Fluid and Electrolyte Balance

• Fluid and electrolyte balance involves regulating extracellular fluid (ECF) volume, body fluid osmolality, and plasma electrolyte concentrations

Fluid Compartments

• Intracellular fluid (ICF) is ~2/3 of body fluid and is inside cells
• Extracellular fluid (ECF) is ~1/3 of body fluid and is outside cells

Extracellular Fluid Includes

• Interstitial fluid, which is between cells
• Intravascular fluid, which is plasma

Optimal Fluid & Electrolyte Balance Requires

• Intake and absorption matching output
• Volume, osmolality, and electrolytes within normal ranges

Intake and Absorption Facts

• Oral intake is the most common route
• Increased osmolality triggers thirst
• GI health and vitamin D affect Calcium and magnesium absorption

Hormonal Regulation and Control

• Hormones play a major role in controlling fluid and electrolyte levels

Aldosterone

• Secreted by the adrenal cortex
• It increases sodium and water reabsorption in the kidneys
• It Promotes potassium excretion
• Low blood volume or high potassium activates it

Antidiuretic Hormone (ADH)

• Released by the posterior pituitary
• It promotes water reabsorption in the kidneys
• Increases blood volume
• Decreases osmolality
• Dehydration or high blood osmolality triggers it

Parathyroid Hormone (PTH)

• Increases blood calcium levels
• It promotes calcium reabsorption from bones
• It promotes absorption in the intestines and kidneys

Calcitonin

• Secreted by the thyroid gland
• Lowers blood calcium levels through calcium deposition in bones
• It opposes PTH

Renin-Angiotensin-Aldosterone System (RAAS) Activation

• RAAS is activated when blood pressure or blood volume drops

RAAS Steps

• Renin is released by the kidneys due to decreased perfusion
• Renin converts angiotensinogen (from the liver) into angiotensin I
• Angiotensin I converts to angiotensin II by ACE (in the lungs)

Angiotensin II Actions

• Causes vasoconstriction to raise blood pressure
• Stimulates aldosterone release to retain sodium and water
• Stimulates ADH to retain water.

RAAS Importance

• The RAAS system is crucial for maintaining fluid balance, especially in dehydration, blood loss, or hypotension
• Dysfunction in RAAS can cause symptoms

Imbalances; Causes and Outcomes

• Imbalances can result from output exceeding intake/absorption, or vice versa, or from altered distribution

Output > Intake/Absorption

• Vomiting, diarrhea, and diuretics can cause Output > Intake/Absorption
• ECV deficit, hypernatremia, and electrolyte deficits can result in Output > Intake/Absorption

Output < Intake/Absorption

• Excessive IV fluids, water intoxication, and kidney failure can cause Output < Intake/Absorption
• ECV excess, hyponatremia, and electrolyte excess can result in Output < Intake/Absorption

Altered Distribution

• Fluid shifts into "third spaces" (e.g., ascites, edema)

Potassium Function and Imbalance

• Nerve/muscle activity and heart rhythm
• Low potassium symptoms: Cramps, fatigue, arrhythmias
• High potassium symptoms: Weakness, paralysis, arrhythmias

Calcium Function and Imbalance

• Muscle contraction and nerve signaling
• Low calcium symptoms: Spasms, tetany, tingling
• High calcium symptoms: Weakness, confusion, slow reflexes

Magnesium Function and Imbalance

• Muscle relaxation and enzyme function
• Low magnesium symptoms: Cramps, tremors, seizures
• High magnesium symptoms: Weakness, low BP, respiratory depression

Sodium Function and Imbalance

• Fluid balance and nerve impulses
• Low sodium symptoms: Confusion, seizures
• High sodium symptoms: Thirst, twitching, restlessness

Shared Symptom: Muscle Weakness

• Electrolytes involved: High K⁺, Ca²⁺, Mg²⁺
• Relationship: Depresses neuromuscular activity

Shared Symptom: Cramps/Spasms

• Electrolytes involved: Low K⁺, Ca²⁺, Mg²⁺
• Relationship: Increases excitability

Shared Symptom: Arrhythmias

• Electrolytes involved: Low/High K⁺, Low Mg²⁺
• Relationship: Cardiac instability

Shared Symptom: Confusion

• Electrolytes involved: Low Na⁺, High Ca²⁺, Mg²⁺
• Relationship: CNS effect (swelling or suppression)

Shared Symptom: Seizures

• Electrolytes involved: Low Na⁺, Ca²⁺, Mg²⁺
• Relationship: Neuronal hyperexcitability

Symptom: Tingling/Numbness

• Electrolytes involved: Low Ca²⁺, Mg²⁺
• Relationship: Nerve sensitivity

Consequences of Imbalance Include

• Impaired perfusion and oxygenation
• Impaired cerebral function
• Impaired neuromuscular function

At-Risk Populations Include

• Older adults
• Infants/young children
• Individuals with chronic illness (kidney, heart)
• Patients on medications affecting fluid/electrolyte balance (diuretics, steroids)