5. Fluid & Electrolyte - MASTERY CONCEPT

Discuss the normal distribution of water in the body.

46–60% of body weight is water; 2/3 ICF and 1/3 ECF. ECF = intravascular, interstitial, transcellular.

Name the main system regulators of F&E balance.

Kidneys, thirst, ADH, and angiotensin II–aldosterone.

Define diffusion and osmosis.

Diffusion: particles move high → low concentration. Osmosis: water moves toward higher solute concentration.

Define serum osmolality and discuss how it is affected by physiologic factors.

Serum osmolality = concentration of particles in solution; normal 275–295 mOsm/kg. Dehydration ↑; excess water ↓.

Define trans‐cellular fluid.

ECF located in specialized spaces, such as cerebrospinal, synovial, and GI fluids.

Discuss how water is regulated in the body. Name the main hormone involved.

Kidneys regulate water; ADH promotes water reabsorption and decreases urine output.

Discuss how sodium is regulated in the body. Name the main hormone involved.

Aldosterone promotes sodium reabsorption; water follows sodium, increasing fluid volume/BP.

Trace the mechanism and the outcome of stimulation of the RAA mechanism.

Renin → angiotensin I → angiotensin II → aldosterone → sodium/water retention → ↑ blood volume and BP.

Define the relationship of fluid volume, sodium and blood pressure (BP).

Sodium retains water; more sodium/water → ↑ fluid volume → ↑ BP.

Define isotonic/hypotonic/hypertonic fluids and their effect on cell size.

Isotonic: no cell change

Hypotonic: swells because more solutes inside

Hypertonic: shrinks because more solutes outside

Discuss the main difference between crystalloids and colloids.

Crystalloids contain readily dissolved salts; colloids contain larger molecules that do not readily dissolve.

Name examples of IV fluids which are considered crystalloid/colloid.

Crystalloids: NS, LR, D5W, ½ NS, ¼ NS, D5NS. Colloid examples are not specified in the PPT.

Describe the 4 forces controlling movement of fluid between the vascular space and the interstitial space.

BHP pushes out; IFHP pushes in; BCOP pulls in; IFOP pulls out.

Identify and describe the 4 causes of edema. Be able to give examples.

↑ capillary pressure; ↓ capillary colloid osmotic pressure; ↑ capillary permeability; lymph obstruction/damage.

Give clinical examples of third spacing

Ascites, burns, peritonitis, bowel obstruction.

Describe how edema is assessed and give examples of when it can be harmful.

Assess for swelling/pitting and changes in tissue/fluid volume. It can be harmful when it interferes with organ function, especially pulmonary edema.

Identify normal serum values for potassium, sodium, magnesium, & calcium.

Na: 135–145 mEq/L

K: 3.5–5 mEq/L

Mg: 1.8–3.0 mg/dL

Ca: ionized 4–5.5 mg/dL, total 8.5–10.5 mg/dL.

Identify common causes of increased or decreased levels of each of the above.

Na: excess water/ADH ↓; sodium gain or water loss ↑

K: GI/renal/skin losses ↓; excess intake, cell release, or decreased renal elimination ↑

Mg: impaired intake/absorption or losses ↓; excess intake/decreased excretion ↑

Ca: decreased intake/absorption or renal loss ↓; increased absorption/bone resorption or decreased elimination ↑.

Identify common clinical manifestations of each of the above.

Na: cramps, weakness, headache, seizures/coma. K: weakness, paralysis, dysrhythmias. Mg: muscle excitability or weakness, arrhythmias, seizures. Ca: tetany/seizures when low; polyuria, constipation, lethargy when high.