Medical School · Year 4 · Critical Care · includes a quiz and discussion video
Seminar 4: Acute Kidney Injury in Critical Illness
Year 4: Critical Care Elective
Learning Objectives
By the end of this seminar, students will be able to:
- Classify acute kidney injury using KDIGO staging criteria based on serum creatinine and urine output
- Differentiate pre-renal, intrinsic, and post-renal causes of AKI in critically ill patients
- Implement prevention strategies including nephrotoxin avoidance, hemodynamic optimization, and contrast protocols
- Manage fluid and electrolyte abnormalities associated with AKI including hyperkalemia and metabolic acidosis
- Identify indications for renal replacement therapy and select appropriate modality based on patient characteristics
- Counsel patients and families on AKI prognosis, recovery expectations, and need for nephrology follow-up
I. AKI Definition and Classification
Acute kidney injury is defined by standardized criteria that enable consistent diagnosis and severity staging across clinical settings. The Kidney Disease Improving Global Outcomes (KDIGO) classification establishes three stages based on changes in serum creatinine or urine output. Stage 1 AKI is defined as a creatinine rise of 1.5-1.9 times baseline or an increase of 0.3 mg/dL or greater within 48 hours, or urine output less than 0.5 mL/kg/hour for 6-12 hours. Stage 2 AKI requires creatinine 2-2.9 times baseline or urine output less than 0.5 mL/kg/hour for 12 hours or longer. Stage 3 AKI is the most severe, defined as creatinine 3 times baseline, creatinine of 4 mg/dL or greater, initiation of renal replacement therapy, or urine output less than 0.3 mL/kg/hour for 24 hours or anuria for 12 hours.
The traditional classification of AKI into pre-renal, intrinsic, and post-renal categories provides a framework for identifying etiology and guiding treatment. Pre-renal AKI results from decreased renal perfusion without structural kidney damage, occurring in hypovolemia, heart failure, and distributive shock. The kidney responds appropriately to perceived volume depletion by retaining sodium and concentrating urine. Intrinsic AKI involves direct damage to renal parenchyma, whether tubular, glomerular, interstitial, or vascular in origin. Post-renal AKI results from obstruction to urine outflow at any level from the collecting system to the urethra.
Biomarkers provide tools for AKI diagnosis and differentiation that complement clinical assessment. Serum creatinine remains the standard marker but has significant limitations, including delayed rise after injury and dependence on muscle mass. The BUN to creatinine ratio above 20:1 suggests pre-renal physiology, though this ratio can be affected by gastrointestinal bleeding and corticosteroid use. Novel biomarkers including neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 (KIM-1) may detect tubular injury earlier than creatinine rise. Cystatin C provides an alternative filtration marker less dependent on muscle mass.
The ICU environment presents unique challenges for AKI diagnosis and interpretation of renal biomarkers. Fluid resuscitation dilutes serum creatinine, potentially masking the severity of kidney injury. Muscle wasting during critical illness reduces creatinine generation, causing creatinine to underestimate the degree of renal dysfunction. Sepsis represents the most common cause of AKI in the ICU and may involve both hemodynamic and direct inflammatory mechanisms. Nephrotoxin exposure is common given the multiple medications required for critically ill patients. These factors necessitate integration of multiple data sources rather than reliance on any single marker.
<image>Figure 1. AKI Definition and Classification. Panel A presents KDIGO staging criteria showing creatinine and urine output thresholds for stages 1, 2, and 3 AKI. Panel B illustrates the pre-renal, intrinsic, and post-renal classification framework with mechanisms for each category. Panel C compares biomarkers including creatinine, BUN/Cr ratio, NGAL, and cystatin C with their applications and limitations. Panel D addresses ICU-specific considerations including fluid dilution effects, muscle wasting, sepsis predominance, and nephrotoxin exposure.</image>
II. Causes of AKI in Critical Illness
Pre-renal causes of AKI result from conditions that decrease effective renal perfusion pressure or blood flow. Hypovolemia from hemorrhage, dehydration, or third-spacing reduces circulating volume and renal perfusion. Cardiogenic shock with low cardiac output reduces forward flow to the kidneys despite adequate volume status. Distributive shock from sepsis, anaphylaxis, or neurogenic injury causes maldistribution of blood flow away from renal beds. Hepatorenal syndrome represents a special form of pre-renal failure in cirrhosis, where splanchnic vasodilation triggers renal vasoconstriction. The common mechanism in all pre-renal states is reduced glomerular filtration pressure; the kidney itself remains structurally intact and will recover with restoration of perfusion.
Intrinsic renal causes involve direct injury to kidney parenchyma through various mechanisms. Acute tubular necrosis (ATN) represents the most common intrinsic cause, resulting from ischemic injury after prolonged hypoperfusion or nephrotoxic injury from medications and contrast agents. Acute interstitial nephritis (AIN) occurs as an allergic reaction to drugs, most commonly beta-lactam antibiotics, proton pump inhibitors, and NSAIDs. Glomerulonephritis and vasculitis cause rapidly progressive kidney injury requiring urgent evaluation and treatment. Vascular causes including atheroembolic disease and renal artery thrombosis can precipitate AKI, particularly after vascular procedures.
Nephrotoxins in the ICU warrant particular attention given their frequency and preventability. Aminoglycoside antibiotics cause dose-dependent tubular injury; once-daily dosing with drug level monitoring reduces nephrotoxicity while maintaining efficacy. Vancomycin is associated with AKI, particularly with trough levels above 15-20 mcg/mL and concomitant nephrotoxin exposure. Amphotericin B, particularly the deoxycholate formulation, causes both tubular injury and renal vasoconstriction. Iodinated contrast agents used in CT imaging and angiography cause contrast-induced nephropathy, especially in patients with baseline kidney disease. NSAIDs and ACE inhibitors/ARBs affect intrarenal hemodynamics and should be avoided or used cautiously in high-risk patients.
Post-renal obstruction should always be considered and excluded in AKI, as it represents a potentially reversible cause. Ureteral obstruction can result from nephrolithiasis, external compression from masses, or surgical injury. Bladder outlet obstruction from benign prostatic hyperplasia, prostate cancer, or neurogenic bladder is common in elderly men. Urinary catheter obstruction from kinking, blood clots, or sediment causes acute anuria that is immediately reversible with catheter replacement. Renal ultrasound represents the initial diagnostic study to evaluate for hydronephrosis indicating obstruction. Bilateral obstruction or obstruction of a solitary kidney is required to cause significant AKI.
<image>Figure 2. Causes of AKI in Critical Illness. Panel A categorizes pre-renal causes including hypovolemia, cardiogenic shock, distributive shock, and hepatorenal syndrome with their pathophysiology. Panel B describes intrinsic causes including ATN from ischemia or nephrotoxins, AIN from drug reactions, glomerulonephritis, and vascular disease. Panel C highlights ICU nephrotoxins including aminoglycosides, vancomycin, amphotericin, contrast agents, and NSAIDs with risk reduction strategies. Panel D addresses post-renal obstruction at ureteral, bladder, and catheter levels with diagnostic approach using ultrasound.</image>
III. Prevention of AKI
Avoidance of nephrotoxins represents a cornerstone of AKI prevention in hospitalized patients. Daily medication review should assess whether each potentially nephrotoxic agent remains necessary and whether alternatives exist. Dose adjustment for renal function prevents accumulation of drugs dependent on renal clearance. Monitoring drug levels for aminoglycosides and vancomycin enables dose optimization. When nephrotoxins are required, minimizing duration of exposure and avoiding concurrent nephrotoxic agents reduces risk. NSAIDs should generally be avoided in critically ill patients; ACE inhibitors and ARBs may need temporary discontinuation during acute illness though should be resumed when appropriate.
Contrast-induced AKI prevention follows established protocols for patients requiring iodinated contrast. Pre-procedure hydration with normal saline or sodium bicarbonate solution expands intravascular volume and reduces contrast concentration in renal tubules. Using the minimum contrast volume necessary for adequate imaging limits nephrotoxin exposure; volumes less than 100 mL carry lower risk than larger volumes. Avoiding contrast altogether in high-risk patients, when clinically appropriate, eliminates risk entirely. The role of N-acetylcysteine remains uncertain despite widespread use; current evidence does not support routine administration but it is unlikely to cause harm.
Hemodynamic optimization maintains renal perfusion pressure and prevents ischemic injury. Mean arterial pressure targets of at least 65 mmHg ensure adequate perfusion in most patients, though higher targets may be appropriate for those with chronic hypertension. Avoiding prolonged hypotensive episodes during procedures and critical illness reduces cumulative ischemic exposure. Vasopressor therapy when needed maintains perfusion pressure that would otherwise be inadequate. Neither hypervolemia nor routine use of any specific vasopressor has been shown to prevent AKI; the key principle is maintaining adequate perfusion without causing harm from fluid overload.
Monitoring enables early detection of AKI and assessment of treatment response. Daily serum creatinine measurement identifies rising values before significant injury accumulates. Hourly urine output monitoring through urinary catheter or other means provides real-time assessment of renal function. Fluid balance calculation identifies trends toward overload or deficit. Drug level monitoring guides dosing of medications with narrow therapeutic windows. Electronic clinical decision support systems can alert clinicians to nephrotoxin combinations and prompt dose adjustments based on renal function.
<image>Figure 3. AKI Prevention. Panel A outlines nephrotoxin avoidance strategies including medication review, dose adjustment, level monitoring, and avoidance of concurrent nephrotoxins. Panel B describes contrast-induced nephropathy prevention with hydration, contrast minimization, avoidance when possible, and uncertain role of N-acetylcysteine. Panel C presents hemodynamic optimization principles including MAP targets, avoiding hypotension, and appropriate vasopressor use. Panel D addresses monitoring strategies including daily creatinine, hourly urine output, fluid balance, and drug levels with clinical decision support.</image>
IV. Management of AKI
Initial management of AKI focuses on identifying the cause and implementing targeted treatment. Identifying whether AKI is pre-renal, intrinsic, or post-renal directs the treatment approach. All potentially nephrotoxic medications should be reviewed and discontinued or substituted when possible. Hemodynamic optimization through volume resuscitation or vasopressor support restores renal perfusion in pre-renal states. Renal ultrasound should be obtained to rule out obstruction, particularly in patients with risk factors or unexplained oliguria. Treatment of underlying conditions such as sepsis, heart failure, or obstruction addresses the primary problem.
Fluid management in AKI requires careful attention to avoid both hypovolemia and hypervolemia. Patients who are volume depleted should receive crystalloid resuscitation to restore intravascular volume and renal perfusion. Patients who are volume overloaded may require fluid restriction and diuresis to prevent respiratory compromise and tissue edema. Balancing these extremes avoids the harm of both persistent hypoperfusion and fluid overload. Crystalloid solutions are preferred over synthetic colloids, which have been associated with increased AKI risk in some studies. The type of crystalloid matters less than avoiding both extremes of volume status.
Diuretics have a specific role in managing volume overload but do not prevent or treat AKI itself. Loop diuretics increase urine output and can facilitate management of fluid overload in oliguric patients. Converting oliguric to non-oliguric AKI may simplify fluid management but has not been shown to improve renal outcomes. Diuretics do not prevent AKI or hasten recovery; they should not be used in euvolemic patients simply because AKI is present. High doses of loop diuretics may be required in advanced AKI due to reduced drug delivery to the nephron. Continuous infusion may provide more consistent diuresis than intermittent boluses in some patients.
Medication dose adjustments become essential as kidney function declines. Antibiotics requiring renal clearance, including vancomycin, aminoglycosides, and many beta-lactams, require dose reduction or interval extension. Anticoagulants including low-molecular-weight heparin and direct oral anticoagulants accumulate and increase bleeding risk. Opioid metabolites, particularly from morphine, accumulate in renal failure and can cause prolonged sedation and respiratory depression. ACE inhibitors and ARBs may need to be held during acute illness though are often indicated long-term. Pharmacist consultation helps optimize medication regimens in patients with AKI.
<image>Figure 4. AKI Management. Panel A outlines initial steps including cause identification, nephrotoxin discontinuation, hemodynamic optimization, and obstruction exclusion. Panel B describes fluid management principles balancing resuscitation needs against volume overload risks. Panel C addresses diuretic use for volume overload, emphasizing that diuretics do not treat AKI itself but facilitate fluid management. Panel D presents medication dose adjustment requirements for antibiotics, anticoagulants, opioids, and cardiovascular medications.</image>
V. Electrolyte Abnormalities in AKI
Hyperkalemia represents the most immediately dangerous electrolyte abnormality in AKI. Potassium accumulates when renal excretion fails, with levels rising more rapidly in patients with ongoing potassium intake, tissue breakdown, or acidosis causing transcellular shifts. ECG changes including peaked T waves, widened QRS complex, and loss of P waves indicate cardiac toxicity requiring emergent treatment. Calcium gluconate provides cardiac membrane stabilization as the first intervention for ECG changes or severe hyperkalemia. Insulin with dextrose shifts potassium intracellularly within 15-30 minutes. Potassium binders including sodium polystyrene sulfonate (Kayexalate) and patiromer enhance gastrointestinal elimination. Dialysis provides definitive removal when other measures are insufficient.
Metabolic acidosis develops as the kidneys fail to excrete the daily acid load generated by metabolism. The acidosis is typically a high anion gap acidosis due to accumulation of uremic acids, though non-gap acidosis from impaired renal bicarbonate regeneration can also occur. Mild acidosis may require no specific treatment beyond addressing the underlying AKI. Moderate acidosis with pH below 7.2 may warrant consideration of sodium bicarbonate administration, though evidence for benefit is limited. Severe, refractory acidosis represents an indication for dialysis. Compensatory hyperventilation should be expected and not suppressed with sedation.
Hyperphosphatemia results from decreased renal phosphorus excretion and may contribute to hypocalcemia and vascular calcification. Dietary phosphorus restriction limits ongoing accumulation. Phosphate binders including calcium-based binders and non-calcium binders such as sevelamer reduce intestinal phosphorus absorption. Dialysis effectively removes phosphorus when levels are severely elevated. The significance of hyperphosphatemia is greater in chronic kidney disease than in acute illness, but management prevents complications.
Additional electrolyte abnormalities in AKI require recognition and appropriate treatment. Hypocalcemia may be asymptomatic or cause muscle cramps, tetany, and cardiac arrhythmias; replacement is indicated for symptomatic hypocalcemia. Hyponatremia commonly results from volume overload with dilutional effect and responds to fluid restriction and diuresis. Hypermagnesemia occurs when magnesium-containing medications continue in renal failure; discontinuation of magnesium sources usually suffices, with dialysis for severe symptomatic cases. Serial electrolyte monitoring guides ongoing management and identifies emerging abnormalities.
<image>Figure 5. Electrolyte Abnormalities in AKI. Panel A presents hyperkalemia management including ECG monitoring, calcium for cardioprotection, insulin/dextrose for shifting, binders for elimination, and dialysis for refractory cases. Panel B describes metabolic acidosis pathophysiology, indications for bicarbonate therapy, and role of dialysis for severe cases. Panel C addresses hyperphosphatemia treatment with dietary restriction, phosphate binders, and dialysis. Panel D covers additional abnormalities including hypocalcemia, hyponatremia, and hypermagnesemia with treatment approaches.</image>
VI. Renal Replacement Therapy Indications
Indications for renal replacement therapy in AKI are summarized by the mnemonic AEIOU. Acidosis that is severe (pH below 7.1) and refractory to medical management represents an indication for dialysis. Electrolyte abnormalities, particularly hyperkalemia with ECG changes unresponsive to medical therapy, require dialysis for definitive correction. Intoxication with dialyzable substances including methanol, ethylene glycol, lithium, and salicylates can be treated with dialysis when drug levels or clinical status warrant. Fluid overload causing pulmonary edema refractory to diuretics requires ultrafiltration to restore euvolemia. Uremia with encephalopathy, pericarditis, or bleeding represents end-stage renal dysfunction requiring dialysis.
The timing of renal replacement therapy initiation remains an area of ongoing investigation. Earlier initiation when indications are emerging rather than fully developed has not shown consistent benefit in clinical trials. Waiting until clear indications develop allows some patients to recover renal function without dialysis. Very delayed initiation with prolonged severe uremia may increase complications. Current practice generally initiates dialysis when specific indications are present rather than at arbitrary creatinine or BUN thresholds. Clinical judgment integrating all patient factors guides individual decisions.
Three principal modalities are available for acute renal replacement therapy. Intermittent hemodialysis (IHD) uses high blood and dialysate flow rates over 3-4 hour sessions, providing rapid solute clearance and fluid removal. Continuous renal replacement therapy (CRRT) operates 24 hours per day at lower flow rates, providing gentler, sustained solute and fluid removal. Sustained low-efficiency dialysis (SLED) represents a hybrid approach with extended duration (6-12 hours) at intermediate flow rates. Each modality has advantages and disadvantages depending on patient characteristics and clinical goals.
Selection among modalities depends on patient stability and treatment goals. Hemodynamically unstable patients tolerate CRRT better than IHD due to slower fluid shifts. Patients with elevated intracranial pressure benefit from CRRT, which avoids the rapid osmotic changes of IHD that can worsen cerebral edema. Continuous solute clearance with CRRT may be preferred for sustained removal of toxins or medications. IHD is more efficient for emergent treatment of severe hyperkalemia or poisoning requiring rapid clearance. Practical factors including nursing expertise, equipment availability, and anticoagulation requirements also influence modality selection.
<image>Figure 6. Renal Replacement Therapy Indications. Panel A presents the AEIOU mnemonic: Acidosis (refractory), Electrolytes (hyperkalemia with ECG changes), Intoxication (dialyzable toxins), Overload (refractory pulmonary edema), and Uremia (encephalopathy, pericarditis). Panel B discusses timing considerations and the evidence regarding early versus late initiation. Panel C describes the three RRT modalities: IHD (intermittent, rapid clearance), CRRT (continuous, gentle), and SLED (hybrid approach). Panel D outlines selection criteria based on hemodynamic stability, intracranial pressure, clearance needs, and practical factors.</image>
VII. CRRT Management
Vascular access for CRRT requires placement of a large-bore dialysis catheter capable of supporting the required blood flow rates. The internal jugular vein is generally preferred for catheter placement due to lower infection and malposition rates compared to femoral access. Femoral vein access provides a reliable alternative when internal jugular access is not feasible. Subclavian access is avoided when possible due to risks of stenosis that may compromise future permanent access. Catheter position should be confirmed radiographically before initiating therapy. Proper catheter care with sterile dressing and hub care prevents catheter-related bloodstream infections.
Anticoagulation prevents clotting of the extracorporeal circuit and maintains filter patency. Regional citrate anticoagulation has become the preferred method, using citrate infusion pre-filter to chelate calcium and prevent clotting, with calcium infusion post-filter to restore systemic calcium. This approach provides effective anticoagulation without systemic anticoagulant effects, reducing bleeding risk. Systemic heparin anticoagulation represents an alternative for patients in whom citrate is contraindicated or unavailable. No anticoagulation may be used in patients with active bleeding or severe coagulopathy, accepting shorter filter life in exchange for bleeding safety.
Dosing of CRRT involves prescribing the effluent rate that determines solute clearance. Current guidelines recommend effluent doses of 20-25 mL/kg/hour for acute kidney injury. Higher doses have not demonstrated benefit in clinical trials and increase costs. The prescribed dose often exceeds the delivered dose due to treatment interruptions for procedures, filter clotting, and other factors. Monitoring delivered dose and adjusting prescription to account for down time ensures adequate clearance. Medication dosing requires adjustment to account for drug removal by CRRT.
Complications of CRRT require monitoring and management. Hypotension can occur from rapid fluid removal; reducing ultrafiltration rate or administering volume addresses this. Hypothermia results from extracorporeal circulation; warming the replacement fluid prevents excessive heat loss. Electrolyte abnormalities including hypophosphatemia, hypomagnesemia, and hypocalcemia (with citrate anticoagulation) require monitoring and replacement. Catheter malfunction from thrombosis or fibrin sheath formation may require repositioning or replacement. Citrate toxicity manifests as metabolic alkalosis and low ionized calcium despite total calcium replacement, requiring reduction in citrate delivery.
<image>Figure 7. CRRT Management. Panel A addresses vascular access including preferred internal jugular placement, alternatives, position confirmation, and catheter care. Panel B describes anticoagulation options with emphasis on regional citrate anticoagulation as preferred, systemic heparin as alternative, and no anticoagulation for high bleeding risk. Panel C presents dosing recommendations of 20-25 mL/kg/hour effluent, monitoring delivered versus prescribed dose, and medication dosing adjustments. Panel D outlines complications including hypotension, hypothermia, electrolyte abnormalities, catheter malfunction, and citrate toxicity with management approaches.</image>
VIII. Prognosis and Recovery
Outcomes following AKI in critical illness span a spectrum from complete recovery to permanent dialysis dependence. The majority of patients who survive their critical illness will experience some degree of renal recovery. Progression to chronic kidney disease occurs in 10-20% of AKI survivors. Progression to end-stage renal disease requiring chronic dialysis occurs in less than 5% of AKI episodes, though rates are higher in patients with pre-existing CKD or severe AKI. Mortality associated with AKI depends heavily on the underlying cause and comorbidities; AKI is more often a marker of illness severity than a direct cause of death.
Multiple factors influence the likelihood and extent of renal recovery. Baseline kidney function prior to the acute illness strongly predicts outcomes; patients with pre-existing CKD have higher rates of non-recovery and progression. Duration of AKI before recovery begins correlates with worse outcomes; prolonged AKI indicates more severe injury. The etiology of AKI matters; pre-renal causes generally recover well with restoration of perfusion while severe ATN may have prolonged or incomplete recovery. Severity of AKI as measured by KDIGO stage predicts outcomes, with stage 3 AKI having worst prognosis. Older age is associated with slower and less complete recovery.
Strategies to support renal recovery focus on maintaining perfusion and avoiding additional injury. Continued avoidance of nephrotoxins prevents compounding initial injury with subsequent insults. Hemodynamic support maintains renal perfusion during the vulnerable recovery period. Adequate nutrition with appropriate protein intake supports healing; severe protein restriction is not beneficial in AKI. Appropriate fluid balance avoids both the hypoperfusion of hypovolemia and the venous congestion of hypervolemia. Recovery may continue for weeks to months after the initial insult.
Post-ICU follow-up addresses ongoing renal needs and monitors for late complications. Nephrology referral is appropriate for patients with persistent kidney dysfunction at hospital discharge. Serum creatinine monitoring tracks recovery trajectory and identifies patients with incomplete recovery. Medication review ensures appropriate adjustment for current kidney function and discontinuation of no-longer-needed nephrotoxins. Blood pressure control in patients with persistent CKD slows further progression. Education about the increased risk of future AKI and CKD progression helps patients and primary care providers with long-term management.
<image>Figure 8. Prognosis and Recovery. Panel A presents outcome statistics including rates of recovery, progression to CKD, progression to ESRD, and factors affecting mortality. Panel B describes factors influencing recovery including baseline function, AKI duration, etiology, severity, and age. Panel C outlines strategies to support recovery including nephrotoxin avoidance, hemodynamic support, nutrition, and fluid balance. Panel D addresses post-ICU follow-up including nephrology referral, creatinine monitoring, medication review, and patient education.</image>
IX. Special Populations
Sepsis-associated AKI represents the most common cause of AKI in the intensive care unit. The pathophysiology is multifactorial, involving both hemodynamic factors from distributive shock and direct inflammatory injury to tubular epithelium. Prevention through early implementation of sepsis bundles with appropriate fluid resuscitation and antibiotics may limit severity. Management focuses on treating the underlying sepsis while avoiding additional nephrotoxic insults. Prognosis for recovery is generally favorable in patients who survive their sepsis, with most regaining functional renal capacity.
Cardiac surgery-associated AKI occurs frequently due to the combination of cardiopulmonary bypass, hemodynamic instability, and nephrotoxin exposure. Risk factors include pre-existing CKD, diabetes, advanced age, and prolonged bypass time. Prevention strategies include minimizing bypass duration when possible, maintaining adequate perfusion pressure, and avoiding concurrent nephrotoxins in the perioperative period. Hemodynamic optimization in the postoperative period supports renal perfusion. Outcomes are variable depending on severity and pre-existing risk factors.
Rhabdomyolysis causes AKI through myoglobin-mediated tubular injury and renal vasoconstriction. Aggressive fluid resuscitation targeting urine output of 200-300 mL/hour dilutes myoglobin and promotes excretion before tubular precipitation occurs. Crystalloid, typically normal saline or balanced solution, serves as the primary resuscitation fluid. Alkalinization of urine with sodium bicarbonate may reduce myoglobin precipitation in renal tubules, though evidence is limited. Avoidance of nephrotoxins during the vulnerable period is essential. Renal replacement therapy may be needed for severe cases with oliguria despite aggressive hydration.
Hepatorenal syndrome represents a unique form of renal failure occurring in advanced liver disease. Type 1 hepatorenal syndrome involves rapid, severe decline in renal function with poor prognosis. Type 2 hepatorenal syndrome shows more gradual, moderate dysfunction, often with refractory ascites. Medical treatment combines albumin infusion with vasoconstrictors (terlipressin, norepinephrine, or midodrine/octreotide combinations) to restore effective arterial volume and renal perfusion. Liver transplantation represents the definitive treatment for appropriate candidates. Transjugular intrahepatic portosystemic shunt (TIPS) may benefit selected patients. Dialysis provides support but does not address the underlying hepatic pathophysiology.
<image>Figure 9. Special Populations. Panel A describes sepsis-associated AKI as the most common ICU AKI cause, with multifactorial pathophysiology, prevention through sepsis bundles, and generally favorable recovery in survivors. Panel B addresses cardiac surgery AKI with risk factors, prevention through minimizing bypass and maintaining perfusion, and variable outcomes. Panel C presents rhabdomyolysis management with aggressive fluids targeting high urine output, consideration of alkalinization, nephrotoxin avoidance, and RRT if needed. Panel D outlines hepatorenal syndrome types, medical treatment with albumin and vasoconstrictors, and definitive therapy through liver transplantation.</image>
X. Ethical Considerations
Decisions to initiate renal replacement therapy involve complex discussions that should integrate medical facts with patient values and goals. Goals of care conversations should establish what the patient hopes to achieve and what outcomes would be acceptable or unacceptable. Prognosis for both renal recovery and overall survival informs realistic expectations. Quality of life considerations include the burden of dialysis and functional status with treatment. Shared decision-making between the medical team and patient/family ensures that treatment aligns with patient values. For patients without decision-making capacity, surrogate decision-makers apply substituted judgment based on known patient preferences.
Decisions to discontinue renal replacement therapy may become appropriate when recovery is not occurring or overall prognosis is poor. Persistent multi-organ failure despite maximal support suggests that continuing dialysis will not achieve meaningful recovery. Reassessing goals of care when the clinical situation changes allows for treatment redirection. Patient or surrogate decisions to discontinue dialysis and transition to comfort care should be respected as autonomous choices. Comfort measures continue and are intensified when life-sustaining treatment is withdrawn. Death typically occurs within hours to days after dialysis discontinuation depending on the degree of renal failure and fluid overload.
Resource allocation considerations arise given the intensive resources required for renal replacement therapy. CRRT machines and supplies are limited in most institutions. Nursing expertise and staffing affect the number of patients who can simultaneously receive CRRT. The financial costs of CRRT are substantial. Fair allocation policies ensure equitable access when resources are constrained. These considerations should not override individual patient needs but may inform system-level decisions about resource deployment.
Communication throughout the course of AKI supports patients and families facing uncertainty and difficult decisions. Early discussion of the possibility of AKI and its implications sets expectations. Honest prognostic information, even when uncertain, enables informed decision-making. Regular updates on kidney function trajectory keep families engaged. Support for the emotional burden of decision-making acknowledges the difficulty of choices families may face. Documentation of discussions ensures continuity when multiple providers are involved.
<image>Figure 10. Ethical Considerations. Panel A addresses initiating RRT with emphasis on goals of care discussions, prognosis communication, quality of life considerations, and shared decision-making. Panel B presents considerations for stopping RRT including non-recovery, reassessing goals, respecting autonomous choices, and comfort care provision. Panel C discusses resource allocation including machine and supply limitations, staffing requirements, costs, and fair allocation policies. Panel D outlines communication approaches including early discussion, honest prognosis, regular updates, emotional support, and documentation.</image>
Summary
Acute kidney injury is classified using KDIGO criteria based on creatinine rise and urine output reduction, with three stages of increasing severity. The traditional classification into pre-renal (decreased perfusion), intrinsic (parenchymal damage including ATN), and post-renal (obstruction) guides diagnostic evaluation and treatment. Prevention strategies include avoiding nephrotoxins, optimizing hemodynamics to maintain renal perfusion, and using hydration protocols for contrast exposure. Management involves identifying and treating the underlying cause, discontinuing nephrotoxins, and carefully managing fluid balance to avoid both hypovolemia and hypervolemia. Hyperkalemia is the most dangerous electrolyte abnormality, requiring ECG monitoring and treatment with calcium, insulin/dextrose, binders, and dialysis for severe cases. Renal replacement therapy indications are summarized by AEIOU: refractory Acidosis, Electrolyte abnormalities (hyperkalemia), Intoxication, fluid Overload, and Uremia. CRRT is preferred for hemodynamically unstable patients, using regional citrate anticoagulation when possible and targeting effluent doses of 20-25 mL/kg/hour. Most AKI survivors recover renal function, though CKD progression occurs in 10-20% and ESRD in less than 5%. Special populations include sepsis (most common), cardiac surgery, rhabdomyolysis (requiring aggressive hydration), and hepatorenal syndrome (requiring albumin and vasoconstrictors). Ethical considerations include shared decision-making about initiating and discontinuing dialysis aligned with patient goals.
Key Terms
AKI (Acute Kidney Injury): Acute decline in kidney function defined by increased serum creatinine or decreased urine output according to KDIGO staging criteria.
ATN (Acute Tubular Necrosis): Intrinsic renal injury resulting from ischemic or nephrotoxic damage to tubular epithelial cells, the most common cause of intrinsic AKI.
KDIGO (Kidney Disease Improving Global Outcomes): International organization that established the standardized criteria for AKI staging used worldwide.
CRRT (Continuous Renal Replacement Therapy): A form of dialysis providing continuous, slow removal of fluid and solutes over 24 hours, preferred for hemodynamically unstable patients.
CVVH (Continuous Venovenous Hemofiltration): A CRRT mode using convection (hemofiltration) to remove solutes by drawing fluid across a membrane with replacement fluid infusion.
Effluent: The waste fluid produced during dialysis containing removed water and solutes; effluent rate determines dialysis dose.
Citrate: Regional anticoagulant used in CRRT that chelates calcium to prevent clotting in the extracorporeal circuit without systemic anticoagulation.
AEIOU: Mnemonic for indications for dialysis: Acidosis (refractory), Electrolytes (hyperkalemia), Intoxication, Overload (fluid), Uremia (symptomatic).
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