Fluid & Electrolytes – Med-Surg/Pharmacology Review

Question-and-Answer flashcards covering homeostasis, osmolality, fluid compartments, osmosis, ADH, kidney function, fluid losses, diffusion, active transport, and detailed electrolyte imbalances for potassium, sodium, and calcium.

What is homeostasis?

The body’s ability to maintain internal balance and stable conditions despite external changes.

What does fluid balance mean in the context of homeostasis?

Maintaining the correct amounts of water and electrolytes in the body.

What is the normal range for serum osmolality?

285–295 mOsm/kg.

Serum osmolality >295 mOsm/kg indicates what condition?

Dehydration (blood is too concentrated).

Serum osmolality <285 mOsm/kg suggests what problem?

Over-hydration or water excess (blood is diluted).

What is urine osmolality and its normal range?

A measure of how concentrated the urine is; normal 50–1,200 mOsm/kg.

High urine osmolality tells you what about body water?

The kidneys are conserving water; urine is concentrated.

Low urine osmolality signifies what?

The body is excreting excess water; urine is dilute.

Name two key bedside assessments related to osmolality.

Strict intake & output plus watching for edema/weight change (and lab trends).

Roughly what percentage of total body water is intracellular?

About 67 %.

How much body water is stored in the interstitial (extracellular) compartment?

Approximately 25 % of total body water.

What portion of body water is intravascular (plasma)?

Roughly 8 %.

Define osmosis.

Movement of water through a semi-permeable membrane from low solute concentration toward higher solute concentration to equalize both sides.

Why is 0.45 % normal saline used for dehydration?

It is hypotonic; water shifts into cells via osmosis to rehydrate them.

What dangerous complication can result from excessive hypotonic fluid causing cell swelling in the brain?

Cerebral edema (headache, confusion, seizures).

Where is the thirst center located?

The lamina terminalis near the hypothalamus in the brain.

What physiologic change triggers the thirst mechanism?

An increase in serum osmolality indicating dehydration.

Why might elderly patients dehydrate without feeling thirsty?

They can have a blunted thirst mechanism.

Which hormone is known as the body’s “water saver”?

Antidiuretic hormone (ADH or vasopressin).

Where is ADH released from?

The posterior pituitary gland.

How does ADH act on the kidneys?

It increases water reabsorption and reduces urine output, restoring fluid volume.

State three major kidney functions related to homeostasis.

Filtering waste, maintaining fluid/electrolyte balance, and overall homeostatic regulation.

About how many gallons of blood do the kidneys filter daily?

Roughly 50 gallons (≈190 L).

Name two lab values used to evaluate kidney function.

Blood Urea Nitrogen (BUN) and serum creatinine (or GFR).

Differentiate sensible from insensible fluid loss.

Sensible losses can be measured (urine, vomit, liquid stool, bleeding, sweat); insensible losses are not easily measured (respiration, skin evaporation, water in formed stool).

Give two classic physical signs of dehydration.

Poor skin turgor and dark concentrated urine (others: sunken eyes, dry mucous membranes, low BP).

Define diffusion in physiology.

Passive movement of particles (solutes/electrolytes) from an area of higher to lower concentration without energy use.

Provide an everyday example illustrating diffusion.

Food coloring dispersing evenly in a glass of water.

By what process does oxygen move from alveoli into blood?

Diffusion down its concentration gradient.

Why are potassium disorders closely monitored on ECG?

Because K⁺ imbalances disturb cardiac electrical activity, causing arrhythmias.

What is active transport?

Energy-requiring movement of substances against their concentration gradient, e.g., the sodium-potassium pump.

During one sodium-potassium pump cycle, how many Na⁺ and K⁺ ions move?

3 sodium ions are pumped out and 2 potassium ions pumped into the cell per ATP.

List the four electrolytes emphasized in this lecture.

Potassium, Sodium, Calcium, and Magnesium.

State the normal adult serum potassium range.

3.5–5.0 mEq/L.

Define hypokalemia and its adult critical value.

Serum K⁺ <3.5 mEq/L; critical <3.0 mEq/L.

Give two common causes of hypokalemia.

Diuretic therapy (non-K⁺-sparing), vomiting/diarrhea, laxative abuse, poor intake, amphotericin B.

List two early symptoms of mild hypokalemia.

Fatigue and muscle weakness (also constipation).

What cardiac issue is associated with severe hypokalemia?

Life-threatening arrhythmias visible on ECG.

Name two standard treatments for hypokalemia.

Oral/IV potassium supplementation and increasing potassium-rich foods (while addressing the cause).

Define hyperkalemia and its adult critical value.

Serum K⁺ >5.0 mEq/L; critical >6.1 mEq/L.

What is the most common cause of hyperkalemia?

Renal (kidney) failure.

Give two additional causes of hyperkalemia.

Potassium-sparing diuretics, dehydration, burns/trauma, blood transfusions, excess intake, diabetes.

List two dangerous manifestations of hyperkalemia.

Muscle weakness/paralysis and severe cardiac arrhythmias or heart failure.

Provide two treatments for hyperkalemia.

IV calcium gluconate and loop diuretics (others: insulin + glucose, dialysis, K⁺ restriction).

What is the normal serum sodium range?

135–145 mEq/L.

Define hyponatremia and its critical threshold.

Serum Na⁺ <135 mEq/L; critical <120 mEq/L.

What is the most common cause of hyponatremia?

Excessive water intake (dilutional).

Give two moderate clinical signs of hyponatremia.

Lethargy and confusion (also headaches, restlessness, irritability).

Why must hypernatremia be corrected slowly?

Rapid correction can cause cerebral edema and neurologic damage.

Hypernatremia critical serum level?

160 mEq/L.

Which two populations are at high risk for impaired thirst leading to hypernatremia?

Elderly adults and infants.

Name two high-sodium foods heart-failure patients should limit.

Processed meats (e.g., deli meat/hot dogs) and canned soups/vegetables (also cheese, soy sauce).

Which vitamin is required for calcium absorption?

Vitamin D.

List two good dietary sources of calcium.

Dairy products (milk, yogurt, cheese) and leafy greens like spinach or kale (also canned sardines/salmon).

Give two common causes of hypocalcemia.

Vitamin D deficiency and loop diuretic/laxative overuse (others: multiple transfusions, menopause, Mg/PO₄ imbalance).

Chvostek and Trousseau signs are characteristic of which electrolyte disorder?

Hypocalcemia.

State two GI symptoms associated with hypercalcemia.

Constipation and abdominal pain (also nausea, vomiting, loss of appetite).

Name two causes of hypercalcemia.

Cancer and vitamin D toxicity (also lithium therapy, thiazide diuretics, prolonged immobility, renal failure).

What oral medication may be used for mild symptomatic hypercalcemia?

Oral phosphate to block calcium absorption.

How can prolonged immobility contribute to hypercalcemia?

Bone demineralization releases calcium into the bloodstream.

What is the normal urine osmolality range used to gauge renal concentrating ability?

50–1,200 mOsm/kg.

Sweating is classified as which type of fluid loss?

Sensible fluid loss (measurable).

Why are electrolyte drinks advised during intense exercise?

They replace sodium and other electrolytes lost in sweat, preventing hyponatremia.

Which common lab panels assess overall electrolyte status?

Basic Metabolic Panel (BMP) and Comprehensive Metabolic Panel (CMP).

Besides thirst, how does the body compensate for high serum osmolality?

ADH release increases kidney water reabsorption to dilute the blood.

Why is strict intake & output recording vital in fluid management?

It helps detect early fluid imbalances such as dehydration or fluid overload.