What is a potential consequence of using isosulfan blue (lymphazurin) injection for sentinel node biopsy?

Isosulfan Blue Injection and Pulse Oximetry Interference

Isosulfan blue injection for sentinel node biopsy results in inaccurate pulse oximetry readings (falsely low oxygen saturation values). This effect is well-documented in the FDA drug label and multiple research studies 1.

Mechanism and Clinical Presentation

When isosulfan blue is injected for sentinel lymph node mapping:

• The dye is absorbed into the circulation and interferes with pulse oximeter's ability to accurately measure oxygen saturation
• This causes falsely low SpO2 readings that do not reflect true arterial oxygenation status 1, 2
• Key characteristics of this interference:
  • Begins approximately 15-20 minutes after injection
  • Reaches maximum effect around 30-35 minutes post-injection
  • Can persist for up to 4-6 hours (sometimes longer)
  • Typically shows a 5% median decrease in SpO2 readings (range 2-11%)

Evidence and Verification

The FDA drug label explicitly warns that "Isosulfan blue injection 1% interferes with measurements of oxygen saturation in peripheral blood by pulse oximetry and can cause falsely low readings" 1. Multiple studies have confirmed this effect:

• Arterial blood gas analysis during these episodes shows normal arterial partial pressure of oxygen (PaO2) and normal true oxygen saturation (SaO2) 2, 3
• The discrepancy between pulse oximetry readings and actual arterial oxygen saturation has been demonstrated in controlled prospective studies 4, 5

Clinical Management

When using isosulfan blue for sentinel node biopsy:

1. Anticipate the decrease in SpO2 readings approximately 15-30 minutes after injection
2. Verify true oxygenation status with arterial blood gas analysis if clinically indicated
3. Monitor the patient for actual signs of hypoxemia (not just relying on pulse oximetry)
4. Inform the anesthesia team before injection about the expected interference
5. Document that the decreased SpO2 is likely due to dye interference, not true hypoxemia

Important Considerations

• This effect is more pronounced with isosulfan blue than with methylene blue 5
• The interference occurs with both subcutaneous and intradermal injections 4
• Isosulfan blue can also cause falsely elevated readings of methemoglobin by arterial blood gas analyzer 1
• In such cases, cooximetry may be needed to verify actual methemoglobin levels

Potential Complications

Besides pulse oximetry interference, be aware that isosulfan blue can cause:

• Hypersensitivity reactions including anaphylaxis (approximately 2% of patients) 1
• Precipitation when mixed with local anesthetics like lidocaine in the same syringe 1

The interference with pulse oximetry is a predictable, temporary effect that should be anticipated when using isosulfan blue for sentinel lymph node procedures.