August 2025
INTRODUCTION —
Helium is an inert gas that is lower in density than nitrogen and oxygen and second only to hydrogen in abundance in the universe. However, it is quite rare in the atmosphere, comprising less than a thousandth of a percent of all gases. Worldwide helium stores are depleting, and there is a need for its increased production. Although the need for heliox is relatively small, it is essential for other medical applications such as cooling of MRI equipment. In 1934, Barach first described the airway physiology of breathing heliox and advocated for its use in a variety of diseases [1]. Although heliox has been revisited over the years as a potential therapeutic option for a variety of upper and lower airway conditions, the overall strength of evidence for its use remains low.
The physiology and clinical applications of helium-oxygen mixtures in patients with pulmonary disease will be reviewed here. The general management of central airway obstruction is discussed separately. (See "Clinical presentation, diagnostic evaluation, and management of malignant central airway obstruction in adults".)
FLUID DYNAMICS —
Therapeutic interventions to improve ventilation often aim to increase compliance (ie, decrease lung elasticity/stiffness), decrease airway resistance, or both. To decrease resistance to airflow, bronchodilators, glucocorticoids, and airway clearance are used to increase airway caliber. Another potential method to improve airflow is to decrease the density of the inhaled gas. While the density and viscosity of oxygen, nitrogen, and air are very similar (table 1), substituting helium, a low-density gas, for nitrogen changes the physical properties of the inhaled gas. This underlies the theoretical rationale for the clinical application of heliox. By decreasing gas density, the pressure (work) required for flow can be decreased in the absence of any anatomical change. The following discussion describes the physiology of the effect of gas density on airflow.
●Fluid characteristics of laminar versus turbulent flow – The principles of fluid dynamics in the lungs are complex and described here in the context of gas properties and heliox [2]. Laminar flow is characterized by streamlines parallel to the sides of the airway, with gas in the center of the airway moving more rapidly than at the edge. Turbulent flow typically occurs at branch points, sharp angles, and at changes in tube (airway) diameter (figure 1).
For turbulent flow, the pressure required is determined by:
∆P= ρlV24πr5
where ΔP is the pressure gradient, ρ is density, l is length, V is flow, and r is radius.
For laminar flow, the relationship is:
∆P= 8ηlVr4
where η is viscosity.
Laminar flow is more efficient than turbulent flow, meaning the pressure (work) required is less for laminar flow. Thus, laminar flow is desirable.
●Determinants of laminar versus turbulent flow in a tube – Whether flow is laminar or turbulent through a tube is determined by the Reynolds number (Re):
Re ≈ inertial forces/viscous forces ≈ (vrρ)/η
where v is gas velocity. Laminar flow predominates when Re is <2000, and turbulent flow predominates when Re is >4000. The lower density of heliox relative to nitrogen-oxygen mixtures (helium is one-tenth the density of air) decreases Re and increases the likelihood that the flow will be laminar (table 1).
The entrance length (EL) of a tube (airway) is the distance from the beginning of the tube that is needed for laminar flow to become established (figure 2):
EL = 0.03 x d x Re
When Re is low, not only is there a tendency for laminar flow, but it will be established more quickly after changes in airway caliber [2]. When there are frequent branch points (eg, in the airways), EL may be longer than the length of an airway, which inhibits laminar flow. This effect is ameliorated by reducing gas density with heliox.
Note that the work required (∆P) for laminar flow is viscosity dependent, not density dependent. Heliox has a slightly higher viscosity than air that negatively affects the required pressure in laminar conditions. Thus, the benefit for heliox is in converting turbulent flow to laminar flow; there is no benefit to use of heliox if flow is already laminar.
●Determinants of flow through an orifice (constriction) – For gas flow through an orifice (eg, axial acceleration), flow has only a weak dependence on the Reynolds number and is affected by density as follows:
V2= ∆Pρ
In other words, flow through an orifice (eg, constricted airway) will increase if the density of the gas decreases (eg, heliox). Graham’s law states that the rate of diffusion is inversely related to the square root of gas density. Thus, heliox (80 percent He/20 percent O2) will diffuse at a rate 1.8 times faster than oxygen.
●In vivo physiology – In normal lungs, most resistance is due to the large airways; overall resistance is lower in the small airways due to the large total cross-sectional area (figure 3). Flow is primarily turbulent from the trachea to the bronchioles, particularly when flow is high. Heliox reduces the pressure (work) requirement for turbulent flow, which is density dependent [3,4]. Flow through peripheral airways is laminar and thus is less likely to be affected by the low density of heliox. However, there might be some benefit due to axial acceleration and diffusion. The complexity of physical principles describing the effects of breathing heliox makes difficult the prediction of which patients might benefit from this therapy.
CLINICAL APPLICATIONS —
The potential use of helium has been explored in a variety of disease processes characterized by airflow limitation. The aim of therapeutic heliox is to capitalize on the physical properties of the gas to improve airflow and decrease work of breathing, as predicted by the fluid dynamic paradigm described above. As an inert gas, heliox has no pharmacologic properties. There are no evidence-based guidelines regarding the use of heliox. Despite the absence of guidelines, a therapeutic trial of heliox may be reasonable in clinical situations associated with marked airway narrowing in which a temporizing therapy may provide a bridge to more definitive treatment [4].
The energy expenditure (pressure) required to overcome airflow resistance is negligible during resting ventilation in the normal lung. Thus, the physical properties of the inspired gas do not ordinarily play a significant role in determining the work of breathing or in limiting ventilation. However, with alterations in airway geometry, particularly during excessive ventilatory demand, the resistive work of breathing can become sufficiently elevated to limit ventilation and cause respiratory muscle fatigue. Under these circumstances, decreasing the density of the inhaled gas with heliox should decrease the applied force required to achieve a given flow rate and, thereby, reduce the work of breathing.
Most clinical trials of heliox have enrolled fewer than thirty patients, as heliox is generally initiated in emergent situations that may preclude clinical trial enrollment. Inclusion criteria and clinical outcomes are not standardized across studies, making direct comparisons difficult. Furthermore, many patients (eg, asthma, bronchiolitis, COPD) are treated with multiple interventions simultaneously. With these limitations in mind, the following is a brief review of clinical trials of heliox therapy in both pediatric and adult patient populations.
Use in children — Children have smaller airways than adults and are more commonly affected by diseases that cause upper airway obstruction. There have been several reports describing the use of heliox in pediatric populations, although clear demonstration of clinically important benefits is lacking:
●Upper airway obstruction – Heliox is not a part of standard therapy for upper airway obstruction in children. However, a few cases have been described in which heliox was used as a temporizing measure while awaiting definitive management [5-7]. In the largest case series, 42 pediatric patients received a total of 44 heliox treatments with a positive response in 32 interventions [7]. The most common cause of upper airway obstruction was postextubation edema (29 patients); other causes included laryngomalacia, laryngotracheal stenosis, vocal cord paralysis, airway hemangioma, mucositis, and foreign body. The article did not specify whether responders had postextubation stridor or another diagnosis, nor was heliox compared against other therapies. The evaluation and management of upper airway obstruction in children is described separately. (See "Emergency evaluation of acute upper airway obstruction in children".)
●Postextubation stridor – Data are insufficient to support a role for heliox in the management of postextubation stridor in children. While a clinical trial found a reduction in respiratory distress with heliox and a case series suggested that heliox helped with avoidance of reintubation, no large clinical trials have been reported. In the case series of children with upper airway obstruction described above, heliox was thought to be beneficial in 20 of 29 children with postextubation airway edema, but it is unknown how much heliox added to traditional measures [7]. (See "Extubation management in the adult intensive care unit", section on 'Postextubation management'.)
●Croup – Some studies of heliox for moderate to severe croup have shown a modest short-term benefit, although data are mixed. A more detailed discussion of the use of heliox in croup can be found separately. (See "Croup: Management", section on 'Respiratory care'.)
●Bronchiolitis – Heliox is not associated with clinically significant benefit in bronchiolitis in infants and children. The use of heliox in bronchiolitis is discussed separately. (See "Bronchiolitis in infants and children: Treatment, outcome, and prevention", section on 'Therapies of unproven or uncertain benefit'.)
●Asthma – Heliox has questionable efficacy in critically ill patients with asthma, and its use has been declining over time [8]. If desired, it can be delivered via high-flow nasal canula, nonrebreathing mask, or aerosol mask, although the ideal delivery method is unknown [9]. Results of a retrospective cohort study using data from 97 PICUs among children 3 to 17 years of age reported that heliox as adjunctive therapy for children with critical asthma was uncommon (2.5 percent) and not associated with either mechanical ventilation or decreased mechanical ventilation duration in adjusted models [10].
A systematic review pooled and analyzed results from ten trials enrolling over 500 patients with acute asthma [11]. Studies included both adult and pediatric populations. No significant improvement in recovery of pulmonary function or in hospital admission were identified. A separate analysis using the same data noted a possible improvement in hospital admissions in the pediatric population alone based on two trials of 71 total patients (RR 0.69, 95% CI 0.48-0.99) [12]. Publication bias was likely to be present in this analysis.
However, the above studies focused on the use of heliox as a form of adjunct therapy. Three subsequent randomized trials evaluating the efficacy of heliox to deliver nebulized albuterol demonstrated mixed results [13-15]. In a meta-analysis that included these studies (584 adults, 113 children), the use of heliox to deliver the nebulizers was associated with a significant improvement in peak expiratory flow and hospital admissions [16]. (See 'Use in adults' below.)
●Respiratory distress syndrome – Respiratory distress syndrome (RDS) is a major cause of respiratory distress in preterm infants. In RDS, insufficient surfactant leads to alveolar atelectasis and hypoxemia. One older randomized trial assessed the effect of heliox versus air in infants requiring mechanical ventilation for RDS and did not find a significant clinical benefit [17]. Notably, this study was published prior to widespread use of surfactant replacement therapy and inhaled nitric oxide. A subsequent systematic review and meta-analysis assessed the effects of heliox with noninvasive ventilation (NIV) in preterm infants with RDS in the modern era [18]. It included two RCTs and one quasi-randomized controlled trial with a total of 123 neonates. Heliox with NIV significantly decreased the incidence of intubation (RR 0.42; 95% CI: 0.23–0.78). Its use was also associated with a reduction in PaCO2 and less frequent surfactant administration. Regardless, it seems that heliox is used infrequently in this patient population. Neonatal RDS is predominantly a parenchymal disease, not an airway disease, and therapy is focused on maintenance of alveolar stability with surfactant administration and application of continuous positive airway pressure. (See "Respiratory distress syndrome (RDS) in preterm neonates: Clinical features and diagnosis" and "Respiratory distress syndrome (RDS) in preterm neonates: Management".)
●Bronchopulmonary dysplasia – Bronchopulmonary dysplasia (BPD) is a disease of premature infants that is sometimes associated with increased airway resistance. Heliox is not part of standard care for BPD. However, in a case series of premature infants with BPD who required mechanical ventilation, heliox resulted in improved oxygenation and increased tidal volume, although outcomes such as ventilator liberation were not reported [19]. (See "Bronchopulmonary dysplasia (BPD): Management and outcome".)
●Meconium aspiration syndrome – Meconium aspiration syndrome (MAS) is a form of acute respiratory distress caused by fetal aspiration of amniotic fluid containing meconium. In a nonblinded trial, 71 neonates with MAS were randomly assigned to mechanical ventilation with heliox or oxygen-air for six hours; oxygen was titrated to a target pulse oxygen saturation of 90 to 95 percent. The PaO2/FiO2 was significantly higher with heliox (301±22 versus 261±25), and time to extubation was shorter (78±30 versus 114±28.07 hours) [20]. Additional studies would be needed before implementing the use of heliox in such patients.
Use in adults — The greatest theoretical benefit of heliox is achieved by decreasing turbulent flow in large airways and at branch points in the tracheobronchial tree. Thus, patients with upper airway obstruction would be expected to derive the greatest benefit from heliox therapy. However, because upper airway compromise is relatively rare and often a medical emergency, few controlled studies of heliox treatment in this setting have been published. For this reason, study of the use of heliox in adults has primarily focused on treating patients with severe asthma and chronic obstructive pulmonary disease (COPD), in which benefit of heliox remains unclear.
●Upper airway obstruction – Upper airway obstruction has been a common indication for heliox [3,21]. However, no controlled trials have been performed in this setting. In some patients, the immediate improvement is dramatic. However, it should be remembered that heliox has no pharmacologic properties and thus definitive treatments must be continued; heliox treats the symptoms rather than the cause of the obstruction.
●Asthma – While a few case series have suggested a beneficial effect of heliox in acute asthma, no studies in adults have demonstrated an advantage of heliox above and beyond standard oxygen therapy. Thus, the routine use of heliox has not been indicated in acute asthma.
•Asthma exacerbations without intubation – A Cochrane systematic review pooled and analyzed results from 10 trials enrolling over 500 patients (both children and adults) found no significant improvement in recovery of pulmonary function in patients who were treated with heliox [11]. Furthermore, no significant difference in outcome was noted when adults were analyzed separately, or when high versus low concentrations of helium were compared. Other systematic reviews have reached the same conclusions [22]. The low certainty of evidence regarding the benefit for heliox in this setting is reflected in the declining use of this therapy. (See 'Use in children' above.)
•Asthma complicated by respiratory failure – Heliox has not demonstrated consistent benefit in patients with respiratory failure due to asthma. In a single-center, prospective observational study which enrolled 13 subjects undergoing mechanical ventilation for severe asthma (n = 8) or exacerbation of COPD (n = 5), heliox was administered at a concentration of 65 to 70 percent [23]. With heliox, there was a small reduction in peak inspiratory pressure (54±13 versus 48±11 cm H2O) and PaCO2 (64±15 versus 62±15 mmHg), but there was no significant change in plateau pressure or dynamic hyperinflation (auto-PEEP).
•Heliox as the driving gas for nebulizer treatments – A meta-analysis of eleven randomized trials evaluated the efficacy of heliox as the driver for beta-agonist nebulizers in adults and children presenting with acute asthma exacerbations [16]. Seven studies included 584 adults, and helium-oxygen mixtures of 80:20, 79:21, and 70:30 were used. Heliox was associated with a significantly higher change in peak expiratory flow (seven studies, 505 patients; mean improvement difference compared with oxygen nebulizers 17 percent, 95% CI 5-29 percent), and a post hoc subgroup analysis demonstrated that this improvement was greatest in patients with the most severe disease (PEF <50 percent predicted). Furthermore, the use of heliox to drive nebulizers was associated with a lower rate of hospital admission (seven studies, 445 patients; admission rate 26 versus 34 percent, RR 0.77, 95% CI 0.62-0.98).
A study not included in the meta-analysis administered nebulized albuterol driven by heliox or air to 132 subjects with asthma of varying baseline severity [24]. The proportion of patients experiencing a greater than 12 percent or 200 mL increase in FEV1 30 minutes after treatment was significantly higher in the heliox group, though only in the subset of patients with a baseline FEV1 less than 50 percent predicted.
●Stable COPD – Whether heliox is of benefit to patients with stable COPD remains unclear. Based on small studies, heliox is associated with improvements in some physiologic outcomes, but only modest improvement in clinically important outcomes, such as exercise tolerance [25-30]. The technical aspects and cost of heliox delivery for patients with stable COPD are significant, and this remains an important consideration for this large group of patients. Additional studies are needed to determine if the use of heliox and the associated additional expense are justified. (See 'Cost and availability' below.)
Examples of some of the larger trials include:
•In a randomized, crossover trial, 82 patients with moderate to severe COPD had their exercise performance and dyspnea evaluated while receiving one of four different gases: Heliox28 (72:28), Heliox21 (79:21), Oxygen28 (72 percent nitrogen:28 percent oxygen), or medical air (79 percent nitrogen:21 percent oxygen) [26]. Patients breathing Heliox28 had better exercise performance and less dyspnea than all other groups, with the largest improvements in those most severely obstructed. Exercise performance and dyspnea were improved with all gases when compared with medical air. In a separate study of 12 patients with severe COPD (mean FEV1 45 percent predicted), the use of heliox (79 percent nitrogen:21 percent oxygen) during exercise decreased dynamic hyperinflation, improved exercise tolerance, and improved lower-extremity oxygen delivery and utilization [27].
•In a separate study, the impact of heliox on pulmonary function during cardiopulmonary exercise testing was assessed in 10 patients with mild COPD. Heliox was associated with an increase in minute ventilation without any change in work of breathing [28].
•In a randomized trial of 30 patients with moderate-to-severe COPD, subjects underwent an exercise program for two months by conducting leg-cycle training three days a week while breathing either room air, 40 percent supplemental oxygen, or a 60:40 helium-oxygen mixture. There was no difference between groups with regards to the increase in power output achieved, peak workload, or total endurance time [29].
•In a subsequent randomized, crossover study of 11 patients with GOLD stage II or III COPD, subjects exercised to achieve 80 percent of their predetermined maximal work rate while breathing either room air or a 79:21 heliox mixture [30]. The use of heliox was associated with a significant reduction in Borg ratings for both dyspnea and leg discomfort, in addition to a reduction in end-expiratory lung volume and hyperinflation.
●COPD exacerbation – Heliox has not demonstrated consistent benefit in patients with respiratory failure due to COPD, whether during mechanical ventilation [23] or noninvasive ventilation (NIV) [31-36]. Several studies have compared NIV with either air or heliox in patients with exacerbations of chronic obstructive pulmonary disease. Taken together, the data show that the addition of heliox to NIV decreases respiratory effort and intrinsic positive end expiratory pressure (PEEP), but does not improve outcomes such as requirement for intubation or mortality [31-36]. As an example, in a large, multicenter trial, 204 patients presenting with an acute exacerbation of COPD were randomly assigned to NIV with or without heliox [35]. Intubation rate, 28-day mortality, and dyspnea did not differ significantly between the groups, suggesting that the combination of NIV plus heliox was not superior to NIV alone. Perhaps these results are not surprising given that COPD is a disease of small airways, flow through small airways is laminar, and laminar flow is density independent [37]. (See 'Fluid dynamics' above.)
The use of NIV for COPD exacerbations is discussed in detail elsewhere. (See "Noninvasive ventilation in adults with acute respiratory failure: Benefits and contraindications".)
Additionally, a randomized, open-label trial evaluated the utility of noninvasive ventilation using either heliox or oxygen in patients hospitalized with severe hypercapnic COPD exacerbations [36]. After 445 patients were randomized, the trial was stopped prematurely because of the low overall rate of NIV failure (14.7 versus 14.5 percent), which was the primary outcome. In the 85 percent of people successfully treated with NIV, duration of NIV, length of ICU stay, and length of hospital stay were nearly identical; there were no significant differences in mortality. The heliox group demonstrated a faster improvement in the secondary outcomes of respiratory rate, pH, PaCO2 and encephalopathy score. In patients requiring intubation, those receiving heliox had significantly shorter duration of ventilation and length of ICU stay. However, there was no significant difference in the rate of NIV failure, time to noninvasive ventilation failure, ICU mortality, or six-month mortality.
●Postextubation dyspnea – In a study focusing on physiologic rather than clinical endpoints, researchers evaluated recently extubated patients without significant lung disease to quantify intrathoracic pressure swings and estimate the work of breathing [38]. Fifteen of 18 patients exhibited a decrease in work of breathing with heliox, although gas exchange parameters were unchanged. Additionally, patients reported decreased dyspnea while breathing heliox.
●Lung-protective mechanical ventilation – The effect of heliox on carbon dioxide elimination during lung protective ventilation was evaluated in an observational study including 24 patients ventilated with a pressure control mode following a cardiac arrest. Tidal volume was maintained (6 mL/kg) and rates were targeted to maintain prespecified pH and PaCO2 ranges. Following three hours of ventilation with a heliox (50:50) mixture, a decrease in both respiratory rate and PaCO2 levels was noted [39]. However, there was no control group, and only one of the patients enrolled had an underlying pulmonary condition (COPD). As such, additional studies are needed to determine if heliox is useful in patients intubated for primary respiratory failure.
Pulmonary function testing — Helium gas is used in pulmonary function testing to measure lung volumes by gas dilution. This application is not based on low density, but on the fact that helium is inert and has low solubility in blood. The measurement of lung volume by the inert gas dilution technique is performed routinely in pulmonary function laboratories. In the past, heliox was used to assess the presence of small airways disease. Patients performed forced expiratory flow-volume curves breathing heliox or air, and the curves were superimposed. The greater the overlap in flows at low lung volume, the greater the presence of small airways disease (helium volume of isoflow). The test takes advantage of the fact that gas flow through small airways is laminar, and laminar flow is not affected by the density of the gas [40,41]. (See "Overview of pulmonary function testing in adults", section on 'Lung volumes'.)
TECHNICAL ISSUES
Optimizing helium-oxygen ratio — The optimal helium-oxygen ratio is not known, although most protocols employ a mixture that includes 70 to 80 percent helium and 30 to 20 percent oxygen. If 30 percent oxygen is insufficient to correct hypoxemia, a mixture of 40 percent oxygen with 60 percent helium may provide sufficient oxygen without sacrificing airflow [42]. However, increases in the oxygen fraction diminish the beneficial effect of using a low-density gas. Because heliox is used for treatment of airflow obstruction, a high inspired oxygen fraction is typically not necessary. Due to the risk of administering a hypoxic gas mixture, the source gas should be heliox (eg, 80 percent helium/20 percent oxygen) and never pure helium mixed with oxygen. The 80/20 gas mixture can be used with titration of oxygen to achieve the desired inspired oxygen concentration. Downstream oxygen concentration is measured, and it is assumed that helium is the remaining concentration. This is like mixing air and oxygen for the desired oxygen concentration. Because helium is inert, it does not affect the performance of electrochemical oxygen analyzers that are typically used clinically.
To be clinically effective, heliox must be delivered in a manner that minimizes air entrainment. This can be with a well-fitted nonrebreather mask or by high-flow nasal cannula.
Aerosol delivery — The effect of heliox on airflow in the lungs makes it an attractive carrier gas for aerosol delivery [43]. Heliox affects the delivery of medications that are administered via jet nebulizers; nebulization time may be prolonged and particle size of nebulized medications decreased. Some of these effects can be offset by increasing the heliox flow. Alternatively, a mesh nebulizer can be used as an alternative to the jet nebulizer because its performance is not affected heliox. Clinical trials designed to take advantage of improved medication delivery in asthma and COPD have yielded mixed results [44-46]. (See 'Clinical applications' above and "Delivery of inhaled medication in adults", section on 'Factors affecting drug delivery' and "Delivery of inhaled medication in adults", section on 'Metered dose inhaler'.)
For a given flow, the use of heliox as a driving gas (instead of compressed air) results in a lower pressure drop across the jet nebulizer orifice. This causes a lower inhaled mass of medication or longer nebulization time to deliver the same amount of drug [47]. To compensate, the flow should be increased by approximately 50 percent [47,48]. To understand the effects of heliox on nebulizer function and aerosol delivery, it is important to consider that nebulizers use Bernoulli's principle to generate an aerosol. Mathematically, this can be described by the equation:
(P1-P2) = 0.5 x m x (v22 - v12)
where P1-P2 is the pressure drop across the nebulizer orifice, m is the mass of the gas, and (v22 - v12) reflects the change in velocity of the gas across the orifice [47]. On the other hand, heliox can decrease the particle size of the nebulized solution, which may enhance drug delivery to the lower airways. This hypothesis has been evaluated in several studies examining lung deposition of heliox-driven aerosols in humans. In one report, nine participants with stable asthma inhaled radiolabeled Teflon particles suspended in either air or heliox [49]. Heliox inhalation resulted in significantly lower oral deposition as well as higher particle retention in the lungs at 24 hours. Another report found a similar increase in lung deposition in patients with induced bronchoconstriction who received heliox-driven nebulized therapy [50]. In contrast, a study involving 32 participants with stable moderate-to-severe asthma found that deposition of radiolabeled bronchodilators to the middle and lower lung fields was enhanced with the addition of positive expiratory pressure; however, there was no significant difference in deposition between the oxygen and heliox groups [51].
Device accuracy — Graham's law states that the flow of gas through an orifice is inversely proportional to the square root of its density. Thus, the actual flow of heliox through an oxygen flow meter is 1.8 times greater than the indicated flow [48].
Some pneumotachometers, such as those in mechanical ventilators, are inaccurate when used with heliox. Pneumotachometers that use a hot wire flow sensor are particularly affected due to the high thermal conductivity of helium (table 1). Several ventilators are equipped for heliox delivery, such as many Hamilton, Servo, and Avea models [52,53].
The lack of a clearly defined calibration scheme for pneumotachometers has been raised as a possible confounder in many of the studies investigating the role of heliox in acute asthma [54]. It is possible, particularly in studies where peak expiratory flow (PEF) improved in the absence of a clear change in the forced expiratory volume in one second (FEV1), that much of this effect might be due to inaccurate sensing of low-density gas flow rates [55].
Cost and availability — Helium-oxygen mixtures are usually supplied in H cylinders (159 cubic feet) in ratios of 80:20, 70:30, or 60:40. They can also be supplied in smaller E cylinders, but the usage time is short for these. The cost of heliox is greater than that of oxygen. With flows of 12 to 15 L/min, three to six of these cylinders may be used each day in nonintubated patients [48], and approximately three tanks per day in patients receiving mechanical ventilation [32]. With higher flows (eg, high-flow nasal cannula), even more gas is required. A low-pressure heliox-based rebreather system has been described to conserve gas. Although the demand for heliox is relatively small, helium is essential for other medical applications such as cooling of MRI equipment, and helium stores are depleting worldwide.
Medical staff should be familiar with the use of medical gas cylinders, as cylinders containing oxygen, heliox, or other medical gases may appear identical. In North America, physicians need to work with their respiratory therapy colleagues for safe and effective use of heliox.
SOCIETY GUIDELINE LINKS —
Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Supplemental oxygen".)
SUMMARY AND RECOMMENDATIONS
●Physiologic basis – Helium is an inert, low-density gas; heliox is a mixture of helium (usually 70 to 80 percent) and oxygen (usually 20 to 30 percent). The potential therapeutic effects of heliox relate to its low density and its propensity towards laminar airflow. The reduction in turbulent flow acts to decrease the pressure requirements, pleural pressures swings, and dynamic hyperinflation. These factors may reduce the work of breathing in some patients. (See 'Fluid dynamics' above.)
●Clinical applications – There are no evidence-based guidelines regarding the use of heliox. Rarely, heliox may be reasonable in clinical situations associated with marked airway narrowing in which a temporizing therapy may provide a bridge to definitive treatment. (See 'Clinical applications' above.)
●Potential use cases – Data are insufficient to recommend heliox for the routine management of postextubation stridor, croup, bronchiolitis in children, respiratory distress syndrome of the neonate, asthma, or chronic obstructive pulmonary disease (COPD). For children with severe respiratory symptoms due to croup who are at risk for respiratory failure, heliox may be tried in an attempt to avoid the need for intubation. Rarely, in patients with a severe asthma exacerbation that is associated with hypercapnia and dyspnea despite maximal other therapy, heliox may improve ventilation while waiting for response to other therapies. Even more rarely, heliox might be used in mechanically ventilated patients with severe asthma or COPD. (See 'Clinical applications' above.)
●Assessing impact – The effects of heliox are typically seen within several minutes, so the patient and clinician can often assess its therapeutic efficacy quite quickly. We guide therapy based on serial clinical assessment, since the measurement of common indices of pulmonary status (eg, peak expiratory flow and forced expiratory volume in one second [FEV1]) may be inaccurate unless instruments are calibrated for use with heliox. Careful attention is given to respiratory rate, accessory muscle use, pulsus paradoxus, air entry, and the patient's subjective sense of dyspnea. (See 'Clinical applications' above.)
●Technical issues – Standard medical equipment is calibrated for air-oxygen mixtures, so several issues arise when using high concentrations of helium instead.
•The optimal helium-oxygen ratio is not known, although most protocols employ helium-to-oxygen ratios of 80:20 or 70:30. Treatment with the highest helium ratio that will maintain SpO2 above 90 percent is suggested, since the benefits of heliox are proportional to the percentage of helium in the inhaled gas. An important limitation of heliox is the low fractional concentration of inspired oxygen (FiO2) in the gas mixture, which may not be adequate for patients with hypoxemia. (See 'Optimizing helium-oxygen ratio' above.)
•The use of heliox during mechanical ventilation requires appropriate calibration of the ventilator and meticulous respiratory monitoring due to the variable effect of heliox on ventilator performance. The use of heliox in this setting should be limited to centers with substantial experience. (See 'Device accuracy' above.)
•Heliox also affects the performance of diagnostic equipment and the delivery of aerosolized medication. When heliox is used as the driving gas to deliver nebulized medications, the flow of heliox should be increased to prevent prolongation of the delivery time. (See 'Technical issues' above.)
ACKNOWLEDGMENTS —
The UpToDate editorial staff acknowledges David Feller-Kopman, MD, Carl O'Donnell, ScD, and Margaret M Hayes, MD, ATSF, who contributed to an earlier version of this topic review.
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