Discussion
In this large cohort of hospitalised patients, AKI was detected in
15.2% of admissions, a proportion that agrees with other studies on
general populations of inpatients in developed countries reporting the
incidence ranging from 12% to 20% (7, 15, 16). The
variability in the incidence may depend on adopted definitions for AKI
and baseline SCr, the frequency of creatinine measurements and clinical
settings. Patients with AKI were relatively old, half of them had more
than 72 years, with a high burden of comorbidities. This is consistent
with the existing evidence of AKI being particularly common in the
elderly (17). Reduced renal reserve in older age(18) together with polypharmacy and greater
susceptibility to nephrotoxic drugs, poses this population at high risk
of AKI (19). Furthermore, advanced age is a risk
factor for impaired recovery from AKI (20),
progression to CKD and it is still not conclusively proven that elderly
fully benefit from RRT (21). AKI development was
related to a higher number of comorbidities, including but not limited
to cardiovascular, diabetes, chronic pulmonary disease, hypertension and
CKD, which confirms the conviction that AKI is a broad clinical syndrome
of various etiologies more likely to occur in patients with a higher
burden of comorbidities (10).
In epidemiological studies on AKI in hospital settings, the syndrome is
often distinguished between community- and hospital-acquired assuming
different causes and underlying pathophysiological processes. In our
analysis, CA-AKI represented 38% of AKI population, which differs in
comparison to previous investigations on AKI present at admission. In
the study of Sawhney at el., the proportion was
27%(22); nevertheless, AKI originates in the
community has been consistently found to be more common than
hospital-acquired accounting for about 70% of all AKI episodes. This
could be explained by the adoption of different criteria to define AKI(23), the extension of the time window for CA-AKI
detection up to 48 hours (24) or defining the baseline
SCr as normal when the value was unknown (25).
We observed that the risk profile did not differ much between CA- and
HA-AKI(22), however, our results confirmed that
pre-existing CKD, liver diseases, dementia and history of cancer are
more common among patients presenting AKI at admission to the
hospital(24). These patients also sustained more
severe AKI than HA-AKI patients (23). One explanation
could be more prevalent or possibly more severe CKD in patients with
CA-AKI since the incidence and the severity of AKI increase considerably
with lower levels of baseline eGFR (26). Besides, the
high proportion of emergency admission and primary diagnoses in this
group indicate that severe renal impairment could result indirectly from
an acute condition that necessitated hospitalisation (for example severe
infections) or directly from post-renal causes (urinary tract
obstructions).
RRT during inpatient was required in 8.3% of CA- and 3.9% of HA-AKI
and a large proportion of these patients died before discharge (30% and
50%, respectively) (data not shown) supporting the evidence that
dialysis-requiring AKI is a strong predictor of mortality(17, 27). Given such poor prognosis along with the
rapidly escalating incidence of dialysis-requiring AKI(28), development of new instruments such as
standardised management recommendations on RRT initiation and
discontinuation may be a measure to improve outcomes(29).
Overall, one in five of AKI patients died during the hospital stay which
corresponds to mortality rates seen in other studies(4, 22), while in the absence of AKI, mortality runs
at 3.6%. When comparing outcomes between CA- and HA-AKI, conclusions of
a recent meta-analysis pointed out less severe clinical manifestation
and lower mortality in CA-AKI (30). Higher risk of
death in HA-AKI is commonly attributed to underlying chronic illness,
specifically cardiovascular disease, increased incidence of
complications during the hospital stay or iatrogenic origin of AKI
(nephrotoxicity, surgeries) (24, 31), which are
considered to do more harm to kidney than prerenal causes(32). In contrary, we did not find differences in
in-hospital and 6th-month mortalities between CA- and
HA-AKI in our cohort. These discordant conclusions cannot be explained
by the time window we adopted to identify CA-AKI (first 24 hours), which
differs from the criteria used by other authors; patients in whom AKI
was detected in each of the first three consecutive days after admission
had a comparable risk of death during hospitalisation (23.3%, 21.0 and
20% respectively). We suppose the reason for the discrepancy in
findings may be dissimilarity in characteristics of underlying
populations (age, prevalence of risk factors, in particular, CKD,
socioeconomic status) and in settings, in which previous studies were
conducted. Our hospital is a tertiary centre which provides specialist
care, also for seriously ill patients transferred from smaller centres;
therefore, the severity of AKI and mortality might have been affected.
Estimates of the regression model highlighted that severity of AKI,
rather than its origin, is a strong and independent determinant of
resource utilisation and mortality. It was particularly noticeable for
AKI stage 3 but even mild episodes of kidney dysfunction also
substantially impacted outcomes of the interest. It should be
remembered; however, that reported causes of death are mostly related to
coexisting conditions, including causes of AKI, rather than kidney
injury(33, 34). This reinforces the fact that AKI is
not a single condition and points to a need for a detailed
characterisation of affected patients encompassing etiology, adequacies
in management and the level of recovery to improve individualised
patient-centred care effectively.
Noteworthy, the risk of death for AKI stage 1 was found to be
significantly different in the community- and in the hospital-acquired
syndrome. Arguably, this resulted from variant criteria determining
stage 1 in the two groups; 15% of all AKI episodes (in patients with
SCr concentration above 1.0 mg/dL) was defined by an absolute increase
of 0.3 mg/dL above the reference SCr without reaching a relative
increase of ≥ 50% within a week. Our observations of divergent
prognosis are in line with the latest study of Sparrow et al. proving
that in patients with AKI stage 1 defined as an absolute change in SCr
concentration had shorter stays and were less likely to die in a
hospital than those with a 50% relative increase(35).
Among HA-AKI, the highest
instantaneously
incidence was observed on the second day after admission. We suspect
that part of these cases was community-acquired, with later
manifestation due to the limited ability of SCr to timely reflect
changes in kidney function. Nevertheless, whatever the origin, early
risk assessment (for example, at the moment of hospital admission) and
identification of high-risk patients provide the opportunity to
intervene in the treatment and protect the kidneys from further damage.
It is estimated that 20% of hospital-acquired AKI are avoidable(36). Given that each day more than 1% of patients in
our cohort developed AKI, the risk should be re-evaluated during the
whole stay. In patients with AKI present at admission, sufficiently
early recognition and accurate management have shown to have a positive
impact on prognosis(37).
There are some limitations to our study. We did not apply urine criteria
to define AKI, as data on urine output were not available, and this
might decrease the overall incidence of AKI. Limitations in recording
data in structured electronic records also relate to etiologies of the
syndrome; therefore, future research into the causes of AKI must include
other sources of information. Baseline SCr was known for 20% of
patients and missing data were estimated using multiple imputations that
showed to be more accurate than commonly used surrogate methods.
Finally, this study was conducted at a single tertiary medical centre,
and the epidemiological profile of AKI of this population may not be
generalisable to patients in other centres or lower health care level
settings.
Availability of electronic medical records improves our ability to
report a comprehensive depiction of AKI occurrence and related outcomes
in the real-life setting. Our study provided valuable insights into the
understanding of magnitude, complexity and strain of the syndrome in
this population. There is a necessity for further efforts to increase
the awareness of AKI among clinicians and health care professionals and
to induce strategies for effective prevention, recognition and
management of the syndrome.