Fluid & Electrolytes: Sodium, Potassium & Calcium

Comprehensive practice flashcards covering fluid and electrolyte concepts for Sodium, Potassium, and Calcium, including normal lab values, causes, signs and symptoms, ECG changes, and nursing interventions.

What is the normal serum reference range for sodium ($\text{Na}^+$)?

$$135-145\,\text{mEq/L}$$

Where is sodium primarily located in the body, and what are its primary functions?

Sodium is the most abundant electrolyte in the extracellular fluid (ECF). It regulates fluid balance (where sodium goes, water follows) and is vital for muscle contraction, cardiac contraction, and nerve impulse transmission.

How do the kidneys respond when serum sodium levels fall?

Decreased serum sodium stops ADH and natriuretic peptide (NP) release and triggers the renin-angiotensin-aldosterone system (RAAS), resulting in increased kidney sodium reabsorption and water excretion.

What threshold defines hyponatremia?

A serum sodium level below $136\,\text{mEq/L}$.

What is the maximum target increase for serum sodium within a 24-hour period when administering 3% hypertonic saline?

$8-10\,\text{mEq/L}$ in 24 hours (rapid correction risks cerebral edema and severe neurological complications).

What threshold defines hypernatremia?

A serum sodium level greater than $145\,\text{mEq/L}$.

What initial neuromuscular manifestations occur in hypernatremia before progressing to severe weakness?

Neuromuscular excitability, including muscle twitching and hyperactive reflexes.

What is the normal serum reference range for potassium ($\text{K}^+$)?

$$3.5-5.0\,\text{mEq/L}$$

Where is potassium primarily distributed within body fluids?

Inside the cell, making it the major intracellular fluid (ICF) cation.

Which electrolyte deficiency frequently co-occurs with low potassium levels?

Hypomagnesemia (low magnesium levels often lead to low potassium levels).

What classic electrocardiogram (ECG) change is associated with hypokalemia?

Inverted T waves.

What are the maximum IV infusion rate limits for potassium chloride (KCL) via peripheral versus central venous access?

Up to $10\,\text{mEq/hr}$ via a peripheral intravenous line (PIV), and up to $20\,\text{mEq/hr}$ only via a central venous access device (CVAD).

Why is potassium NEVER administered via IV push, IM, or subcutaneous routes?

Direct or rapid injection of concentrated potassium causes fatal cardiac arrest and extreme tissue necrosis.

Which electrolyte imbalance causes the sequence of ECG changes shown in this diagram?

Hyperkalemia (serum potassium level greater than $5.0\,\text{mEq/L}$).

Which immediate intravenous treatments are given to stabilize the heart and shift potassium into cells during severe hyperkalemia?

IV Calcium gluconate (protects the myocardium) along with IV regular insulin and Dextrose 50% (shifts potassium into cells).

What is the normal serum reference range for total calcium?

$9-10.5\,\text{mg/dL}$ ($2.25-2.75\,\text{mmol/L}$)

Which three substances directly regulate serum calcium homeostasis?

Vitamin D, calcitonin, and parathyroid hormone (PTH).

How do parathyroid hormone (PTH) and calcitonin differ in their effects on blood calcium levels?

Parathyroid hormone (PTH) raises blood calcium levels by stimulating osteoclast activity and renal reabsorption; calcitonin lowers blood calcium levels by inhibiting osteoclasts and limiting intestinal and renal absorption.

What clinical sign of hypocalcemia is depicted in this image?

Trousseau's sign (carpopedal spasm induced by inflating a blood pressure cuff above systolic pressure).

What clinical sign of hypocalcemia is depicted in this image?

Chvostek's sign (facial muscle twitching when tapping the facial nerve in front of the ear).

What childhood condition is caused by severe calcium and Vitamin D deficiency, causing bow legs and stunted growth?

Rickets.

What electrolyte imbalance is associated with the clinical manifestations summarized in this graphic?

Hypercalcemia (serum calcium level greater than $10.5\,\text{mg/dL}$).

Why are thiazide diuretics replaced with loop diuretics (such as furosemide) in the management of hypercalcemia?

Thiazide diuretics inhibit calcium excretion and increase serum calcium levels, whereas loop diuretics promote renal calcium excretion.