Heliox improves pulsus paradoxus and peak expiratory flow in nonintubated patients with severe asthma

Therapeutic Gases and Inhaled Anesthetics as Adjunctive Therapies in Critically Ill Patients

The administration of exogenous oxygen to support adequate gas exchange is the cornerstone of respiratory care. In the past few years, other gaseous molecules have been introduced in clinical practice to treat the wide variety of physiological derangement seen in critical care patients.Inhaled nitric oxide (NO) is used for its unique selective pulmonary vasodilator effect. Recent studies showed that NO plays a pivotal role in regulating ischemia-reperfusion injury and it has antibacterial and antiviral activity.Helium, due to its low density, is used in patients with upper airway obstruction and lower airway obstruction to facilitate gas flow and to reduce work of breathing.Carbon monoxide (CO) is a poisonous gas that acts as a signaling molecule involved in many biologic pathways. CO's anti-inflammatory and antiproliferative effects are under investigation in the setting of acute respiratory distress and idiopathic pulmonary fibrosis.Inhaled anesthetics are widely used in the operative room setting and, with the development of anesthetic reflectors, are now a valid option for sedation management in the intensive care unit.Many other gases such as xenon, argon, and hydrogen sulfide are under investigation for their neuroprotective and cardioprotective effects in post-cardiac arrest syndrome.With all these therapeutic options available, the clinician must have a clear understanding of the physiologic basis, therapeutic potential, and possible adverse events of these therapeutic gases. In this review, we will present the therapeutic gases other than oxygen used in clinical practice and we will describe other promising therapeutic gases that are in the early phases of investigation.

Ventilated Patients With COVID-19 Show Airflow Obstruction

Objective:

Many patients with coronavirus disease 2019 (COVID-19) need mechanical ventilation secondary to acute respiratory distress syndrome. Information on the respiratory system mechanical characteristics of this disease is limited. The aim of this study is to describe the respiratory system mechanical properties of ventilated COVID-19 patients.

Design, Setting, and Patients:

Patients consecutively admitted to the medical intensive care unit at the University of Iowa Hospitals and Clinics in Iowa City, USA, from April 19 to May 1, 2020, were prospectively studied; final date of follow-up was May 1, 2020.

Measurements:

At the time of first patient contact, ventilator information was collected including mode, settings, peak airway pressure, plateau pressure, and total positive end expiratory pressure. Indices of airflow resistance and respiratory system compliance were calculated and analyzed.

Main Results:

The mean age of the patients was 58 years. 6 out of 12 (50%) patients were female. Of the 21 laboratory-confirmed COVID-19 patients on invasive mechanical ventilation, 9 patients who were actively breathing on the ventilator were excluded. All the patients included were on volume-control mode. Mean [±standard deviation] ventilator indices were: resistive pressure 19 [±4] cmH₂O, airway resistance 20 [±4] cmH₂O/L/s, and respiratory system static compliance 39 [±16] ml/cmH₂O. These values are consistent with abnormally elevated resistance to airflow and reduced respiratory system compliance. Analysis of flow waveform graphics revealed a pattern consistent with airflow obstruction in all patients.

Conclusions:

Severe respiratory failure due to COVID-19 is regularly associated with airflow obstruction.

Pulsus paradoxus

OBJECTIVES

Reviewed the etiologies, pathophysiologic mechanisms, detection and clinical significance of pulsus paradoxus in various conditions.

DATA SOURCE

We searched PubMed, EMBASE, and the CINAHL from inception to June 2017. We used the following search terms: Pulsus paradoxus, pericardial effusion, acute asthma, ventricular interdependence and so forth. All types of study were chosen.

RESULTS AND CONCLUSION

Legendary physician Sir William Osler truly said that "Medicine is learned by the bedside and not in the classroom." Bedside history taking and physical examination should be an integral component of clinical teaching curriculum imparted to medical students. Pulsus paradoxus is a valuable physical sign seen in many clinical conditions. Pulsus paradoxus is defined by an inspiratory fall in systolic blood pressure of greater than 10 mm Hg. Two prototype examples of pulsus paradoxus are cardiac tamponade and acute asthma. Exaggerated swings of intrapleural pressure, bi-ventricular interactions and increase afterload of the left ventricle are few of the pathophysiological mechanisms involved in the causation of pulsus paradoxus. The sensitivity of pulsus paradoxus in the diagnosis of cardiac tamponade is very high. In acute asthma, it also correlates with the severity of airflow obstruction.

Effects of a helium/oxygen mixture on individuals' lung function and metabolic cost during submaximal exercise for participants with obstructive lung diseases

BACKGROUND

Helium/oxygen therapies have been studied as a means to reduce the symptoms of obstructive lung diseases with inconclusive results in clinical trials. To better understand this variability in results, an exploratory physiological study was performed comparing the effects of helium/oxygen mixture (78%/22%) to that of medical air.

METHODS

The gas mixtures were administered to healthy, asthmatic, and chronic obstructive pulmonary disease (COPD) participants, both moderate and severe (6 participants in each disease group, a total of 30); at rest and during submaximal cycling exercise with equivalent work rates. Measurements of ventilatory parameters, forced spirometry, and ergospirometry were obtained.

RESULTS

There was no statistical difference in ventilatory and cardiac responses to breathing helium/oxygen during submaximal exercise. For asthmatics, but not for the COPD participants, there was a statistically significant benefit in reduced metabolic cost, determined through measurement of oxygen uptake, for the same exercise work rate. However, the individual data show that there were a mixture of responders and nonresponders to helium/oxygen in all of the groups.

CONCLUSION

The inconsistent response to helium/oxygen between individuals is perhaps the key drawback to the more effective and widespread use of helium/oxygen to increase exercise capacity and for other therapeutic applications.

Evaluation of lung function and deposition of aerosolized bronchodilators carried by heliox associated with positive expiratory pressure in stable asthmatics: a randomized clinical trial

While administration of medical aerosols with heliox and positive airway pressure are both used clinically to improve aerosol delivery, few studies have differentiated their separate roles in treatment of asthmatics. The aim of this randomized, double blinded study is to differentiate the effect of heliox and oxygen with and without positive expiratory pressure (PEP), on delivery of radiotagged inhaled bronchodilators on pulmonary function and deposition in asthmatics. 32 patients between 18 and 65 years of age diagnosed with stable moderate to severe asthma were randomly assigned into four groups: (1) Heliox + PEP (n = 6), (2) Oxygen + PEP (n = 6), (3) Heliox (n = 11) and (4) Oxygen without PEP (n = 9). Each group received 1 mg of fenoterol and 2 mg of ipratropium bromide combined with 25 mCi (955 Mbq) of Technetium-99m and 0.9% saline to a total dose volume of 3 mL placed in a Venticis II nebulizer attached to a closed, valved mask with PEP of 0 or 10 cm H2O. Both gas type and PEP level were blinded to the investigators. Images were acquired with a single-head scintillation camera with the longitudinal and transverse division of the right lung as regions of interest (ROIs). While all groups responded to bronchodilators, only group 1 showed increase in FEV1%predicted and IC compared to the other groups (p < 0.04). When evaluating the ROI in the vertical gradient we observed higher deposition in the middle and lower third in groups 1 (p = 0.02) and 2 (p = 0.01) compared to group 3. In the horizontal gradient, a higher deposition in the central region in groups 1 (p = 0.03) and 2 (p = 0.02) compared to group 3 and intermediate region of group 2 compared to group 3. We conclude that aerosol deposition was higher in groups with PEP independent of gas used, while bronchodilator response with Heliox + PEP improved FEV1 % and IC compared to administration with Oxygen, Oxygen with PEP and Heliox alone. Trial registration NCT01268462.

Bench experiments comparing simulated inspiratory effort when breathing helium-oxygen mixtures to that during positive pressure support with air

BACKGROUND

Inhalation of helium-oxygen (He/O2) mixtures has been explored as a means to lower the work of breathing of patients with obstructive lung disease. Non-invasive ventilation (NIV) with positive pressure support is also used for this purpose. The bench experiments presented herein were conducted in order to compare simulated patient inspiratory effort breathing He/O2 with that breathing medical air, with or without pressure support, across a range of adult, obstructive disease patterns.

METHODS

Patient breathing was simulated using a dual-chamber mechanical test lung, with the breathing compartment connected to an ICU ventilator operated in NIV mode with medical air or He/O2 (78/22 or 65/35%). Parabolic or linear resistances were inserted at the inlet to the breathing chamber. Breathing chamber compliance was also varied. The inspiratory effort was assessed for the different gas mixtures, for three breathing patterns, with zero pressure support (simulating unassisted spontaneous breathing), and with varying levels of pressure support.

RESULTS

Inspiratory effort increased with increasing resistance and decreasing compliance. At a fixed resistance and compliance, inspiratory effort increased with increasing minute ventilation, and decreased with increasing pressure support. For parabolic resistors, inspiratory effort was lower for He/O2 mixtures than for air, whereas little difference was measured for nominally linear resistance. Relatively small differences in inspiratory effort were measured between the two He/O2 mixtures. Used in combination, reductions in inspiratory effort provided by He/O2 and pressure support were additive.

CONCLUSIONS

The reduction in inspiratory effort afforded by breathing He/O2 is strongly dependent on the severity and type of airway obstruction. Varying helium concentration between 78% and 65% has small impact on inspiratory effort, while combining He/O2 with pressure support provides an additive reduction in inspiratory effort. In addition, breathing He/O2 alone may provide an alternative to pressure support in circumstances where NIV is not available or poorly tolerated.

Bench and mathematical modeling of the effects of breathing a helium/oxygen mixture on expiratory time constants in the presence of heterogeneous airway obstructions

Background

Expiratory time constants are used to quantify emptying of the lung as a whole, and emptying of individual lung compartments. Breathing low-density helium/oxygen mixtures may modify regional time constants so as to redistribute ventilation, potentially reducing gas trapping and hyperinflation for patients with obstructive lung disease. In the present work, bench and mathematical models of the lung were used to study the influence of heterogeneous patterns of obstruction on compartmental and whole-lung time constants.

Methods

A two-compartment mechanical test lung was used with the resistance in one compartment held constant, and a series of increasing resistances placed in the opposite compartment. Measurements were made over a range of lung compliances during ventilation with air or with a 78/22% mixture of helium/oxygen. The resistance imposed by the breathing circuit was assessed for both gases. Experimental results were compared with predictions of a mathematical model applied to the test lung and breathing circuit. In addition, compartmental and whole-lung time constants were compared with those reported by the ventilator.

Results

Time constants were greater for larger minute ventilation, and were reduced by substituting helium/oxygen in place of air. Notably, where time constants were long due to high lung compliance (i.e. low elasticity), helium/oxygen improved expiratory flow even for a low level of resistance representative of healthy, adult airways. In such circumstances, the resistance imposed by the external breathing circuit was significant. Mathematical predictions were in agreement with experimental results. Time constants reported by the ventilator were well-correlated with those determined for the whole-lung and for the low-resistance compartment, but poorly correlated with time constants determined for the high-resistance compartment.

Conclusions

It was concluded that breathing a low-density gas mixture, such as helium/oxygen, can improve expiratory flow from an obstructed lung compartment, but that such improvements will not necessarily affect time constants measured by the ventilator. Further research is required to determine if alternative measurements made at the ventilator level are predictive of regional changes in ventilation. It is anticipated that such efforts will be aided by continued development of mathematical models to include pertinent physiological and pathophysiological phenomena that are difficult to reproduce in mechanical test systems.

Management of severe asthma exacerbation in children

BACKGROUND

Asthma is a common disease in children and acute severe asthma exacerbation can be life-threatening. This article aims to review recent advances in understanding of risk factors, pathophysiology, diagnosis and treatment of severe asthma exacerbation in children.

DATA SOURCES

Articles concerning severe asthma exacerbation in children were retrieved from PubMed. Literatures were searched with MeSH words "asthma", "children", "severe asthma exacerbation" and relevant cross references.

RESULTS

Severe asthma exacerbation in children requires aggressive treatments with β2-agonists, anticholinergics, and corticosteroids. Early initiation of inhaled β-agonists and systemic use of steroids are recommended. Other agents such as magnesium and aminophylline have some therapeutic benefits. When intubation and mechanical ventilation are needed, low tidal volume, controlled hypoventilation with lower-than-traditional respiratory rates and permissive hypercapnia can be applied.

CONCLUSIONS

Researchers should continue to detect the risk factors, pathophysiology, diagnosis and treatment of severe asthma exacerbation in children. More studies especially randomized controlled trials are required to evaluate the efficacy and safety of standard and new therapies.

Helium in the adult critical care setting

Helium is a low-density inert gas whose physical properties are very different from those of nitrogen and oxygen. Such properties could be clinically useful in the adult critical care setting, especially in patients with upper to more distal airway obstruction requiring moderate to intermediate levels of FiO₂. However, despite decades of utilization and reporting, it is still difficult to give any firm clinical recommendation in this setting. Numerous case reports are available in the context of upper airway obstruction of different origins, but there is a lack of controlled studies for this indication. One study reported a helium-induced beneficial effect on surrogates of work of breathing after extubation in non-COPD patients, possibly in relation to laryngeal consequences of tracheal intubation. Physiological benefits of helium-oxygen breathing have been demonstrated in the context of acute severe asthma, but there is a lack of large controlled studies demonstrating an effect on pertinent clinical endpoints, except for a study reported only as an abstract, which mentioned a reduction in the intubation rate in helium-treated patients. Finally, there are a number of physiological studies in the context of COLD-COPD patients demonstrating a beneficial effect, mainly by a reduction in the resistive inspiratory work of breathing but also by a reduction in hyperinflation. Reduction of hypercapnia was mainly observed in spontaneously breathing and noninvasively ventilated helium-treated patients but not in intubated patients during controlled ventilation, suggesting that the decrease in PaCO₂ was mainly in relation to a diminution in CO₂ production, related to the diminution in work of breathing and not an improved alveolar ventilation. Moreover, there is little evidence that helium-oxygen could improve parameters of heterogeneity in such patients. Two RCTs were unable to demonstrate a reduction in the intubation rate in such setting, but they were likely underpowered. An adequately powered international multicentric study is ongoing and will help to determinate the exact place of the helium-oxygen mixture in the future. The place of the mixture during the weaning period will deserve further evaluation.

Analytic review: management of life-threatening asthma in adults

Asthma remains a troubling health problem despite the availability of effective treatment. A small but significant number of asthmatics experience life-threatening attacks culminating in intensive care unit admission. Standard treatment includes high dose systemic corticosteroids and inhaled bronchodilators. Patients with especially severe attacks may develop respiratory failure and need endotracheal intubation and mechanical ventilation. Severe airway obstruction may lead to dynamic hyperinflation and the possibility of hemodynamic collapse and barotrauma. Fortunately, most intubated asthmatics survive if physicians adhere to key management principles intended to avoid or minimize hyperinflation. The purpose of this review is to discuss the pathogenesis of life-threatening asthma and to provide practical guidance to promote rationale, safe, and effective management.

Acute severe asthma: new approaches to assessment and treatment

The precise definition of a severe asthmatic exacerbation is an issue that presents difficulties. The term 'status asthmaticus' relates severity to outcome and has been used to define a severe asthmatic exacerbation that does not respond to and/or perilously delays the repetitive or continuous administration of short-acting inhaled beta(2)-adrenergic receptor agonists (SABA) in the emergency setting. However, a number of limitations exist concerning the quantification of unresponsiveness. Therefore, the term 'acute severe asthma' is widely used, relating severity mostly to a combination of the presenting signs and symptoms and the severity of the cardiorespiratory abnormalities observed, although it is well known that presentation does not foretell outcome. In an acute severe asthma episode, close observation plus aggressive administration of bronchodilators (SABAs plus ipratropium bromide via a nebulizer driven by oxygen) and oral or intravenous corticosteroids are necessary to arrest the progression to severe hypercapnic respiratory failure leading to a decrease in consciousness that requires intensive care unit (ICU) admission and, eventually, ventilatory support. Adjunctive therapies (intravenous magnesium sulfate and/or others) should be considered in order to avoid intubation. Management after admission to the hospital ward because of an incomplete response is similar. The decision to intubate is essentially based on clinical judgement. Although cardiac or respiratory arrest represents an absolute indication for intubation, the usual picture is that of a conscious patient struggling to breathe. Factors associated with the increased likelihood of intubation include exhaustion and fatigue despite maximal therapy, deteriorating mental status, refractory hypoxaemia, increasing hypercapnia, haemodynamic instability and impending coma or apnoea. To intubate, sedation is indicated in order to improve comfort, safety and patient-ventilator synchrony, while at the same time decrease oxygen consumption and carbon dioxide production. Benzodiazepines can be safely used for sedation of the asthmatic patient, but time to awakening after discontinuation is prolonged and difficult to predict. The most common alternative is propofol, which is attractive in patients with sudden-onset (near-fatal) asthma who may be eligible for extubation within a few hours, because it can be titrated rapidly to a deep sedation level and has rapid reversal after discontinuation; in addition, it possesses bronchodilatory properties. The addition of an opioid (fentanyl or remifentanil) administered by continuous infusion to benzodiazepines or propofol is often desirable in order to provide amnesia, sedation, analgesia and respiratory drive suppression. Acute severe asthma is characterized by severe pulmonary hyperinflation due to marked limitation of the expiratory flow. Therefore, the main objective of the initial ventilator management is 2-fold: to ensure adequate gas exchange and to prevent further hyperinflation and ventilator-associated lung injury. This may require hypoventilation of the patient and higher arterial carbon dioxide (PaCO(2)) levels and a more acidic pH. This does not apply to asthmatic patients intubated for cardiac or respiratory arrest. In this setting the post-anoxic brain oedema might demand more careful management of PaCO(2) levels to prevent further elevation of intracranial pressure and subsequent complications. Monitoring lung mechanics is of paramount importance for the safe ventilation of patients with status asthmaticus. The first line of specific pharmacological therapy in ventilated asthmatic patients remains bronchodilation with a SABA, typically salbutamol (albuterol). Administration techniques include nebulizers or metered-dose inhalers with spacers. Systemic corticosteroids are critical components of therapy and should be administered to all ventilated patients, although the dose of systemic corticosteroids in mechanically ventilated asthmatic patients remains controversial. Anticholinergics, inhaled corticosteroids, leukotriene receptor antagonists and methylxanthines offer little benefit, and clinical data favouring their use are lacking. In conclusion, expertise, perseverance, judicious decisions and practice of evidence-based medicine are of paramount importance for successful outcomes for patients with acute severe asthma.

The role of heliox in paediatric respiratory disease

Helium-oxygen (heliox) gas mixtures have been studied for over 70 years as an adjunctive therapy for airway obstruction in a variety of respiratory diseases. The medical use of heliox is based on the physical properties of helium as its low density makes it advantageous in promoting more efficient flow through narrowed passages. Clinical evidence of the efficacy of heliox in treating paediatric respiratory diseases is increasing in the medical literature. This article consists of a comprehensive review of the literature investigating the utility of heliox in the treatment of paediatric respiratory disorders, including upper and lower airway obstruction, mechanical ventilation, and aerosol delivery.

A multicenter, randomized trial of noninvasive ventilation with helium-oxygen mixture in exacerbations of chronic obstructive lung disease

OBJECTIVE

To assess the effect of a helium-oxygen mixture on intubation rate and clinical outcomes during noninvasive ventilation in acute exacerbation of chronic obstructive pulmonary disease.

DESIGN

Multicenter, prospective, randomized, controlled trial.

SETTING

Seven intensive care units.

PATIENTS

A total of 204 patients with known or suspected chronic obstructive pulmonary disease and acute dyspnea, Paco2> 45 mm Hg and two among the following factors: pH <7.35, Paco2 <50 mm Hg, respiratory rate >25/min.

INTERVENTIONS

Noninvasive ventilation randomly applied with or without helium (inspired oxygen fraction 0.35) via a face mask.

MEASUREMENTS AND MAIN RESULTS

Duration and complications of NIV and mechanical ventilation, endotracheal intubation, discharge from intensive care unit and hospital, mortality at day 28, adverse and serious adverse events were recorded. Follow-up lasted until 28 days since enrollment. Intubation rate did not significantly differ between groups (24.5% vs. 30.4% with or without helium, p = .35). No difference was observed in terms of improvement of arterial blood gases, dyspnea, and respiratory rate between groups. Duration of noninvasive ventilation, length of stay, 28-day mortality, complications and adverse events were similar, although serious adverse events tended to be lower with helium (10.8% vs. 19.6%, p = .08).

CONCLUSIONS

Despite small trends favoring helium, this study did not show a statistical superiority of using helium during NIV to decrease the intubation rate in acute exacerbation of chronic obstructive pulmonary disease.

Inhalational therapies for the ICU

PURPOSE OF REVIEW

Although drug therapy is most commonly delivered via the intravenous route, novel inhaled agents have been introduced for use in the ICU. Additionally, drugs previously delivered intravenously are now being delivered via the respiratory tract in an effort to reduce systemic toxicity and maximize effectiveness.

RECENT FINDINGS

Aerosolized antibiotics have seen increased use in an effort to reduce systemic effects, reduce ventilator-associated pneumonia, and direct high drug concentrations at the site of infection. Drug-resistant pneumonia has also been effectively treated with aerosolized antibiotics. Secretion management includes a host of devices, therapies, and drugs, but the evidence for these is scant. Cardiac drugs via the endotracheal route should be used only when intravenous access is delayed. Inhaled nitric oxide has a defined role in care of infants, although new indications have limited and conflicting data. The use of helium-oxygen mixtures provides symptom relief in a wide variety of scenarios associated with turbulent flow in large airways.

SUMMARY

Inhaled nitric oxide has an established role in neonatal intensive care and a limited role in adult intensive care. Heliox provides symptom relief, but at present cannot be considered routine as a consequence of the multiple technological challenges. Inhaled antimicrobials appear to provide a therapeutic advantage in select individuals with pneumonia. Secretion management is best achieved by adequate humidification and as needed suctioning. The role of inhaled carbon monoxide in critical care holds significant promise, but is currently in early clinical trials.

Heliox in airway management

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.

Acute severe asthma

Acute severe asthma remains a major economic and health burden. The natural history of acute decompensations is one of resolution and only about 0.4% of patients succumb overall. Mortality in medical intensive care units is higher but is less than 3% of hospital admissions. "Near-fatal" episodes may be more frequent, but precise figures are lacking. However, about 30% of medical intensive care unit admissions require intubation and mechanical ventilation with mortality of 8%. Morbidity and mortality increase with socioeconomic deprivation and ethnicity. Seventy to 80% of patients in emergency departments clear within 2 hours with standardized care. The relapse rate varies between 7 and 15%, depending on how aggressively the patient is treated. The airway obstruction in the 20-30% of people resistant to adrenergic agonists in the emergency department slowly reverses over 36-48 hours but requires intense treatment to do so. Current therapeutic options for this group consist of ipratropium and corticosteroids in combination with beta2 selective drugs. Even so, such regimens are not optimal and better approaches are needed. The long-term prognosis after a near-fatal episode is poor and mortality may approach 10%.

Asthma exacerbations. 5: assessment and management of severe asthma in adults in hospital

It is difficult to understand why there is such a huge discrepancy between the management of severe asthma recommended by evidence-based guidelines and that observed in clinical practice. The recommendations are relatively straightforward and have been widely promoted both in guidelines and reviews. Specialist physicians need to be more proactive in their implementation of such guidelines through the use of locally derived protocols and assessment sheets, reinforced by audit. The common occurrence of severe asthma and its considerable burden to the community would support such an approach.

Clinical review: use of helium-oxygen in critically ill patients

Use of helium-oxygen (He/O₂) mixtures in critically ill patients is supported by a reliable and well understood theoretical rationale and by numerous experimental observations. Breathing He/O₂ can benefit critically ill patients with severe respiratory compromise mainly by reducing airway resistance in obstructive syndromes such as acute asthma and decompensated chronic obstructive pulmonary disease. However, the benefit from He/O₂ in terms of respiratory mechanics diminishes rapidly with increasing oxygen concentration in the gaseous mixture. Safe use of He/O₂ in the intensive care unit requires specific equipment and supervision by adequately experienced personnel. The available clinical data on inhaled He/O₂ mixtures are insufficient to prove that this therapy has benefit with respect to outcome variables. For these reasons, He/O₂ is not currently a standard of care in critically ill patients with acute obstructive syndromes, apart from in some, well defined situations. Its role in critically ill patients must be more precisely defined if we are to identify those patients who could benefit from this therapeutic approach.

Room air entrainment during beta-agonist delivery with heliox

Studies of the efficacy of heliox in patients with severe asthma have shown mixed results. Among the factors that are responsible for variable outcomes, the failure of heliox delivery systems to prevent room air entrainment (RAE) during beta-agonist delivery is probably the most critical. While keeping the rotameter flow rate (FR) of heliox mixed 70:30 to a nebulizer at 10 L/min, the FR of heliox from a second gas source to a T-connector (TC) was increased during the delivery of the beta-agonist with a conventional T-nebulizer delivery system (TNDS). A negative peak inspiratory flow (pneumotachometer reading) or a helium concentration of < 70% (quadralizer reading) were indicators of RAE. RAE was tested during spontaneous tidal breathing and acute asthma. A rotameter FR of 10 L/m to the nebulizer with no flow from a second gas source to a TC (conventional TNDS) resulted in a significant drop in helium concentration during tidal breathing (46.2%) and acute asthma (27.5%) due to RAE. This degree of helium dilution can negate the beneficial effects of heliox to lung mechanics almost completely. A rotameter FR of 10 L/m each to a nebulizer and a TC resulted in a helium concentration 69.8% during tidal breathing (no RAE), but 49% (significant RAE) during asthma events. A rotameter FR of 15 L/m (pressure regulator setting, 100 lbs per square inch) to a TC, while maintaining a rotameter FR of 10 L/m to a nebulizer prevented RAE during asthma (helium concentration, 69.9%). Conventional TNDS may be used to deliver the beta-agonist with heliox during asthma without RAE.

Heliox for nonintubated acute asthma patients

BACKGROUND

Helium and oxygen mixtures (heliox), have been used sporadically in respiratory medicine for decades. Their use in acute respiratory emergencies such as asthma has been the subject of considerable debate. Despite the lapse of more than 60 years since it was first proposed, the role of heliox in treating patients with severe acute asthma remains unclear.

OBJECTIVES

To determine the effect of the addition of heliox to standard medical care on the course of acute asthma, as measured by pulmonary function testing and clinical endpoints.

SEARCH STRATEGY

Randomised controlled trials were identified from the Cochrane Airways Group Specialised Register. In addition, we contacted primary authors and experts and searched reference lists of articles. Searches are current to August 2005.

SELECTION CRITERIA

1) randomised, single or double blind, controlled trials; 2) children or adults with a clinical diagnosis of acute asthma seen in emergency departments or equivalent acute care settings; and 3) compared treatment with inhaled heliox to placebo (oxygen or air).

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed the studies for inclusion and quality assessment; disagreement was resolved by a third review author and consensus.

MAIN RESULTS

This review has been updated in 2006 to include four new trials giving atotal of ten trials involving 544 acute asthma patients. Seven studies involved adults and three studies dealt solely with children. Three were assessed as high quality (Jadad score > 3). Pulmonary function tests were recorded during heliox administration (15 to 60 min). Pooling of the eight trials contributing data to this review showed no significant group differences (standardised mean differences -0.28; 95% confidence interval (CI) -0.56 to 0.01). There was significant heterogeneity among the studies. Heliox use did improve pulmonary function only in the subgroup of patients with the most severe baseline pulmonary function impairment; however, this conclusion is based on a small number of studies. There were no significant differences between groups when adults versus children, and high versus low heliox dose studies were compared. Finally, at the end of treatment, participants treated with heliox showed no significant different risk of admission to hospital (RR 0.83 (95%CI 0.66 to 1.08, P = 0.17, I(2) = 0%).

AUTHORS' CONCLUSIONS

The existing evidence does not provide support for the administration of helium-oxygen mixtures to all ED patients with acute asthma. At this time, heliox treatment does not have a role to play in the initial treatment of patients with acute asthma. Nevertheless, new evidence suggests certain beneficial effects in patients with more severe obstruction. Since these conclusions are based upon between-group comparisons and small studies, they should be interpreted with caution.

Asthma pathophysiology and evidence-based treatment of severe exacerbations

PURPOSE

The pathogenesis of asthma and the treatment approach for acute exacerbations are described. The pharmacology, efficacy, safety, and cost of the beta2 agonist, albuterol, a racemic mixture of equal amounts of R- and S-enantiomers, and levalbuterol, the R-enantiomer, are compared.

SUMMARY

Asthma symptoms are the result of bronchial hyperresponsiveness, bronchospasm, and chronic airway inflammation. Short-acting, inhaled beta2 agonists; oxygen; intravenous fluids; and corticosteroids are the mainstays of treatment for acute exacerbations. The R-enantiomer of albuterol is responsible for bronchodilation. The S-enantiomer exhibits broncho-constricting activity in vitro, which may be mediated by muscarinic receptors and may be opposed by adding the anticholinergic agent ipratropium bromide. Levalbuterol improves pulmonary function to a greater extent than racemic albuterol and reduces the need for costly hospitalizations in patients with acute asthma exacerbations.

CONCLUSION

Levalbuterol is an alternative to racemic albuterol with the potential to improve patient outcomes and reduce costs in the treatment of acute asthma exacerbations.

Continuous noninvasive measurement of pulsus paradoxus complements medical decision making in assessment of acute asthma severity

BACKGROUND

Pulsus paradoxus (PP) is a pathophysiologic parameter that is indicative of asthma severity. The ability of PP to categorize acutely asthmatic patients in accordance with the earlier National Asthma Education and Prevention Program (NAEPP) expert panel report 1 guidelines was determined.

METHODS

An arterial tonometric BP monitor, which was interfaced to an analog-digital converter, executed a periodic amplitude analysis algorithm, which computed PP in real time. The PP measurement was compared to the criterion standard of emergency physicians in determining the hospital admission vs hospital discharge disposition following the NAEPP standardized treatment. Receiver operating characteristics (ROCs) were calculated, and the PP threshold, which maximized sensitivity and specificity, was identified. In a separate laboratory investigation, PP was induced in a healthy volunteer by inspiration through a fixed resistance. Plethysmographic waveform changes, induced by PP, were measured by a second analog-to-digital converter that was connected to a pulse oximeter.

RESULTS

A total of 79 patients were enrolled in the study, of whom 63 met a priori inclusion criteria and had uninterrupted data acquisition. The mean PP for patients who were appropriately discharged from the hospital was 9.1 mm Hg (95% confidence interval [CI], 7.3 to 10.9 mm Hg) and differed from the PP of 17.6 mm Hg (95% CI, 13.5 to 21.8; p < 0.001) for patients admitted to the hospital/relapsed. The sensitivity and specificity for physician disposition were 0.83 and 0.89, respectively, and for PP values were 0.78 and 0.78, respectively. The Wilcoxon area under the ROC curve was 0.82 (95% CI, 0.64 to 0.99) following treatment. The risk ratio was 5.32 for hospital admission among patients with a PP of > 11.3 mm Hg. Changes in the photoplethysmography peak height were correlated to PP from the BP monitor by a regression line with a slope of 0.01 V/mm Hg.

CONCLUSIONS

Continuous PP can aid in determining disposition among emergency department (ED) patients with acute asthma. ED physicians equipped with a PP monitor would be able to objectify the work of breathing and would more closely adhere to NAEPP guidelines. The possibility that a PP detection algorithm could reside in a pulse oximeter warrants further investigation.

Current management of status asthmaticus in the pediatric ICU

Status asthmaticus (SA) in the pediatric ICU (PICU) can progress to a life-threatening emergency. The goal of management is to improve hypoxemia, improve bronchoconstriction, and decrease airway edema through the administration of continuous nebulized beta2 adrenergic agonist with intermittent anticholinergics, corticosteroids, and oxygen. Adjunctive therapies, such as magnesium, methylxanthines, intravenous beta-agonists, heliox, and noninvasive ventilation should be considered in the child who fails to respond to initial therapies. The restoration of adequate pulmonary functions, resolution of airway obstruction, and avoidance of mechanical ventilation should guide management. This article reviews the pathophysiology, assessment, and management of the child who has SA in the PICU to provide the critical care nurse with current information to facilitate optimal care.

Albuterol nebulized in heliox in the initial ED treatment of pediatric asthma: a blinded, randomized controlled trial

OBJECTIVE

A prospective blinded, randomized controlled trial was undertaken to compare the initial response of albuterol nebulized in heliox or control in the treatment of moderately severe asthma in children presenting to a pediatric ED.

METHODS

Patients were randomized to receive heliox (n = 20) or control (n = 21). The primary outcome was to compare a modified dyspnea index score at 10 and 20 minutes after randomization. Secondary outcomes were to determine if heliox decreased admission rates or endotracheal intubation.

RESULTS

There was no statistically significant difference found at 10 or 20 minutes after randomization with heliox (P = .169 and P = .062, respectively). No statistical difference in admission rate was found, and no patients required endotracheal intubation in either group.

CONCLUSIONS

Our results demonstrate that albuterol nebulized with heliox offered no clinical benefit over standard therapy in the initial treatment of moderately severe asthma in the ED.

Helium/oxygen-driven albuterol nebulization in the treatment of children with moderate to severe asthma exacerbations: a randomized, controlled trial

BACKGROUND

Helium and oxygen mixtures (heliox) increase both pulmonary aerosol delivery and gas delivery relative to oxygen. We aimed to compare the effectiveness of a 70%:30% helium/oxygen (heliox)-driven continuous aerosol delivery versus 100% oxygen-driven delivery in the treatment of asthmatic children with moderate to severe exacerbations.

METHODS

We enrolled 30 children aged 2 to 18 years who presented to an urban, pediatric emergency department (ED) with moderate to severe asthma as defined by a pulmonary index (PI) score of > or =8. PI scores can range from 0 to 15. In this randomized, controlled, single-blind trial conducted in a convenience sample of children, all patients in the trial received an initial nebulized albuterol (5 mg) treatment driven by 100% oxygen and a dose of oral prednisone or prednisolone. Subsequently, patients were randomly assigned to receive continuously nebulized albuterol (15 mg/hour) delivered by either heliox or oxygen using a nonrebreathing face mask. The primary outcome measure was degree of improvement as assessed in blinded video-recorded PI scores over 240 minutes (at 30-minute intervals for the first 3 hours) or until ED discharge (if <240 minutes).

RESULTS

The mean change in PI score from baseline to 240 minutes or ED discharge was 6.67 for the heliox group compared with 3.33 for the oxygen group. Eleven (73%) patients in the heliox group were discharged from the hospital in <12 hours compared with 5 (33%) patients in the conventional group.

CONCLUSION

Continuously nebulized albuterol delivered by heliox was associated with a greater degree of clinical improvement compared with that delivered by oxygen among children with moderate to severe asthma exacerbations.

Heliox administration in the pediatric intensive care unit: an evidence-based review

OBJECTIVE

To provide a comprehensive, evidence-based review of helium-oxygen gas mixtures (heliox) in the management of pediatric respiratory diseases.

DATA SOURCE

A thorough, computerized bibliographic search of the preclinical and clinical literature regarding the properties of helium and its application in pediatric respiratory disease states.

DATA SYNTHESIS

After an overview of the potential benefits and technical aspects of helium-oxygen gas mixtures, the role of heliox is addressed for asthma, aerosolized medication delivery, upper airway obstruction, postextubation stridor, croup, bronchiolitis, and high-frequency ventilation. The available data are objectively classified based on the value of the therapy or intervention as determined by the study design from which the data are obtained.

CONCLUSIONS

Heliox administration is most effective during conditions involving density-dependent increases in airway resistance, especially when used early in an acute disease process. Any beneficial effect of heliox should become evident in a relatively short period of time. The medical literature supports the use of heliox to relieve respiratory distress, decrease the work of breathing, and improve gas exchange. No adverse effects of heliox have been reported. However, heliox must be administered with vigilance and continuous monitoring to avoid technical complications.

Heliox for asthma in the emergency department: a review of the literature

January 2002 saw the relaunch by BOC of Heliox, a gaseous mixture of helium and oxygen, for the use in a wide range of respiratory conditions. Despite a lapse of over 65 years since it was first used, and a large number of studies and case reports advocating its use, it remains an enigma, its use sporadic, and its role undefined. This paper reviews the discovery of helium and early medical use of helium oxygen mixtures and outlines areas where Heliox already has confirmed benefit as well as one or two areas that are currently under investigation. It will also look specifically at the use of Heliox in acute exacerbations of asthma and perform a thorough review of the current literature.

Patterns of helium-oxygen (heliox) usage in the critical care environment

The objective of this study was to describe the patterns of heliox use in critical care units of an academic medical center. The design was a prospective case series involving 7 critical care units of an academic medical center. All patients receiving heliox therapy over a 4-year period were studied, with prospective recording of patient demographics and the location, mode, indication for, and duration of heliox use. Use pattern comparisons based on anatomic location (upper vs lower airway) and age group (pediatric vs adult) were performed by alpha(2) analysis and unpaired Student t test. Eighty-nine patients, aged 17.4 +/- 20.9 years, received heliox for 30.5 +/- 44.6 hours on 92 occasions. Pediatric (</= 18 years) applications accounted for 72.8% of heliox use. Use was greater in frequency and scope during the final 2 study years, particularly in adults. Applications were split between upper airway (47%) and lower airway (53%) disorders. Airway manipulation was required in more adults (7/16) than in children (3/27) with upper airway obstruction (P < .05). The use patterns mirrored current literature emphases on postextubation stridor and asthma. This is the first description of heliox use patterns in the tertiary care critical care environment. Heliox use may be as dependent on practitioner experience as on published data. As a benign and relatively inexpensive therapy, heliox use should continue to be attractive, although ongoing study regarding efficacy in a number of settings is indicated.

New Anesthesia Techniques

Advances in anesthesia involve refinements in understanding, technique, and technology. These refinements have led to better control of the anesthetic state, effective anesthesia for a wider variety of situations, and the ability to bring sicker patients to the operating room. Although the molecular mechanisms underlying the general anesthetic state are unknown, evidence suggests a specific, receptor-based effect. This concept has allowed anesthesiologists to treat anesthetic end points of immobility, lack of awareness, and autonomic control separately. It is likely that anesthesia and naturally occurring sleep interact physiologically. New, processed EEG monitors may allow anesthesiologists to titrate more finely anesthetic dose, with possible benefits in terms of speed of recovery and detection of intraoperative awareness. Since the 1990s, new anesthetic drugs (propofol, desflurane/sevoflurane, cisatracurium) have enhanced greatly control of the anesthetic state. The new intravenous anesthetic agent dexmedetomidine offers sedation with preserved respiration and cognitive function. Although its role has yet to be defined fully, it currently plays a role in ICU sedation and monitored anesthesia care. New anesthesia ventilators have better monitoring and better flow delivery at high airway pressures. These improvements significantly narrow the performance gap between anesthesia and ICU ventilators. In patients with COPD, pulmonary hypertension, or severe hypoxemia, heliox may improve gas flow, and NO may reduce pulmonary vascular resistance and improve oxygenation.

Effects of helium–oxygen mixtures on endotracheal tubes: an in vitro study

QUESTION

To determine flow pattern and critical Reynolds numbers in endotracheal tubes submitted to different helium-oxygen mixtures under laboratory conditions.

MATERIALS AND METHODS

Flow-pressure relationships were performed for seven endotracheal tubes (rectilinear position, entry length applied) with distal end open to atmosphere (predicted internal diameters: 6-9 mm). Nine helium-oxygen mixtures were tested, with FIHe varying from zero to 0.78 (increment: 10%). Nine flows were tested, with rates varying from 0.25 to 1.60 l s(-1) (increment: 0.15 l s(-1)). Gas flow resistance was calculated, and for each endotracheal tube, a Moody diagram was realised. Flow regime and critical Reynolds numbers were then determined (fully established laminar, nonestablished laminar, smooth turbulent, or rough).

RESULTS

Even low concentration of helium in inspiratory mixture reduces endotracheal tubes resistance. Effect is maximal for high flows, small tube and high FIHe. Critical Reynolds numbers are inversely correlated to tube diameter.

ANSWER

Under laboratory conditions, flow pattern in endotracheal tubes varies from fully established laminar to rough. Knowledge of the critical Reynolds numbers allows correct application of fluid mechanic formula when studying tube or gaseous mixture effects on respiratory mechanisms.

Development of Aerosol Drug Delivery with Helium Oxygen Gas Mixtures

Aerosol drug delivery using helium-oxygen gas mixtures (heliox) is considered in terms of flow physics, atomization, and aerosol mechanics. Theoretical considerations are then related to past studies of the physiological effects of the inhalation of heliox and its potential use as a drug delivery medium. Past clinical trials of heliox investigating this use are reviewed and technical recommendations made for its successful development. It is proposed that improved peripheral lung drug delivery with heliox is highly dependent on proper administration, especially the inclusion of proper reservoir system for the gas.

Therapeutic benefits of helium-oxygen delivery to infants via nasal cannula

OBJECTIVE

The benefits of helium-oxygen (heliox) administration for pediatric upper and lower respiratory disorders have been well described. However, while most studies advocate delivery via a sealed or semisealed facemask system, such systems may not be tolerated in the young child. This report describes the successful and efficacious delivery of heliox via nasal cannula to 5 infants.

METHODS

A mixture of 80% helium/20% oxygen was blended with 100% oxygen from a wall source and delivered via nasal cannula to 5 spontaneously breathing infants with respiratory distress at flow rates of 2 to 3 liters per minute. Treatment efficacy was retrospectively extracted from nursing, respiratory therapist, and physician entries in the medical record, specifically focusing on changes in respiratory rate, work of breathing, and oxygenation and/or ventilation parameters.

RESULTS

All 5 infants tolerated the nasal cannula well. In 2, nasal cannulae were used after attempts to use a facemask system were not tolerated. All patients demonstrated rapid improvements in respiratory parameters including a decreased work of breathing (n = 5), respiratory rate (n = 4), transcutaneous CO2 (n = 2), and stridor (n = 2), or improved oxygenation (n = 1). In 1 patient, the recurrence of distress shortly after discontinuing heliox was rapidly reversed with heliox reinstitution.

CONCLUSIONS

In infants with respiratory distress who do not tolerate a facemask, the use of nasal cannula represents a viable and efficacious alternative for heliox delivery.

Severe exacerbations of asthma

All asthmatics regardless of their perceived severity, are at risk of exacerbation, particularly if they are suboptimally treated in the outpatient arena. Fortunately most patients recover after administration of bronchodilators and anti-inflammatory medications, but preventable deaths continue to occur and refractory cases result in hospitalization and need for mechanical ventilation. We begin this article by reviewing the pathophysiology of acute exacerbations to build a foundation for the assessment of clinical status and to provide the rationale for a carefully contemplated and evidence-based therapeutic approach. We end this article with an in-depth examination of the particular problems that are encountered during mechanical ventilation and offer a strategy that helps minimize complications. In the final analysis, however, the greatest gains in the field of acute asthma will come not from its treatment but from its prevention by enhanced educational and environmental efforts and by the delivery of optimal medications at home.

Acute asthma in adults: a review

All patients with asthma are at risk of having exacerbations. Hospitalizations and emergency department (ED) visits account for a large proportion of the health-care cost burden of asthma, and avoidance or proper management of acute asthma (AA) episodes represent an area with the potential for large reductions in health-care costs. The severity of exacerbations may range from mild to life threatening, and mortality is most often associated with failure to appreciate the severity of the exacerbation, resulting in inadequate emergency treatment and delay in referring to hospital. This review describes the epidemiology, costs, pathophysiology, mortality, and management of adult AA in the ED and in the ICU.

Effects of helium-oxygen on respiratory mechanics, gas exchange, and ventilation-perfusion relationships in a porcine model of stable methacholine-induced bronchospasm

OBJECTIVE

To explore the consequences of helium/oxygen (He/O(2)) inhalation on respiratory mechanics, gas exchange, and ventilation-perfusion (VA/Q) relationships in an animal model of severe induced bronchospasm during mechanical ventilation.

DESIGN

Prospective, interventional study.

SETTING

Experimental animal laboratory, university hospital.

INTERVENTIONS

Seven piglets were anesthetized, paralyzed, and mechanically ventilated, with all ventilator settings remaining constant throughout the protocol. Acute stable bronchospasm was obtained through continuous aerosolization of methacholine. Once steady-state was achieved, the animals successively breathed air/O(2) and He/O(2) (FIO(2) 0.3), or inversely, in random order. Measurements were taken at baseline, during bronchospasm, and after 30 min of He/O(2) inhalation.

RESULTS

Bronchospasm increased lung peak inspiratory pressure (49+/-6.9 vs 18+/-1 cm H(2)O, P<0.001), lung resistance (22.7+/-1.5 vs 6.8+/-1.5 cm H(2)O x l(-1).s, P<0.001), dynamic elastance (76+/-11.2 vs 22.8+/-4.1 cm H(2)O x l(-1), P<0.001), and work of breathing (1.51+/-0.26 vs 0.47+/-0.08, P<0.001). Arterial pH decreased (7.47+/-0.06 vs 7.32+/-0.06, P<0.001), PaCO(2) increased, and PaO(2) decreased. Multiple inert gas elimination showed an absence of shunt, substantial increases in perfusion to low VA/Q regions, and dispersion of VA/Q distribution. He/O(2) reduced lung resistance and work of breathing, and worsened hypercapnia and respiratory acidosis.

CONCLUSIONS

In this model, while He/O(2) improved respiratory mechanics and reduced work of breathing, hypercapnia and respiratory acidosis increased. Close attention should be paid to monitoring arterial blood gases when He/O(2) is used in mechanically ventilated acute severe asthma.

Helium-oxygen therapy for pediatric acute severe asthma requiring mechanical ventilation

OBJECTIVE

To illustrate the use of helium-oxygen gas mixtures as therapy for pediatric patients with acute severe asthma requiring conventional mechanical ventilation.

DESIGN

Retrospective review.

SETTING

Tertiary care children's teaching hospital.

PATIENTS

All mechanically ventilated patients with severe asthma admitted to the pediatric intensive care unit from August 1994 to October 2000.

INTERVENTIONS

Within 24 hrs of intubation or admission, patients were stabilized on volume ventilation, bronchodilator therapy, corticosteroids, and antibiotics when indicated. Hypercapnia was permitted while maintaining arterial blood gas pH > or =7.25. A helium-oxygen gas mixture then was begun with helium flow set at 5-7 L/min, and oxygen flow was titrated to maintain desired oxygen saturation. Only sedated, chemically paralyzed patients with adequate pre-helium-oxygen and post-helium-oxygen measurements were statistically analyzed.

MEASUREMENTS AND MAIN RESULTS

Twenty-eight mechanically ventilated patients with severe asthma placed on helium-oxygen gas mixtures were identified who met study entry criteria. Mean patient age was 8.8 yrs (range, 1.1-14.6). Before helium-oxygen therapy began, mean peak inspiratory pressure was 40.5 +/- 4.2 cm H(2)O, mean arterial blood gas pH was 7.26 +/- 0.05, and mean CO(2) partial pressure was 58.2 +/- 8.5 torr. After patients were placed on helium-oxygen therapy, there was a significant decrease in mean peak inspiratory pressure to 35.3 +/- 3.0 cm H(2)O. Mean pH increased significantly to 7.32 +/- 0.06, and mean partial pressure CO(2) decreased significantly to 50.5 +/- 7.4 torr. Initial mean inspired helium was 57 +/- 4% (range, 32-74). Mechanical ventilation days ranged from 1 to 23 days (mean, 5.0). Hospital stay ranged from 4 to 29 days (mean, 10.1), with an average pediatric intensive care unit stay of 6.9 days (range, 2-24). There were two incidences of pneumothorax.

CONCLUSIONS

In the pediatric patient with severe asthma requiring conventional mechanical ventilation, helium-oxygen administration appears to be a safe therapy and may assist in lowering peak inspiratory pressure and improving blood gas pH and partial pressure CO(2).

Asthma evaluation and management

Asthma is a chronic inflammatory illness with acute exacerbations, which often is encountered in the ED setting. Knowledge of the presentation and treatment of asthma is crucial for any physician treating patients with this disease. Beta-agonist, anticholinergic, and corticosteroid therapy continue to be the mainstay of emergency therapy despite advances in newer medications. Proper attention to long-term treatment of asthma and aggressive treatment of acute exacerbations should help reduce morbidity and mortality.

Heliox vs air-oxygen mixtures for the treatment of patients with acute asthma: a systematic overview

OBJECTIVE

To evaluate, by systematic review, the efficacy of heliox on respiratory mechanics and outcomes in patients with acute asthma.

METHODS

The search strategy included searching electronic databases (MEDLINE, EMBASE, and The Cochrane Library) and the references of relevant articles. Study quality was assessed based on allocation concealment. Randomized controlled trials (RCTs) comparing heliox to an air-oxygen mixture (airO(2)) as an adjunct treatment in patients with acute asthmatic attacks were analyzed. For the qualitative portion of the analysis, all reports of the use of heliox in patients with acute asthma were included.

RESULTS

Four RCTs (n = 278) were found to have a common respiratory parameter (peak expiratory flow rate as a percentage of predicted) suitable for meta-analysis. Within the 92% confidence interval (CI), there was a small benefit with the use of heliox compared to airO(2) (weighted mean difference, + 3%; 95% CI, - 2 to + 8%). There was also a slight improvement in the dyspnea index (weighted mean difference, 0.60; 95% CI, 0.04 to 1.16) with the use of heliox over airO(2). Overall, five RCTs, one nonrandomized unblinded parallel trial, one retrospective case-matched control trial, three case series, and one case report had results in favor of heliox; one RCT and one case series showed no improvement with heliox; one RCT showed a possible detrimental effect with heliox; and 1 small RCT was inconclusive. Most investigators did not prevent entrainment of room air during heliox use or compensate for the lower nebulizing efficiency of heliox.

CONCLUSION

Based on surrogate markers, heliox may offer mild-to-moderate benefits in patients with acute asthma within the first hour of use, but its advantages become less apparent beyond 1 h, as most conventionally treated patients improve to similar levels, with or without it. The effect of heliox may be more pronounced in more severe cases. There are insufficient data on whether heliox can avert tracheal intubation, or change intensive care and hospital admission rates and duration, or mortality.

Use of helium-oxygen mixtures in the treatment of acute asthma: a systematic review

STUDY OBJECTIVE

To determine the effect of the addition of heliox to standard medical care on the course of acute asthma.

DESIGN

Systematic review of randomized and nonrandomized prospective, controlled trials of children and adults that compared heliox to placebo when used in conjunction with other standard acute treatments.

MAIN OUTCOME MEASURES

Pulmonary function tests, hospital admissions, physiologic measures, side effects, and clinical outcomes.

RESULTS

Seven trials were selected for inclusion, with a total of 392 patients with acute asthma. Six studies involved adults, and one study dealt solely with children. The main outcome variable was spirometric measurements (peak expiratory flow or FEV(1)) in six trials. Two studies evaluated the effect of heliox on airways resistance. No significant differences were demonstrated between heliox or oxygen/air groups (standardized mean difference [SMD], - 0.20; 95% confidence interval [CI], - 0.91 to 0.51; p = 0.6). However, the four studies that used heliox to deliver nebulized therapy showed a nonsignificant increase in pulmonary function (SMD, - 0.21; 95% CI, - 0.43 to 0.01; p = 0.06). In two studies of the same subgroup, heliox mixtures produced a significantly greater increase of heart rate than oxygen/air (weighted mean difference, 9.0; 95% CI, 1.27 to 16.8; p = 0.02). However, the four studies that used heliox to deliver nebulized therapy reported a nonsignificant difference in hospital admissions (odds ratio, 1.07; 95% CI, 0.46 to 2.48; p = 0.9). Overall, heliox appears to be safe and well tolerated.

CONCLUSIONS

The existing evidence does not provide support for the administration of helium-oxygen mixtures to emergency department patients with moderate-to-severe acute asthma. However, these conclusions are based on between-group comparisons and small studies, and these results should be interpreted with caution.