fluids. and electrolytes

Main fluid compartments

ICF, ECF, interstitial

ICF

25 L

ECF

plasma -3.5-6L

interstitial

~10-12 L

shifts

↑interstitial → edema; ↓plasma → hypotension; ↓ICF → cellular dehydration.

Filtration

= water via hydrostatic pressure (e.g., BP, edema in right HF).

Diffusion

= particles high→low (Na+, glucose w/ insulin).

Osmosis =

water moves to higher osmolarity (cell shrink/swell).

Na+

136-145 mEq/L;

K+

3.5-5.0 mEq/L;

Ca+

+ 9-10.5 mg/dL;

Mg+

+ 1.8-2.6 mEq/L;

Osm

270-300 mOsm/L.

Aldosterone

reabsorption sodium and water; excretes potassium. (excess → HTN, hypokalemia).

ADH

↑H2O reabsorption (excess/SIADH → hyponatremia).

Natriuretic peptides

↑Na+/H2O loss.

RAAS

Increases blood pressure and blood volume when perfusion low.

Hyponatremia (Na+ <136) causes

Causes: diuretics, kidney disease, SIADH, diaphoresis.

hyponatremia s/s

S/S: confusion, seizures, coma; muscle weakness, ↓DTRs; N/V, diarrhea.

Hyponatremia complications

Complications: cerebral edema, death.

Hypernatremia (Na+ >145) causes

Causes: dehydration, kidney disease, steroids

Hypernatremia s/s

. S/S: agitation/confusion or lethargy; twitching → weakness; ↓contractility.

hypernatremia complications

Complications: neuro deficits, seizures, circulatory overload.

Hypokalemia (K+ <3.5) causes

Causes: GI loss, diuretics, steroids.

hypokalemia s/s

S/S: weakness, ↓DTRs, shallow respirations; thready pulse, arrhythmias; constipation/ileus.

Hypokalemia complications

Complications: resp failure, fatal arrhythmias.

Hyperkalemia (K+ >5.0)

Causes: renal disease, ACE inhibitors, blood transfusions. S/S: bradycardia, hypotension, peaked T waves; twitching → paralysis; diarrhea. Complications: cardiac arrest.

Hypocalcemia (Ca++ <9)

Causes: Vit D deficiency, CKD, diarrhea. S/S: paresthesias, cramps, tetany; Chvostek/Trousseau signs; weak pulse, hypotension; diarrhea, brittle bones. Complications: seizures, fractures.

Hypercalcemia (Ca++ >10.5)

Causes: malignancy, thiazides, dehydration. S/S: confusion, lethargy; severe weakness, ↓DTRs; constipation, N/V. Complications: kidney stones, arrhythmias.

Hypomagnesemia (Mg++ <1.8)

Causes: malnutrition, diarrhea, diuretics. S/S: ↑DTRs, painful cramps, tetany, seizures; HTN, dysrhythmias. Complications: sudden death from arrhythmias.

Hypermagnesemia (Mg++ >2.6)

Causes: renal failure, Mg++ excess. S/S: bradycardia, hypotension, lethargy, ↓DTRs, weak muscles, resp depression. Complications: cardiac arrest.