Systematic Review of Heliox-Driven Nebulized Bronchodilators in Asthma (Ann Allergy Asthma Immunol, 2014) [MEDLINE]
Heliox-Driven Nebulized Bronchodilator Resulted in a 17.2% Improvement in Peak Flow, as Compared to Nebulized Bronchodilator Oxygen-Driven Delivery: greatest improvements were observed in most severe subset of patients (those with peak expiratory flow <50% predicted)
Heliox-Driven Nebulized Bronchodilator Resulted in Decreased Hospital Admission Rates, as Compared to Oxygen-Driven Nebulized Bronchodilator Delivery
Systematic Review of Heliox in Ashtma Exacerbation (Chest, 2003) [MEDLINE]
No Clinical Benefit: although conclusions were based on between-group comparisons and small studies -> results should be interpreted with caution
ECHO ICU Trial (Intensive Care Med Exp, 2015): randomized multi-center trial of heliox x 72 hrs versus air–oxygen with non-invasive ventilation in severe hypercapnic COPD exacerbation
Severe Hypoxemia (see Hypoxemia, [[Hypoxemia]]): heliox use is limited to patients without significant hypoxemia (due to the predominance of helium in the mixture)
As the Percentage of Oxygen Increases in a Heliox Mixture, the Percentage of Helium Decreases -> Gas Density Increases (Negating the Effects of the Lower Density of Helium)
Pharmacology
Chemical Properties of Helium
Helium is a Non-Toxic Noble Gas: inert and does not interact with living tissues
Density: 0.18 g/m3 (which is much lower than the density of oxygen)
Heliox
Heliox is a Mixture of Helium:Oxygen
80:20 Mixture
70:30 Mixture
Heliox Converts Turbulent Flow to Laminar Flow
In Turbulent Conditions, Heliox Decreases the Driving Pressure Necessary for a Given Flow (or Increases the Flow for a Given Driving Pressure)
Greatest Proportion of Increase in Flow with Heliox Occurs at a 40% Helium Concentration: however, increasing the helium concentrations up to 80% will lead to a further linear increase in flow
Heliox Decreases Airway Resistance
Heliox Increases Penetration of Aerosolized Drugs into Distal Airways
Heliox Improves V/Q Matching
Heliox Enhances CO2 Excretion in the Lung: CO2 diffuses 4-5x faster through a mixture of helium and oxygen than through a mixture of nitrogen and oxygen -> a greater amount of CO2 can be eliminated per unit time for the same partial pressure of CO2
In Distal Airways (Where Flow is Laminar), Heliox Has Increased Viscosity, as Compared to Nitrogen: this increases resistance in distal airways
This fact may explain the unclear benefit of heliox in conditions affecting the distal airways
Physiologic Effects of Heliox
Decreased Airway Resistance with Decreased Work of Breathing
Decreased Auto-PEEP
Decreased Hyperinflation
Decreased pCO2: due to enhanced CO2 diffusion, increased alveolar ventilation, and/or decreased CO2 production (associated with decreased work of breathing)
Heliox Effects on Delivery of Nebulized Bronchodilators
When Using Nebulizers with Heliox, Particle Size and Inhaled Mass of Albuterol Significantly Decrease
In order to achieve drug delivery comparable to air, one must increase the concentration of drug or increase the flow of helium
Although nebulizer performance is affected when it is powered by heliox, the clinical implications remain to be determined
However, correction factors have been developed that can be applied when using heliox during mechanical ventilation
Administration
40% helium + 60% oxygen: indicated for hypoxemic patients
79% helium + 21% oxygen: indicated for patients with upper airway obstructing lesions without hypoxemia
Adverse Effects
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References
Quantitative effects of respired helium and oxygen mixtures on gas flow using conventional oxygen masks. Anaesthesia 1983; 38:879-882 [MEDLINE]
Effect of helium concentration on experimental upper airway obstruction. Ann Otol Rhinol Laryngol 1990: 99:556-561 [MEDLINE]
Helium-oxygen mixture in the treatment of postextubation stridor in pediatric trauma patients. Crit Care Med 1991; 19:356-359 [MEDLINE]
Helium-oxygen improves clinical asthma scores in children with acute bronchiolitis. Crit Care Med 1998; 26:1731-1736 [MEDLINE]
The effect of Heliox in acute severe asthma: a randomized controlled trial. Chest 1999; 116:296-300 [MEDLINE]
Beneficial effects of helium:oxygen versus air:oxygen noninvasive pressure support in patients with decompensated chronic obstructive pulmonary disease. Crit Care Med 1999; 27:2422-2429 [MEDLINE]
The effect of Heliox on nebulizer function using a β-agonist bronchodilator. Chest 1999; 115:184-189 [MEDLINE]
Calibration of seven ICU ventilators for mechanical ventilation with helium-oxygen mixtures. Am J Respir Crit Care Med 1999; 160:22-32 [MEDLINE]
Use of helium-oxygen mixtures in the treatment of acute asthma: a systematic review. Chest. 2003 Mar;123(3):891-6 [MEDLINE]
Heliox-driven beta2-agonists nebulization for children and adults with acute asthma: a systematic review with meta-analysis. Ann Allergy Asthma Immunol 2014; 112: 29–34 [MEDLINE]
An international phase III randomized trial on the efficacy of helium/oxygen during spontaneous breathing and intermittent non-invasive ventilation for severe exacerbations of chronic obstructive pulmonary disease (The ECHO ICU Trial). Intensive Care Med Exp 2015; 3 (suppl 1): A422 (Poster)
High-flow oxygen therapy and other inhaled therapies in intensive care units. Lancet. 2016 Apr 30;387(10030):1867-78. doi: 10.1016/S0140-6736(16)30245-8. Epub 2016 Apr 28 [MEDLINE]
