Fluids, Electrolytes, and Renal Failure

Vocabulary practice flashcards covering body fluid compartments, mechanisms of transport, IV fluid tonicities, normal electrolyte ranges and ECG patterns, Arterial Blood Gas analysis, and renal failure phases and stages.

Intracellular Fluid (ICF)

The fluid compartment located inside the body's cells, accounting for the primary fluid volume of the body.

Extracellular Fluid (ECF)

The fluid located outside of the cells, which is further subdivided into intravascular fluid (blood plasma) and interstitial fluid (fluid between cells).

Transcellular Fluid

Specialized extracellular fluid compartments contained within epithelial-lined spaces, including cerebrospinal fluid (CSF), synovial fluid, and aqueous humor.

Osmosis

The movement of fluid across a membrane from an area of low solute concentration to an area of high solute concentration.

Diffusion

The passive movement of solutes from an area of higher concentration to an area of lower concentration (for example, alveolar gas exchange between $O_2$ and $CO_2$).

Isotonic IV Solution

A solution with an osmolality and solute concentration similar to blood that stays within the intravascular space; examples include $0.9\%\,\text{NaCl}$ (Normal Saline), Lactated Ringer's, and $D_5W$ (in the bag).

Hypertonic IV Solution

A solution with a higher concentration and osmolality than blood that pulls fluid from cells into the intravascular space, causing cellular dehydration/shrinkage; requires slow infusion. Examples include $3\%\,\text{Saline}$, $5\%\,\text{Saline}$, $D_{10}W$, $D_5$ in $0.9\%\,\text{Saline}$, $D_5$ in $0.45\%\,\text{Saline}$, and $D_5$ in Lactated Ringer's.

Hypotonic IV Solution

A solution with a lower concentration and osmolality than blood that shifts fluid out of the intravascular space into the cells, leading to cellular swelling and edema; requires slow infusion. Examples include $D_5W$ (in the body), $2.5\%\,\text{Dextrose}$, $0.25\%\,\text{NaCl}$, and $0.45\%\,\text{NaCl}$ (half-normal saline).

Fluid Volume Excess (FVE)

An intravascular and interstitial fluid overload characterized clinically by increased body weight, peripheral edema, distended neck veins, crackles in the lungs, elevated blood pressure, elevated central venous pressure ($>12\,\text{mmHg}$), decreased hematocrit due to hemodilution, and decreased serum osmolality ($<275\,\text{mOsm/kg}$).

Fluid Volume Deficit (FVD)

A reduction in fluid volume characterized clinically by decreased body weight, dry skin with poor skin turgor (tenting), sunken eyes, flat neck veins, hypotension, tachycardia, hemoconcentration (elevated hematocrit), elevated BUN, elevated urine specific gravity ($>1.025$), and elevated serum osmolality ($>300\,\text{mOsm/kg}$).

Serum Osmolality

The measure of solute concentration in the blood, with a normal reference range of $275-300\,\text{mOsm/kg}$.

Central Venous Pressure (CVP)

The blood pressure in the venae cavae near the right atrium, reflecting intravascular volume status, with a normal range of $8-12\,\text{mmHg}$.

Urine Specific Gravity (USG)

An assessment of the kidney's ability to concentrate or dilute urine and preserve water, with a normal reference range of $1.010-1.025$.

Potassium ($K^+$)

The major intracellular cation with a normal reference range of $3.5-5.0\,\text{mEq/L}$; it regulates musculoskeletal contraction and cardiac electrical regularity.

Hypokalemia ECG Changes

Electrocardiographic alterations caused by low serum potassium ($<3.5\,\text{mEq/L}$), characterized by ST depression, flat or inverted T waves, and prominent U waves ("HypUkalemia ShuT Down FlaT").

Hyperkalemia ECG Changes

Electrocardiographic alterations caused by elevated serum potassium ($>5.0\,\text{mEq/L}$), characterized by flat P waves, prolonged PR interval, wide QRS complexes, and tall, tented T waves ("Wide PRolonged Tall but Flat").

DISCS Mnemonic

The clinical management protocol for hyperkalemia: D – Diuretics (loop diuretics), I – Insulin with dextrose, S – Salbutamol, C – Calcium Gluconate (cardioprotective), S – Sodium Polystyrene sulfonate (Kayexalate).

Sodium ($Na^+$)

The major extracellular/intravascular cation with a normal reference range of $135-145\,\text{mEq/L}$; it serves as the primary determinant of blood osmolality and regulates neuromuscular activity.

Calcium ($Ca^{2+}$)

An essential mineral with a normal range of $9-10\,\text{mg/dL}$ critical for bone structure, musculoskeletal contraction, and cardiac muscle contraction; an excess in the kidneys causes supersaturation and osmotic diuresis.

Magnesium ($Mg^{2+}$)

An electrolyte and vasodilator with a normal range of $1.5-2.5\,\text{mEq/L}$ whose neuromuscular actions mirror those of calcium.

Phosphorus ($P$)

An electrolyte with a normal range of $2.5-4.5\,\text{mg/dL}$ that maintains an inverse proportional relationship with calcium ($\uparrow Ca \rightarrow \downarrow P$ and $\downarrow Ca \rightarrow \uparrow P$).

Allen's Test

A vascular assessment procedure performed prior to radial artery puncture for Arterial Blood Gas (ABG) sampling to evaluate collateral circulation and patency of the ulnar artery.

Acute Kidney Injury (AKI) Classifications

Etiological categories of sudden renal functional decline: Prerenal (hypoperfusion to the kidney such as hemorrhage or dehydration), Intrarenal (intrinsic tissue damage such as glomerulonephritis or rhabdomyolysis), and Postrenal (obstruction distal to the renal parenchyma such as renal calculi, BPH, or bladder cancer).

Oliguric Phase of AKI

The second phase of Acute Kidney Injury lasting $8-15\,\text{days}$, characterized by urine output $<30\,\text{mL/hr}$ or $<400\,\text{mL/day}$, reduced GFR, fluid volume excess, azotemia, elevated BUN and creatinine, hyperkalemia, hyperphosphatemia, hypocalcemia, and metabolic acidosis.

Diuretic Phase of AKI

The third phase of Acute Kidney Injury characterized by high urine output ($4-5\,\text{L/day}$, polyuria), gradual recovery of GFR, and risk for hypokalemia, hyponatremia, and fluid volume deficit.

Recovery (Convalescent) Phase of AKI

The final phase of Acute Kidney Injury lasting $1-2\,\text{years}$, during which renal function and laboratory parameters gradually return to normal values.

End-Stage Renal Disease (ESRD)

The terminal stage of Chronic Kidney Disease (CKD Stage 5) defined by an estimated Glomerular Filtration Rate (GFR) of $<15\,\text{mL/min}$, requiring renal replacement therapy.