Discussion
The findings of this study demonstrated high mortality rates in patients
with PARDS; only a third of patients survived, and nearly a quarter of
survivors exhibited new morbidities, with respiratory, feeding, and
motor functions being predominantly affected. Additionally, severe PARDS
was an independent risk factor for mortality.
The 64.4% mortality rate observed among patients in this study was more
than double the previously reported rate of 24% [15]. A multicenter
study from China found a similar mortality rate of 61% in patients with
PARDS; however, the large variability in mortality rates could be due to
various factors, such as differences in referral infrastructure, PICU
admission and discharge policies, illness severity, patient composition,
level of patient care, and accessibility of resources [16]. The
present study also excluded patients who were admitted for <24
h, most of whom were in a near-death state upon admission. As a result,
mortality rates may have been underestimated. Several factors could
explain the high mortality rate in our center. The mean PELOD-2 score of
9 upon admission was higher than that reported for the mortality groups
in other centers (mean PELOD-2 score of 7.9) [2]. Additionally,
every patient in this study was treated with invasive ventilation.
Patients undergoing mechanical ventilation have greater disease severity
than those undergoing noninvasive ventilation. In addition, more than
half of the patients were diagnosed with severe PARDS, which would be
expected to contribute to the high mortality rate. A previous study
reported a mortality rate of 10–15% in patients with mild/moderate
PARDS and 33% in patients with severe PARDS [17]. Moreover,
patients who withdrew from treatment midway would be expected to have a
higher mortality rate.
Consistent with the findings of other studies, multi-organ dysfunction
was the leading cause of death in patients with PARDS [18]. In this
study, severe PARDS was found to be an independent risk factor for
mortality, which is also consistent with previous studies [19].
However, the present results demonstrated associations between both the
OI and P/F and survival rates. At the onset of PARDS, both the
prevalence and severity of non-pulmonary organ failure were shown to
increase with severity of hypoxemia [20]. When assessing severe
PARDS, the OI was consistent with the P/F ratio. Consequently, our
study’s results further support the utility of the P/F ratio as a
reliable and practical metric for assessing the prognosis of patients
with severe PARDS.
Multi-organ failure, including sepsis-associated delirium, septic
encephalopathy, capillary leakage-induced edema of the extremities, and
intestinal failure leading to feeding intolerance, affects mortality
rates and functional status at discharge. In addition to dysfunction
caused by the disease itself, treatment factors can also cause new
morbidity. For example, in the current study, lower extremity deep vein
thrombosis, jugular vein thrombosis, intracranial hemorrhage, and
cerebral infarction, which are adverse events that are being
increasingly investigated, could have developed during ECMO treatment.
Two patients developed lower extremity deep vein thromboses after this
treatment, leading to a motor domain FSS score of 2 at discharge. All
the included patients were in critical condition at the time of
admission. Although survivors showed greatly improved functional status
after discharge, 24.5% experienced residual dysfunction. A recent study
reported similar residual dysfunction among survivors of PARDS, with
24.5% of patients being discharged to a rehabilitation facility
[12]. Similarly, consistent with the present findings, another study
revealed new morbidities in 15.6% of patients with PARDS upon discharge
with an FSS score of 7 [5].
The results demonstrated that respiratory, feeding, and motor functions
were the domains most affected at the time of PICU discharge. More than
half the survivors exhibited respiratory dysfunction, most likely due to
71.7% (38/53) of them having direct PARDS. Most cases of mild
respiratory dysfunction (respiratory FSS score = 2) were due to
localized lung injuries, including pleural effusion, lobar pneumonia,
pneumothorax, and pulmonary fibrosis; patients with these injuries
required oxygen therapy or suction after discharge. Further, respiratory
function may affect the quality of life after discharge. One study
reported respiratory dysfunction in 36.8% of patients with PARDS, 33%
of whom continued to experience mild-to-moderate impairment of lung
function 3 months after discharge [21].
Furthermore, feeding dysfunction is a common factor affecting the
long-term outcomes of PARDS and is likely to be altered in the PICU. One
study revealed a significant increase in FSS feeding domain scores
compared with scores measured upon admission [12]. Another study
found that 37.8% of patients with PARDS still required enteral
assistance [5] which was higher than the 17% rate of feeding
dysfunction in the present study. Most of those patients required
preterm milk, special formulas, liquid meals, feeding assistance, and
nasogastric tube feeding after discharge, although there was minimal
need for total parenteral nutrition at discharge.
Motor dysfunction was one of the main complications experienced by
survivors, with the most common causes being mental disorders, edema or
venous thrombosis of the extremities, and finger ischemia or necrosis.
Thus, special attention should be paid to the respiratory, feeding, and
motor domains of PARDS survivors.
Strengths
This is one of a few studies that provide data from an Asian population
on the use of the FSS to assess illness severity upon PICU admission and
discharge, with a focus on factors affecting mortality rate and
functional status at discharge. Additionally, this study describes the
functional status of a subgroup of patients with PARDS who underwent
invasive ventilation. Finally, respiratory, feeding, and motor
dysfunctions were identified as the most common areas requiring
rehabilitation.
Limitations
This study had a small sample size; thus, the true incidence of the
disease could not be accurately estimated. Additionally, the study was
based on data from a single pediatric center. Therefore, there is a risk
of missing data and information bias. Moreover, because this was a
retrospective study, patients who had nearly drowned or had severe
pneumonia, aspiration pneumonia, lung contusions, or severe sepsis but
had not obtained a PARDS diagnosis may have been missed. Further, the
FSS has not been validated for retrospective assessment of PARDS, and
its ability to predict outcomes in patients in the PICU has not been
investigated. Thus, it is unclear whether FSS dysfunction upon hospital
discharge reflects baseline functional disability or new morbidities
associated with PARDS. Additional limitations include the fact that the
study did not list modifiable risk factors for functional status
dysfunction (FSS > 8) at hospital discharge in patients
with PARDS.
Further research should focus on investigating the functional status of
patients from multiple centers, and follow-up clinical trials involving
patients with PARDS are warranted. In addition, future studies should
establish an objective outcome measure of mortality or significant
functional morbidity upon hospital discharge.