Module 2: Fluids, Electrolytes, and Acid-Base Imbalances

Vocabulary flashcards covering fluid dynamics, electrolyte functions and normal ranges, physiological mechanisms of imbalances, acid-base disorders, and intravenous therapy concepts from Module 2.

Intracellular Fluid (ICF)

Fluid located within cells, accounting for approximately two-thirds of total body water.

Extracellular Fluid (ECF)

Fluid located outside cells, accounting for approximately one-third of total body water, consisting of interstitial fluid, intravascular fluid (plasma), and transcellular fluid (CSF, pleural, synovial, GI fluids).

Hydrostatic Pressure

The pressure that pushes water out of capillaries and into tissues.

Oncotic Pressure

The pressure (mostly exerted by albumin) that pulls water back into capillaries from tissues.

Edema

Excess fluid accumulation in the interstitial space caused by increased capillary pressure, decreased plasma proteins, impaired lymph drainage, or lymphatic blockage.

Antidiuretic Hormone (ADH)

Also known as vasopressin, a hormone that increases water reabsorption by the kidneys.

Aldosterone

A hormone that increases sodium and water retention in the body.

Natriuretic Peptides

Hormones (ANP, BNP, urodilatin) that reduce blood volume and blood pressure.

Sodium ($Na^+$)

The major cation regulating water balance, blood pressure, and supporting nerve and muscle activity, with a normal serum range of $135\text{--}145\,mEq/L$.

Hyponatremia

Low extracellular sodium concentration ($<135\,mEq/L$) that lowers extracellular osmolality, causing water to enter cells and swell—especially brain cells.

Hypernatremia

Elevated extracellular sodium concentration ($>145\,mEq/L$) that draws water out of cells, causing cellular dehydration and CNS symptoms.

Potassium ($K^+$)

The major intracellular cation that maintains electrical neutrality inside cells and supports nerve and muscle activity, especially in the heart, with a normal serum range of $3.5\text{--}5.0\,mEq/L$.

Hypokalemia

Low serum potassium ($<3.5\,mEq/L$) that hyperpolarizes cell membranes and decreases excitability, causing ECG changes such as flattened T waves, U waves, and increased risk of arrhythmias.

Hyperkalemia

Elevated serum potassium ($>5.0\,mEq/L$) that depolarizes cell membranes and disrupts cardiac repolarization and conduction, causing ECG changes such as peaked T waves, widened QRS, bradycardia, and risk of cardiac arrest.

Calcium ($Ca^{2+}$)

An essential electrolyte that supports bone structure, nerve transmission, muscle contraction, and blood clotting, with a normal total serum range of $8.8\text{--}10.5\,mg/dL$.

Hypocalcemia

Low serum calcium ($<8.8\,mg/dL$) that increases neuronal membrane excitability leading to spontaneous depolarization, tetany, muscle twitching, spasms, seizures, Chvostek sign, and Trousseau sign.

Hypercalcemia

Elevated serum calcium ($>10.5\,mg/dL$) that increases the threshold for depolarization, decreasing neuromuscular excitability and causing constipation, muscle weakness, lethargy, kidney stones, and a shortened QT interval.

Magnesium ($Mg^{2+}$)

An electrolyte that stabilizes nerve and muscle cells, regulates cardiac conduction, and serves as an enzymatic cofactor, with a normal serum range of $1.8\text{--}3.0\,mg/dL$.

Hypomagnesemia

Low serum magnesium ($<1.8\,mg/dL$) that removes inhibitory control on calcium channels, increasing neuromuscular excitability and causing tremors, seizures, hyperreflexia, and torsades de pointes.

Hypermagnesemia

Elevated serum magnesium ($>3.0\,mg/dL$) that suppresses acetylcholine release and neuromuscular activity, causing weakness, bradycardia, and respiratory depression.

Phosphate ($PO_4^{3-}$)

An electrolyte primarily involved in energy production (ATP), bone mineralization, and buffering of acids and bases, with a normal serum range of $2.5\text{--}5.0\,mg/dL$.

Hypophosphatemia

Low serum phosphate ($<2.5\,mg/dL$) that reduces ATP production, impairing muscle and organ function, especially in the diaphragm and heart.

Hyperphosphatemia

Elevated serum phosphate ($>5.0\,mg/dL$) that binds to $Ca^{2+}$, forming insoluble salts, reducing free calcium, and promoting soft tissue calcification.

Normal Arterial Blood pH

The physiological normal range for arterial blood pH, which is $7.35\text{--}7.45$.

Normal $PaCO_2$ Range

The normal partial pressure of carbon dioxide in arterial blood, which is $35\text{--}45\,mmHg$.

Normal Bicarbonate ($HCO_3^-$) Range

The normal concentration range of bicarbonate in arterial blood, which is $21\text{--}28\,mEq/L$.

Metabolic Acidosis

An acid-base disturbance caused by acid accumulation or bicarbonate loss (e.g., DKA, renal failure, diarrhea, lactic acidosis) resulting in lowered pH, which the lungs attempt to compensate for via hyperventilation.

Metabolic Alkalosis

An acid-base disturbance caused by loss of $H^+$ or gain of $HCO_3^-$ (e.g., vomiting, NG suction, diuretic use) resulting in elevated pH, which triggers respiratory compensation via hypoventilation to retain $CO_2$.

Respiratory Acidosis

An acid-base disturbance caused by $CO_2$ retention (e.g., COPD, CNS depression, airway obstruction) that increases carbonic acid and lowers pH, compensated over time by renal retention of $HCO_3^-$.

Respiratory Alkalosis

An acid-base disturbance caused by excessive $CO_2$ loss due to hyperventilation (e.g., anxiety, pain, fever, sepsis) that raises pH, causing cerebral vasoconstriction and electrolyte shifts.

Kussmaul Breathing

A compensatory respiratory pattern of deep, labored breathing seen in metabolic acidosis, especially diabetic ketoacidosis, to blow off excess $CO_2$.

Isotonic IV Fluids

Intravenous solutions such as $0.9\%$ Normal Saline (NS) that have an osmolality equal to plasma and expand plasma volume without shifting cellular water.

Hypotonic IV Fluids

Intravenous solutions such as $0.45\%$ NS or D5W (after glucose is metabolized) that have lower osmolality than plasma and move water into cells.

Hypertonic IV Fluids

Intravenous solutions such as $3\%$ NaCl, D5NS, and D5LR that have higher osmolality than plasma and pull water out of cells into the vascular space.

Colloid Fluids

Intravenous fluids used to increase oncotic pressure and pull water into the vasculature, primarily indicated in hypovolemia, burns, or low albumin states.

Third Spacing

The shift of fluid into non-functional body spaces (e.g., ascites, pleural effusion) where it cannot be dynamically used, reducing effective circulating blood volume.

Chvostek Sign

A clinical sign of hypocalcemia consisting of facial muscle twitching elicited by tapping over the facial nerve.

Trousseau Sign

A clinical sign of hypocalcemia consisting of carpal spasm induced by inflating a blood pressure cuff above systolic pressure for several minutes.

Severe Hyperkalemia Treatment

Medical interventions including IV calcium gluconate, insulin with glucose, sodium bicarbonate, or emergency dialysis to stabilize cardiac tissues and lower extracellular potassium.