Combined Evaluation of Pulmonary Fluids by Lung Ultrasounds and Transthoracic Electrical Bioimpedance in Preterm Infants With Respiratory Distress Syndrome

Introduction Respiratory distress syndrome (RDS) is among the most common complications of preterm birth, and typically becomes manifested soon after birth. The rapid reuptake of fetal lung fluids plays an important role in transitional events at birth. Most of this fluid is reabsorbed through epithelial alveolar cells by an active sodium transporter. Mechanical events play a role in this exchange too. A failure of the rapid reuptake of fetal lung fluids after birth, with subsequent liquid retention in the alveolar space, together with the deficit of surfactant proteins ensuing from lung immaturity represent the leading mechanisms for the development of RDS, which may require different levels of respiratory support, ranging from mechanical ventilation to less invasive modalities (nasal cannulas or continuous positive airway pressure (CPAP)).

An increasingly used method for lung evaluation in the newborn is lung ultrasound, which allows to evaluate the alveolar fluid and to differentiate among several pathological conditions (transient tachypnea of the newborn, meconium aspiration, respiratory distress syndrome, pneumothorax, and pleural effusion) and, in the preterm population, has also been proved to predict of the need for respiratory support and for surfactant administration. Compared to traditional radiological assessments, this non-invasive technique does not imply the use of X-ray; however, it requires specific training, it is operator-dependent and does not allow a continuous and trend able evaluation over time, but only serial assessments.

Transthoracic electrical bioimpedance (TEB) allows continuous, non-invasive and real-time monitoring of static and dynamic thoracic fluids. It has been recently introduced in neonatal clinical practice to monitor such hemodynamic parameters as cardiac output, providing useful clinical information in hospitalized preterm infants, or neonates undergoing hemodynamic procedures. This technique allows quantifying static thoracic fluid contents (TFC) in a non-invasive and continuous manner. Compared to ultrasound, this method provides continuous and non-operator dependent data on the lung fluid status over time and does not require specific training for its use and interpretation.

Current literature reported a significant correlation between TFC values and respiratory distress, but, to date, it has not been investigated whether this parameter may predict RDS evolution, or if it is influenced by specific neonatal characteristics associated with pulmonary overflow, such as the presence of a patent ductus arteriosus (PDA), which is a common finding over the transitional period, defined as the first 72 hours of life.

Combining lung ultrasound to transthoracic electrical bioimpedance could open to new diagnostic and prognostic perspectives in preterm infants with RDS during the first days of life.