Acute Kidney Injury and Kidney Replacement Therapy in the Critically Ill Patient
Answer: C
Both RIFLE class “F” and AKIN stage 3 are met
using similar SCr and UOP criteria. For this case, the
SCr increased by at least 3-fold above baseline, and
the patient’s UOP was less than 0.3 mL/kg/hour for 24
hours. Although A and B are true, the worse values in
the RIFLE class and AKIN staging systems should be
chosen when determining the class and stage of AKI.
Answer D is incorrect because his renal indices have not
been present for at least 3 months. Collectively, both the
RIFLE and the AKIN criteria have been included in the
KDIGO criteria, which is the current standard definition.
This patient has severe sepsis that led to decreased renal
perfusion, causing AKI. Enalapril likely contributed to
the injury by altering renal hemodynamics (Answer A is
correct). Neither glipizide nor acetaminophen is likely to
cause AKI (Answers B–D are incorrect).
Answer: A
Acute kidney injury cannot currently be diagnosed
with a specific blood test or imaging study (Answer C
is incorrect). The degree of kidney dysfunction and the
patient’s symptoms and coexisting diseases may provide
clues regarding the etiology of the patient’s kidney injury
(Answer A is correct). Drug-induced AKI is most com-
mon in the setting of additional insults and may occur
even after the drug is discontinued. Given a patient’s
history and presentation as well as a patient’s physical
examination, a clinician may pursue additional test-
ing to find the DIKD phenotype. Serum markers (e.g.,
SCr, UOP) are often nonspecific (Answer C is incor-
rect); kidney biopsy is only warranted for certain DIKD
phenotypes (e.g., AIN, glomerular diseases) and is often
not pursued in the acute setting (Answer D is incorrect).
Renal ultrasonography would be helpful for nephroli-
thiasis/crystalluria phenotypes or evidence of postrenal
AKI not alleviated with urinary catheter placement
(Answer B is incorrect).
Answer: C
Intermittent hemodialysis is often used in critically ill
patients because many physicians are familiar with this
therapy; however, about 20%–30% of patients receiving
IHD become hypotensive and require discontinuation or
a switch to an alternative therapy. Although prolonged
intermittent KRT methods like SLED or EDD are an
option, some form of continuous KRT would likely be
chosen because of this patient’s unfavorable hemody-
namics. Continuous renal replacement therapies such as
CVVH, CVVHD, and CVVHDF are often used because
they allow for slower flow rates and improved hemo-
dynamics. However, there is no clear benefit with one
therapy over another.
Answer: D
Protein binding primarily determines drug clearance
during KRT. Other factors that contribute to drug clear-
ance include low MW and low Vd. Drug charge leading
to dialyzer adhesion has only a limited effect on drug
clearance during continuous KRT and has been poorly
studied. When available, SC should be identified from
the package insert information or the primary literature
or calculated from the concentration of the solute in the
ultrafiltrate divided by the concentration of the solute in
the plasma. When unavailable, SC can be estimated as
SC = 1 − fb. In this case, the SC = 1 – 0.12 = ~0.88
(Answer D is correct; Answers A–C are incorrect).
Answer: B
The general approach to calculating clearance during
CVVH multiplies the SC (the degree to which a sub-
stance is able to pass through the membrane) by the
ultrafiltration rate. If predilution (i.e., before the fil-
ter) fluids are used, clearance across the membrane is
reduced, which must be accounted for in the formula.
Clearance in that case can be estimated using the follow-
ing equation: CVVHpre-dilution = QUF x SC x [Qb/(Qb
+ Qrf)] (where QUF is ultrafiltration flow rate (liters per
hour), Qb is blood flow rate [converted to liters per hour
for consistent units], and Qrf is predilution replacement
fluid flow rate, as stated earlier). In this case, clearance
= 2 L/hr x 0.88 x [12 L/hr/(12 L/hr + 2 L/hr)] = 1.5 L/hr
(Answer B is correct; Answers A, C, and D are incorrect).