Prerenal Kidney Failure

Use KDIGO-compatible criteria to establish AKI: serum creatinine increase of at least 0.3 mg/dL within 48 hours, increase to at least 1.5 times baseline within 7 days, or urine output below 0.5 mL/kg/hour for 6 hours. Obtain serial creatinine and accurately measured urine output rather than relying on a single creatinine value, because the syndrome evolves over hours to days. BMJ+2BMJAcute kidney injury - Diagnosis recommendations | BMJ Best Practice USPubMedAcute kidney injury: current concepts and new insightsPubMedPrerenal Kidney Failure - StatPearls - NCBI Bookshelf

Treat hemodynamic instability as a perfusion emergency while the cause is being defined. In hypovolemia, prompt crystalloid administration is recommended; in vasomotor shock or risk of AKI, fluids and vasopressors are used to support perfusion. Do not presume that all AKI with low urine sodium is volume depletion: fluids may be detrimental in cardiogenic shock or obstructive AKI. BMJ+1BMJAcute kidney injury - Diagnosis recommendations | BMJ Best PracticePubMedTreatment of Acute Kidney Injury: A Review of Current ... - PMC

Review the preceding 24 to 48 hours for hemorrhage, vomiting, diarrhea, sweating, inadequate replacement of ongoing losses, sepsis, burns, pancreatitis, major surgery, hypotension, iodinated contrast exposure, and new or intensified medications. Contrast exposure, ACE inhibitor or ARB use, and NSAID exposure may be co-contributors; identify whether the medication timeline matches the creatinine rise. BMJ+1BMJAcute kidney injury - Diagnosis recommendations | BMJ Best Practice USPubMedAcute Kidney Injury - StatPearls - NCBI Bookshelf - NIH

Order urinalysis with microscopy, urine sodium, urine creatinine, serum sodium, serum creatinine, and urine osmolality when the result will alter the hypoperfusion-versus-intrinsic branch. A urine sodium concentration below 20 mEq/L and urine osmolality above 500 mOsm/kg support intact tubular sodium retention and concentration in renal hypoperfusion. Recent iodinated contrast can confound interpretation of high urine osmolality. BMJ+1BMJAcute kidney injury - Diagnosis recommendations | BMJ Best PracticeBMJAcute kidney injury - Diagnosis recommendations | BMJ Best Practice US

Calculate FENa as (urine sodium × plasma creatinine) divided by (plasma sodium × urine creatinine) ×100. A FENa below 1% indicates sodium avidity and preserved tubular integrity; values above 2% to 3% favor tubular injury. Interpret this as a time-sensitive physiologic clue rather than a definitive etiologic test, because urine chemistries vary with the phase of AKI and extreme sodium avidity can produce FENa below 1% even when AKI is present. ScienceDirectScienceDirectExcretion Fraction - an overview

The definitive bedside discriminator for suspected volume-responsive prerenal AKI is response to a carefully monitored fluid challenge when there is no contraindication. Improvement in urine output or renal function after fluids supports renal hypoperfusion; lack of improvement should prompt reassessment for acute tubular necrosis or another intrinsic or postrenal process rather than assuming a larger fluid deficit. PubMedPubMedAcute Kidney Injury - StatPearls - NCBI Bookshelf - NIH

In extracellular fluid loss, the key decision is whether ongoing losses exceed replacement. Hemorrhage, vomiting, diarrhea, sweating, burns, sepsis, pancreatitis, and insufficient hospital fluid replacement all support this branch. Give crystalloid promptly when hypovolemia is present, monitor urine output and creatinine response, and continue to replace documented ongoing losses rather than using creatinine alone as the endpoint. BMJ+1BMJAcute kidney injury - Diagnosis recommendations | BMJ Best PracticeBMJAcute kidney injury - Diagnosis recommendations | BMJ Best Practice US

In reduced cardiac output or acute cardiorenal syndrome, renal hypoperfusion can coexist with excess total body volume. Patients with stable heart failure are often mildly hypervolemic but may become hypovolemic after overaggressive diuresis, severe diarrhea, or other losses. Compare recent weight, diuretic changes, and loss history with evidence of congestion before administering fluid; misclassification can lead to fluid administration in a congested patient or unnecessary diuresis in a depleted patient. ccjmccjmAcute cardiorenal syndrome: Mechanisms and clinical implications | Cleveland Clinic Journal of medicine

Impaired renal autoregulation is a medication-sensitive branch. NSAIDs can impair autoregulation, while ACE inhibitors and ARBs may contribute to AKI during an acute hemodynamic insult. Temporarily withholding kidney-hemodynamically active drugs in hypotension or dehydration, eliminating nephrotoxins, and adjusting medication doses to renal function are immediate actions while the precipitant is corrected. BMJ+2BMJAcute kidney injury - Diagnosis recommendations | BMJ Best PracticePubMedAcute kidney injury—an overview of diagnostic methods and clinical managementPubMedAcute Kidney Injury - StatPearls - NCBI Bookshelf - NIH

Cirrhosis requires a separate diagnostic frame because prerenal AKI, acute tubular necrosis, and hepatorenal syndrome have materially different prognosis and treatment. AKI occurs in approximately 20% of hospitalized patients with cirrhosis, and hepatorenal syndrome has the worst prognosis among these common causes, with reported survival of 35%. A low FENa is not sufficiently discriminating in advanced cirrhosis; persistent AKI after correction of reversible contributors warrants focused evaluation for ATN versus hepatorenal syndrome. ScienceDirect+1ScienceDirectExcretion Fraction - an overviewaasldWhy are patients with cirrhosis susceptible to hepatorenal syndrome (HRS)? | AASLD

If renal function and urine output do not improve after correction of a credible hemodynamic insult, reassess the three-category framework: intrinsic renal disease, obstruction, or ongoing low effective perfusion. Acute tubular necrosis may recover slowly over weeks to months, whereas prerenal physiology should improve when renal blood flow is restored. PubMedPubMedAcute Kidney Injury - StatPearls - NCBI Bookshelf - NIH

Use urinalysis and urine microscopy to seek evidence of intrinsic disease, and reconnect abnormalities to the exposure and systemic history. Ischemia, nephrotoxins, sepsis, rhabdomyolysis, glomerular disease, and acute interstitial nephritis are recognized intrinsic causes; contrast exposure and medication timing are especially important in hospitalized AKI. PubMed+1PubMedAcute kidney injury—an overview of diagnostic methods and clinical managementPubMedAcute Kidney Injury - StatPearls - NCBI Bookshelf - NIH

Evaluate for postrenal disease early when the history or clinical setting permits obstruction. Obstructive AKI belongs in the initial differential of every AKI evaluation, and fluids may be harmful when obstruction is the mechanism. Prompt relief of obstruction, not continued volume expansion, is the corrective intervention. PubMed+1PubMedTreatment of Acute Kidney Injury: A Review of Current ... - PMCPubMedAcute Kidney Injury - StatPearls - NCBI Bookshelf - NIH

In acute heart failure with uncertain volume status, routine pulmonary artery catheterization is not supported, although elevated filling pressures can be demonstrated invasively. Reserve invasive hemodynamic assessment for cases in which noninvasive clinical data do not resolve a management-critical uncertainty. ccjmccjmAcute cardiorenal syndrome: Mechanisms and clinical implications | Cleveland Clinic Journal of medicine

Monitor serum creatinine and urine output after the intervention that corrected the suspected perfusion defect. Absence of AKI by both creatinine and urine-output criteria within 7 days defines recovery; reversal within 48 hours is transient AKI, whereas recovery in 2 to 7 days is persistent AKI. Lack of recovery within 7 days is termed acute kidney disease. Wolters KluwerWolters KluwerDefining Early Recovery of Acute Kidney Injury : Clinical Journal of the American Society of Nephrology

Arrange clinical reassessment at 3 months after an AKI episode to determine whether new or worsening CKD has developed. This follow-up remains appropriate even when pre-AKI kidney function was normal, because AKI is linked to subsequent CKD through maladaptive repair and fibrosis pathways. Wolters KluwerWolters KluwerDefining Early Recovery of Acute Kidney Injury : Clinical Journal of the American Society of Nephrology