Introduction
Respiratory distress syndrome (RDS) is the most common cause of neonatal morbidity and mortality in preterm infants 1. The incidence of RDS is inversely proportional to gestational age, occurring in > 90% in preterm infants born < 28 weeks2. These infants are rescued with surfactant administration via an endotracheal tube and supported with nasal continuous positive airway pressure after a brief period of mechanical ventilation. The European guidelines for management of RDS in preterm infants reserve the use of mechanical ventilation to rescue babies who are not responding to positive pressure ventilation via face mask nasal prongs. Tracheal extubation is expected to ensue shortly after surfactant administration and stabilization of oxygenation3. However, due to certain limitations, this practice has not been fully adopted outside the Western world, thereby allowing mechanical ventilation for several days.
Both mechanical ventilation and tracheal intubation are independently associated with intraventricular hemorrhage in premature infants4. The exposure of infants to multiple intubations is not a safe practice. Studies demonstrated significant hemodynamic derangements that occur during intubation of premature infants5. Consequently, intubation has been associated with increased risk for intraventricular hemorrhage in premature infants4. Since there is no clear criteria to guide clinicians when to extubate, infants may not necessarily succeed the extubation attempt and are subsequently re-intubated. Therefore, there is an unmet need to device an indicator for readiness to extubate in order to avoid the risks associated with re-intubation.
Lung ultrasound can recognize a normal aerated lung in contrast to interstitial or alveolar patterns. In the last decade, lung ultrasounds have been increasingly used in critically ill patients, and evidence based international guidelines are published for the use of lung ultrasounds in adult critical care 6. It is simple and raises no threat of radiation. Evidence-based guidelines for lung ultrasound utilization in neonates have been recently published7.
Echocardiography is considered the gold standard tool to detect anatomical cardiovascular defects, assess cardiac function, evaluate abnormal pulmonary circulation and estimate the response to therapeutic interventions. However, it requires specific skills and detailed training for a caregiver to perform neonatal echocardiography8. Focused heart ultrasound is a simplified protocol of bedside ultrasound screening of pulmonary hypertension by measuring left ventricular eccentricity index (LVEI). LVEI is a quantifiable measure of the amount of distortion of ventricular septal geometry that is related to increased right ventricular systolic or diastolic pressures and volumes. LVEI has been associated with pulmonary hypertension in children and adults but has not been validated in premature infants 9.
This prospective study was conducted on premature infants supported with mechanical ventilation for several days. Infants had point of care lung ultrasound and LVEI measurements. The aim of this study was to test the hypothesis that a LUS combined with LVEI would predict success of extubation in mechanically ventilated preterm infants. In addition, correlations of LVEI with pulmonary artery pressures and patent ductus arteriosus were made.