Are Subpleural Consolidations on Lung Ultrasound Early Findings of Acute Chest Syndrome?

Background: Acute chest syndrome (ACS) is a common complication in patients with sickle cell disease (SCD) and is a leading cause of morbidity and mortality.Chest X-ray (CXR) is recommended for evaluating ACS in patients with SCD because clinical findings alone have a low sensitivity. Children with SCD are repeatedly exposed to diagnostic radiation for the evaluation of ACS. Lung ultrasound (LUS) has been compared to CXR as an alternative imaging modality for evaluating ACS, and a lung consolidation > 1 cm is sensitive and specific for diagnosing patients with ACS. Consolidations < 1 cm, or subpleural consolidations, can detect pneumonia earlier than CXR; however, the significance of these findings for evaluating ACS is unknown. We evaluated LUS with consolidations <1 cm to determine if they could identify patients with ACS.

Methods: This is a prospective observational study that took place from November 2014-July 2016 in 2 urban pediatric emergency departments (EDs). The study population consisted of a convenience sample of patients with SCD from birth to 18 years of age at risk for ACS and who received a clinically-indicated CXR for suspected ACS. ACS was defined as a new pulmonary infiltrate on CXR together with the presence of fever, cough, chest pain, or respiratory symptoms. LUS were performed to evaluate for lung consolidation and determine the sensitivity, specificity, positive and negative likelihood ratios (LR+ and LR-) of LUS to identify ACS. In a subanalysis, the charts of patients who had a negative CXR interpreted by a pediatric radiologist or consolidation < 1 cm on LUS at the time of enrollment were reviewed for development of ACS within 7 days of the visit. The development of ACS in patients with subpleural findings on LUS was compared to patients with negative ultrasound findings. Fischer's-Exact Test was used to determine significance between the 2 groups with α = 0.05.

Results: One hundred sixty-eight patients were enrolled. ACS was diagnosed in 14% of patients, while a CXR was negative in 150 cases. The sensitivity of LUS to predict ACS was 91%, specificity was 91%, LR+ 10.5, LR- 0.1. Thirty-six cases had subpleural consolidation on LUS and 3 patients (8%) developed ACS. Of the 114 patients with negative LUS, 7 (6%) developed ACS. There was no statistical difference between these groups with p-value of 0.7.

Conclusions: Patients with subpleural consolidations on LUS were no more likely to develop ACS than those patients with a negative LUS. The small number of patients who developed ACS may have failed to show a statistical difference between these groups. Further studies with serial ultrasound examinations are needed to better define the significance of this finding.