I recently received an inpatient consultation to see a CKD
5D patient. The reason for consult, as is mostly the case with dialysis
patients was that he “needs hemodialysis”.
This dialysis patient wasn’t the average bear though. He had
had a witnessed cardiac arrest, was treated by EMS, and defibrillated. He had a
return of spontaneous circulation after being pulseless for 20 minutes. As soon
as he got to the ER, he was initiated on our standard institutional therapeutic
hypothermia protocol. I was called in to
dialyze him because (it wasn’t his usual day) the cardiologist wanted to
perform a left heart cath on him the following day, and they “did not want
dialysis to interfere with that schedule”. My clinical assessment did not
reveal a severe degree of volume overload. He wasn’t hyperkalemic, and had only
a mild degree of lactic acidosis that was nicely compensated by him being
appropriately ventilated. Due to the concerns that I talk about below, I did
not see an emergent reason to dialyze him.
I would like to focus on a few teaching points from a
nephrologist’s perspective that I took away from this scenario:
Therapeutic hypothermia entails cooling post cardiac arrest
patients to 32-34 degrees Celsius, ideally within 6 hours of a cardiac arrest. Both intravascular and surface cooling methods
are used. At my institution, the protocol involves administering up to 3 liters
of 0.9% saline (which has been cooled to a temperature of 4 degrees Celsius),
over an hour. This is complemented by cooling vests. Once target temperature is
reached, the cooling phase is continued for 12-24 hours, after which the
patient is rewarmed gradually at the rate of 0.5 degrees Celsius/hour.
Sub-physiological body temperatures expectedly have adverse
effects. Hypothermia can hamper leukocyte function, increasing infection
risk later . Cardiac effects include bradycardia and prolonged QT interval
(both were present in this patient). Finally, for us nephrologists, here are
some adverse effects and pertinent points that we need to keep in mind for such
Hypothermia can cause hypokalemia via two different
mechanisms. Low temperature causes a transcellular shift of potassium in to the
intracellular compartment. This effect is possibly mediated
by increased beta adrenergic and sympathetic activity . In fact, hypokalemia
in the setting of hypothermia must be repleted extremely cautiously, if at all,
given the risk of rebound hyperkalemia as potassium moves back out of the cells
when the patient is rewarmed. This rebound hyperkalemia can be frequently fatal due to
The second mechanism by which hypothermia causes hypokalemia
is by the induction of polyuria, also known as “cold diuresis”. This hypokalemia
is mediated by increased urinary flow, and is seen in conjunction with
and hypomagnesemia. I didn’t observe any of these in my patient, maybe
because of his oligo-anuric status at baseline. Nevertheless, close monitoring
of volume status and electrolytes is required.
Hypothermia interferes with platelet function and with the
clotting cascade. In fact, as per this review , 22% of
patients had bleeding post-hypothermia induction. That might be a concern when
making the decision to dialyze post-hypothermia patients with heparin.
The other issue that I ran in to, that was specific to
dialysis patients, was the concern about the patient’s temperature. As we know,
most HD machines warm blood before returning in to the patient. With most
warmer cannot actually be turned off and only goes as low as 35 degrees
Celsius. In other words, dialysis can inadvertently warm the patient up to this
temperature (from the target temp of 32 degrees, per the hypothermia protocol)!
CRRT machines do have adjustable temp settings that goes down to 32 degrees, so
that might be a safer alternative. Given the risk of inadvertently warming the patient, and
because I did not see any emergent indication for dialysis, I did not dialyze
the patient. I believed that in that situation, his hypothermia protocol took
precedence over dialysis.
In my experience, I have observed that referring non-renal
physicians often consider inpatient hemodialysis an ancillary service, akin to
placing an order for an x-ray or a lab draw. Seasoned fellows have heard this
phrase all too often, “I want you to come down and dialyze this patient”. You
are then left with the unenviable task of explaining to the non-renal physician
that the decision to dialyze would be made by the nephrologist after proper
assessment of the patient (isn’t why they consulted you in the first place?).
Let’s not allow our familiarity and comfort with dialysis technology lull us in
to putting our guard down. Dialysis is an inherently intense and complicated
procedure where multiple clinical parameters need to be closely watched. It’s a
fact that is often lost in translation.