Introduction to Fluid and Electrolyte Disorders

I. Edema

Definition of Edema

  • Accumulation of fluid in the tissue spaces.

Related Terms

  • Effusion: Fluid moves from blood vessels into body cavities.

  • Anasarca: Severe, generalized edema.

  • Hydrocephalus: Fluid accumulation in the brain.

  • Ascites (Hydroperitoneum): Fluid accumulation in the peritoneal cavity.

Fluid Compartments

  • First Space: Intravascular (blood) compartment.

  • Second Space: Interstitial fluid compartment.

  • Third Space: Fluid trapped in places where it normally should not be (body cavities, joints, eyes, ears, muscle compartments).

Types of Edema Fluid

Transudate

  • Non-inflammatory

  • Low protein

  • Caused by changes in hydrostatic or osmotic pressure

Exudate

  • Inflammatory

  • High protein

  • Contains many cells

Causes of Edema

1. Increased Capillary Filtration Pressure (Hydrostatic Pressure)

Increased Arterial Pressure

  • Hypertension

  • Inflammation

  • Calcium channel blockers

Increased Venous Pressure

  • Heart failure

  • Liver disease

  • Venous thrombosis

Increased Blood Volume

  • Kidney disease

  • Premenstrual fluid retention

  • Heat exposure

2. Decreased Capillary Colloidal Osmotic Pressure

Protein Loss

  • Kidney disease

  • Severe burns

Decreased Protein Production

  • Liver disease

  • Starvation

3. Increased Capillary Permeability

  • Burns

  • Tissue injury

  • Inflammation

  • Allergic reactions

  • Cancer

4. Lymphatic Obstruction (Lymphedema)

  • Infection

  • Trauma

  • Tumors

  • Lymph node removal

Assessment of Edema

Signs and Symptoms

  • Swelling

  • Tight, shiny skin

  • Weight gain

Assessment Methods

  • Daily weights

  • Measure affected area

  • Visual inspection

  • Check for pitting

Pitting Edema Scale

  • 1+: Barely detectable

  • 2+: Rebounds in 15 seconds

  • 3+: Lasts 30 seconds

  • 4+: Deep indentation lasting >30 seconds

Non-Pitting Edema

  • Common with lymphedema

  • Tissue feels firm and swollen

Treatment of Edema

Medications

  • Diuretics

  • Albumin replacement

Procedures

  • Paracentesis

  • Shunts

Physical Interventions

  • Compression stockings

  • Compression pumps

  • Massage

  • Elevation

  • Range of motion exercises

II. Disorders of Thirst and ADH

Hypodipsia

Definition

  • Decreased thirst sensation

Causes

  • Hypothalamic lesions

  • Stroke

  • Dementia

  • Aging

Polydipsia

Definition

  • Excessive thirst

Causes

  • Water deficit

  • Psychogenic polydipsia

  • Anticholinergic medications

  • Decreased saliva production

  • Increased angiotensin

Diabetes Insipidus (DI)

Characteristics

  • Polyuria

  • Polydipsia

Types

Neurogenic DI

  • Decreased ADH production or release

Nephrogenic DI

  • Kidneys do not respond to ADH

Risk

  • Hypertonic dehydration

Syndrome of Inappropriate ADH (SIADH)

Characteristics

  • Excess ADH secretion

  • Water retention

  • Hyponatremia

Causes

  • Surgery

  • Stress

  • Pain

  • Lung tumors

  • Brain tumors

III. Fluid Volume Disorders

Isotonic Fluid Volume Deficit (Hypovolemia)

Causes

Decreased Intake

  • Inability to access fluids

  • Dementia

  • Swallowing disorders

Increased Losses

  • Diarrhea

  • Polyuria

  • Sweating

  • Burns

  • Bleeding

  • Third spacing

Manifestations

  • Thirst

  • Weight loss

  • Oliguria

  • Tachycardia

  • Sunken eyes

  • Poor skin turgor

  • Sunken fontanels

Treatment

  • Fluid replacement

  • Electrolyte replacement

Isotonic Fluid Volume Excess

Causes

  • Heart failure

  • Kidney disease

  • Liver disease

  • Steroid use

  • Excess sodium intake

Manifestations

  • Weight gain

  • Edema

  • JVD

  • Increased blood pressure

  • Pulmonary edema

  • Crackles

  • Shortness of breath

Treatment

  • Fluid restriction

  • Sodium restriction

  • Loop diuretics

IV. Diuretics

Thiazide Diuretics

  • Hydrochlorothiazide

  • Block sodium reabsorption in distal tubule

Potassium-Sparing Diuretics

  • Prevent potassium loss

Loop Diuretics

  • Furosemide (Lasix)

  • Strongest diuretics

Osmotic Diuretics

  • Mannitol

Carbonic Anhydrase Inhibitors

  • Increase sodium and potassium excretion

V. Sodium Imbalances

Hyponatremia

Definition

  • Sodium < 135 mEq/L

Causes

  • Water retention

  • Excess water intake

  • Diuretics

  • Vomiting

  • Sweating

  • Wound drainage

Manifestations

Neurological

  • Headache

  • Lethargy

  • Confusion

  • Anxiety

Muscular

  • Weakness

  • Muscle cramps

GI

  • Nausea

  • Vomiting

  • Diarrhea

Treatment

  • Treat underlying cause

  • Increase sodium intake

  • Hypertonic saline (slowly)

Hypernatremia

Definition

  • Sodium >145 mEq/L

Causes

  • Diarrhea

  • Fever

  • Sweating

  • Diabetes insipidus

  • Hyperaldosteronism

  • Sodium overload

Manifestations

  • Intense thirst

  • Oliguria

  • Dry skin

  • Dry mucous membranes

  • Agitation

  • Seizures

  • Coma

  • Hypotension

Treatment

  • Treat underlying cause

  • Oral or IV fluids

  • Correct slowly

VI. Potassium Imbalances

Hypokalemia

Causes

  • Poor intake

  • GI losses

  • Renal losses

  • Diuretics

Manifestations

  • Muscle weakness

  • GI dysfunction

  • Cardiac arrhythmias

ECG

  • ST depression

Hyperkalemia

Causes

  • Renal failure

  • Excess potassium intake

  • Rapid IV potassium

  • Cellular potassium shifts

Manifestations

  • Cardiac arrhythmias

  • Cardiac arrest

ECG

  • Peaked T waves

  • ST depression

VII. Calcium, Magnesium, and Phosphate

Relationship Between Calcium, Magnesium, and Phosphorus

  • These electrolytes work together to regulate:

    • Muscle contraction

    • Nerve function

    • Bone health

    • Cardiac function

  • Changes in one often affect the others.

Hypocalcemia

Causes

  • Hypoparathyroidism

  • Vitamin D deficiency

  • Kidney disease

  • Pancreatitis

Manifestations

  • Muscle spasms

  • Neuromuscular irritability

  • Seizures

Hypercalcemia

Causes

  • Hyperparathyroidism

  • Cancer

  • Vitamin D disorders

  • Prolonged immobilization

Manifestations

  • Kidney stones

  • Bone pain

  • Polyuria

  • Arrhythmias

  • Coma

Hypomagnesemia

Causes

  • Alcoholism

  • Diarrhea

  • Poor intake

  • Diuretics

Manifestations

  • Muscle cramps

  • Weakness

  • Arrhythmias

Hypermagnesemia

Causes

  • Excess magnesium intake

  • Kidney failure

Manifestations

  • Nausea

  • Vomiting

  • Muscle weakness

Hypophosphatemia

Causes

  • Malnutrition

  • Alcoholism

  • Cancer

Manifestations

  • Muscle weakness

Hyperphosphatemia

Causes

  • Kidney disease

  • Crush injuries

Manifestations

  • Often asymptomatic

  • Severe cases resemble hypocalcemia

VIII. Acid-Base Balance

Normal Values

  • pH: 7.35–7.45

  • PaCO₂: 35–45 mmHg

  • HCO₃⁻: 22–26 mEq/L

  • PaO₂: 80–100 mmHg

  • SaO₂: 95–100%

Acidosis

  • pH < 7.35

Respiratory Acidosis

Cause: Hypoventilation → ↑CO₂

Examples:

  • COPD

  • Pulmonary edema

  • Airway obstruction

Compensation:

  • Kidneys retain bicarbonate

  • Excrete hydrogen ions

Metabolic Acidosis

Cause: Excess acids or loss of bicarbonate

Examples:

  • Diarrhea

  • Diabetic ketoacidosis

  • Kidney disease

Compensation:

  • Hyperventilation

  • Renal compensation

Alkalosis

  • pH > 7.45

Respiratory Alkalosis

Cause: Hyperventilation → ↓CO₂

Examples:

  • Panic attacks

  • Fever

  • High altitude

Compensation:

  • Kidneys excrete bicarbonate

Metabolic Alkalosis

Cause: Loss of hydrogen ions or excess bicarbonate

Examples:

  • Vomiting

  • Gastric suction

  • Antacid overuse

Compensation:

  • Hypoventilation

  • Renal bicarbonate excretion

IX. ABG Interpretation

Step 1: Check pH

  • pH > 7.45 = Alkalosis

  • pH < 7.35 = Acidosis

Step 2: Check PaCO₂

  • Opposite direction of pH = Respiratory problem

Step 3: Check HCO₃⁻

  • Same direction as pH = Metabolic problem

Compensation

  • The remaining value moves opposite the pH to help correct the imbalance