Clinical Characteristics of Severe Acute Chest Syndrome in Children with Sickle Cell Disease

Background: Acute chest syndrome (ACS) is a form of acute lung injury that is a leading cause of morbidity and mortality in children and adults with sickle cell disease (SCD). Despite advances in health maintenance and disease-modifying therapies for SCD, ACS remains a common and often severe complication. There is still limited understanding of why some patients suffer more severe ACS episodes. Few studies have specifically investigated clinical parameters associated with severe ACS in the pediatric population. The purpose of this study is to determine the association between hematologic and radiologic clinical findings and severe ACS in children and adolescents with SCD.

Methods: We conducted a single-institution retrospective chart review of 120 pediatric patients with HbSS or HbSβ ₀ thalassemia and at least one documented episode of ACS, and then further classified patients by their most severe ACS event. We extracted laboratory and radiologic data to compare clinical findings. Infections reported in patient encounters were verified by documented viral PCR and blood cultures. Continuous variables were analyzed using Welch's t-test; categorical variables were analyzed using Fisher's exact test.

Results: Eighty patients in the moderate ACS group were excluded for this analysis. Twenty patients (median age 5.6 years, SD 4.20) had mild ACS defined by no supplemental oxygen requirement, only one segmental or lobar infiltrate on chest radiography, and transfusion of less than 3 units (or 15 cc/kg) of red blood cells. Twenty patients (median age 7.6 years, SD 4.01) had severe ACS characterized by acute respiratory failure requiring mechanical (invasive or non-invasive) ventilation and/or exchange transfusion. Median length of stay for patients with severe ACS was longer than for the mild cohort (mean: 8 days vs 2 days, p <0.001). The median absolute neutrophil count (ANC) was significantly higher in the severe ACS cohort (19.8 x 10 ³µL vs. 9.4 x 10 ³ µL, p = 0.004). The median platelet count nadir was significantly lower in the severe ACS group compared to the mild group (165 x 10 ³ µL vs. 309 x 10 ³ µL, p <0.001). Review of radiologic data showed that the median number of lobes affected in the severe ACS group were 3, compared to 1 lobe in the mild group (p <0.001). Approximately 65% of patients with mild ACS had left-sided disease (p = 0.18), while 85% of patients with severe ACS had bilateral disease (p = 0.002). The risk of pleural effusions was also significantly increased with severe ACS [OR 76.00 (95% CI 9.235-825.6), p <0.001]. When we analyzed infection at time of ACS, the proportion of laboratory-confirmed viral infections were twice as high in the mild ACS cohort (41.2%), compared to the severe ACS cohort (20.0%, p = 0.279). There were no bloodstream bacterial infections found in either cohort.

Conclusion: Severe ACS in children is a clinically distinct phenotype associated with longer length of stay, higher ANC and lower platelet nadir counts during active ACS, increased involvement of 3 or more lung lobes, and presence of pleural effusions. A lower proportion of confirmed viral infections were found in the severe ACS cohort compared to mild ACS patients, although did not reach statistical significance. Future prospective studies investigating the utility of these specific laboratory and radiographic parameters as components of an ACS severity prediction score are warranted.