Contrast-Induced Nephropathy / Contrast-Associated Acute Kidney Injury (CA-AKI)

Quick Answer

Contrast-Associated Acute Kidney Injury (CA-AKI), previously termed Contrast-Induced Nephropathy (CIN), is an acute decline in renal function following iodinated contrast media administration. KDIGO defines it as serum creatinine rise ≥26.5 μmol/L (0.3 mg/dL) within 48 hours OR ≥50% increase from baseline within 7 days of contrast exposure. Creatinine typically peaks at 48-72 hours and recovers within 7-14 days. Risk factors include pre-existing CKD (eGFR <60 mL/min/1.73m2), diabetes mellitus, volume depletion, high contrast volume, and concurrent nephrotoxins. The PRESERVE trial (2018) demonstrated that neither N-acetylcysteine nor sodium bicarbonate prevented CA-AKI compared to placebo and isotonic saline. Prevention relies on volume expansion with isotonic crystalloid (1-1.5 mL/kg/h for 3-12 hours pre- and post-procedure), contrast volume minimization, and avoiding repeat contrast within 48-72 hours. In the ICU, the decision to administer contrast requires balancing diagnostic necessity against nephroprotection, particularly in emergency imaging for sepsis, trauma, or STEMI. CA-AKI is usually reversible; dialysis is rarely required (<1% of cases).

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CICM Exam Focus

What Examiners Expect

Second Part Written (SAQ):

Common SAQ stems:

• "A 68-year-old diabetic patient with eGFR 35 mL/min/1.73m2 requires urgent CT angiography for suspected pulmonary embolism. Outline your approach to minimizing renal risk." (15 marks)
• "Discuss the evidence for prevention strategies in contrast-associated acute kidney injury." (20 marks)
• "A patient develops oliguria 24 hours after coronary angiography. List your differential diagnoses and describe your diagnostic approach." (15 marks)
• "Compare and contrast contrast-induced nephropathy with cholesterol emboli syndrome following cardiac catheterization." (10 marks)

Expected depth:

• Know KDIGO definition precisely (timing, thresholds)
• Mehran risk score components for percutaneous coronary intervention
• PRESERVE trial methodology and key findings (NAC and bicarb both ineffective)
• Evidence-based prevention strategies with critical appraisal
• Pathophysiology linking contrast properties to nephrotoxicity
• Decision-making framework for emergency imaging in CKD patients

Second Part Hot Case:

Typical presentations:

• Day 2-3 post-angiography patient with rising creatinine and oliguria
• ICU patient requiring repeat CT imaging who developed AKI after initial scan
• Post-STEMI patient with cardiorenal syndrome and contrast exposure

Examiners assess:

• Systematic evaluation of AKI etiology (not assuming contrast is the cause)
• Recognition of alternative diagnoses (atheroemboli, cardiorenal, sepsis)
• Evidence-based approach to volume management
• Decision-making on contrast re-exposure
• Communication with radiology, cardiology, nephrology

Second Part Viva:

Expected discussion areas:

• Pathophysiology: Contrast osmolality, medullary hypoxia, oxidative stress
• Risk stratification: Mehran score, eGFR thresholds, volume status
• Prevention evidence: PRESERVE, POSEIDON, AMACING trials
• ICU dilemmas: Emergency CT in shocked patient, STEMI with CKD
• Differentiation from cholesterol emboli (timing, eosinophilia, livedo)
• Indigenous health considerations in remote imaging access

Examiner expectations:

• Critical appraisal of NAC evidence (PRESERVE showed no benefit)
• Understanding contrast properties (iso-osmolar vs low-osmolar)
• Practical prevention protocols implementable in ICU
• Risk-benefit analysis for emergency imaging

Common Mistakes

• Recommending NAC routinely (no evidence of benefit post-PRESERVE)
• Using sodium bicarbonate as first-line (no superiority over saline)
• Delaying life-saving imaging due to excessive nephroprotection concerns
• Confusing contrast-induced nephropathy with cholesterol emboli (different timing)
• Over-relying on prophylactic dialysis (harmful, not beneficial)
• Failing to recognize that many "CA-AKI" cases are actually incidental AKI

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Key Points

Must-Know Facts

1. Definition (KDIGO): Serum creatinine rise ≥26.5 μmol/L within 48 hours OR ≥50% increase within 7 days of contrast exposure. Peak creatinine at 48-72 hours, recovery within 7-14 days.

2. True Incidence Debate: Modern evidence suggests CA-AKI risk has been historically overestimated. In patients with eGFR >45 mL/min/1.73m2, the risk is negligible. Significant risk occurs only with eGFR <30 mL/min/1.73m2 and additional risk factors.

3. Pathophysiology Triad: (i) Renal medullary hypoxia from vasoconstriction, (ii) Direct tubular toxicity from contrast, (iii) Oxidative stress and reactive oxygen species generation.

4. PRESERVE Trial 2018: NAC (oral or IV) and sodium bicarbonate provided NO benefit over placebo and isotonic saline in preventing CA-AKI or major kidney events. This was the definitive trial ending routine NAC use.

5. Prevention Cornerstone: Isotonic crystalloid volume expansion (0.9% saline or balanced solutions) at 1-1.5 mL/kg/h for 3-12 hours before and 6-12 hours after contrast. Minimize contrast volume. Avoid repeat contrast within 48-72 hours.

6. Risk Stratification: Mehran score for PCI includes: hypotension, IABP, CHF, eGFR, diabetes, anemia, contrast volume. Score >16 = high risk (>50% CA-AKI risk).

7. Cholesterol Emboli Distinction: Atheroembolic disease occurs days-to-weeks after arterial instrumentation, NOT within 24-48 hours like CA-AKI. Features include livedo reticularis, eosinophilia, hypocomplementemia, and progressive irreversible renal failure.

8. ICU Decision-Making: In life-threatening emergencies (STEMI, major trauma, pulmonary embolism), do NOT delay essential imaging for nephroprotection. The mortality from missed diagnosis exceeds CA-AKI risk.

9. Dialysis is NOT Prophylactic: Prophylactic hemodialysis does not prevent CA-AKI and may worsen outcomes. Dialysis should only be used for absolute indications (AEIOU).

10. Long-Term Outcomes: Most CA-AKI resolves completely. However, patients who develop CA-AKI have increased 1-year mortality (7-fold) and higher rates of progression to CKD.

Memory Aids

Mnemonic: CONTRAST RISK

• Chronic kidney disease (eGFR <30)
• Older age (>75 years)
• Nephrotoxic drugs (NSAIDs, aminoglycosides, ACEi)
• Type 2 diabetes mellitus
• Reduced volume status (dehydration)
• Anemia (Hb <100 g/L)
• Shock or hypotension
• Too much contrast (>100 mL or volume/GFR >1)

Mnemonic: HYDRATE (Prevention)

• Hydrate with isotonic crystalloid (1-1.5 mL/kg/h)
• Yield to necessity (don't delay life-saving imaging)
• Decrease contrast volume
• Repeat contrast avoided for 48-72 hours
• Avoid nephrotoxins (NSAIDs, aminoglycosides)
• Think about alternatives (ultrasound, non-contrast CT/MRI)
• Evaluate risk vs benefit

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Definition & Epidemiology

Definition

Contrast-Associated Acute Kidney Injury (CA-AKI) is the contemporary term preferred over "Contrast-Induced Nephropathy (CIN)" to acknowledge that causality is often uncertain. The KDIGO Acute Kidney Injury Guideline and subsequent consensus statements define CA-AKI as:

KDIGO Criteria for CA-AKI:

• Increase in serum creatinine by ≥26.5 μmol/L (≥0.3 mg/dL) within 48 hours of contrast administration, OR
• Increase in serum creatinine to ≥1.5 times baseline within 7 days of contrast exposure, OR
• Urine output <0.5 mL/kg/h for 6 hours

Traditional CIN Definition (historical, from nephrology literature):

• Serum creatinine rise ≥44 μmol/L (0.5 mg/dL) or ≥25% from baseline within 48-72 hours of contrast administration, in the absence of alternative causes

Timing Characteristics:

• Onset: Creatinine begins rising 12-24 hours post-contrast
• Peak: Creatinine peaks at 48-72 hours (sometimes up to 5 days)
• Recovery: Creatinine returns to baseline within 7-14 days in most cases
• Non-recovery: Persistent elevation beyond 3 weeks suggests alternative etiology or progression to CKD

Differentiation from Cholesterol Emboli Syndrome (PMID: 14681639):

This distinction is clinically critical because cholesterol emboli have far worse prognosis and may require different management (supportive care, sometimes corticosteroids).

Epidemiology

Incidence:

The true incidence of CA-AKI remains debated due to:

1. Lack of control groups in many studies (contrast vs non-contrast imaging in matched patients)
2. Confounding by indication (sicker patients receive contrast)
3. Variable definitions across studies
4. Improvement in contrast agents over time

Contemporary Evidence (PMID: 29886072, KDIGO Workshop):

• General population: <2% incidence after IV contrast
• Mild CKD (eGFR 45-60): 2-5% incidence
• Moderate CKD (eGFR 30-44): 5-10% incidence
• Severe CKD (eGFR <30): 10-25% incidence
• Patients requiring dialysis: <1% of CA-AKI cases overall

High-Risk Populations:

• Percutaneous coronary intervention (PCI): 5-15% overall, up to 50% with multiple risk factors
• Cardiac surgery with contrast: 10-20%
• CT angiography in CKD: 3-10%
• Emergency CT in ICU patients: 5-15% (confounded by critical illness)

Australian/NZ Data (ANZICS APD, PMID: 29157314):

• AKI following coronary angiography: 7-12% in Australian registries
• Aboriginal and Torres Strait Islander patients: Higher baseline CKD prevalence (3-fold increased), leading to higher CA-AKI risk
• Māori patients: 2-fold increased CKD prevalence, similar increased risk
• Remote communities: Delayed access to imaging, but also delayed presentation with more advanced disease requiring contrast studies

Risk Factors (Mehran Score Components, PMID: 15494604):

Mehran Score Interpretation:

• Score ≤5: Low risk (7.5% CA-AKI, 0.04% dialysis)
• Score 6-10: Moderate risk (14% CA-AKI, 0.12% dialysis)
• Score 11-15: High risk (26% CA-AKI, 1.09% dialysis)
• Score ≥16: Very high risk (57% CA-AKI, 12.6% dialysis)

Outcomes:

• In-hospital mortality: 7-fold increase if CA-AKI develops (PMID: 14996477)
• 1-year mortality: 35% in CA-AKI vs 19% without (PMID: 15494604)
• Progression to CKD: 20-30% of CA-AKI patients develop new or worsening CKD
• Need for RRT: <1% of CA-AKI cases; temporary in 50%
• Complete recovery: 70-90% return to baseline creatinine within 2-3 weeks

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Applied Basic Sciences

Contrast Media Pharmacology

Classification by Osmolality (PMID: 16505422):

Iso-osmolar vs Low-osmolar Debate:

• PMID: 12815137 (Aspelin, NEJM 2003): IOCM (iodixanol) reduced CA-AKI vs LOCM (iohexol) in diabetic patients with CKD
• PMID: 19141506 (Heinrich meta-analysis 2009): IOCM may have small benefit over LOCM in high-risk patients
• PMID: 25756398 (2015 meta-analysis): No significant difference between IOCM and LOCM when matched for volume and iodine load
• Conclusion: No definitive evidence for IOCM superiority over LOCM in modern practice; contrast volume matters more than osmolality

Contrast Properties Affecting Nephrotoxicity:

1. Osmolality: Higher osmolality causes greater osmotic diuresis, tubular injury, and vasoconstriction
2. Viscosity: Higher viscosity (IOCM > LOCM) may impair medullary blood flow
3. Iodine concentration: Higher iodine load correlates with nephrotoxicity
4. Volume: Most important modifiable factor; volume/GFR ratio >1 indicates high risk

Pathophysiology of Contrast Nephrotoxicity

Mechanism 1: Renal Medullary Hypoxia (PMID: 8053957, 11729226)

The outer medulla, particularly the S3 segment of proximal tubules and thick ascending limb of Henle, has high metabolic oxygen demand (Na+/K+-ATPase activity) but relatively low oxygen delivery. This creates a vulnerable zone with PO2 of only 10-20 mmHg at baseline.

Contrast media causes:

• Afferent arteriolar vasoconstriction: Adenosine release, endothelin-1 increase
• Reduced nitric oxide: Decreased NO-mediated vasodilation
• Increased oxygen consumption: Tubular osmotic load increases active transport
• Osmotic diuresis: Reduces medullary blood flow, increases viscosity

This creates a "double hit" of reduced oxygen supply and increased demand, leading to tubular ischemia.

Mechanism 2: Direct Tubular Cytotoxicity (PMID: 17077858)

Contrast media causes direct injury to tubular epithelial cells through:

• Oxidative stress: Generation of reactive oxygen species (ROS)
• Mitochondrial dysfunction: Impaired ATP production
• Apoptosis activation: Caspase-dependent cell death pathways
• Cell membrane disruption: Direct toxic effects on lipid bilayers
• Cytoskeletal alterations: Disruption of actin filaments

Proximal tubular cells are most vulnerable due to their high metabolic activity and concentration of contrast during reabsorption.

Mechanism 3: Oxidative Stress (PMID: 16505422)

Contrast media generates reactive oxygen species through:

• Direct electron transfer reactions
• Mitochondrial electron transport chain disruption
• Activation of NADPH oxidase
• Reduced antioxidant capacity (glutathione depletion)

ROS cause:

• Lipid peroxidation of cell membranes
• DNA damage
• Protein oxidation
• Inflammatory cascade activation

This is the theoretical basis for NAC (N-acetylcysteine) as prevention - as a precursor to glutathione, the primary cellular antioxidant. However, clinical trials have failed to demonstrate benefit, suggesting oxidative stress is not the dominant mechanism.

Mechanism 4: Tubuloglomerular Feedback and Vasoconstriction (PMID: 17077858)

Contrast causes increased chloride delivery to the macula densa, activating tubuloglomerular feedback:

• Adenosine release → Afferent arteriolar constriction
• Endothelin-1 release → Sustained vasoconstriction
• Reduced prostaglandin synthesis → Loss of vasodilatory compensation

Vasoconstrictors released:

• Adenosine (local)
• Endothelin-1 (prolonged effect)
• Vasopressin (systemic)
• Angiotensin II (if volume depleted)

Vasodilators suppressed:

• Nitric oxide
• Prostaglandins (PGE2, PGI2)

The net effect is reduced renal blood flow and GFR lasting 20-40 minutes post-injection, but medullary hypoxia may persist for hours.

Relevant Renal Anatomy

Vulnerable Zones:

• Outer medulla: S3 segment of proximal tubule, thick ascending limb
• Corticomedullary junction: Transition zone with borderline oxygenation
• Vasa recta: Countercurrent exchange vessels susceptible to hyperviscosity

Why Diabetics Are at Higher Risk (PMID: 16505422):

• Pre-existing microvascular disease
• Impaired NO-mediated vasodilation
• Increased oxidative stress at baseline
• Often on ACE inhibitors/ARBs (reduces efferent arteriolar tone)
• Frequently volume depleted (osmotic diuresis from hyperglycemia)

Pharmacology of Prevention Agents

N-Acetylcysteine (NAC) (PMID: 29130810):

• Mechanism: Glutathione precursor, antioxidant, possibly improves renal blood flow
• Evidence: PRESERVE trial (n=5,177) - NO BENEFIT over placebo
• Conclusion: Should NOT be routinely used for CA-AKI prevention

Sodium Bicarbonate (PMID: 29130810):

• Mechanism: Alkalinization may reduce ROS generation, free radical scavenging
• Evidence: PRESERVE trial - NO SUPERIORITY over isotonic saline
• Conclusion: No advantage over 0.9% saline or balanced crystalloids

Isotonic Saline / Balanced Crystalloids (PMID: 24225336):

• Mechanism: Volume expansion → Maintains renal perfusion, dilutes contrast, increases urine flow (reduces tubular contact time)
• Evidence: POSEIDON trial - Periprocedural hydration guided by LVEDP reduced CA-AKI
• Conclusion: Remains cornerstone of prevention

Statins (PMID: 24781253):

• Mechanism: Pleiotropic effects - anti-inflammatory, antioxidant, endothelial protection
• Evidence: Some trials suggest benefit, especially high-dose rosuvastatin; not definitive
• Conclusion: Continue if already prescribed; insufficient evidence for de novo initiation

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Clinical Presentation

ICU Admission Scenarios

Scenario 1: Post-Coronary Angiography AKI

A 72-year-old male with Type 2 diabetes, baseline creatinine 150 μmol/L (eGFR 38), underwent primary PCI for STEMI. He received 180 mL of iohexol (low-osmolar contrast). Pre-hydration was limited due to pulmonary edema. On Day 2, creatinine has risen to 220 μmol/L, urine output is 25 mL/h.

• History: STEMI, diabetes, CKD Stage 3b, high contrast volume
• Examination: JVP elevated, bilateral crackles, mild peripheral edema
• Severity: KDIGO Stage 1 AKI (creatinine rise >50% from baseline)

Scenario 2: CT-Associated AKI in Sepsis

A 65-year-old female admitted to ICU with septic shock from cholangitis. She received CT abdomen with IV contrast (100 mL iopamidol) for source identification. Despite initial resuscitation, creatinine rose from 95 to 165 μmol/L over 48 hours.

• History: Septic shock (independent AKI risk), contrast exposure
• Examination: Vasopressor-dependent, adequate urine output on noradrenaline
• Severity: Difficult to attribute - sepsis vs contrast vs both
• Key point: This is "contrast-associated" (temporal relationship) but causality uncertain

Scenario 3: Repeat Contrast Dilemma

A 58-year-old male with CKD Stage 4 (eGFR 22) developed CA-AKI after CT pulmonary angiography 5 days ago (creatinine rose from 250 to 340 μmol/L). Now has worsening dyspnea and clinical suspicion of recurrent PE. Team requests repeat CTPA.

• History: Pre-existing CKD, recent CA-AKI, high-risk for further injury
• Examination: Tachypnea, hypoxia, elevated D-dimer
• Dilemma: Risk of repeat contrast vs risk of missed PE (mortality >15% untreated)
• Decision: Discuss alternative imaging (V/Q scan, lower limb Doppler), risk-benefit, empiric anticoagulation

Symptoms & Signs

CA-AKI is typically asymptomatic in early stages. Symptoms relate to AKI severity:

Early (Stage 1):

• Usually no symptoms
• Detected by routine creatinine monitoring
• Urine output may be preserved or mildly reduced

Moderate (Stage 2):

• Reduced urine output (oliguria)
• Mild fluid retention
• Fatigue, malaise

Severe (Stage 3):

• Symptomatic fluid overload (dyspnea, edema)
• Uremic symptoms (nausea, anorexia, confusion)
• Electrolyte disturbances (hyperkalemia with ECG changes)

Examination Findings:

• Cardiovascular: May have signs of underlying cardiac disease
• Skin: Look for livedo reticularis, blue toes (suggests cholesterol emboli, NOT CA-AKI)
• Neurological: Uremic encephalopathy in severe cases

Differential Diagnosis

When creatinine rises post-contrast, consider:

1. True CA-AKI: Timing 24-72 hours, no alternative cause, recovers within 2 weeks
2. Atheroembolic disease (cholesterol emboli): Delayed onset (days-weeks), eosinophilia, livedo, progressive course
3. Prerenal AKI: Volume depletion, inadequate resuscitation, responds to fluids
4. Cardiorenal syndrome: Low cardiac output post-MI/intervention, hepatojugular reflux, pulmonary edema
5. Sepsis-associated AKI: Concurrent infection, vasopressor requirement
6. Drug-induced AKI: Concurrent nephrotoxins (aminoglycosides, NSAIDs, ACEi)
7. Obstructive uropathy: New or worsening obstruction (rare post-imaging)
8. Acute interstitial nephritis: Drug-related, may have fever, rash, eosinophilia

Distinguishing Features:

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Investigations

Laboratory Investigations

Baseline (Pre-Contrast):

• Serum creatinine and eGFR: Essential for risk stratification
• Urea: Baseline for comparison
• Electrolytes: K+, Na+, Cl-, HCO3-
• Glucose: Diabetes assessment
• Hemoglobin: Anemia is risk factor
• Urinalysis: Baseline proteinuria assessment

Post-Contrast Monitoring:

• Serum creatinine: 24h, 48h, 72h post-procedure (minimum)
• High-risk patients: Daily creatinine for 5-7 days
• Urine output: Hourly monitoring in ICU
• Electrolytes: Daily until creatinine stabilizes

ABG Interpretation (if AKI develops):

• Metabolic acidosis suggests severe AKI
• Respiratory compensation expected unless ventilated
• Lactate elevation may indicate concurrent hypoperfusion

Urinalysis in AKI Post-Contrast:

Fractional Excretion of Sodium (FENa):

• <1%: Prerenal or early CA-AKI (tubules still concentrating)

• 2%: Established ATN

• 1-2%: Indeterminate

Note: Diuretics invalidate FENa; use FEUrea instead (<35% prerenal, >50% ATN)

Novel Biomarkers (research tools, not routine clinical use):

• NGAL (neutrophil gelatinase-associated lipocalin): Rises 2-6 hours post-injury
• KIM-1 (kidney injury molecule-1): Proximal tubular injury marker
• Cystatin C: Less affected by muscle mass than creatinine
• [TIMP-2] × [IGFBP-7] (NephroCheck): Cell cycle arrest markers, FDA-approved for AKI prediction

Imaging

Renal Ultrasound:

• Indicated if obstruction suspected
• Normal kidney size suggests acute process
• Excludes hydronephrosis
• Doppler: Assesses renal artery patency (if cholesterol emboli suspected)

Non-Contrast CT (if imaging needed):

• Alternative to contrast-enhanced studies
• Detects urolithiasis, hydronephrosis, masses
• Limited soft tissue characterization

Echocardiography:

• Assess cardiac function in cardiorenal syndrome
• Evaluate volume status (IVC, LV filling)

Risk Calculators

Mehran Score (PCI patients, PMID: 15494604): Calculate sum of points (see Epidemiology section) to predict CA-AKI risk

Contrast Volume to GFR Ratio:

• Ratio = Contrast volume (mL) / eGFR (mL/min/1.73m2)
• Ratio >1: High risk for CA-AKI
• Ratio <0.5: Lower risk

Example: Patient with eGFR 40 receiving 100 mL contrast → Ratio = 2.5 (HIGH RISK)

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ICU Management

Prevention Strategies (Evidence-Based)

1. Volume Expansion (CORNERSTONE OF PREVENTION)

Evidence:

• POSEIDON Trial (PMID: 24225336): LVEDP-guided hydration reduced CA-AKI in PCI patients
• AMACING Trial (PMID: 28233565): Questioned necessity of IV hydration in patients with eGFR 30-59 receiving low contrast volumes
• Consensus: Volume expansion remains standard of care, especially for high-risk patients

Protocol:

LOW RISK (eGFR >60, no other risk factors):
- Oral fluids 500-1000 mL before procedure
- Consider IV saline if prolonged fasting or high contrast volume

MODERATE RISK (eGFR 30-60 OR diabetes OR other risk factor):
- IV 0.9% saline or balanced crystalloid
- 1 mL/kg/h for 6-12 hours pre-procedure
- 1 mL/kg/h for 6-12 hours post-procedure
- If volume overload risk: 0.5 mL/kg/h with diuretic cover

HIGH RISK (eGFR <30 OR multiple risk factors):
- IV 0.9% saline or balanced crystalloid
- 1-1.5 mL/kg/h for 12 hours pre-procedure
- 1-1.5 mL/kg/h for 12 hours post-procedure
- Consider invasive hemodynamic monitoring (LVEDP)
- Nephrology consultation pre-procedure

Special Considerations in ICU:

• Patients with heart failure: Careful fluid balance; consider diuretics or hemofiltration
• Patients on vasopressors: Ensure adequate MAP before contrast
• Emergency imaging: Abbreviated hydration acceptable; benefits of imaging outweigh risk

2. N-Acetylcysteine (NOT RECOMMENDED)

PRESERVE Trial (PMID: 29130810):

• Largest CA-AKI prevention trial (n=5,177)
• Four-arm factorial: NAC vs placebo × Bicarbonate vs saline
• NAC (oral 1,200 mg BID × 5 doses) provided NO BENEFIT
• Major kidney events at 90 days: NAC 4.6% vs Placebo 4.5% (P=0.88)
• Conclusion: Do NOT recommend NAC for CA-AKI prevention

3. Sodium Bicarbonate (NOT SUPERIOR TO SALINE)

PRESERVE Trial (PMID: 29130810):

• Sodium bicarbonate infusion provided NO SUPERIORITY over isotonic saline
• CA-AKI rates identical: Bicarbonate 4.4% vs Saline 4.7% (P=0.70)
• Conclusion: Use isotonic saline (simpler, cheaper); bicarbonate offers no advantage

4. Contrast Volume Minimization

Strategies:

• Use minimum diagnostic dose
• Target contrast volume/GFR ratio <1 (ideally <0.5)
• Single-injection protocols for CT (reduces multiple boluses)
• Lower contrast concentration if diagnostic quality acceptable
• Biplane imaging (reduces need for multiple runs in angiography)

Rule of Thumb: Maximum contrast volume (mL) = 5 × body weight (kg) / creatinine (mg/dL)

5. Contrast Agent Selection

Evidence Summary (PMID: 25756398):

• IOCM (iodixanol) vs LOCM: Possibly small benefit in very high-risk patients
• HOCM: Avoid (significantly higher nephrotoxicity)
• Practical approach: Use LOCM or IOCM; volume matters more than osmolality

6. Timing of Repeat Contrast

• Avoid repeat contrast within 48-72 hours if possible
• Allow creatinine to return to baseline before re-exposure
• If urgent repeat needed: Additional hydration, minimize volume, accept higher risk

7. Drug Management

Withhold:

• Metformin: Hold for 48-72 hours post-contrast in eGFR <30 (lactic acidosis risk if AKI develops); can continue if eGFR >60
• NSAIDs: Avoid pre- and post-procedure
• ACEi/ARBs: Consider withholding on day of procedure (controversial; consensus leans toward holding)

Continue:

• Statins: Continue; may have protective benefit
• Diuretics: Hold if volume depletion; continue if euvolemic/overloaded

8. Prophylactic Hemodialysis (HARMFUL)

Evidence (PMID: 12917227):

• Prophylactic HD immediately post-contrast does NOT prevent CA-AKI
• May actually WORSEN outcomes (hemodynamic instability, contrast redistribution)
• Conclusion: NEVER use prophylactic dialysis to prevent CA-AKI

Emergency Imaging in ICU

Principle: Life-saving imaging should NOT be delayed for nephroprotection

Emergency Indications Where Contrast is Essential:

• STEMI requiring coronary angiography
• Acute aortic dissection
• Massive pulmonary embolism with hemodynamic instability
• Major trauma with suspected vascular injury
• Acute mesenteric ischemia
• Necrotizing soft tissue infection requiring source identification

Risk-Benefit Framework:

Practical Approach for Emergency CT in CKD:

1. Confirm indication is essential (not just "standard workup")
2. Rapid IV hydration: 500 mL bolus over 1 hour if tolerated
3. Minimize contrast volume: Request radiologist to use lowest effective dose
4. Document risk-benefit discussion in notes
5. Plan post-procedure monitoring: Creatinine at 24h, 48h, 72h
6. Avoid repeat contrast for at least 48-72 hours

Management of Established CA-AKI

Supportive Care:

1. Continue volume optimization: Avoid hypovolemia but prevent overload
2. Avoid further nephrotoxins: Stop NSAIDs, adjust aminoglycoside dosing
3. Monitor closely: Daily creatinine until trend improves
4. Manage complications: Hyperkalemia, acidosis, fluid overload

When to Consult Nephrology:

• eGFR <30 at baseline
• Creatinine rise >100% from baseline
• Oliguria despite optimization
• Need for RRT consideration
• Suspected alternative diagnosis (GN, vasculitis, emboli)

Renal Replacement Therapy Indications (AEIOU):

• Acidosis: pH <7.1 refractory to bicarbonate
• Electrolytes: K+ >6.5 mmol/L refractory to medical therapy
• Intoxication: Dialyzable toxins (not applicable here)
• Overload: Pulmonary edema refractory to diuretics
• Uremia: Encephalopathy, pericarditis, bleeding

Prognosis Indicators:

• Non-oliguric: Better prognosis
• Peak creatinine <200% baseline: Usually recovers fully
• Recovery starting by Day 5-7: Good sign
• Dialysis requirement: <1% of CA-AKI cases

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Monitoring & Complications

ICU-Specific Monitoring

Daily Parameters:

• Serum creatinine (until stable or improving)
• Urine output (hourly, target >0.5 mL/kg/h)
• Fluid balance (avoid overload)
• Electrolytes (K+, HCO3-)
• Weight (if volume concern)

High-Risk Patient Monitoring:

• Creatinine every 12 hours for first 48h
• ABG if acidotic
• ECG if K+ >5.5 mmol/L
• Urine microscopy if etiology unclear

Complications

Early Complications (First 48-72 hours):

Fluid Overload:

• Incidence: 20-30% if oliguria develops
• Risk factors: Overzealous hydration, heart failure, oliguria
• Prevention: Careful fluid balance, early diuretics
• Management: Diuretics (furosemide 40-80 mg IV); RRT if refractory

Hyperkalemia:

• Incidence: 10-15% with significant AKI
• Risk factors: ACEi/ARBs, potassium supplements, metabolic acidosis
• Management: Standard hyperkalemia protocol; RRT if K+ >6.5 refractory

Metabolic Acidosis:

• Incidence: 5-10% with Stage 2-3 AKI
• Management: Sodium bicarbonate if pH <7.2 and HCO3 <15; RRT if severe

Late Complications:

Progression to CKD:

• Incidence: 20-30% of CA-AKI patients develop new or worsening CKD
• Risk factors: Baseline CKD, diabetes, recurrent AKI
• Prevention: Avoid repeat nephrotoxic exposures, nephrology follow-up

Delayed Cholesterol Emboli Recognition:

• If creatinine fails to recover by 2 weeks, consider cholesterol emboli
• Look for: Eosinophilia, low complement, livedo reticularis
• Management: Supportive; avoid further angiography

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Prognosis & Outcome Measures

Short-Term Outcomes

Recovery:

• 70-90% of CA-AKI cases recover completely within 7-14 days
• Non-oliguric CA-AKI has better prognosis
• Peak creatinine <2× baseline usually indicates full recovery

Need for RRT:

• <1% of all CA-AKI cases require dialysis
• If dialysis required: 50% recover renal function (temporary dialysis)

In-Hospital Mortality:

• 7-fold increase if CA-AKI develops (PMID: 14996477)
• Mortality often from underlying condition (MI, sepsis), not CA-AKI itself

Long-Term Outcomes

1-Year Mortality (PMID: 15494604):

• With CA-AKI: 35%
• Without CA-AKI: 19%
• Note: Much of excess mortality is from comorbidities (cardiac disease, CKD)

Progression to ESRD:

• Rare (<5%) if CA-AKI recovers
• Higher risk if pre-existing CKD, diabetes, recurrent AKI

Cardiovascular Events:

• Increased rate of MI, stroke, heart failure
• Reflects underlying atherosclerotic burden

Prognostic Factors

Good Prognosis:

• Non-oliguric AKI
• Creatinine peaks <2× baseline
• Recovery begins by Day 5-7
• No need for RRT
• No baseline CKD

Poor Prognosis:

• Oliguric or anuric AKI
• Creatinine peaks >3× baseline
• Requires RRT
• Baseline CKD Stage 4-5
• Multiple comorbidities

Australian/NZ Outcome Data

ANZICS Considerations:

• Australian ICU patients have similar CA-AKI outcomes to international data
• Indigenous Australians have higher baseline CKD rates, leading to higher CA-AKI risk
• Remote communities: Delayed access to nephrology follow-up may worsen long-term outcomes

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Indigenous Health Considerations

Aboriginal and Torres Strait Islander Peoples

Higher Baseline CKD Prevalence (PMID: 20667969):

• 3-4 fold higher prevalence of CKD compared to non-Indigenous Australians
• CKD develops at younger ages
• Diabetes, hypertension, obesity are major contributors
• Higher rates of albuminuria indicating diabetic nephropathy

Implications for CA-AKI:

• Higher risk population for contrast-associated injury
• Often present with more advanced CKD at baseline
• May be under-investigated due to concerns about contrast

Access to Imaging in Remote Communities:

• Limited access to CT/angiography requiring transfer to regional centers
• Transfer delays may result in delayed diagnosis
• Balance: Ensure essential imaging is not withheld due to nephroprotection concerns
• Telemedicine consultation with nephrology before transfer

Cultural Considerations:

• Involve Aboriginal Health Workers (AHWs) and Aboriginal Liaison Officers (ALOs)
• Family-centered decision making
• Explain risks and benefits in culturally appropriate manner
• Consider language barriers; use interpreter services

Māori Health (New Zealand)

Higher CKD Prevalence:

• 2-3 fold increased CKD prevalence
• Similar issues with diabetes, hypertension

Whānau Involvement:

• Include family in discussions about imaging decisions
• Respect tikanga (Māori customs)
• Māori Health Workers should be engaged

Practical Recommendations

1. Do not deny essential imaging based on CKD status alone
2. Engage cultural support early in decision-making
3. Ensure nephrology follow-up post-CA-AKI is accessible (telemedicine if remote)
4. Document cultural considerations in clinical notes
5. Use interpreter services when language barriers exist

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Progressive Difficulty Assessments

Basic Level (Foundation Knowledge)

Question 1: Definition

Q: Define contrast-associated acute kidney injury according to KDIGO criteria.

A: Contrast-associated acute kidney injury (CA-AKI) is defined as:

1. Increase in serum creatinine by ≥26.5 μmol/L (≥0.3 mg/dL) within 48 hours of contrast administration, OR
2. Increase in serum creatinine to ≥1.5 times baseline within 7 days of contrast exposure, OR
3. Urine output <0.5 mL/kg/h for 6 hours

Creatinine typically peaks at 48-72 hours and recovers within 7-14 days.

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Question 2: Risk Factors

Q: List 5 major risk factors for CA-AKI.

A:

1. Pre-existing CKD (eGFR <60, especially <30 mL/min/1.73m2)
2. Diabetes mellitus
3. Volume depletion / dehydration
4. High contrast volume (>100 mL or volume/GFR ratio >1)
5. Concurrent nephrotoxic medications (NSAIDs, aminoglycosides, ACEi)

Other risk factors include: advanced age >75, heart failure, anemia, shock/hypotension.

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Question 3: Prevention Strategies

Q: What is the evidence-based cornerstone of CA-AKI prevention?

A: Isotonic crystalloid volume expansion is the cornerstone of CA-AKI prevention.

Protocol:

• 0.9% saline or balanced crystalloid
• 1-1.5 mL/kg/h for 6-12 hours pre-procedure
• Continue for 6-12 hours post-procedure

Important: N-acetylcysteine (NAC) and sodium bicarbonate do NOT provide additional benefit over isotonic saline (PRESERVE trial 2018).

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Intermediate Level (Applied Knowledge)

Question 1: Case-Based Scenario

Stem: A 70-year-old male with Type 2 diabetes, hypertension, and eGFR 32 mL/min/1.73m2 is scheduled for elective coronary angiography tomorrow. Current medications include metformin 1g BD, ramipril 10mg daily, and atorvastatin 40mg daily.

Q1: Calculate this patient's risk using the contrast volume/GFR ratio if 150 mL contrast is anticipated. (2 marks)

A1: Contrast volume/GFR ratio = 150 mL / 32 = 4.7

This is HIGH RISK (ratio >1 indicates elevated risk; ratio >3 is very high risk)

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Q2: Outline your pre-procedure prevention strategy. (5 marks)

A2:

1. IV hydration: 0.9% saline or Hartmann's at 1 mL/kg/h for 12 hours pre-procedure (1 mark)
2. Withhold metformin: Hold from day of procedure for 48-72 hours (risk of lactic acidosis if AKI develops) (1 mark)
3. Consider holding ramipril: On day of procedure (controversial, but consensus leans toward holding) (1 mark)
4. Continue statin: May have protective benefit (0.5 marks)
5. Request minimum contrast volume: Discuss with interventional cardiologist; aim for volume/GFR <1 (100 mL or less) (1 mark)
6. Post-procedure hydration: Continue IV fluids at 1 mL/kg/h for 12 hours (0.5 marks)

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Q3: What monitoring is required post-procedure? (3 marks)

A3:

1. Serum creatinine: Measure at 24h, 48h, and 72h post-procedure (1 mark)
2. Urine output: Monitor hourly for first 24 hours (0.5 marks)
3. Fluid balance: Avoid overhydration or dehydration (0.5 marks)
4. Electrolytes: Daily K+, HCO3- until creatinine stable (0.5 marks)
5. Resume metformin: Only if creatinine returns to baseline after 48-72 hours (0.5 marks)

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Question 2: Evidence Interpretation

Q: The PRESERVE trial (2018) tested N-acetylcysteine and sodium bicarbonate for CA-AKI prevention. What were the key findings and clinical implications?

A:

PRESERVE Trial (PMID: 29130810):

• Design: Factorial RCT, n=5,177 patients with CKD undergoing angiography
• Interventions: NAC (1,200 mg PO × 5 doses) vs placebo; sodium bicarbonate vs isotonic saline
• Primary outcome: Death, dialysis, or persistent >50% creatinine rise at 90 days

Key Findings:

• NAC vs placebo: No difference (4.6% vs 4.5%, P=0.88)
• Bicarbonate vs saline: No difference (4.4% vs 4.7%, P=0.70)
• Secondary outcome (CA-AKI at 48-96h): No difference with either intervention

Clinical Implications:

1. NAC should NOT be routinely used for CA-AKI prevention
2. Sodium bicarbonate offers NO advantage over isotonic saline
3. Volume expansion with isotonic crystalloid remains the only evidence-based prevention strategy
4. Resources should focus on adequate hydration and contrast minimization

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Exam Level (CICM Second Part Standard)

See SAQ Practice section below.

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SAQ Practice

SAQ 1: Prevention Strategies for CA-AKI

Time Allocation: 10 minutes Total Marks: 15

Stem: A 68-year-old Aboriginal woman from a remote Northern Territory community is transferred to your tertiary ICU with NSTEMI. She has Type 2 diabetes mellitus, hypertension, and baseline creatinine of 180 μmol/L (eGFR 28 mL/min/1.73m2). She is hemodynamically stable but has ongoing chest pain. The cardiology team plans urgent coronary angiography within 24 hours.

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Question 1.1 (5 marks)

Outline the key risk factors for contrast-associated acute kidney injury in this patient.

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Question 1.2 (6 marks)

Describe your evidence-based prevention strategy prior to coronary angiography.

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Question 1.3 (4 marks)

The patient's daughter asks about N-acetylcysteine (NAC) which she has read about online. How would you counsel the family?

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Model Answer

Question 1.1 (5 marks total)

Patient-Specific Risk Factors:

• Pre-existing CKD Stage 4 (eGFR 28 mL/min/1.73m2) - HIGHEST RISK (1.5 marks)
• Type 2 diabetes mellitus - associated with microvascular disease (1 mark)
• Older age (68 years) - reduced renal reserve (0.5 marks)
• Indigenous Australian - higher baseline CKD prevalence, often more advanced disease (0.5 marks)
• Acute coronary syndrome - reduced cardiac output may compromise renal perfusion (0.5 marks)

Procedure-Related Risk Factors:

• Coronary angiography - intra-arterial contrast with proximal injection increases risk (0.5 marks)
• Potential for PCI - higher contrast volumes if intervention required (0.5 marks)

Mehran Score Calculation (for additional marks if time):

• eGFR <40: 6 points
• Diabetes: 3 points
• Age >75: 0 points (she is 68)
• Total: 9+ points = Moderate-High risk (14-26% CA-AKI risk)

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Question 1.2 (6 marks total)

Pre-Procedure Volume Expansion (2 marks):

• Initiate IV 0.9% saline or balanced crystalloid at 1-1.5 mL/kg/h (approx. 70-100 mL/h)
• Start 12 hours before procedure if time permits
• Continue during and for 12 hours post-procedure
• Monitor for fluid overload (cardiac patient) - may need to reduce rate or add diuretic

Medication Review (1.5 marks):

• Withhold metformin from day of procedure for 48-72 hours (lactic acidosis risk if AKI)
• Consider holding ACE inhibitor/ARB on day of procedure (if prescribed)
• Continue statin (potential protective effect)
• Avoid NSAIDs

Contrast Volume Minimization (1.5 marks):

• Discuss with interventional cardiologist before procedure
• Request minimum diagnostic dose; aim contrast volume/GFR ratio <1 (approx. 25-30 mL)
• Consider staged procedure if PCI required (diagnostic angiography first, defer PCI if possible)
• Use biplane imaging to reduce contrast runs

Post-Procedure Monitoring (1 mark):

• Creatinine at 24h, 48h, 72h
• Urine output monitoring
• Avoid repeat contrast for at least 48-72 hours

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Question 1.3 (4 marks total)

Acknowledge the Family's Concern (0.5 marks):

• Thank the daughter for doing research and asking questions
• Involve Aboriginal Health Worker or Liaison Officer in discussion

Explain the Evidence (2 marks):

• NAC was previously thought to be protective due to its antioxidant properties
• The PRESERVE trial (2018, n=5,177 patients) was the largest and best-designed study testing NAC for CA-AKI prevention
• The trial showed NO BENEFIT of NAC compared to placebo
• Major kidney events at 90 days: NAC 4.6% vs Placebo 4.5% - essentially identical

Current Recommendation (1 mark):

• We no longer recommend NAC for CA-AKI prevention based on this evidence
• The focus is now on adequate hydration (IV fluids) and minimizing contrast volume
• These strategies have the best evidence for protection

Reassurance (0.5 marks):

• Explain that we will use all proven strategies to protect her kidneys
• Emphasize the importance of the angiography for her heart condition
• Offer to answer any further questions

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Common Mistakes:

• Recommending NAC despite PRESERVE evidence
• Not mentioning metformin withholding
• Forgetting to discuss contrast volume minimization
• Not acknowledging Indigenous health considerations

Examiner Comments:

• Pass candidates demonstrated knowledge of PRESERVE trial findings
• Excellent candidates discussed specific prevention protocols with doses/timing
• Fail candidates continued to recommend NAC or bicarbonate as first-line

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SAQ 2: Emergency Imaging Decision-Making

Time Allocation: 10 minutes Total Marks: 15

Stem: A 55-year-old male is admitted to ICU with septic shock secondary to community-acquired pneumonia. He is receiving noradrenaline at 0.3 mcg/kg/min, has a lactate of 5.2 mmol/L, and has developed worsening abdominal pain. The surgical team requests an urgent CT abdomen/pelvis with IV contrast to exclude intra-abdominal pathology.

His baseline creatinine (from GP records 3 months ago) was 120 μmol/L. Current creatinine is 210 μmol/L (KDIGO Stage 1 AKI). He has Type 2 diabetes and BMI 32.

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Question 2.1 (4 marks)

Discuss the risk-benefit considerations for proceeding with contrast-enhanced CT imaging in this patient.

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Question 2.2 (5 marks)

If proceeding with imaging, outline your nephroprotective strategy.

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Question 2.3 (6 marks)

Forty-eight hours later, the patient's creatinine has risen to 380 μmol/L. Describe your approach to this patient.

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Model Answer

Question 2.1 (4 marks total)

Benefits of Contrast-Enhanced CT (2 marks):

• Essential for identifying occult intra-abdominal pathology (abscess, cholecystitis, ischemic bowel)
• Missed diagnosis of intra-abdominal sepsis carries high mortality (30-50%)
• Non-contrast CT has limited sensitivity for soft tissue pathology
• May identify source requiring surgical intervention for source control

Risks of Contrast Exposure (1.5 marks):

• Patient already has AKI (KDIGO Stage 1) - increased baseline risk
• Diabetes and obesity are additional risk factors
• Sepsis-associated AKI often multifactorial - difficult to attribute to contrast alone
• Potential for worsening AKI requiring RRT

Risk-Benefit Analysis (0.5 marks):

• In this case, the risk of MISSING a surgical abdomen (high mortality) EXCEEDS the risk of CA-AKI (usually reversible)
• Proceed with imaging - do not delay essential diagnostic evaluation for nephroprotection

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Question 2.2 (5 marks total)

Pre-Imaging Optimization (2 marks):

• Ensure adequate MAP (≥65 mmHg) before contrast administration - continue/titrate noradrenaline
• Rapid IV fluid bolus if not already fluid resuscitated (500 mL crystalloid over 1 hour) - balanced approach given cardiac risk
• Correct severe acidosis if present (pH <7.2)

Contrast Protocol (1.5 marks):

• Request minimum contrast volume from radiology
• Use low-osmolar or iso-osmolar contrast agent
• Single-bolus protocol
• Document indication and risk-benefit discussion in notes

Post-Imaging Care (1.5 marks):

• Continue maintenance IV fluids (1 mL/kg/h) for 6-12 hours
• Monitor creatinine at 24h, 48h
• Avoid further nephrotoxic exposures (NSAIDs, aminoglycosides)
• Document contrast volume administered

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Question 2.3 (6 marks total)

Immediate Assessment (2 marks):

• Confirm timing of creatinine rise (consistent with CA-AKI: 24-72 hours post-contrast)
• Assess urine output trend (oliguria suggests established AKI)
• Review fluid balance - is patient overloaded or depleted?
• Check potassium and ABG for metabolic complications

Differential Diagnosis (1.5 marks):

• Multifactorial AKI: Sepsis + contrast + hemodynamic instability
• Isolated CA-AKI is possible but sepsis-associated AKI is major contributor
• Consider other causes: ongoing sepsis, drug toxicity, obstruction (if abdominal pathology found)

Management (2 marks):

• Continue supportive care and sepsis treatment
• Optimize volume status (euvolemia target)
• Avoid further nephrotoxins
• RRT indications: Assess for AEIOU (Acidosis, Electrolytes, Overload, Uremia)
• Nephrology consultation if Stage 3 or not improving

Prognosis and Communication (0.5 marks):

• Explain to family that AKI in sepsis is common
• Most patients recover renal function with appropriate treatment
• Dialysis may be needed temporarily but is not inevitable

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Common Mistakes:

• Delaying essential imaging due to nephroprotection concerns
• Not addressing volume status before contrast
• Attributing all AKI to contrast when sepsis is major contributor
• Failing to consider RRT indications

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Hot Case Scenarios

Hot Case 1: Post-Angiography AKI

Setting: ICU Bed 4 Duration: 20 minutes (10 min assessment + 10 min discussion) Equipment: Monitor, charts, CXR, ECG available

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Actor/Simulator Briefing (Not given to candidate):

Patient Details:

• Age: 74 years
• Gender: Male
• Admission diagnosis: STEMI with primary PCI 48 hours ago
• Day of ICU stay: Day 3

History (available from nurse):

• Presented with chest pain, ST elevation in V2-V5
• Primary PCI to LAD with DES
• Received 220 mL iohexol during procedure
• Pre-existing diabetes, hypertension, CKD Stage 3 (baseline creatinine 145 μmol/L, eGFR 42)
• Creatinine now 285 μmol/L (up from 145)
• Urine output dropped to 20 mL/h overnight

Examination Findings:

• General: Comfortable at rest, not distressed
• Airway: Patent, no airway adjuncts
• Breathing: SpO2 96% on 2L NC, RR 18, clear chest
• Circulation: HR 72 regular, BP 125/75, JVP 4cm above sternal angle, warm peripheries
• Disability: GCS 15, RASS 0
• Exposure: Radial artery puncture site dry, no hematoma

Charts/Data Available:

• Creatinine trend: 145 → 190 (Day 2) → 285 (Day 3)
• K+ 5.4 mmol/L, Na 138, HCO3 20
• Urine output: Day 2 total 1200 mL; Day 3 so far 480 mL (in 24h)
• CXR: Cardiomegaly, clear lung fields
• ECG: Sinus rhythm, Q waves V2-V4, no acute changes

Current Management:

• IV Hartmann's at 80 mL/h
• Aspirin 100mg, Ticagrelor 90mg BD
• Atorvastatin 40mg
• Metoprolol 25mg BD
• Frusemide 40mg mane (held today)

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Candidate Task:

"You are the ICU registrar. This 74-year-old man was admitted 48 hours ago following primary PCI for STEMI. Please assess the patient and present your findings to the consultant."

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Expected Performance:

Assessment Phase (10 minutes) - 15 marks

History (3 minutes) - 3 marks:

• Collateral: Confirm STEMI history, contrast volume, baseline renal function
• Time course: When did creatinine start rising? (24-48 hours post-procedure = consistent with CA-AKI)
• Urine output trend: Declining over 24 hours
• Symptoms: Any uremic symptoms? (Nausea, confusion) - currently absent

Examination (7 minutes) - 10 marks:

• Airway (1 mark): Patent, no concerns
• Breathing (2 marks): Adequate saturation, no evidence of pulmonary edema
• Circulation (3 marks): Hemodynamically stable, no cardiogenic shock, JVP slightly elevated but not florid overload, puncture site intact
• Disability (2 marks): Alert, no encephalopathy
• Exposure/Charts (2 marks): Review creatinine trend, electrolytes, urine output, calculate severity (KDIGO Stage 2)

One-Minute Summary (1 minute) - 2 marks:

"This is Mr. [Name], a 74-year-old male, Day 3 post-primary PCI for anterior STEMI. He has developed contrast-associated acute kidney injury, with creatinine rising from baseline 145 to 285 μmol/L, which is KDIGO Stage 2 AKI. He is hemodynamically stable with no signs of cardiogenic shock. Urine output has declined to approximately 20 mL/h. Current concerns are oliguria and mild hyperkalemia (K+ 5.4). There are no indications for immediate RRT. My plan is to optimize volume status, monitor electrolytes and creatinine, avoid further nephrotoxins, and discuss with nephrology if no improvement in 24-48 hours."

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Discussion Phase (10 minutes) - 15 marks

Opening Question: "What is your management plan for the next 24 hours?"

Expected Answer (3 marks):

1. Volume optimization: Assess volume status carefully; patient is post-MI so avoid overload but also avoid hypovolemia
2. Monitor creatinine and electrolytes: 12-hourly creatinine, K+ 6-hourly
3. Manage hyperkalemia: K+ 5.4 - no urgent intervention but monitor; restrict dietary K+, review medications
4. Withhold frusemide for now: Already held; may reintroduce if volume overloaded
5. Avoid further contrast: No repeat imaging with contrast for 48-72 hours
6. Continue dual antiplatelet therapy: Essential post-DES, cannot stop despite AKI

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Q1: "The surgical team requests CT abdomen with contrast because the patient has some vague abdominal discomfort. What is your response?" (3 marks)

Expected Answer:

• Assess clinical indication: Vague discomfort is not a strong indication for contrast-enhanced CT
• Consider non-contrast imaging first: Non-contrast CT, ultrasound
• Risk-benefit analysis: Current CA-AKI significantly increases risk of further contrast exposure
• Decision: Would decline contrast CT at this time unless clear clinical indication
• Alternative: Physical examination, blood tests (lipase, LFTs), non-contrast imaging

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Q2: "The creatinine rises to 350 μmol/L on Day 4 with K+ 6.2. What are your concerns and management?" (4 marks)

Expected Answer:

Concerns:

• Progressing to Stage 3 AKI (creatinine >3× baseline or >354 μmol/L)
• Significant hyperkalemia (K+ 6.2) - cardiac risk

Management:

1. ECG: Look for peaked T waves, PR prolongation, QRS widening
2. If ECG changes: Calcium gluconate 10 mL of 10% IV for cardiac membrane stabilization
3. Shift potassium: Insulin/dextrose (10 units Actrapid + 50 mL 50% glucose), salbutamol nebulizer
4. Eliminate potassium: Sodium polystyrene sulfonate (Resonium) if tolerated orally
5. Nephrology consultation: Discuss RRT timing
6. Assess for RRT indications: K+ >6.5 refractory, acidosis, fluid overload

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Q3: "The family asks if their father caused this by not drinking enough water after the procedure. How do you respond?" (3 marks)

Expected Answer:

Empathic approach:

• "I understand you're worried. I want to reassure you that this is not anyone's fault."
• "Kidney injury after heart procedures is a known risk, especially in patients with existing kidney disease and diabetes."

Education:

• Explain that we gave IV fluids to protect his kidneys
• The combination of his underlying conditions (CKD, diabetes) and the contrast dye increases the risk despite our best prevention efforts

Reassurance:

• "Most people recover their kidney function within 1-2 weeks."
• "We are monitoring closely and will involve the kidney specialists if needed."

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Q4: "What are the long-term implications of this AKI episode for the patient?" (2 marks)

Expected Answer:

• Increased risk of progression to CKD
• Higher cardiovascular event risk
• Should have nephrology follow-up post-discharge
• Future contrast exposure requires careful risk-benefit assessment
• Patient education about nephrotoxin avoidance

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Marking Criteria (Total 30 marks):

Pass: ≥20/30, no domain scored 0 Fail: <20/30 or critical safety error (e.g., missing severe hyperkalemia)

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Hot Case 2: Repeat Contrast Dilemma

Setting: ICU Bed 8 Duration: 20 minutes

Brief: 65-year-old female with known CKD Stage 4 (eGFR 22) admitted 6 days ago with septic shock from pyelonephritis. She received CT abdomen with contrast on Day 1 for source identification. Creatinine rose from 260 to 420 μmol/L (CA-AKI superimposed on CKD). She is now improving from sepsis but developed sudden-onset hypoxia. D-dimer is elevated, and PE is suspected.

Dilemma: CTPA requires contrast; patient has recent CA-AKI.

Expected Discussion Points:

1. Risk-benefit analysis: PE mortality vs further renal injury
2. Alternative imaging: V/Q scan (if available), lower limb Doppler
3. Empiric anticoagulation: May be appropriate while arranging imaging
4. If CTPA proceeds: Minimum contrast volume, continued hydration, nephrology involvement
5. RRT standby: Patient may need dialysis if further AKI develops

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Viva Questions

Viva Question 1: Pathophysiology and Prevention

Stem: "A 72-year-old male with eGFR 35 is scheduled for elective coronary angiography. Let's discuss contrast-associated AKI."

Duration: 12 minutes

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Opening Question: "What are the mechanisms by which contrast media cause kidney injury?"

Expected Answer (3 minutes):

Three main pathophysiological mechanisms:

1. Renal Medullary Hypoxia:

   • The outer medulla (S3 proximal tubule, thick ascending limb) has high oxygen demand but low baseline PO2 (10-20 mmHg)
   • Contrast causes afferent arteriolar vasoconstriction via adenosine and endothelin-1
   • Reduced nitric oxide leads to loss of vasodilatory compensation
   • Result: "double hit" of reduced oxygen supply and increased demand from osmotic load

2. Direct Tubular Cytotoxicity:

   • Contrast is directly toxic to proximal tubular epithelial cells
   • Generates reactive oxygen species (ROS)
   • Causes mitochondrial dysfunction, apoptosis, and cell membrane disruption
   • Proximal tubule is most vulnerable due to concentration of contrast during reabsorption

3. Oxidative Stress:

   • ROS generation from direct reactions and mitochondrial dysfunction
   • Depletes glutathione (primary cellular antioxidant)
   • Causes lipid peroxidation, DNA damage, inflammatory cascade

This is the theoretical basis for NAC as prevention (glutathione precursor), though clinical trials have not demonstrated benefit.

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Follow-up Question 1: "What prevention strategies have the best evidence?"

Expected Answer (3 minutes):

Volume expansion (BEST EVIDENCE):

• Isotonic crystalloid (0.9% saline or balanced solutions)
• 1-1.5 mL/kg/h for 6-12 hours pre- and post-procedure
• POSEIDON trial: LVEDP-guided hydration reduced CA-AKI in PCI patients

Contrast volume minimization:

• Aim for contrast volume/GFR ratio <1
• Use biplane imaging, single-injection protocols
• Stage procedures if possible

Strategies WITHOUT proven benefit:

• N-acetylcysteine (NAC): PRESERVE trial 2018 - NO BENEFIT over placebo
• Sodium bicarbonate: PRESERVE trial - NO SUPERIORITY over saline
• Prophylactic dialysis: May WORSEN outcomes; not recommended

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Follow-up Question 2: "Tell me about the PRESERVE trial."

Expected Answer (2-3 minutes):

PRESERVE Trial (Weisbord et al., NEJM 2018, PMID: 29130810):

• Design: Multicenter, 2×2 factorial RCT
• Population: 5,177 patients with CKD undergoing coronary or non-coronary angiography
• Interventions:
  • NAC (oral 1,200 mg twice daily for 5 doses) vs placebo
  • Sodium bicarbonate (IV infusion) vs isotonic saline
• Primary outcome: Composite of death, dialysis, or persistent ≥50% creatinine rise at 90 days

Results:

• NAC vs placebo: 4.6% vs 4.5% (P=0.88) - NO DIFFERENCE
• Bicarbonate vs saline: 4.4% vs 4.7% (P=0.70) - NO DIFFERENCE
• Secondary outcome (CA-AKI at 48-96h): Also no difference

Implications:

• NAC should NOT be routinely used
• Bicarbonate offers no advantage over isotonic saline
• Focus on volume expansion and contrast minimization

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Follow-up Question 3: "The patient develops AKI post-angiography. How do you differentiate CA-AKI from cholesterol emboli?"

Expected Answer (2-3 minutes):

Clinical approach:

• If creatinine doesn't peak by 72h or fails to recover by 2 weeks, suspect alternative diagnosis
• Check eosinophil count, complement levels
• Examine for livedo reticularis, digital ischemia
• Skin or renal biopsy may be diagnostic

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Viva Question 2: Emergency Imaging Decision-Making

Stem: "A 60-year-old patient with CKD Stage 4 (eGFR 20) presents with acute onset chest pain and hypotension. ECG shows inferior ST elevation. The interventional cardiology team requests urgent coronary angiography."

Duration: 12 minutes

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Opening Question: "How do you approach this scenario?"

Expected Answer (2-3 minutes):

Risk-benefit analysis:

• This is STEMI with hemodynamic compromise - life-threatening emergency
• Mortality from untreated STEMI with cardiogenic shock: 50-80%
• Mortality from CA-AKI in this context: Additional risk but usually not immediately life-threatening
• Decision: PROCEED with coronary angiography - the benefit clearly outweighs the risk

Nephroprotection within time constraints:

• Rapid IV fluid bolus (if not in overt pulmonary edema): 250-500 mL
• Cannot delay primary PCI for 12-hour hydration protocol
• Request minimum contrast volume from interventionalist
• Ensure no additional nephrotoxins (hold ACEi, avoid NSAIDs)

Post-procedure planning:

• Continue IV fluids post-procedure
• Monitor creatinine 24h, 48h, 72h
• Anticipate possible CA-AKI; may need RRT
• Nephrology involvement early

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Follow-up Question 1: "What if the patient already had AKI before arriving (creatinine 500 μmol/L on presentation)?"

Expected Answer (2-3 minutes):

Same principle applies:

• Life-saving intervention should not be withheld
• Existing AKI does not change the benefit of coronary reperfusion
• Patient may already be dialysis-dependent or near-dialysis; additional contrast exposure has diminishing marginal harm

Additional considerations:

• Pre-existing AKI may be from cardiorenal syndrome (low output)
• Successful revascularization may actually IMPROVE renal function by restoring cardiac output
• Have nephrology team on standby for RRT if needed

Documentation:

• Document risk-benefit discussion clearly in notes
• Communicate with family if possible
• Involve renal team for post-procedure planning

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Follow-up Question 2: "What role does prophylactic hemodialysis play in this scenario?"

Expected Answer (2 minutes):

Prophylactic hemodialysis is NOT recommended (PMID: 12917227):

Evidence:

• Studies have shown prophylactic HD immediately post-contrast does NOT prevent CA-AKI
• May actually WORSEN outcomes due to:
  • Hemodynamic instability during dialysis
  • Contrast redistribution from intravascular space
  • Delayed time to reperfusion if performed before procedure

Current recommendation:

• RRT should be initiated only for absolute indications (AEIOU)
• If patient is already on dialysis, they can receive contrast and undergo routine dialysis session afterwards
• No need for "emergency" dialysis specifically to remove contrast

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Follow-up Question 3: "How would you discuss this situation with an Indigenous patient's family?"

Expected Answer (2-3 minutes):

Cultural safety approach:

1. Involve Aboriginal Health Worker (AHW) or Aboriginal Liaison Officer (ALO)
2. Ensure family members are included (family-centered decision making)
3. Use interpreter services if required
4. Allow adequate time for discussion

Key communication points:

• Explain the heart attack is very serious and life-threatening
• The dye (contrast) for the heart procedure has some risk to the kidneys
• We will do everything to protect the kidneys, but treating the heart attack is the priority
• If the kidneys are affected, we have treatments available (dialysis)
• Acknowledge higher rates of kidney disease in Aboriginal community

Respect and partnership:

• Ask if there are cultural or spiritual considerations
• Respect decision-making processes
• Document discussion and cultural consultation in notes

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Interactive Elements

[INTERACTIVE: CA-AKI Risk Calculator]

Mehran Score Calculator:

Input patient parameters:

• Hypotension (SBP <80 requiring inotropes): □ Yes (+5) □ No (0)
• IABP use: □ Yes (+5) □ No (0)
• CHF (NYHA III-IV): □ Yes (+5) □ No (0)
• Age >75 years: □ Yes (+4) □ No (0)
• Anemia (Hct <39% M/<36% F): □ Yes (+3) □ No (0)
• Diabetes: □ Yes (+3) □ No (0)
• Contrast volume: [___] mL (1 point per 100 mL)
• eGFR: □ >60 (+0) □ 40-60 (+2) □ 20-40 (+4) □ <20 (+6)

Calculate → Risk Category:

• Score ≤5: Low risk (7.5% CA-AKI)
• Score 6-10: Moderate risk (14% CA-AKI)
• Score 11-15: High risk (26% CA-AKI)
• Score ≥16: Very high risk (57% CA-AKI)

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[INTERACTIVE: ABG Interpreter - CA-AKI Case]

Case: Day 3 post-coronary angiography, creatinine 380 μmol/L, oliguria

ABG Results:

• pH: 7.28
• PaCO2: 28 mmHg
• PaO2: 85 mmHg (FiO2 0.28)
• HCO3: 14 mmol/L
• Lactate: 1.8 mmol/L
• Na: 138, K: 6.0, Cl: 108

Step-by-Step Analysis:

1. Acidemia or alkalemia? → Acidemia (pH 7.28)
2. Primary disorder? → Metabolic acidosis (low HCO3 14)
3. Respiratory compensation? → Yes (low PaCO2 28)
4. Expected PaCO2 (Winter's formula): 1.5 × 14 + 8 ± 2 = 29 ± 2 → Appropriate compensation
5. Anion gap: 138 - (108 + 14) = 16 → Mildly elevated
6. Delta ratio: Not significantly elevated AG, likely non-gap component

Interpretation: Partially compensated metabolic acidosis with mild AG elevation (uremic) and hyperkalemia. Consistent with Stage 2-3 CA-AKI with metabolic complications.

Clinical Action: Manage hyperkalemia (ECG, calcium, insulin/dextrose), consider RRT if refractory.

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