Baylor University Medical Center Proceedings April 2017 - 168

Light source

Dialysate in

Dialysate out

Photodetector

Figure. Diffraction of light in the blood leak detector. Substances that deflect or
scatter light, such as hemoglobin or medications causing discoloration of fluids,
will result in a loss of transparency at the base of the column, triggering the
blood leak detector.

DISCUSSION
There is a severe paucity of data available today to guide the
management of hydroxocobalamin use in critically ill patients
requiring renal replacement therapy. The case presented here
highlights several new and emerging critical concerns with
this medication that can impede the delivery of life-saving
treatment.
First, while the use of hydroxocobalamin remains an advantage
compared to the cyanide antidote kit due to its low toxicity proﬁle,
universal discoloration of bodily ﬂuids can impede the delivery
of hemodialysis by inducing a "pseudo-blood leak" (10). The
hemodialysis machine operates on the principle that blood passes
on one side of a semipermeable membrane. An aqueous solution,
the dialysate is pumped on the opposite side, typically in the
opposite direction of the blood ﬂow, to maximize the diﬀusion
gradient across the membrane. All hemodialysis machines contain
a blood leak detector that alarms if red blood cells penetrate into
the dialysate (Figure). This is a vital safety feature of hemodialysis
machines. The blood leak alarm system consists of a photodetector
at the bottom of the dialysate column with a light source at the
top. Substances that deﬂect or scatter light such as hemoglobin
or medications causing discoloration of ﬂuids will result in a loss
of transparency at the base of the column, triggering the blood
leak detector (11). Hydroxocobalamin administration results in
discoloration of the dialysate and triggers this alarm. Activation
of the blood leak detector in the Fresenius 2008K machine causes
the blood pump to stop, the venous clamp on the level detector
to occlude, the ultraﬁltration pump to stop, and the remaining
time on dialysis clock to halt (12).
Very limited data are available on the types of dialysis machines
that may be aﬀected by hydroxocobalamin. While the Fresenius
2008K hemodialysis machine used in our case can be interfered
by hydroxocobalamin, not all types of hemodialysis machines
share this property. There is evidence that the Gambro Phoenix
168

X36 and the NxStage machine are unaﬀected (10, 13). It has been
postulated that hemodialysis machines that utilize a photodetector
consisting of a single optical emitter designed to detect light scatter
and signal drop oﬀ are unlikely to be aﬀected by hydroxocobalamin (10). However, photodetectors that use a dual LED array
that depends on light absorption, such as those on the Fresenius
2008K, are susceptible to the "pseudo-blood leak" phenomenon.
Another critical concern this case raises is the empiric
administration of hydroxocobalamin. An increased awareness
of the adverse eﬀects of hydroxocobalamin in patients potentially requiring emergent renal replacement therapy is needed
among emergency room physicians, critical care physicians, and
nephrologists alike. This will help increase multidisciplinary
communication, better inform management decisions and
therapeutic options for the critically ill, and help steward dialysis resources. In the case presented, empiric hydroxocobalamin was administered and the patient was eventually found to
have not overdosed on cyanide. In another recent case at our
institution, a potential kidney donor had received hydroxocobalamin prior to being considered a donor. The transplant team
decided to decline the kidney for transplantation in part due
to the possibility that intermittent hemodialysis to treat delayed graft function could not be performed due to interference from hydroxocobalamin. While the outcomes of similar
scenarios involving transplant donors have not previously been
reported, this scenario and the case presented here highlight
the critical need for more data to help guide management
decisions in patients exposed to hydroxocobalamin requiring
renal replacement therapy.
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Volume 30, Number 2

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