Acute Kidney Injury Lecture Notes

Comprehensive vocabulary flashcards covering renal anatomy, pathophysiology, KDIGO staging criteria, diagnostic markers, and clinical management strategies for Acute Kidney Injury (AKI).

Nephron

The functional structural unit of the kidney, located across the renal cortex and medulla, which receives $20\%\text{ to }25\%$ of cardiac output to filter blood, reabsorb nutrients, and secrete waste products.

Glomerular Filtration Rate (GFR)

The rate at which fluid is filtered across the glomerulus as a result of a pressure gradient, with a normal baseline value ranging between $80\text{ and }125\,\text{mL/min}$.

Renin-Angiotensin-Aldosterone System (RAAS)

A renal neurohormonal pathway triggered by hypovolemia, renal ischemia, or decreased blood sodium concentration; specialized juxtaglomerular cells secrete renin, converting liver-produced angiotensinogen to angiotensin I, which pulmonary converting enzyme turns into angiotensin II to cause peripheral vasoconstriction and stimulate adrenal aldosterone secretion.

Azotemia

The pathological accumulation of nitrogenous waste products (such as blood urea nitrogen and creatinine) in the bloodstream.

Acute Kidney Injury (AKI)

A sudden deterioration of renal function characterized clinically by low urine output (oliguria), accumulation of nitrogenous waste products (azotemia), and fluid, electrolyte, and acid-base disturbances.

KDIGO Criteria

A standardized grading classification developed by Kidney Disease Improving Global Outcomes to categorize acute kidney injury into stages 1, 2, and 3 based on incremental elevations in serum creatinine and duration or volume of reduced urine output.

KDIGO Stage 1

An acute kidney injury classification defined by serum creatinine increasing to $1.5\text{--}1.9$ times baseline or an absolute increase of $\ge 0.3\,\text{mg/dL}$ ($\ge 26.5\,\mu\text{mol/L}$), or urine output falling below $0.5\,\text{mL/kg/h}$ for $6\text{--}12\,\text{h}$.

KDIGO Stage 2

An acute kidney injury classification defined by serum creatinine increasing to $2.0\text{--}2.9$ times baseline, or urine output falling below $0.5\,\text{mL/kg/h}$ for $\ge 12\,\text{h}$.

KDIGO Stage 3

An acute kidney injury classification defined by serum creatinine rising to $3.0$ times baseline, an increase in serum creatinine to $\ge 4.0\,\text{mg/dL}$ ($\ge 353.6\,\mu\text{mol/L}$), initiation of renal replacement therapy, or in patients $< 18\,\text{yr}$ a decrease in eGFR to $< 35\,\text{mL/min/1.73 m}^2$, or urine output $< 0.3\,\text{mL/kg/h}$ for $\ge 24\,\text{h}$ or anuria for $\ge 12\,\text{h}$.

Mechanisms of Oliguria in AKI

The pathophysiological cascades leading to diminished urine output in prerenal (hypoperfusion and neurohormonal reabsorption), intrarenal (tubular injury, cast formation, obstruction, and tubular backleak), and postrenal (urinary tract obstruction, retrograde pressure, and vascular vasoconstriction) etiologies.

Prerenal Etiology

The category of acute kidney injury caused by conditions external to the kidneys that diminish blood flow and lead to renal hypoperfusion, such as volume depletion, vasodilation, or decreased cardiac output.

Intrarenal Etiology

The category of acute kidney injury characterized by direct physiological damage to renal tissue, including vascular, glomerular, or hematological damage, and acute tubular necrosis (ATN) from ischemia, nephrotoxic agents, contrast dye, or rhabdomyolysis.

Postrenal Etiology

The category of acute kidney injury resulting from mechanical obstruction of urinary outflow, which elevates retrograde intratubular pressure and decreases glomerular filtration rate until the obstruction is removed.

Initiation Phase of AKI

The earliest course of acute kidney injury spanning the time from the precipitating event to the first clinical signs of decreased renal perfusion, lasting from several hours up to $2\,\text{days}$, during which damage is potentially reversible.

Oliguric Phase of AKI

The clinical phase of acute kidney injury wherein urine output drops below $400\,\text{mL/day}$, accompanied by daily elevations in BUN and creatinine, fluid overload, electrolyte imbalances, metabolic acidosis, and the potential necessity for renal replacement therapy.

Recovery Phase of AKI

The resolution phase of acute kidney injury characterized by gradual return of tubular concentrating capacity, taking $4\text{ to }6\,\text{months}$ for serum BUN and creatinine to normalize, frequently with residual impairment of baseline GFR.

BUN to Creatinine Ratio

A clinical diagnostic parameter with a normal physiological ratio between $10:1$ and $20:1$; a ratio exceeding $20:1$ indicates nonrenal origins such as dehydration, hypovolemia, or enhanced catabolism.

Urine Creatinine Clearance

A quantitative $24\text{-hour}$ urine diagnostic assay used to estimate glomerular filtration rate, with normal values ranging from $84\text{ to }138\,\text{mL/min}$.

Daily Weight

The single most important objective clinical nursing intervention used to track fluid gains, losses, and overall hydration balance in a patient with acute kidney injury.

Hyperkalemia ECG Progression

Sequential electrocardiographic abnormalities caused by elevated serum potassium, progressing from peaked T waves at $6\text{--}7\,\text{mEq/L}$, flattened P waves with prolonged PR and ST depression at $7\text{--}8\,\text{mEq/L}$, atrial standstill and QRS widening at $8\text{--}9\,\text{mEq/L}$, to a sinusoidal wave pattern at $> 9\,\text{mEq/L}$.

Percutaneous Dialysis Catheter

A central venous vascular access line placed into a large central vein—such as the internal jugular or subclavian vein—tunneled under subcutaneous tissue with a cuff and terminating in the right atrium for temporary renal replacement therapy.

Diffusion (Dialysis)

A primary physical mechanism of hemodialysis involving the passive movement of solute particles across a semipermeable membrane down a concentration gradient from higher concentration to lower concentration.

Ultrafiltration (Dialysis)

A physical principle governing renal replacement therapy that drives fluid removal across a semipermeable membrane via artificially created hydrostatic or osmotic pressure gradients.

Arteriovenous Access (Fistula vs. Graft)

Surgical conduits constructed in the upper extremity for hemodialysis, either by direct surgical anastomosis of an artery and vein (such as the radial artery to the basilic vein) or by interposing a synthetic looped graft (between the brachial artery and antecubital vein).

Continuous Renal Replacement Therapy (CRRT)

A continuous, slow dialytic therapy performed at the bedside by critical care staff nurses, indicated for hemodynamically unstable patients who cannot tolerate the rapid fluid and solute shifts of intermittent hemodialysis.

Slow Continuous Ultrafiltration (SCUF)

A specific modality of continuous renal replacement therapy focused almost exclusively on continuous fluid removal without dialysate or replacement fluids.

Continuous Venovenous Hemofiltration (CVVH)

A modality of continuous renal replacement therapy that removes fluid along with small to middle solutes driven primarily by convective clearance via hydrostatic pressure and replacement fluid administration.

Continuous Venovenous Hemodialysis (CVVHD)

A modality of continuous renal replacement therapy providing small solute clearance predominantly driven by diffusion across a semipermeable membrane using countercurrent dialysate fluid flow.

Continuous Venovenous Hemodiafiltration (CVVHDF)

A combined modality of continuous renal replacement therapy utilizing both convective solute clearance (replacement fluid) and diffusive solute clearance (dialysate fluid) simultaneously with ultrafiltration.

Peritoneal Dialysis

A renal replacement modality utilizing the patient's rich peritoneal membrane as a semipermeable filter to eliminate fluids and waste products; infrequently utilized in critical care due to lower efficiency and the risk of peritonitis.

Nurse Burnout

A critical occupational phenomenon characterized by emotional exhaustion, depersonalization, reduced fulfillment, and an inability to cope with persistent professional stress.