SHM Converge Scientific Abstract ePoster Gallery-Sulfhemoglobinemia: The Proof Is in the Phenazopyridine

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This case report describes a 95-year-old woman with severe, unexplained hypoxemia and a pulse oximetry reading of 57% despite a normal exam, normal chest imaging, and a very high PaO2 on 100% FiO2. Her oxygen saturation did not improve with supplemental oxygen or BiPAP, and the ABG sample appeared dark, suggesting a dyshemoglobinemia. Initial workup showed anemia, mild methemoglobinemia, low haptoglobin, elevated LDH, and schistocytes, raising concern for medication-related hemolysis. Review of her medications revealed one month of phenazopyridine use, which can cause both hemolytic anemia and sulfhemoglobinemia. After stopping phenazopyridine and transfusing packed red blood cells, she remained clinically stable and oxygen was weaned appropriately. A send-out sulfhemoglobin level later returned elevated at 11%, confirming the diagnosis.<br /><br />The discussion emphasizes that sulfhemoglobinemia is a rare dyshemoglobinemia caused by sulfur binding to hemoglobin’s porphyrin ring. This alters the hemoglobin dissociation curve and can produce strikingly low SpO2 readings that do not correct with oxygen therapy. It is difficult to diagnose because routine co-oximetry typically detects methemoglobin and carboxyhemoglobin, but not sulfhemoglobin, so specialized testing is often required. Phenazopyridine is a known trigger, especially with prolonged or excessive use, and is usually intended for short-term use only. Management consists of discontinuing the offending drug, providing supportive care, and transfusing blood products in severe cases.<br /><br />The case highlights the importance of considering dyshemoglobinemia when hypoxemia is refractory to escalating oxygen therapy, especially when clinical findings do not match the pulse oximetry reading.

Asset Subtitle

Lauren Ward

Meta Tag

Author List Brad Butcher, Dhruv Khant, Lauren Ward

Category Clinical Vignettes

Concept Hypoxemia

Concept Dyshemoglobinemia

Concept Sulfhemoglobinemia

Concept Phenazopyridine

Concept Pulse Oximetry

Distinguished Non-Finalist

Presenter Organization UPMC Critical Care Medicine

Presenting Author Lauren Ward

Track Adult

Keywords

sulfhemoglobinemia

phenazopyridine

dyshemoglobinemia

hypoxemia

pulse oximetry

methemoglobinemia

hemolytic anemia

co-oximetry

schistocytes

oxygen therapy

Hypoxemia

Dyshemoglobinemia

Sulfhemoglobinemia

Phenazopyridine

Pulse Oximetry