Therapeutics Exam Review: Fluids, Electrolytes, Acid-Base, and Obesity

Comprehensive vocabulary flashcard set covering IV fluids, sodium disorders, acid-base balance, potassium, magnesium, phosphorus, calcium, and obesity pharmacotherapy.

Total Body Water (TBW)

The total volume of water in the body, accounting for approximately $60\%$ of body weight in a typical adult (lower in females, older adults, and patients with obesity), calculated as $\text{Estimated TBW} = 0.6 \times \text{body weight in kg}$.

Intracellular Fluid (ICF)

The body fluid compartment inside cells that contains two-thirds ($2/3$) of total body water (about $28\,\text{L}$ in a $70\,\text{kg}$ adult), primarily composed of potassium, magnesium, phosphate, and proteins.

Extracellular Fluid (ECF)

The body fluid compartment outside cells that contains one-third ($1/3$) of total body water (about $14\,\text{L}$ in a $70\,\text{kg}$ adult), primarily composed of sodium, chloride, and bicarbonate.

Interstitial Fluid

The sub-compartment of the extracellular fluid ($ECF$) surrounding cells in tissues, making up $75\%$ of total $ECF$ (approximately $10.5\,\text{L}$ in a $70\,\text{kg}$ adult).

Intravascular Fluid

The sub-compartment of the extracellular fluid ($ECF$) within blood vessels, making up $25\%$ of total $ECF$ (approximately $3.5\,\text{L}$ in a $70\,\text{kg}$ adult).

Tonicity

The effective osmotic pressure gradient that determines water movement between extracellular and intracellular fluid across the cell membrane.

Oncotic Pressure

The pulling osmotic pressure created by plasma proteins (predominantly albumin) inside the intravascular space that regulates fluid movement across the capillary wall.

100-50-20 Daily Method

A formula for calculating daily basal fluid requirements: $100\,\text{mL/kg}$ for $0\text{--}10\,\text{kg}$, $1000\,\text{mL} + 50\,\text{mL}$ per kg above $10\,\text{kg}$ for $10\text{--}20\,\text{kg}$, and $1500\,\text{mL} + 20\,\text{mL}$ per kg above $20\,\text{kg}$ for $>20\,\text{kg}$.

5% Albumin

An iso-oncotic colloid fluid used for selective intravascular volume resuscitation that stays primarily intravascular, providing roughly $3$ times the intravascular volume expansion of normal saline.

25% Albumin

A hyper-oncotic colloid fluid that draws water from the interstitium into the intravascular space; used to support diuresis in hypoalbuminemic, hypotensive patients with interstitial edema.

0.9% Sodium Chloride (Normal Saline)

An isotonic crystalloid solution containing $154\,\text{mEq/L}$ sodium and $154\,\text{mEq/L}$ chloride ($308\,\text{mOsm/L}$) that expands the extracellular space ($750\,\text{mL}$ interstitial and $250\,\text{mL}$ intravascular per 1 liter infused).

Hyperchloremic Metabolic Acidosis

A non-anion gap metabolic acidosis caused by large volume administration of $0.9\%$ NaCl due to its high chloride content ($154\,\text{mEq/L}$).

Antidiuretic Hormone (ADH)

A hormone acting at the renal collecting duct to increase aquaporin-mediated water reabsorption, which concentrates urine and reduces serum tonicity.

Pseudohyponatremia

An isotonic laboratory artifact in measured serum sodium caused by severe hyperlipidemia or hyperproteinemia without an actual decrease in serum tonicity.

Free Water Deficit

A calculated water deficit in hypernatremia, determined by $\text{TBW} \times \left[\left(\frac{\text{serum Na}}{140}\right) - 1\right]$, replaced over $48\text{--}72\,\text{hours}$.

Anion Gap

A calculated laboratory value defined as $\text{Na} - (\text{Cl} + \text{HCO}_3)$; a value greater than $12\,\text{mEq/L}$ defines an anion-gap metabolic acidosis in this course.

MUDPILES

A mnemonic for high-yield causes of anion-gap metabolic acidosis: Methanol, Uremia, DKA, Propylene glycol, Ischemia or Intoxication, Lactic acidosis, Ethylene glycol, Salicylates.

Base Deficit

An estimate of the bicarbonate amount needed to increase serum bicarbonate toward $24\,\text{mEq/L}$, calculated as $0.5 \times \text{weight in kg} \times (24 - \text{serum HCO}_3)$.

Contraction Alkalosis

A chloride-sensitive metabolic alkalosis resulting from extracellular volume loss and heavy urinary chloride excretion induced by loop diuretics.

Potassium Replacement Rule

A dosing rule predicting that $10\,\text{mEq}$ of oral or IV potassium chloride raises serum potassium concentration by approximately $0.1\,\text{mEq/L}$.

Calcium Gluconate

A cardioprotective agent given as $1\text{--}2\,\text{g}$ IV over $5\text{--}10\,\text{min}$ during hyperkalemia to stabilize cardiac conduction membranes without changing potassium levels.

Sodium Polystyrene Sulfonate (Kayexalate)

An acute oral cation-exchange binder ($15\text{--}60\,\text{g}$ PO) for hyperkalemia associated with GI adverse effects, hypomagnesemia, edema, and rare colonic necrosis.

Sodium Zirconium Cyclosilicate (Lokelma)

An oral potassium binder ($10\,\text{g}$ PO TID up to $48\,\text{hours}$ for acute use) that exchanges sodium for potassium; requires separating other oral medications by at least $2\,\text{hours}$.

Patiromer (Veltassa)

A chronic-use oral potassium binder (initial $8.4\,\text{g}$ daily) with an onset of $6\text{--}8\,\text{hours}$; requires separating other oral medications by at least $3\,\text{hours}$.

Corrected Calcium

The total serum calcium adjusted for hypoalbuminemia, calculated as $\text{Corrected Ca} = \text{measured Ca} + 0.8 \times (4 - \text{albumin})$.

Calcium Citrate

An oral calcium salt with $20\%$ elemental calcium that does not require food or gastric acid for absorption, making it preferred for patients taking PPIs or H2 blockers.

Calcium Carbonate

An oral calcium salt with $40\%$ elemental calcium that requires food and an acidic gastric environment for adequate absorption.

Satiation

The sensation of fullness during a meal that leads to meal termination and governs meal size.

Satiety

The state of reduced hunger after a meal that determines the time interval before eating again.

Leptin

An adipose-derived hormone that suppresses appetite and promotes energy expenditure by inhibiting NPY/AgRP and activating POMC/$\alpha\text{-MSH}$ pathways.

Ghrelin

A gastric peptide secreted prior to meals that activates NPY/AgRP pathways to stimulate hunger and food intake.

Phentermine

A short-term sympathomimetic appetite suppressant that increases norepinephrine and dopamine signaling to reduce hunger.

Orlistat

A non-systemic gastric and pancreatic lipase inhibitor ($120\,\text{mg}$ TID with meals) that reduces dietary fat absorption in the GI lumen by approximately $30\%$.

Contrave

An anti-obesity combination product consisting of bupropion (stimulates POMC via NE/DA reuptake inhibition) and naltrexone (blocks endogenous opioid autoinhibition on POMC neurons).

Setmelanotide (Imcivree)

An MC4R agonist targeted specifically for genetically confirmed melanocortin pathway obesity (POMC, PCSK1, or LEPR deficiencies) in patients age $6$ years or older.

Plenity

A non-systemic cellulose and citric acid hydrogel medical device taken before meals with water that expands in the stomach to produce fullness in patients with BMI $$25\text{--}40\,\text{kg/m}^2$.

Orforglipron (Foundayo)

An oral nonpeptide small-molecule GLP-1 agonist taken once daily without food/water restrictions, requiring non-oral or barrier contraception for $30\,\text{days}$ after initiation and each dose escalation.

Oral Semaglutide (Wegovy Tablets)

An oral GLP-1 receptor agonist taken in the morning on an empty stomach with no more than $4\,\text{oz}$ of water, followed by at least a $30\text{-minute}$ wait before any food, beverage, or other oral medications.