Heliox

Indications

Airway Obstruction

Acute Bronchiolitis (see Bronchiolitis, [[Bronchiolitis]])

  • Clinical Efficacy
    • Unclear Clinical Benefit

Asthma Exacerbation (see Asthma, [[Asthma]])

  • Clinical Efficacy
    • 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

Chronic Obstructive Pulmonary Disease (COPD) Exacerbation (see Chronic Obstructive Pulmonary Disease, [[Chronic Obstructive Pulmonary Disease]])

  • Clinical Efficacy
    • 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
      • Trial Stopped for Futility

Upper Airway Obstruction (see Obstructive Lung Disease, [[Obstructive Lung Disease]])

  • Clinical Scenarios
    • Post-Extubation Stridor
  • Clinical Efficacy
    • Unclear Clinical Benefit

Contraindications

  • 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

  • xxxx

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]