Internal Jugular Vein Respiratory Variability as a Marker of Disease Severity in Infant Bronchiolitis

Bronchiolitis is among the leading causes of hospitalization in infants under 2 years of age. Existing clinical severity scores show limited inter-observer agreement and weak correlation with oxygenation. Point-of-care ultrasound (lung ultrasound, diaphragm ultrasound) has been studied as an adjunct severity marker in bronchiolitis. Still, respiratory-cycle variability of the internal jugular vein (IJV) diameter has not previously been investigated in this population. A prior reliability study in healthy children demonstrated that right internal jugular vein (RIJV) diameter can be reliably measured by M-mode ultrasound and does not vary significantly across the respiratory cycle in the absence of respiratory distress; the study authors explicitly proposed that RIJV diameter and its respiratory variation be investigated as a surrogate marker of pulmonary function in children with respiratory distress. This study extends that proposed application to infants with acute bronchiolitis. Eligible infants aged 1-23 months meeting AAP (2014) clinical criteria for acute bronchiolitis will undergo a standardized ultrasound protocol (45-degree head elevation, linear probe, right internal jugular vein imaged approximately 1 cm cephalad to the sternoclavicular junction, B-mode identification followed by M-mode measurement of maximal inspiratory and expiratory diameters) performed by a blinded, trained sonographer. We will record concurrent clinical severity scoring, lung ultrasound, and diaphragm ultrasound (excursion, thickening fraction). The primary analysis will test the correlation between the IJV Variability Index and the Wang Bronchiolitis Severity Score; secondary analyses will examine correlations with additional validated severity scores, physiologic parameters, and clinical outcomes (respiratory support escalation, length of stay), as well as inter-/intra-observer reliability and the discriminative performance of a multimodal point-of-care ultrasound model.

Inclusion criteria

• Infants aged 1-23 months
• Clinical diagnosis of acute bronchiolitis per AAP (2014) criteria (first wheezing episode following an upper respiratory infection prodrome, with tachypnea, retractions, and/or crackles)
• Written informed consent obtained from parent/legal guardian
• Evaluable within the first 6 hours of emergency department presentation

Exclusion criteria

• Underlying congenital heart disease
• Chronic lung disease (bronchopulmonary dysplasia, cystic fibrosis)
• Prior history of recurrent wheezing/suspected asthma
• Anatomical abnormality of the neck or prior history of central venous catheterization or jugular vein thrombosis
• Hemodynamic instability/shock
• Immediate need for intubation/mechanical ventilation precluding ultrasound assessment
• Parent/legal guardian declines consent