Renal Hypoperfusion - Causes, Diagnosis, and Treatment

What Is Renal Hypoperfusion?

Renal perfusion is required to maintain normal urine output. Inadequate renal perfusion causes a decrease in glomerular filtration rate and increases receptive mechanisms. A reduction in the blood flow to the kidneys due to a decrease in effective arterial blood volume is called renal hypoperfusion. It can be due to the loss of blood volume with or without total body volume depletion.

Therefore, a change in these mechanisms can be associated with hemorrhage, cardiac failure, systemic inflammatory response syndrome, sepsis, hypovolemia, and severe dehydration. All these diseases cause reduced cardiac output and hypertension that leads to renal hypoperfusion. Renal hypoperfusion along with decreased glomerular capillary filtration pressure causes acute kidney injury. A renal biomarker of this is decreased urine sodium concentration. A urine sodium level of fewer than 20 milliequivalents per liter supports the presence of inadequate renal perfusion.

What Causes Renal Hypoperfusion?

Hemorrhage - Severe blood loss due to trauma or infection can result in decreased renal perfusion.

Sepsis - Severe infection with blood loss and low BP (blood pressure) can be a reason for renal hypoperfusion.

Hypotension - Decrease in blood pressure due to decreasing the total blood volume.

Anaphylactic Shock - It is a condition that results from systemic hypotension and hypovolaemia.

Renal Artery Stenosis - Reduced blood flow to the renal artery due to the presence of any blockage is called renal artery stenosis. This results in reduced glomerular pressure.

Non-steroidal Anti-inflammatory Drugs (NSAIDs) - Drugs that interfere with blood supply to the renal tissues are NSAIDs and ACE inhibitors. These painkillers commonly cause acute kidney injury in people with an increased risk of kidney problems.

Dehydration - Loss of excess fluids from the body or not consuming enough fluid can result in severe dehydration. This can further result in renal hypoperfusion.

Burns - Severe burns that have led to excessive loss of blood and injury to the renal tissues can result in renal hypoperfusion.

Fluid Shifts - Various diseases such as inflammation of the pancreas called pancreatitis and other liver diseases such as cirrhosis can create fluid shifts in the abdomen.

How Does Renal Hypoperfusion Affect Kidneys?

• Glomerular filtration rate and renal blood flow are maintained with perfusion pressure by contraction and dilation of afferent arterioles by a mechanism that requires changes in the secretion of vasodilatory prostaglandins.

• This is an auto-regulated mechanism that fails when perfusion pressure is sufficiently low.

• Renal hypoperfusion leads to the secretion of renin from the juxtaglomerular apparatus on the afferent arteriole. Renin causes contraction of efferent arteriole, which raises the glomerular capillary pressure thereby maintaining glomerular filtration during hypoperfusion.

• Severe prolonged hypoperfusion results in renal injury with acute oliguric renal failure.

What Are the Symptoms of Renal Hypoperfusion?

Oliguria - A fall in blood pressure below 70mmHg, renal perfusion pressure, and glomerular filtration rate leads to oliguria.

Inadequate Intravascular Volume - The signs of intravascular volume depletion include skin mottling, tachycardia, cold extremities, hypertension, and peripheral cyanosis.

Renal Ischemia - Reduced renal perfusion can cause tubular necrosis. Severe loss of blood volume causes hypertension and can produce lethal tubular cell injury and cell death by necrosis. This can finally lead to acute kidney failure.

Acute Kidney Injury - Severe renal hypoperfusion and low blood pressure can result in acute kidney injury. The symptoms include swelling in the legs, around the eyes, and ankles, nausea, seizures, shortness of breath, and fatigue.

How to Diagnose Renal Hypoperfusion?

Urinalysis - Urine analysis is done to analyze the biochemical markers of renal hypoperfusion. It includes urinary sodium concentration, the presence of albumin in urine, and fractional excretion of urea.

Blood Analysis - Blood analysis is done to measure the levels of sodium, potassium, urea, creatinine, and uric acid.

Kidney biopsy - A kidney biopsy is required to check for the presence of tubular necrosis. It is done in cases where the symptoms do not resolve even after diuretic therapy.

How Is Renal Hypoperfusion Treated?

• Severe renal hypoperfusion can result in renal failure due to low perfusion pressure. It requires an immediate infusion of fluid to restore the volume.

• A dose of Furosemide 4 mg per kg intravenously is generally used to correct the low urine flow when blood pressure appears to be restored.

• Furosemide is generally used to treat prerenal hypoperfusion. Patients with pre-renal hypoperfusion respond to the treatment with an increased urine flow whereas patients with renal failure remain with low urine output.

• Examination of the sodium and urine osmolality in patients with renal hypoperfusion provides the cause of the hypoperfusion state.

• Renal hypoperfusion without tubular necrosis has low sodium and urine osmolality. Whereas, in patients with acute renal failure and tubular necrosis the urine concentration is unmodified.

• If an oliguric patient responds to Furosemide it indicates intact tubular function and that extra fluid is rapidly required to restore renal perfusion.

• In the case of Furosemide-resistant oliguria with serum electrolyte abnormalities, the principal indication is dialysis. Dialysis is done to decrease blood chemicals that accumulate inside the body and remove uremic solutes.

• The prognosis of the patients with acute tubular necrosis is good. They generally recover after a few days of dialysis but the patient can require dialysis for many weeks before recovery.

Conclusion

Renal perfusion is required to maintain normal urine output. A decrease in renal perfusion is called renal hypoperfusion which decreases the glomerular filtration rate and increases tubular resorptive mechanisms. The symptoms include low sodium urine concentration, renal hypoxia, and tubular necrosis. The diagnosis includes urine analysis and blood analysis. The treatment includes the use of diuretic drugs to increase urine output in patients with renal hypoperfusion only. In the case of renal hypoperfusion with tubular necrosis, dialysis is required until the patient gets recovers.