Discussion
In ACS, guidelines from the British Society of Hematology recommend that
patients presenting with fever, hypoxia, tachypnea, tachycardia and
abnormal respiratory exam findings should be treated empirically as well
as receive a CXR11. However, radiological signs can be
delayed compared to physical signs; a normal CXR does not preclude the
diagnosis of ACS if there is clinical suspicion11.
Vichinsky’s study of 939 patients found that 35% had normal lung exams
and 17% presented with lower extremity pain when they presented with
ACS12. Our data demonstrate that clinical findings
such as chest pain, tachypnea and hypoxia were most likely to correlate
with a diagnosis of ACS. While 69% of our febrile patients received a
CXR in the PED, only 13% were ultimately diagnosed with ACS, indicating
that more CXRs and radiation exposure occurred in the febrile population
than may have been necessary. When adjusting for fever and asthma, the
most salient predictors of ACS were hypoxia and chest pain. When
present, these findings were significant predictors of ACS; when absent,
patients had significantly decreased odds of ACS.
While CXR remains a key diagnostic tool in the diagnosis of ACS, many
studies have suggested that lung ultrasound may provide evidence for
diagnosis and evolution of ACS. CXR can be normal in up to approximately
66% of early cases of ACS, including CXRs obtained in patients who were
hypoxemic on presentation13. Historically, lung
ultrasound diagnostic research had been primarily performed in adult
patients; however, more recently, lung ultrasound has been evaluated in
the pediatric population. Multiple studies in pediatric SCD patients
have demonstrated that lung ultrasounds showed a higher number of ACS
associated lesions than CXR13. In a study by Vetter et
al., lung ultrasound was superior to CXR for diagnosing consolidations
and pleural effusions in these patients.13 Future
investigations should evaluate whether lung ultrasound is at least equal
to, if not superior, to CXR to support the broader use of
radiation-sparing bedside alternatives for diagnosing ACS in pediatric
patients.
Strengths of our study include a relatively large sample size; the total
“n” of 424 was robust enough to allow for significant statistical
analysis and supported a meaningful analysis stratifying by risk
factors. Our study evaluated SCD in an understudied patient population,
with a focus on children aged 2 to 12 years old due to the higher
incidence and severity of ACS in this age group. One limitation is that
our data may not be generalizable to patients under 2 years or older
than 12 years. The retrospective study design can limit results due to
risk of bias in documentation, but we evaluated all PED and inpatient
notes and laboratory values to increase likelihood of capturing
important clinical data. As with any retrospective study, we can only
evaluate for associations and not causation, but we performed
multivariable modelling, in addition to bivariate analysis, in order to
control for confounders and better assess for significant predictors. In
addition, we evaluated subjects presenting to the PED in 2016-2018,
which is a more modern cohort than many studies on pediatric SCD and ACS
diagnosis.
In conclusion, studies have demonstrated that the clinical presentation
of ACS differ based on the age of patients. Prior studies have noted
that children under the age of 10 tend to present with fever, cough and
wheezing, whereas adults typically report chest pain and
dyspnea.14 Further research is needed to confirm, but
based on our data, incorporating the presence or absence of chest pain
and hypoxia in pediatric patients may help focus the use of CXR to the
appropriate patient population at risk of developing ACS. By 18 years of
age, most children with SCD will have had on average 26.7 (95% CI:
24.1-29.3; range 0-492.1) radiographic tests while 5% of these patients
will have had more than 100 radiographic tests15. A
high cumulative lifetime of radiation exposure is an established risk
factor for serious life-threatening diseases such as
cancer16. With advancements in standards of medical
care for patients with SCD, the life expectancy for SCD patients has
improved to an average of 54 years old8, which makes
it even more important to reduce cumulative exposure to diagnostic
radiation in this vulnerable population. Thus, this study provides
evidence to support a more critical assessment of risk factors and
presenting symptoms to better triage which pediatric patients warrant
further imaging in the PED at initial presentation to investigate for
possible ACS.