Process by which small
molecules and electrolytes are
difused down a concentration
gradient. Typically, urea & K+ are
removed from the blood, while
Ca++ and bicarbonate are
replaced. Other electrolyte
derangements can also be
targeted by hemodialysis.
Small- to medium-sized
molecules (e.g., infammatory
mediators, etc.) are removed from
the blood utilizing a pressure
gradient across a flter membrane.
The pores in the membrane can
vary based on need. Specifc
molecules can be removed by
varying the flter's pore size.
The method used to remove
only free water across a membrane.
You’ll often see physicians discuss
ultrafltration in terms of how much
water is removed per dose. For
example, "As long as the patient's
hemodynamics tolerate it, the plan
is to continue to pull of 3 liters via
ultrafltration every 24 hours."
56 JEMS | DECEMBER 2017 WWW.JEMS.COM
ACUTE KIDNEY INJURY
to severe azotemia and the development of
pericarditis. Regardless of the clinical manifestation, the only treatment for uremic syndrome is RRT. 10
RR T & DIALYSIS
The process by which metabolic waste products are artificially removed from circulation
has been traditionally known as “dialysis.”
However, this may be a bit of a misnomer, as
hemodialysis is one of the specific modalities
of RRT—a more accurate term to describe the
artificial process for removing waste products
from the body.
Traditional outpatient RRT that prehospital providers are familiar with is highly efficient so that patients need only spend a few
hours in treatment per week. However, this
efficiency comes with a cost. It’s quite taxing
on the body, leading to significant complications in critically ill patients.
This efficiency requires a large extracorporeal circuit and typically removes several liters
of fluid volume per treatment session. In addition to the actual volume removed from the
body during the treatment, there’s a second
fluid shift that occurs from solute removal.
As molecules are filtered out of the blood,
there’s an abrupt fall in plasma osmolality. The
sudden decrease in solutes causes an osmotic
propulsion of free water into the body’s cells.
Simultaneously these phenomena can lead to
an aggressive change in fluid status that’s not
well-tolerated and can be fatal in critically ill
patients. One of the most frequent complications of RRT is hypotension. Any episode of
hypotension in patients with AKI can further
insult the already weakened kidneys.
For these reasons, an alternative form of
RRT was developed several decades ago. Con-
tinuous renal replacement therapy (CRRT)
is like RRT in terms of its actual function;
however, the main difference is that CRRT is
performed continuously over a period of days.
Certain centers may elect to vary the treatment
schedule so that each treatment last 12–16
hours a day for several days instead of 24 hours
a day. However, for the purpose of this article,
we’ll use CCRT to collectively refer to all of
the slow modalities of RRT. (See Figure 1.)
There’s also a growing body of evidence supporting the use of hemofiltration in critically
ill sepsis patients with concomitant AKI. Since
hemofiltration is better at moving medium-and large-sized molecules, it’s hypothesized
that hemofiltration during CRRT may remove
many of the inflammatory mediators that perpetuate the septic pathway. Removal of these
substances may not only help reverse the AKI,
but may also help preserve the cardiovascular
function that can be impaired by their high
serum concentration. 11
Critically ill patients who develop an AKI are
some of the most challenging and resource-intensive patients in the ICU. They often
require care from a host of specialties, advanced
medical technology and a large amount of
human resources. Providing care for these
patients is extremely complex.
Early in my training, I had a professor who
was a retired internist. She had a catchphrase
that’s served me well over the years: “When
the kidneys aren’t working correctly, nothing else is either.” Providers called to care for
these patients must exercise robust critical
thinking, prudent decision-making and sound
When preparing to care and transport these
patients, a report detailing the transfer of care
and history of present illness is needed. In that
report, there are several things that you’ll want
to pay close attention to:
Figure 1: Modalities for administration of continuous renal replacement therapy (CRR T)
Providing care for patients with acute kidney injury
is extremely complex. Photo A.J. Heightman