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EBNEO commentary: Randomised controlled trial of heliox in newborn infants with meconium aspiration syndrome

Helium is a colourless, odourless gas that has no direct pharmacologic or biological effects.1 Helium has oneseventh the density of air. This property allows the gas to achieve a laminar flow even in condition where turbulent flow is expected, for example airway obstruction, which in turn leads to reduced airway resistance and work of breathing.2 Additionally, oxygen and carbon dioxide diffuse faster through helium than through air.1 Heliox is a mixture of helium (usually 70%– 80%) and oxygen (usually 20%– 30%) that retains the properties of helium when lower concentrations of oxygen are used.2 In children, Heliox has been used to treat conditions like asthma, bronchiolitis, upper airway obstruction and croup with inconsistent results, and currently there are no evidencebased guidelines for its use.3 There are technical challenges for the use of heliox for mechanical ventilation. Due to its different physical properties, when heliox is used for mechanical ventilation, function of pneumotachometers and flow sensors can be altered. Helioxcalibrated ventilators are however available.4 This study by Ma et al. was a prospective randomised controlled trial comparing the effect of synchronised intermittent mandatory ventilation (SIMV) with heliox for 6 h followed by SIMV with air– oxygen mixture versus SIMV with air– oxygen mixture alone on the length of mechanical ventilation in infants with meconium aspiration syndrome. The heliox group received ventilation with helium– oxygen mixture, the concentration of oxygen was adjusted to maintain the target saturation. It is not clear what was the concentration of helium that was used for each baby. As the therapeutic effect of heliox depends on the concentration of the helium in the gas mixture, the therapeutic effect is likely to diminish with increasing oxygen requirement. The study showed significant reduction in length of mechanical ventilation, length of hospital stay and better oxygenation in babies treated with heliox. PaO2, pH and PaCO2 measured at 2, 6, 12, 24 and 48 h were significantly better in the group treated with heliox. In keeping with the current guidance, lower target saturation levels were used. However, no information on baseline ventilatory requirements and oxygenation was provided. There is only one previous small study on 8 neonates with meconium aspiration syndrome. SIMV with heliox for 1 h allowed the use of significantly lower FiO2, and increase in the PaO2/FiO2 ratio but no significant difference in oxygenation index.5 In this study, length of mechanical ventilation was not reported. PaO2/FiO2 was used as a measure of oxygenation. As there was wide range of ventilatory pressure used in different infants, oxygenation index would have better reflected the ventilatory requirement.