All that is Red is not Blood: Reddish Discoloration of Dialysis Ultrafiltrate

Dear Editor,

Refractory vasoplegic shock is an uncommon yet potentially life-threatening complication of major cardiac surgery and involves activation of nitric oxide (NO) pathways. The direct contact between blood and cardio-pulmonary bypass circuit causes cytokine release, which in turn activates inducible NO synthase enzymes, promoting high volume NO release that prevents smooth muscle calcium influx, leading to smooth muscle cell hyperpolarization and systemic vasodilation.¹ High-dose hydroxocobalamin, a potential inhibitor of NO synthase and an NO scavenger, is an emerging targeted rescue therapy as an alternate to methylene blue for refractory vasoplegic shock in patients who fail to respond to first-line therapy with catecholamine vasopressors.² Benign discoloration of body fluids is a side effect of hydroxocobalamin, but potential exists for erroneous co-oximetric blood gas results and false blood leak alarm during hemodialysis.³

A 53-year-old male with hypertension, type 2 diabetes, CKD stage IV, and severe ischemic cardiomyopathy underwent orthotopic heart transplantation. Because of severe intraoperative vasoplegia despite using norepinephrine, epinephrine, vasopressin, and dopamine, the patient received intravenous infusion of 5 g hydroxocobalamin (Cyanokit®, SERB Pharmaceuticals, Conshohocken, PA). The patient was initiated on continuous venovenous hemodiafiltration (CVVHDF) on the same day due to hemodynamic-mediated AKI superimposed on the underlying CKD. The ultrafiltrate began to turn red [Figure 1]. Hemolysis work-up was negative, and the fluid tested negative for blood. CVVHDF was continued without difficulty. The ultrafiltrate discoloration gradually faded over the next several days.

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Figure 1:

Reddish discoloration of the dialysis ultrafiltrate.

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Dialysis ultrafiltrate discoloration from hydroxocobalamin may be confused with blood leak from membrane damage. This could shut off certain dialysis machines due to erroneous activation of the blood detector, but CVVHDF systems such as PrismaFlex machines that use a single optical emitter are not impacted.⁴ With increasing use of hydroxocobalamin in vasoplegic states and as an antidote in cyanide poisoning, the treating clinicians should be aware of this phenomenon.