Fluid & Electrolytes: Key Concepts for Nursing and Health Science

Fluid & Electrolytes

Basics Essential for homeostasis; imbalance affects every body system

Body Water %

Body is ~60% water; varies by age, gender, fat

ICF vs ECF

ICF = inside cells (⅔ water) | ECF = outside cells

Electrolytes Definition

Charged particles that regulate water, nerve & muscle function

Cations

(+) Na⁺, K⁺, Ca²⁺, Mg²⁺

Anions

(-) Cl⁻, HCO₃⁻, PO₄³⁻

Osmosis Water

moves toward higher solute concentration

Hydrostatic Pressure

Pushes fluid OUT

Osmotic Pressure

Pulls fluid IN

Diffusion Solutes

move high → low | No energy

Filtration Fluid

moves high → low pressure

Active Transport

Requires ATP (ex: Na/K pump)

Daily Weight

Best indicator of fluid balance

Main Fluid Regulators

Kidneys, heart, lungs, adrenal, pituitary, parathyroid

Older Adult Risk Higher risk of dehydration due to

↓ thirst & kidney function

Fluid Volume Deficit (FVD)

Hypovolemia from loss or low intake

FVD Symptoms

Weight loss, dry mucosa, weak pulse, low BP, concentrated urine

FVD Treatment

Oral or IV fluid replacement

FVD Nursing

Monitor I&O, weight, vitals, turgor, urine output

Fluid Volume Excess (FVE)

Volume overload from increased Na & water

FVE Causes

Heart failure, renal failure, liver failure

FVE Symptoms

Edema, crackles, weight gain, ↑ BP

FVE Nursing Care

I&O, daily weights, diuretics, restrict Na & fluids

Sodium Range

136-145 mEq/L

Sodium Function

ECF volume & nerve impulses

Hyponatremia

Confusion, poor skin turgor, ↓ BP, headache

Hyponatremia

Tx Sodium replacement, fluid restriction

Hypernatremia

Thirst, dry tongue, confusion, ↑ temp

Hypernatremia

Tx Gradual fluid replacement, hypotonic IV

Potassium Range

3.5-5.1 mEq/L

Potassium Function

Major ICF electrolyte; heart rhythm

Hypokalemia

Weakness, fatigue, dysrhythmias, ↓ bowel mobility

Hypokalemia

Tx PO/IV potassium, ECG monitoring

Hyperkalemia

Muscle weakness, paresthesia, dysrhythmias

Hyperkalemia

Tx Limit K intake, Ca gluconate, insulin + glucose, dialysis

Calcium Range

8.6-10.2 mg/dL

Calcium Function

Bone, muscle contraction, clotting

Hypocalcemia

Numbness, tetany, Chvostek & Trousseau, seizures

Hypocalcemia

Tx Calcium + vitamin D, IV calcium gluconate

Hypercalcemia

Lethargy, constipation, bone pain

Hypercalcemia

Tx Fluids, diuretics, calcitonin

Magnesium Range

1.5-2.4 mg/dL

Magnesium Function

Nerve & muscle function; works w/ K & Ca

Hypomagnesemia

Tremors, weakness, ↑ reflexes, dysrhythmias

Hypomagnesemia

Tx Mg replacement, seizure precautions

Hypermagnesemia

↓ reflexes, drowsy, respiratory depression

Hypermagnesemia

Tx Stop Mg intake, Ca gluconate, dialysis

Electrolyte Memory Trick

Na = brain | K = heart | Ca = muscle | Mg = reflexes

Normal pH

7.35-7.45

ABG Normals pH

7.35-7.45 | CO₂ 35-45 | HCO₃ 22-26 | O₂ Sat >94%

ROME Respiratory

Opposite | Metabolic Equal

Metabolic Acidosis

pH↓ HCO₃↓ | DKA, renal failure | Kussmaul breathing

Metabolic Alkalosis

pH↑ HCO₃↑ | vomiting, diuretics | tingling, cramps

Respiratory Acidosis

pH↓ CO₂↑ | COPD, hypoventilation

Respiratory Alkalosis

pH↑ CO₂↓ | anxiety, hyperventilation

Acid-Base Fixes

R Acidosis = ventilate | R Alkalosis = slow breath | M Acidosis = fix cause | M Alkalosis = fluids & electrolyt