Fluid and Electrolytes Lecture Review

Comprehensive Q&A practice flashcards covering fluid compartments, tonicity, fluid volume imbalances, and electrolyte regulation based on lecture notes.

What is homeostasis in the context of fluids and electrolytes?

Homeostasis is the body's ability to maintain a stable internal environment, keeping fluid and electrolyte levels balanced.

What are the two subdivisions of extracellular fluid (ECF)?

Interstitial extracellular fluid (fluid located between cells) and plasma or intravascular extracellular fluid (fluid inside the vascular system).

What is third spacing and what are two common examples?

Third spacing is the abnormal accumulation of fluid in areas not easily accessible for body use, such as ascites in the abdominal cavity or pleural effusions in lung cavities.

What is the primary regulation mechanism for fluid intake and where is it located?

Thirst regulation, located in the hypothalamus, which is stimulated when blood volume decreases or serum osmolarity increases.

What are the average daily fluid intake and output values for an adult?

Average daily fluid intake is approximately $2500\,mL$, and average daily output is $1200\text{ to }1500\,mL$.

What are the normal hourly urine output benchmarks for adults versus pediatric patients?

Adults require $30\text{ to }60\,mL$ per hour; pediatric patients require $1\text{ to }2\,mL/kg$ per hour.

Where are calcium and magnesium absorbed within the gastrointestinal tract?

Calcium is absorbed in the duodenum (requiring vitamin D), and magnesium is absorbed in the ileum.

How does aldosterone regulate extracellular fluid volume and potassium?

Secreted by the adrenal cortex in response to angiotensin II, aldosterone causes the kidneys to retain sodium and water into the blood while excreting potassium in urine.

How does Anti-Diuretic Hormone (ADH) act to regulate body fluid osmolarity?

Released from the posterior pituitary, ADH acts on renal distal tubules and collecting ducts to reabsorb water (without sodium) back into the blood, diluting concentrated extracellular volume.

What fluid shift occurs when a hypotonic IV solution is administered?

Water moves out of the vascular space (extracellular compartment) and into the cells (intracellular compartment), posing a risk of cell swelling and rupture.

What are examples of hypotonic IV solutions?

$0.45\%$ normal saline, $0.225\%$ normal saline, $0.33\%$ normal saline, and $5\%$ dextrose in water ($D5W$).

What is a major contraindication for administering Lactated Ringer's (LR) IV fluid?

Lactated Ringer's ($LR$) should not be administered to patients with liver problems.

How do hypertonic IV solutions affect body cells?

They draw water out of intracellular compartments into the extracellular vascular space, causing cells to dehydrate and shrink.

What are examples of hypertonic IV solutions?

$3\%$ normal saline, $10\%$ dextrose in water ($D10W$), $D5$ in $0.9\%$ normal saline, and $D5$ in $0.45\%$ normal saline.

What weight change corresponds to a fluid volume loss or gain of $1\,L$?

A loss or gain of $1\,L$ of fluid is equivalent to $2.2\,lbs$ ($1\,kg$).

What are the key clinical signs of fluid volume excess?

Weight gain, shortness of breath, peripheral edema, bounding pulses, hypertension, distended neck veins (JVD), dyspnea, increased urine output, and altered mental status.

What signs indicate severe dehydration in pediatric patients?

Absence of urine output, absence of tears, sunken fontanelles, and a rapid, weak pulse.

Why are high-sugar clear liquids avoided during rehydration for pediatric diarrhea?

Simple sugars produce osmotic effects that worsen diarrhea, and excessive clear fluids can dilute blood sodium and trigger hypoglycemia.

What does high urine specific gravity indicate?

High urine specific gravity indicates concentrated urine (dark yellow), typically seen in fluid volume deficit or dehydration.

What are the normal adult serum ranges for sodium and potassium?

Sodium ($Na^+$) is $135\text{ to }145\,mEq/L$ (or $136\text{ to }145\,mEq/L$); Potassium ($K^+$) is $3.5\text{ to }5.0\,mEq/L$.

What are the normal adult serum ranges for calcium, magnesium, and phosphate?

Calcium ($Ca^{2+}$) is $9\text{ to }10.5\,mg/dL$; Magnesium ($Mg^{2+}$) is $1.5\text{ to }3.0\,mEq/L$; Phosphate is $3.0\text{ to }4.5\,mg/dL$.

What primary neurological risk is associated with severe hypernatremia?

Shrinkage of brain cells as water is pulled into the hypertonic vascular space, leading to confusion, seizures, coma, and cerebral bleeding.

What neurological complication arises from severe hyponatremia?

Cerebral edema (brain swelling) caused by fluid shifting out of hypotonic blood into brain tissue.

What safety protocol must be followed when administering hypertonic $3\%$ normal saline for severe hyponatremia?

It must be infused very slowly to prevent rapid, dangerous fluid shifts out of brain cells.

What specific ECG changes indicate hyperkalemia?

Tall, peaked T waves, wide QRS complexes, and absent P waves.

What medications are administered to treat severe hyperkalemia?

Calcium gluconate (to protect the heart), regular insulin (to shift potassium into cells), sodium bicarbonate, Kayexalate (sodium polystyrene sulfonate), and loop diuretics.

What specific ECG findings are seen in hypokalemia?

Flattened or inverted T waves, depressed ST segments, and the presence of U waves.

What is the maximum safe infusion rate for IV potassium replacement?

IV potassium must never be given as a direct IV push and should be infused no faster than $10\text{ to }20\,mEq$ per hour.

How are Chvostek's sign and Trousseau's sign defined in hypocalcemia?

Chvostek's sign is facial muscle twitching when the cheek/facial nerve is tapped; Trousseau's sign is carpal spasm triggered by inflating a blood pressure cuff above systolic pressure.

What life-threatening airway complication can occur with severe hypocalcemia?

Laryngeal spasms, which cause airway constriction and stridor.

How do hypercalcemia and hypocalcemia differ in their effects on the ST segment on an ECG?

Hypercalcemia causes a shortened ST segment, whereas hypocalcemia causes a prolonged ST segment.

What emergency medication reverses the neuromuscular and cardiac toxicity of hypermagnesemia?

Calcium gluconate.

What is refeeding syndrome and how does it affect serum phosphate?

In malnourished patients, feeding stimulates insulin release, driving glucose and phosphorus into cells and causing severe serum hypophosphatemia.

What quick memory categorization summarizes the primary target systems for sodium, potassium, and calcium?

Sodium primarily affects the brain, potassium primarily affects the heart, and calcium primarily affects muscles and bones.