Objective Respiratory syncytial virus (RSV) infection is characterized by increased airway resistance, air-trapping and hypercapnia. Mechanical ventilation (MV) with heliox could reduce these symptoms by reducing respiratory system resistance (Rrs).

Methods 13 previously healthy infants mechanically ventilated for RSV lower respiratory tract disease (LRTD) were included within 24 hrs after PICU admission. At baseline, 30, 60 and 90 mins Rrs was measured using the AVEA ventilator, PaCO₂ from arterial blood samples. Airtrapping was characterized by end-expiratory lung volume (EELV), and assessed using Electrical Impendence Tomography (EIT). Ventilator settings were kept constant, patients were sedated and paralyzed. Gas mixture was switched to heliox (60% helium) after baseline measurements, at 30 mins to conventional gas and at 60 mins to heliox (60% helium). Statistical analysis was performed using the Wilcoxon signed rank test. Data are expressed as mean ± standard error.

Results MV with heliox resulted in a significant decrease in Rrs (69.1±6.9 cmH₂O/L/sec to 50.1±6.0 cmH₂O/L/sec, p = 0.015) and a trend towards decreased EELV (ΔZ −23.4±4.6 to −12.3±10.7). However, this was not accompanied by a significant decrease in PaCO₂. After reintroduction of conventional gas, Rrs significantly increased to 70.7 cmH₂O/L/sec (p = 0.019), EELV further decreased and PaCO₂ increased both non-significantly. Rrs significantly decreased after reintroduction of heliox (42.9±3.2 cmH₂O/L/sec, p = 0.002) and PaCO₂ non-significantly decreased.

Conclusions MV with heliox decreased Rrs and EELV in RSV LRTD without improved CO₂ clearance. Further studies are warranted.