Emerging Therapies for Patients with Airway/Respiratory Disease
Heliox in Airway Management

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Helium-oxygen (“heliox”) mixtures have been used for decades in the treatment of various respiratory problems ranging from acute upper airway obstructions to lower airway derangements, such as asthma and exacerbations of chronic bronchitis. This review presents a brief history of helium and helium-oxygen mixtures and their potential clinical uses, summarizes the results of past research into heliox in respiratory applications, explains the physiology of heliox, and presents more recent literature relating to heliox in the clinical setting.

Section snippets

History

The element helium was discovered in 1868 when the French astronomer Janssen observed a bright yellow line in the sun's atmosphere during a total solar eclipse in India. The gas was given its name later that year when the English astronomer Lockyer also observed it in the solar spectrum and, concluding that it was an element in the sun not found on Earth, named it after the Greek word for sun, helios. Once its physical properties were delineated, many useful applications for helium became

Prior research

In the 1930s, A.L. Barach tested various mixtures of helium and oxygen, finding benefit across a range of concentrations in asthmatic patients and infants with airway obstruction. He concluded that the low density of helium decreased the work of breathing and significantly improved ventilation. There was a paucity of systematic research on heliox until the 1970s; at that time, investigations into its potential benefit in UAO, postextubation stridor, croup, bronchiolitis, asthma, and chronic

Current research

Research in the past decade has focused on pediatric populations with UAOs and lower airway obstructions (LAOs), particularly asthma. In adults, many case reports and case series have been published on the benefit of heliox in UAO; the only randomized clinical trials have studied the use of heliox in asthma or COPD exacerbations. Other issues of concern include determination of the ideal gas mixture (at least 60% helium seems to be most effective; 80% helium means the gas mixture is hypoxic

Physiology of heliox

In several studies, heliox has been found to decrease the work of breathing and improve gas delivery to the lungs. A review of the physical properties of helium and some of the laws of physics that apply to respiratory physiology can help to explain these results.

Helium is a colorless, odorless, tasteless, biologically inert, and therefore nontoxic gas. It is the second most abundant element in the universe (after hydrogen) but is relatively rare on Earth, requiring production by radioactive

Review of current clinical literature

In general, most heliox studies are limited by small sample sizes. Additionally, because UAO or severe LAO is generally an emergent condition, there has been a paucity of controlled studies done in these areas.

To assess objectively the value of each of the publications considered here, a classification system is used based on the study type (including case series) and the rigors of the study design (if any). This approach (Box 1) is modeled after the classification system used in the Guidelines

Research on the use of heliox in children

The small anatomy and reactive physiology of infants and young children put them at greater risk for airway obstruction than older children and adults. Their upper and lower airways are small, predisposed to blockage by secretions, and vulnerable to edema and resultant airway narrowing. As noted previously, resistance to laminar airflow increases in inverse proportion to the fourth power of the airway radius (Hagen-Poiseuille's law); therefore, a small decrease in the radius of the airway

Upper airway obstruction

There are many causes of UAO—acute, as in foreign body aspiration or acute epiglottitis, and more insidious in nature, such as a slow-growing mass. Regardless of the cause, UAO can precipitate acute ventilatory failure.2 Obstruction increases airway resistance, causing increased work of breathing; this eventually leads to respiratory muscle fatigue and the life-threatening problems of hypercapnia and hypoxemia. The obvious goal of removing the obstruction may not always be accomplishable in an

Lower airway obstruction

A study done in 2002 by Piva and colleagues10 tested 20 children with chronic LAO, randomizing them to heliox or oxygen for ventilatory scintigraphy testing (ie, ventilation/perfusion [V/Q] scan). Results showed better gas distribution (lung deposition) with heliox in those with severe LAO; however, there was no difference between oxygen and heliox in milder obstruction, as designated by prior pulmonary function tests. These findings are supported by the previously reviewed respiratory

Upper Airway Obstruction

As with the pediatric population, much of the literature on the use of heliox in adults with UAO is limited to case descriptions.

In the previously mentioned 1999 case report by Smith and Biros,9 two of the five patients were adults who had UAO: one with supraglottitis and one with laryngeal polyps and edema. This class III report examined two adults in severe respiratory distress who were treated in the ED and responded rapidly to heliox, avoiding mechanical ventilation. These investigators

Summary

Overall, the data continue to be inconclusive regarding the overall benefit of heliox in UAO and LAO; however, the following areas seem to be supported in the literature.

Heliox, because of its lower density than air or oxygen regardless of the concentration of helium in the mixture, increases gas particle deposition and improves air flow through constricted passageways by transforming turbulent flow into laminar flow; some studies have shown a concomitant decrease in the work of breathing.

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