Kidney Function and Acute Kidney Injury: Comprehensive Study Notes

Functions of the Kidneys

Acid-Base Balance
- Kidneys primarily control bicarbonate (base) levels in the body.
Perfusion Monitoring
- Kidneys serve as indicators of organ perfusion by detecting oxygen levels, akin to a pulse oximeter.
Hormonal Production
- Erythropoietin
- A hormone released from the kidneys that stimulates red blood cell production in the bone marrow.
- Importance: Kidney dysfunction can lead to anemia due to decreased erythropoietin.
Fluid and Electrolyte Regulation
- Beyond fluid and electrolyte elimination, kidneys also contribute to blood pressure control and acid-base balance.

Definition
- Acute kidney injury (AKI) is characterized by a sudden decrease in glomerular filtration rate (GFR), leading to impaired kidney function.
Phases of AKI
- Onset phase: Initiating event leads to kidney dysfunction.
- Oliguric phase: Marked by reduced urine output (ranges from one to three weeks).
- Diuretic phase: Kidneys begin to recover, leading to higher urine output (1-3 liters/day).
- Recovery phase: Full recovery can take 3-12 months.
Glomerular Filtration Rate (GFR)
- Indicates the filtering ability of the kidneys, with normal qualifying levels of BUN (Blood Urea Nitrogen) and creatinine.

Prerenal Causes
- Issues related to blood flow to kidneys, including hypotension, dehydration, and shock.
- Risk factors:
- Older adults have reduced physiological reserve, increasing dehydration risk.
- Conditions like cardiac surgery can impair blood flow temporarily.
Intrarenal Causes
- Damage to kidney tissues (nephrons) due to nephrotoxic medications (e.g., metformin, vancomycin), infections like pyelonephritis or glomerulonephritis.
Postrenal Causes
- Obstructions in the urinary tract (e.g., kidney stones, enlarged prostate, urethral strictures).

Chemical Markers for Kidney Function
- BUN: Blood Urea Nitrogen—assesses nitrogenous wastes from protein metabolism.
- Creatinine: Indicates how well kidneys filter waste. Elevated levels indicate impaired function.
Significant Laboratory Values
- Potassium levels are critical due to the risk of hyperkalemia when kidneys cannot excrete it.
- Acid-base imbalances often lead to metabolic acidosis in kidney failure patients.

Older adults are more susceptible to AKI due to comorbid conditions (e.g., diabetes, hypertension) and higher exposure to nephrotoxic medications.
AKI can manifest as fluid volume overload due to compromised kidney filtration.
Recognition of signs and symptoms is essential for timely care, such as monitoring urine output and blood pressure.

Hydration Strategies
- Encourage adequate fluid intake (2-3 liters/day) under normal conditions but consider restrictions for heart failure patients.
- Monitor urine output closely (less than 30 ml/hour signals concern).
Medication Management
- Avoid nephrotoxic medications unless necessary; discuss timing for medications like metformin around imaging procedures.
Patient Education
- Educate patients about risks related to dehydration and medication intake; importance of reporting symptoms (e.g., urine color, output).
Assessment Techniques
- Monitor for vital signs indicative of fluid status, such as blood pressure and pulse quality.
- Recognize signs of fluid overload versus deficit, including changes in pulses, blood pressure, and neck vein distention.

Imaging Tests
- Ultrasound: Least invasive method to assess kidney structure/function.
- CT scans (with/without contrast): Can help visualize blood flow.
- KUB (Kidneys, Ureters, Bladder) X-ray: Basic assessment of the swollen urinary tract.
Biopsies
- Kidney biopsy may be indicated for specific diagnoses; monitor blood pressure carefully post-procedure because of bleeding risks.
Urinalysis
- Essential to evaluate urinary specific gravity, color changes, and total urine output to further assess kidney function.

Onset Phase: Triggering events (e.g., severe vomiting, diarrhea) that precede AKI.
Oliguric Phase: Reduced urine output, lasting up to three weeks; requires close monitoring.
Diuretic Phase: Increased urine output indicates gradual kidney recovery; monitor volume loss.
Recovery Phase: Full recovery can take several months; consistent evaluation needed for electrolyte balance and overall kidney health.

Prioritize hydration and risk assessment in high-risk populations.
Understand implications of fluid and electrolyte imbalances on overall health outcomes.
Recognize and document key signs and symptoms of both AKI and its progression to prevent further complications.
Foster patient education about kidney health, especially in populations at risk for dehydration and medication interactions.