Chapter 6 Fluid and Electrolytes

What percentage of body weight is total body water (TBW)?

Adults: ~60%

Newborns: 70%+

Mature women: 50–55%

What are the two major fluid compartments?

Intracellular Fluid (ICF) = 2/3 of TBW

Extracellular Fluid (ECF) = 1/3 of TBW

Where is intracellular fluid (ICF) found?

Inside the cells

• About 28 L in a 70-kg adult

• Rich in potassium (K⁺)

What are the components of extracellular fluid (ECF)?

• Interstitial fluid (2/3)

• Intravascular fluid/plasma (1/3)

• Transcellular fluid

  • CSF

  • Pleural fluid

  • Synovial fluid

What happens when excessive fluid accumulates in the interstitial space?

Edema develops

Conditions that increase water requirements?

Fever, Sweating, Burns, Tachypnea, Polyuria, Vomiting, Diarrhea, Surgical drains

How much extra fluid is needed for every 1°C increase in body temperature?

100–150 mL/day

What is tonicity?

The ability of the extracellular solution to move water into or out of cells by osmosis.

What happens with isotonic solutions?

No net water movement

Cells stay the same size

Examples: 0.9% NS, Lactated ringers, D5W

What happens with hypotonic solutions?

Water moves INTO cells

Cells swell

Examples: 0.45% NS, 0.33% NS

What happens with hypertonic solutions?

Water moves OUT of cells

Cells shrink

Examples: 3% NS, 5% NS, D10W

Define osmosis.

Water moves from

Low solute concentration → High solute concentration

What does ADH do?

Saves water

Acts on kidneys to retain water

What does aldosterone do?

Saves sodium

Water follows sodium

What does ANP do?

Gets rid of sodium and water

Promotes diuresis

Causes of hypovolemia

Vomiting, diarrhea, sweating, hemorrhage, inadequate fluid intake

Manifestations of hypovolemia?

Weight loss, dry mucous membranes, decreased skin turgor, tachycardia, hypotension, oliguria, thirst, confusion

Treatment for hypovolemia?

Treat underlying cause

Fluid replacement

Causes of hypervolemia?

Excess sodium or water intake

Inadequate sodium or water elimination

Manifestations of hypervolemia?

Edema, dyspnea, tachycardia, hypertension, JVD, crackles, weight gain

Treatment for hypervolemia?

Restrict sodium and fluids, diuretics, high Fowler’s position

Normal sodium level?

135-145 mEq/L

Functions of sodium

Regulates fluid volume ‘where sodium goes, water follow’

Maintains osmolarity

Nerve impulses

Muscle contraction

Sodium level in hyponatremia

<135 mEq/L

Manifestations of hyponatremia?

Headache, confusion, weakness, muscle cramps, nausea, hypotension, seizures, anorexia

Cells swells

Treatment for hyponatremia?

Fluid restriction

Increase sodium intake

Sodium level in hypernatremia

>145 mEq/L

Manifestations of hypernatremia

Thirst, dry tongue, agitation, restlessness, seizures, weight gain

Cells shrink

Treatment for hypernatremia?

Fluid replacement

Diuretics

Normal potassium level

3.5-5 mEq/L

Potassiums major role

Electrical conduction

Potassium level in hypokalemia

<3.5 mEq/L

Manifestations of hypokalemia

Weakness, leg cramps, hypotension, flat T waves, dysrhythmias, decreased bowel motility

Treatment for hypokalemia

Potassium replacement

Eliminate cause

Potassium level in hyperkalemia

>5 mEq/L

Manifestations of hyperkalemia

Muscle weakness, paresthesias, diarrhea, dysrhythmias, tall peaked T waves

Treatment for hyperkalemia

Restrict potassium

Insulin with glucose

Dialysis if severe

Normal calcium level

4-5 mEq/L

Major functions of calcium

Muscle contraction, blood clotting, nerve transmission, hormone secretion

Manifestations of hypocalcemia

Tetany, seizures, anxiety, positive Chvostek and Trousseau signs

Treatment for hypocalcemia

Calcium replacement

Decrease phosphorus

Manifestations of hypercalcemia

Weakness, kidney stones, polyuria, confusion, constipation

Treatment of hypercalcemia

Increasing mobility

Administering IV fluids

Medications

Normal magnesium level

1.8-2.5 mEq/L

Manifestations of hypomagnesemia

Tremors, seizures, positive Chvostek sign. Dysrhythmias