Introduction

• Azotemia Azotemia = increased concentration of non-protein nitrogenous waste products, ie urea and creatinine, in the blood.
• Pre-renal azotemia = azotemia due to inadequate renal perfusion.
• Pre-renal azotemia may be present concurrently with primary renal and post-renal azotemia.
• Cause: decreased renal perfusion may be caused by dehydration, reduced cardiac output, hemorrhagic shock, etc.
• Signs: dependent on underlying cause but often include vomiting, lethargy, anorexia, diarrhea, etc.
• Diagnosis: elevated serum BUN and creatinine with urine specific gravity >1.030.
• Treatment: treat underlying cause.
• Prognosis: reversible if treated early; longstanding decreased renal perfusion → renal parenchymal damage.

Pathogenesis

Etiology

• Cardiac failure Heart: congestive heart failure ( → decreased cardiac output).
• Dehydration ( → hypovolemia → decreased renal perfusion).
• Shock ( → decreased renal perfusion).
• Severe hemorrhage → hypovolemia → decreased renal perfusion).
• Hypoadrenocorticism ( → hyponatremia → hypovolemia → decreased renal perfusion).
• Severe liver insufficiency ( → hypoalbuminemia → decreased oncotic pressure → decreased circulating blood volume → decreased renal perfusions).
• Nephrotic syndrome ( → hypoalbuminemia → same path as liver insufficiency).
• Drugs (ACE-inhibitors, antihypertensives → decreased blood pressure → decreased renal perfusion).

Pathophysiology

• Decreased cardiac output or decreased blood volume → decreased effective circulating blood volume → decreased renal perfusion → initially renal autoregulation will preserve glomerular filtration rate and intravascular volume due to increased water reabsorption in the proximal tubules and collecting tubules and increased sodium reabsorption in the distal tubules, but eventually → decreased glomerular filtration rate → decreased excretory function →azotemia.
• If no renal parenchymal damage in the early stages → good urine concentratiing ability.
• Longstanding renal hypoperfusion → renal parenchymal damage → acute tubular necrosis → acute renal failure.

Diagnosis

Treatment

Outcomes