What triggers hemodialysis initiation and how should it be performed in a salicylate overdose setting?

Hemodialysis in Salicylate Overdose: Indications and Implementation

Hemodialysis should be initiated immediately in salicylate overdose when serum levels exceed 100 mg/dL (7.2 mmol/L), when there is altered mental status, or when acute respiratory distress syndrome requiring supplemental oxygen develops, regardless of salicylate concentration. 1

Indications for Hemodialysis

Absolute Indications (Strong Recommendations):

• Serum salicylate concentration >100 mg/dL (7.2 mmol/L) regardless of symptoms 1
• Altered mental status of any degree 1
• New hypoxemia requiring supplemental oxygen (evidence of ARDS) 1
• Failure of standard therapy (supportive measures, bicarbonate, etc.) 1
• Severe salicylate poisoning with clinical deterioration 1

Additional Indications:

• Serum salicylate concentration >90 mg/dL (6.5 mmol/L) with impaired kidney function 1
• Serum salicylate concentration >80 mg/dL (5.8 mmol/L) with impaired kidney function (suggested) 1
• Blood pH ≤7.20 (suggested) 1

Special Considerations:

• Intubated patients with levels >50 mg/dL have significantly higher mortality (44%) without hemodialysis compared to those receiving hemodialysis (16.1%) 2
• Mortality reaches 100% in intubated patients with levels >80 mg/dL who do not receive hemodialysis 2

Implementation of Hemodialysis

Preferred Modality:

• Intermittent hemodialysis is the preferred modality due to its superior efficiency and ability to correct acid-base disturbances simultaneously 1, 3

Technical Specifications:

• High-efficiency hemodialysis with high blood flow rates (200 mL/min or higher) 1, 3
• High surface area dialyzers to maximize clearance 1
• Target salicylate clearance of approximately 80-90 mL/min 3

Alternative Modalities (if hemodialysis unavailable):

1. Hemoperfusion (acceptable alternative with similar clearance rates of ~81 mL/min) 1, 3
2. Continuous renal replacement therapy (less efficient but better than no extracorporeal treatment) 1
3. Exchange transfusion (specifically for neonates) 1

Duration and Monitoring:

• Continue hemodialysis until salicylate levels decrease significantly below toxic thresholds
• Monitor for rebound increases in salicylate levels after discontinuation of hemodialysis 4
• Consider extended or repeated sessions in severe cases 5, 4
• Monitor salicylate levels during and after hemodialysis to detect rebound phenomenon

Pitfalls and Caveats

1. Rebound phenomenon: Salicylate levels may increase after discontinuation of hemodialysis due to redistribution from tissues. In one case report, levels rebounded from 98.2 mg/dL to 129 mg/dL after switching from conventional hemodialysis to slow, low-efficiency dialysis 4

2. Delayed initiation: Waiting too long to initiate hemodialysis can result in fatal outcomes even if dialysis is eventually started. A case report described a patient who died despite receiving hemodialysis when initiated after clinical deterioration had already occurred 5

3. Inadequate duration: A single session of hemodialysis may be insufficient in severe cases. Extended or repeated sessions may be necessary 5

4. Mechanical ventilation risks: Intubated patients are at particularly high risk as it is difficult to achieve the high minute ventilation needed to maintain respiratory alkalosis. Early hemodialysis is critical in these patients 2

5. Reliance on standard therapy alone: Urinary alkalinization and supportive care may be insufficient in severe cases, and delaying hemodialysis can lead to poor outcomes 1

By following these guidelines for initiating and implementing hemodialysis in salicylate overdose, clinicians can significantly reduce morbidity and mortality in these critically ill patients.