More About Heliox and Bronchiolitis
Muttiah Ganeshananthan, MDCystic Fibrosis Center
PinnacleHealth System
Harrisburg, PA 17105-8700
To the Editor.—
The study by Martinón-Torres et al1 using heliox therapy in infants with acute bronchiolitis makes me question the diagnosis of "bronchiolitis" in those infants. It appears from the study that the use of heliox helped to decrease the work of breathing in these infants. It is conceivable that this was achieved by its property of having lower density. It is also known that heliox has higher viscosity, which affects the laminar flow. Laminar flow is the predominant flow in the peripheral airways or bronchioles. Therefore, patients with true "bronchiolitis" where the inflammation and obstruction is in the peripheral airways will have decreased flow with heliox and increased work of breathing. Because this didn’t happen in these infants, one could say that they didn’t have "bronchiolitis" but bronchitis, where the inflammation and obstruction is in the more central airways. These infants had wheezing, implying that they had central airway narrowing. It would be of interest to analyze the data of individual patients to see 1) if there was any correlation between wheezing and response to heliox and 2) if patients who didn’t have wheezing had any response to heliox.
REFERENCE
- Martinón-Torres F,Rodriguez-Nuñez A, Martinón-Sánchez JM. Heliox therapy in infants with acute bronchiolitis.
Pediatrics.2002; 109
:68
–73
[Abstract/Free Full Text]
Federico Martinón-Torres, MD, PhD
Antonio Rodriguez-Nuñez, MD, PhD
Jose María Martinón-Sánchez, MD, PhD
Department of Pediatrics
Hospital Clínico Universitario de Santiago
Santiago de Compostela, Spain
In Reply.—
We appreciate the interest with which Dr Ganeshananthan read our article.1 He has made some interesting points to which we will respond.
The aim of our study was to assess the clinical efficacy of heliox in infants with respiratory syncytial virus (RSV) bronchiolitis, mainly through the analysis of the changes in the respiratory clinical score. In this score, wheezing was only one of the items considered. The positive effects found were discussed according to the existing theoretical data on the properties and mechanisms of action of heliox in the obstructed airway; however, the exact validation of these mechanisms in the bronchiolitis setting has not been established yet and it was out of the scope of our study.
RSV-infected patients can be further subclassified as having RSV bronchiolitis or RSV pneumonia, depending on the predominant clinical-radiological pattern.2 RSV bronchiolitis diagnostic criteria applied in our study were: respiratory obstructive signs, together with segmentary and/or subsegmentary atelectasis and hyperinflation of the lungs on chest x-ray films. All our patients where RSV-infected infants with a predominant obstructive pattern. Bronchiolitis is a heterogeneous entity, which has been said to involve mainly small airways3; if so, the theoretically expected benefits of heliox in this setting would be smaller. However, 2 facts should be considered. First, the exact proportion of peripheral versus large airways involved—and thus its influence on the clinical picture of bronchiolitis—remains controversial and may vary from case to case. Second, even accepting the major involvement of small (viscosity-dependent) airways, it has been theoretically validated that heliox has beneficial effects even when laminar flow conditions predominate: in both models of obstructed airways (ie, large and small airways) heliox provided a significant benefit in the pressure-flow relation, in contrast to any other nitrogen-oxygen mixture.4
We share Ganeshananthan’s interest in evaluating, and possibly establishing, response patterns to heliox therapy according to the predominant clinical-radiological picture, and moreover, to other factors such as antecedents, age/weight of the patient, first episode or recurrence, and length of course before admission/start of therapy. Nevertheless, the reduced number of patients included in our study, does not allow us to obtain significant data in this sense.
In summary, the topic of our study was to evaluate, from the clinical point of view, whether heliox could be useful for the relief of RSV bronchiolitis symptoms. Despite the already stated limitations to our study, the preliminary answer is yes. This should guarantee additional prospective clinical and experimental studies to provide strong evidence as to include or discard heliox in the therapeutics of bronchiolitis.
REFERENCES
- Martinón-Torres F, Rodriguez-Nuñez A, Martinón-Sánchez JM. Heliox therapy in infants with acute bronchiolitis. Pediatrics.2002; 109 :68 –73
- Newth CJL. Time course of severe respiratory syncytial virus infection in mechanically ventilated infants. Acta Paediatr.2000; 89 :893 –899[CrossRef][Medline]
- O’Brodovich HM, Haddad GG. The functional basis of respiratory pathology. In: Chernick V, Kendig EL, eds. Kendig’s Disorders of the Respiratory Tract in Children. Philadelphia, PA: WB Saunders; 1998:27–74
- Papamoschou D. Theoretical validation of the respiratory benefits of helium-oxygen mixtures. Respir Physiol.1995; 99 :183 –190[CrossRef][Web of Science][Medline]
PEDIATRICS (ISSN 1098-4275). ©2002 by the American Academy of Pediatrics
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