Delivery of helium–oxygen mixture during spontaneous breathing: evaluation of three high-concentration face masks

[Does heliox administered by low-flow nasal cannula improve respiratory distress in infants with respiratory syncytial virus acute bronchiolitis? A randomized controlled trial]

OBJECTIVES

The aim of our study is to evaluate whether the use of heliox (79:21) delivered through a low flow nasal cannula would improve respiratory distress in infants with acute bronchiolitis caused by respiratory syncytial virus.

METHODS

We have conducted a prospective randomized controlled study. All patients fulfilled inclusion criteria were randomized to either heliox (79:21) or air via NC at 2 L/min for a continuous 24hours. Measurements were taken at baseline, after 2hours and at the end of the 24hours.

RESULTS

We have included 104 patients into our study. The MCA-S did not show any significant difference between the two groups after 2hours 4.3 vs. 4.1 (P =.78), or at 24hours after 4.2 vs. 4.3 (P =.89). No difference was found in the proportion of participants progressed to MV, n-CPAP or oxygen via nasal cannula (RR 1.0, 0.86 and 0.89) (P= 1.0, .77 and .73). There was no notable reduction in length of treatment in Heliox group 2.42 days vs. 2.79 days in air group P =.65. The in oxygen saturation, PaO₂, and PaCO₂ did not to have any statistical difference between the two studied groups after 2hours and 24hours of treatment.

CONCLUSION

Our data showed absence of any beneficial effect of heliox in a concentration (79:21) delivered through low flow nasal cannula in terms of respiratory distress improvement in infants with RSV acute bronchiolitis.

A Multicenter Randomized Trial Assessing the Efficacy of Helium/Oxygen in Severe Exacerbations of Chronic Obstructive Pulmonary Disease

RATIONALE

During noninvasive ventilation (NIV) for chronic obstructive pulmonary disease (COPD) exacerbations, helium/oxygen (heliox) reduces the work of breathing and hypercapnia more than air/O₂, but its impact on clinical outcomes remains unknown.

OBJECTIVES

To determine whether continuous administration of heliox for 72 hours, during and in-between NIV sessions, was superior to air/O₂ in reducing NIV failure (25-15%) in severe hypercapnic COPD exacerbations.

METHODS

This was a prospective, randomized, open-label trial in 16 intensive care units (ICUs) and 6 countries. Inclusion criteria were COPD exacerbations with Pa_CO2 ≥ 45 mm Hg, pH ≤ 7.35, and at least one of the following: respiratory rate ≥ 25/min, Pa_O2 ≤ 50 mm Hg, and oxygen saturation (arterial [Sa_O2] or measured by pulse oximetry [Sp_O2]) ≤ 90%. A 6-month follow-up was performed.

MEASUREMENTS AND MAIN RESULTS

The primary endpoint was NIV failure (intubation or death without intubation in the ICU). The secondary endpoints were physiological parameters, duration of ventilation, duration of ICU and hospital stay, 6-month recurrence, and rehospitalization rates. The trial was stopped prematurely (445 randomized patients) because of a low global failure rate (NIV failure: air/O₂ 14.5% [n = 32]; heliox 14.7% [n = 33]; P = 0.97, and time to NIV failure: heliox group 93 hours [n = 33], air/O₂ group 52 hours [n = 32]; P = 0.12). Respiratory rate, pH, Pa_CO2, and encephalopathy score improved significantly faster with heliox. ICU stay was comparable between the groups. In patients intubated after NIV failed, patients on heliox had a shorter ventilation duration (7.4 ± 7.6 d vs. 13.6 ± 12.6 d; P = 0.02) and a shorter ICU stay (15.8 ± 10.9 d vs. 26.7 ± 21.0 d; P = 0.01). No difference was observed in ICU and 6-month mortality.

CONCLUSIONS

Heliox improves respiratory acidosis, encephalopathy, and the respiratory rate more quickly than air/O₂ but does not prevent NIV failure. Overall, the rate of NIV failure was low. Clinical trial registered with www.clinicaltrials.gov (NCT 01155310).

Heliox inhalation therapy for bronchiolitis in infants

BACKGROUND

Bronchiolitis is the leading cause of hospitalisation among infants in high-income countries. Acute viral bronchiolitis is associated with airway obstruction and turbulent gas flow. Heliox, a mixture of oxygen and the inert gas helium, may improve gas flow through high-resistance airways and decrease the work of breathing. In this review, we selected trials that objectively assessed the effect of the addition of heliox to standard medical care for acute bronchiolitis.

OBJECTIVES

To assess heliox inhalation therapy in addition to standard medical care for acute bronchiolitis in infants with respiratory distress, as measured by clinical endpoints (in particular the rate of endotracheal intubation, the rate of emergency department discharge, the length of treatment for respiratory distress) and pulmonary function testing (mainly clinical respiratory scores).

SEARCH METHODS

We searched CENTRAL (2015, Issue 2), MEDLINE (1966 to March week 3, 2015), EMBASE (1974 to March 2015), LILACS (1982 to March 2015) and the National Institutes of Health (NIH) website (May 2009).

SELECTION CRITERIA

Randomised controlled trials (RCTs) and quasi-RCTs of heliox in infants with acute bronchiolitis.

DATA COLLECTION AND ANALYSIS

Two review authors independently extracted data and assessed trial quality.

MAIN RESULTS

We included seven trials involving 447 infants younger than two years with respiratory distress secondary to viral bronchiolitis. All children were recruited from a paediatric intensive care unit (PICU; 378 infants), except in one trial (emergency department; 69 infants). All children were younger than two (under nine months in two trials and under three months in one trial). Positive tests for respiratory syncytial virus (RSV) were required for inclusion in five trials. The two other trials were carried out in the bronchiolitis seasons. Seven different protocols were used for inhalation therapy with heliox.When heliox was used in the PICU, we observed no significant reduction in the rate of intubation: risk ratio (RR) 2.73 (95% confidence interval (CI) 0.96 to 7.75, four trials, 408 infants, low quality evidence). When heliox inhalation was used in the emergency department, we observed no increase in the rate of discharge: RR 0.51 (95% CI 0.17 to 1.55, one trial, 69 infants, moderate quality evidence).There was no decrease in the length of treatment for respiratory distress: mean difference (MD) -0.19 days (95% CI -0.56 to 0.19, two trials, 320 infants, moderate quality evidence). However, in the subgroup of infants who were started on nasal continuous positive airway pressure (nCPAP) right from the start, because of severe respiratory distress, heliox therapy reduced the length of treatment: MD -0.76 days (95% CI -1.45 to -0.08, one trial, 21 infants, low quality evidence). No adverse events related to heliox inhalation were reported.We found that infants treated with heliox inhalation had a significantly lower mean clinical respiratory score in the first hour after starting treatment when compared to those treated with air or oxygen inhalation: MD -1.04 (95% CI -1.60 to -0.48, four trials, 138 infants, moderate quality evidence). This outcome had statistical heterogeneity, which remained even after removing the study using a standard high-concentration reservoir mask. Several factors may explain this heterogeneity, including first the limited number of patients in each trial, and the wide differences in the baseline severity of disease between studies, with the modified Wood Clinical Asthma Score (m-WCAS) in infants treated with heliox ranging from less than two to more than seven.

AUTHORS' CONCLUSIONS

Current evidence suggests that the addition of heliox therapy may significantly reduce a clinical score evaluating respiratory distress in the first hour after starting treatment in infants with acute RSV bronchiolitis. We noticed this beneficial effect regardless of which heliox inhalation protocol was used. Nevertheless, there was no reduction in the rate of intubation, in the rate of emergency department discharge, or in the length of treatment for respiratory distress. Heliox could reduce the length of treatment in infants requiring CPAP for severe respiratory distress. Further studies with homogeneous logistics in their heliox application are needed. Inclusion criteria must include a clinical severity score that reflects severe respiratory distress to avoid inclusion of children with mild bronchiolitis who may not benefit from heliox inhalation. Such studies would provide the necessary information as to the appropriate place for heliox in the therapeutic schedule for severe bronchiolitis.

Delivery of heliox with a semi-closed circuit during spontaneous breathing: a comparative economic theoretical study

BACKGROUND

Heliox is a mixture of oxygen and helium which reduces airway resistance in patients with airway obstruction. In clinical practice, patients breathing spontaneously receive heliox via an open circuit. Recently, a semi-closed circuit for heliox administration has been proposed which minimizes consumption of heliox and therefore cost of the heliox therapy; although, the semi-closed circuit is associated with additional costs. The aim of the study is to conduct an economical analysis comparing total cost of heliox therapy using an open versus a semi-closed circuit in spontaneously breathing patients with airway obstruction.

METHODS

Four different systems for heliox administration were analyzed: an open circuit and three alternatives of a semi-closed circuit involving a custom made semi-closed circuit and two standard anesthesia machines. Total costs of heliox therapy were calculated for all the systems. For calculation of gas consumption, the clinical procedures limiting continuous heliox therapy including the aerosol therapy, personal hygiene and nutrition were taken into account. A sensitivity analysis was conducted for main input variables that may influence the results of the study.

RESULTS

Price of gases consumed by a semi-closed system represents less than 20 % of price of gases when a standard open circuit is used. This represents a saving of approximately 540 EUR per patient. The initial cost of the custom-made semi-closed circuit recuperates after treatment of 18 patients. The corresponding number of patients is 32 when a low-cost anesthesia machine is initially acquired and rises to 69 when a highly advanced anesthesia machine is considered.

CONCLUSIONS

Heliox therapy in spontaneously breathing patients using a semi-closed circuit becomes more cost-effective compared to the open circuit, currently used in clinical practice, when applied in a sufficient number of cases. The impact of finding a cheaper way of heliox administration on the clinical practice needs to be ascertained.

Methods for evaluation of helium/oxygen delivery through non-rebreather facemasks

BACKGROUND

Inhalation of low-density helium/oxygen mixtures has been used both to lower the airway resistance and work of breathing of patients with obstructive lung disease and to transport pharmaceutical aerosols to obstructed lung regions. However, recent clinical investigations have highlighted the potential for entrainment of room air to dilute helium/oxygen mixtures delivered through non-rebreather facemasks, thereby increasing the density of the inhaled gas mixture and limiting intended therapeutic effects. This article describes the development of benchtop methods using face models for evaluating delivery of helium/oxygen mixtures through facemasks.

METHODS

Four face models were used: a flat plate, a glass head manikin, and two face manikins normally used in life support training. A mechanical test lung and ventilator were employed to simulate spontaneous breathing during delivery of 78/22 %vol helium/oxygen through non-rebreather facemasks. Based on comparison of inhaled helium concentrations with available clinical data, one face model was selected for measurements made during delivery of 78/22 or 65/35 %vol helium/oxygen through three different masks as tidal volume varied between 500 and 750 ml, respiratory rate between 14 and 30 breaths/min, the inspiratory/expiratory ratio between 1/2 and 1/1, and the supply gas flow rate between 4 and 15 l/min. Inhaled helium concentrations were measured both with a thermal conductivity analyzer and using a novel flow resistance method.

RESULTS

Face models borrowed from life support training provided reasonably good agreement with available clinical data. After normalizing for the concentration of helium in the supply gas, no difference was noted in the extent of room air entrainment when delivering 78/22 versus 65/35 %vol helium/oxygen. For a given mask fitted to the face in a reproducible manner, delivered helium concentrations were primarily determined by the ratio of supply gas flow rate to simulated patient minute ventilation, with the inspiratory/expiratory ratio playing a secondary role. However, the functional dependence of helium concentration on these two ratios depended on the mask design.

CONCLUSIONS

Large differences in mask performance were identified. With continued refinement, the availability of reliable benchtop methods is expected to assist in the development and selection of patient interfaces for delivery of helium/oxygen and other medical gases.