Chapter 64 Renal Failure
Acute
PATHOPHYSIOLOGY
Acute renal failure (ARF) is the abrupt reduction or cessation of renal function secondary to a sudden loss of functioning nephrons. The rapid loss of renal function leads to a reduction in the glomerular filtration rate (GFR). This causes a build-up of urea and creatinine, fluid-electrolyte imbalances, and other related problems. ARF occurs from a variety of causes (see Box 64-1). These causes are grouped into three categories: prerenal (hypoperfusion), intrarenal (intrinsic renal), and postrenal(obstructive). Acute prerenal failure results from decreased blood flow to the kidneys. Subsequent renal hypoxia causes cellular edema and injury and cell death. Acute intrarenal failure results from injury to the kidney tissue. Acute postrenal failure results from urinary outflow obstruction. ARF occurs suddenly and entails multiple problems and potentially threatening complications. Children with ARF and their families need ongoing support and education. ARF outcomes range from complete recovery to the development of chronic renal failure.
Box 64-1 Causes of Acute Renal Failure
Prerenal (Hypoperfusion)
• Severe hypovolemia and/or severe hypotension: severe dehydration, shock, cardiac failure, severe vascular fluid shifts and/or third-space losses, hemorrhage
• Pharmacologic effects: renal vasoconstriction, severe hypotension, impaired renal autoregulatory response owing to blocked prostaglandin production (nonsteroidal antiinflammatory drugs, cyclooxygenase inhibitors and angiotensin-converting enzymes)
Intrarenal (Intrinsic)
• Small renal vessels: embolism, hemolytic-uremic syndrome (HUS), thrombotic thrombocytopenic purpura, severe hypertension
• Glomerulus: glomerulonephritis, renal vasculitis
• Tubules: acute tubular necrosis from ischemia (sepsis, hypovolemia, hypotension) or toxins; obstruction from uric acid, calcium oxylate or other compounds
• Interstitium: interstitial nephritis, pyelonephritis, infiltration from tumors or other agents
• Congenital kidney abnormalities: polycystic kidney disease, renal dysplasia, bilateral agenisis, glomerular maturation arrest
• Nephrotoxic agents: chemotherapy, cyclosporine, antibiotics (aminoglycosides, penicillins, cephalosporins, sulfonamides, amphotericin), radiographic contrast dye, heavy metals (mercury), myoglobin, organic solvents, pesticides, arsenic (rat poisoning)
INCIDENCE
1. Incidence and prognosis vary according to age, etiology, associated problems, underlying condition, geographic location, and type of treatment.
2. ARF in infants and children is most frequently caused by prerenal failure (hypoperfusion).
3. ARF is a common complication of critical illness. ARF in critically ill patients has been associated with high mortality (>60%). When ARF is combined with multisystem organ failure, the risk of death is even higher.
CLINICAL MANIFESTATIONS
The clinical presentation of ARF will vary based on the underlying cause.
1. Azotemia is the cardinal sign for ARF, regardless of type. (In critically ill children, the precipitating disease process frequently overshadows clinical manifestations of ARF.)
2. Oliguria with fluid retention and edema
6. Central nervous system dysfunction
8. Decreased urine output is frequently associated with ARF; patients with nonoliguric ARF may have normal or increased urine output.
COMPLICATIONS
1. Fluid balance complications: fluid overload, intravascular volume depletion from third-space losses, pulmonary edema, ascites causing respiratory difficulty
2. Electrolyte imbalances—arrhythmias, cardiac arrest, seizures
3. Cardiovascular: congestive heart failure, hypertension, hypotension, arrhythmias, shock, cardiac arrest
4. Respiratory: tachypnea, pulmonary edema, respiratory failure
5. Neurologic: altered level of consciousness, seizures, intracranial bleeding in neonates
6. Hematologic: anemia due to lack of erythropoietin and decreased blood cell production, bleeding (coagulopathies)
7. Infection can occur since the child is immunocompromised
8. Skin breakdown due to poor healing, malnutrition, pruritus
9. Malnutrition from decreased caloric intake, nausea, vomiting, diarrhea, and protein loss
LABORATORY AND DIAGNOSTIC TESTS
Refer to Appendix D for normal values and/or ranges of laboratory and diagnostic tests.
1. Blood tests: chemistry panel provides information related to levels of blood urea nitrogen (BUN), creatinine, serum electrolytes (potassium, sodium, calcium, magnesium, and phosphorus), glucose, and protein (albumen, total protein), as well as acid-base status (bicarbonate). Complete blood count (CBC) provides data related to the hematocrit, hemoglobin, and platelets. Serum blood gas results (arterial, capillary, or venous) provide data related to blood pH and acid-base status. Common alterations of these laboratory results in patients with ARF are listed as follows:
