertonic loss of fluid.
Loss of Na in excess of water
What are the expected values for POsm and serum sodium with hypertonic fluid loss?
Decreased- hypovolemic hyponatremia
Detail the osmotic gradient between the ICF and ECF with hypertonic loss of fluid.
Fluid flows from ECF into ICF. ECF is volume is contracted. ICF volume is expanded.
List examples of conditions that can lead to hypertonic fluid loss.
Loop diuretics/thiazides (excessive), Addison disease, 21-hydroxylase deficiency
What is the treatment for hypertonic fluid loss?
Normal saline
Why are sodium containing fluids given slowly, especially in alcoholics?
Avoid central pontine myelinolysis
What are the expected values for POsm and serum sodium with a gain in pure water?
Decreased- euvolemic hyponatremia
Detail the osmotic gradient between the ICF and the ECF with gain in pure water.
Fluid moves from ECF into ICF. ECF and ICF are volume expanded.
When checking skin turgor in a patient with gain in pure water, what finding would you expect?
Normal, because TBNa is normal
What conditions lead to a gain in pure water?
SIADH, compulsive water drinking
What is the treatment for gain in pure water?
Restrict water
A serum sodium less than 120 indicates what disease process?
SIADH
What are the expected values for POsm and serum sodium with a gain of hypotonic solution?
Decreased- hypervolemic hyponatremia
Detail the change in volume of the ICF and the ECF with gain of hypotonic solution.
Expansion of both compartments.
How is pitting edema related to gain of hypotonic solution.
With RHF (increased venous hydrostatic pressure) or cirrhosis/nephrotic syndrome (decreased oncotic pressure), CO is decreased. This is because fluid is trapped in the interstitial space. Decreased CO results in activation of the renin-angiotensin-aldosterone system. This causes the kidney to reabsorb a slightly hypotonic solution. When this occurs the fluid ends up in the interstitial space, which exacerbates pitting edema.
What conditions lead to hypervolemic hyponatremia?
RHF, cirrhosis, nephrotic syndrome
How do you treat gain in hypotonic solution (hypervolemic hyponatremia)?
Restrict water and salt. Diuretics
