Heliox improves pulmonary mechanics in a pediatric porcine model of induced severe bronchospasm and independent lung mechanical ventilation

Abstract

Background: A helium-oxygen gas mixture (heliox) has low gas density and low turbulence and resistance through narrowed airways. The effects of heliox on pulmonary mechanics following severe methacholine-induced bronchospasm were investigated and compared to those of a nitrogen-oxygen gas mixture (nitrox) in an innovative pediatric porcine, independent lung, mechanical ventilation model. Results:All of the lungs showed evidence of severe bronchospasm after methacholine challenge. Prospective definition of 'heliox response' was a 15% or greater improvement in lung function in the lung receiving heliox compared with the matched lung receiving nitrox. Seven out of 10 pigs responded to heliox therapy with respect to resistance and eight out of 10 pigs responded to heliox therapy with respect to compliance and tidal volume (P < 0.03). After crossover from nitrox to heliox, eight out of eight lungs significantly improved with respect to tidal volume, resistance and compliance (P < 0.001). After crossover from heliox to nitrox all eight lungs showed a significant increase in resistance and a significant decrease in tidal volume (P < 0.001). Conclusions:In a pediatric porcine model of acute, severe methacholineinduced bronchospasm and independent lung mechanical ventilation, administration of heliox improves pulmonary mechanics, gas flow, and ventilation. Administration of heliox should be considered for support of pediatric patients with acute, severe bronchospasm requiring mechanical ventilation through small artificial airways.

Helium Administration is More Effective during Piston-Driven High-Frequency Oscillatory Ventilation than during Conventional Mechanical Ventilation: A Study with Rabbit Model

“…The combination of CMV and helium-oxygen mixture has been used in several clinical scenarios [8][9][10] . In animal models, this combination therapy also showed improvements in lung mechanics, gas flow, and ventilation 6) . The combination of HFOV and helium-oxygen mixture has also been used in several clinical settings 5,11) .…”

“…Helium is a biologically inert gas with very low molecular weight and density 1) . There are two advantages on helium administration during mechanical ventilation, such as reducing airway resistance and improving diffusion coefficient of carbon dioxide (CO 2 ) [1][2][3][4][5][6] .…”

“…For constant airway length and thickness, turbulent flow results in greater resistance than laminar flow. Flow patterns can be predicted by the dimensionless Reynolds number, which is measured by the product of gas velocity, airway diameter, and gas density divided by viscosity 6) . Though helium has significantly lower density than air or nitrogen, the viscosity of helium is not markedly different from that of nitrogen 1) (Table 1).…”

Extremely low flow tracheal gas insufflation of helium-oxygen mixture improves gas exchange in a rabbit model of piston-type high-frequency oscillatory ventilation

“…For a given set of airway dimensions, turbulent flow results in a higher resistance than laminar flow. In addition, mechanical ventilation through a narrow ETT and airway, particularly in pediatric and neonatal patients, may further increase the Reynolds number, thus resulting in greater turbulent flow [15,16]. With helium, the calculated Reynolds number is lower (<200), which may change regions of turbulent flow to laminar flow, reducing resistance and energy leakage.…”

Effects of heliox as carrier gas on ventilation and oxygenation in an animal model of piston-type HFOV: a crossover experimental study

“…For a given set of airway dimensions, turbulent flow results in a higher resistance than laminar flow. In addition, mechanical ventilation through a narrow ETT and airway, particularly in pediatric and neonatal patients, may further increase the Reynolds number and thus increase turbulent flow [ 13 , 14 ]. Therefore, with heliox, the calculated Reynolds number is lower, which may change regions of turbulent flow to laminar flow, reducing resistance and energy loss.…”