What is the best approach for urgent hemodialysis in a patient with recent NSTEMI and acute kidney injury or failure?

Urgent Hemodialysis in Recent NSTEMI with Acute Kidney Injury

In a patient with recent NSTEMI and acute kidney injury requiring urgent hemodialysis, proceed with dialysis using unfractionated heparin (UFH) as the anticoagulant due to its short half-life and reversibility, while carefully managing hemodynamic instability through cooled dialysate and high sodium dialysate to minimize myocardial stunning. 1, 2

Anticoagulation Strategy During Hemodialysis

Use unfractionated heparin (UFH) as the preferred anticoagulant because it can be rapidly reversed and has a short half-life, which is critical in the post-NSTEMI period when bleeding risk is elevated. 1

• Start with a reduced UFH bolus of 30-40 U/kg (instead of standard 60 U/kg) followed by 8-10 U/kg/hr infusion, targeting an activated clotting time (ACT) of 180-200 seconds rather than the standard 200-250 seconds. 1
• Avoid enoxaparin or other low-molecular-weight heparins because they cannot be switched to or from UFH without increasing bleeding risk, and they have prolonged half-lives that are problematic in the acute post-MI setting. 1
• Bivalirudin is a reasonable alternative if there is heparin-induced thrombocytopenia or high bleeding risk, as it requires no renal dose adjustment and has less bleeding compared to UFH. 1

Hemodynamic Management During Dialysis

The primary challenge is preventing intradialytic hypotension and myocardial stunning, which can precipitate recurrent ischemia or arrhythmias in the vulnerable post-NSTEMI myocardium. 3, 4, 2

• Cool the dialysate to 35-36°C (rather than standard 37°C) to reduce hemodynamic instability by promoting peripheral vasoconstriction. 3
• Raise dialysate sodium concentration to 145-150 mEq/L to maintain plasma osmolality and support intravascular volume during ultrafiltration. 3
• Limit ultrafiltration rate to <10-13 mL/kg/hr to allow adequate plasma refilling from the extravascular space. 3, 4
• Monitor cardiac index continuously if possible, as mean arterial pressure often remains stable despite severe reductions in cardiac output during dialysis. 4

Timing and Indications for Urgent Dialysis

Proceed with urgent hemodialysis for absolute indications regardless of recent NSTEMI, as the mortality risk from untreated severe AKI exceeds the procedural risk. 2, 5

Absolute indications include:

• Severe hyperkalemia (>6.5 mEq/L) with ECG changes or refractory to medical management 2, 5
• Severe metabolic acidosis (pH <7.1) unresponsive to bicarbonate therapy 2, 5
• Pulmonary edema refractory to diuretics causing respiratory failure 2, 5
• Uremic complications (pericarditis, encephalopathy, bleeding) 2, 5
• Toxic ingestions requiring removal 2

Cardiac Medication Adjustments

Continue aspirin 75-100 mg daily unless there is active bleeding, as the mortality benefit in post-NSTEMI patients outweighs bleeding risk. 1

• Hold P2Y12 inhibitors (clopidogrel, ticagrelor, prasugrel) on dialysis days if the patient is >24-48 hours post-PCI and hemodynamically stable, resuming after the session. 1
• Avoid IV beta-blockers during dialysis due to risk of exacerbating hemodynamic instability; use oral beta-blockers at low doses after stabilization. 1
• Withhold nitrates if systolic blood pressure <90 mmHg or drops ≥30 mmHg below baseline during dialysis. 1

Dialysis Prescription Specifics

Use intermittent hemodialysis rather than continuous renal replacement therapy (CRRT) once the patient is stabilized from the acute NSTEMI phase (typically >24-48 hours post-event). 3, 2

• Prescribe 3-4 hour sessions initially, with blood flow rate of 200-250 mL/min and dialysate flow of 500 mL/min to minimize hemodynamic stress. 3
• Target a Kt/V of 1.2-1.4 per session, but prioritize hemodynamic stability over achieving full dose if the patient becomes unstable. 3
• Assess need for additional sessions based on volume status, electrolytes, and acid-base balance rather than fixed schedule. 3

Monitoring During Dialysis

Continuous ECG monitoring with defibrillator immediately available is mandatory given the risk of arrhythmias from electrolyte shifts and myocardial stunning. 6, 4, 2

• Measure blood pressure every 15-30 minutes, or continuously if available. 3, 4
• Monitor relative blood volume using devices like CRIT-LINE if available, targeting <10-12% reduction. 4
• Check potassium and ionized calcium at mid-dialysis if starting potassium is >6.0 mEq/L. 2, 5

Critical Pitfalls to Avoid

Do not delay dialysis for "cardiac clearance" when absolute indications exist, as the risk of death from hyperkalemia or pulmonary edema exceeds the procedural risk. 2, 5

• Never switch between UFH and enoxaparin during the hospitalization, as this increases bleeding risk significantly. 1
• Do not use standard ultrafiltration rates (>13 mL/kg/hr) in post-NSTEMI patients, as this dramatically increases risk of myocardial stunning and ischemia. 3, 4
• Avoid aggressive volume removal in the first dialysis session; spread ultrafiltration over multiple sessions if possible. 3, 2

Post-Dialysis Management

Reassess volume status and cardiac function after each session, as patients with ischemic cardiomyopathy and renal dysfunction have impaired compensatory mechanisms. 7, 2

• Resume full antiplatelet therapy after dialysis session if no bleeding complications occurred. 1
• Adjust subsequent dialysis prescriptions based on hemodynamic tolerance of the first session. 3
• Consider echocardiography if there were significant hemodynamic changes during dialysis to assess for new wall motion abnormalities. 8, 7