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Clinical Effects of Heliox Administration for Acute Bronchiolitis in Young Infants
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Parviz Habibi, Pulmonary physician Imperial College, London, Mohi Chowdhury, Elizabeth Reus.
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p.habibi{at}imperial.ac.uk Parviz Habibi, et al.
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Chowdhury M (1), Reus E(2), Habibi P(3) 1 Clinical PhD Research Fellow, Imperial College London and St. Mary’s Hospital, London, United Kingdom. Research grant funded by BOC Medical, UK. 2 Senior Paediatric Research Nurse, Department of Paediatrics, Imperial College London, United Kingdom. Research grant funded by BOC Medical, UK. 3 Senior Lecturer & Consultant, Paediatric Respiratory & Critical Care Medicine, Imperial College London and St. Mary’s Hospital, London, United Kingdom. All correspondence to: Dr P. Habibi, Department of Paediatrics, Wright Fleming Institute, Imperial College London, Norfolk Place, London, W2 1PG, United Kingdom. e-mail: p.habibi@imperial.ac.uk. Tel: +44 20 7594 3990. We read with interest the recent article by Cambonie et al in the March edition of Chest (1) which demonstrated potential benefits from administering heliox to infants with bronchiolitis. This is the second published study of the efficacy of heliox use in infants with acute Bronchiolitis. Hollman et al reported a randomized, double-blind, controlled, crossover study of heliox treatment for children with acute bronchiolitis. That study also showed a greater improvement in the modified Wood’s clinical asthma score for those children receiving helium-oxygen (heliox) gas mixtures compared to those receiving nitrogen- oxygen (airox) gas mixtures (2). We would be interested to know the method of randomisation used in the study by Cambonie et al. The exclusion of patients treated with physiotherapy, bronchodilators and steroids was appropriate, however, we question whether a two-hour time period between the administration of steroids and initiation of study treatment was sufficient to remove potential bias since steroids have a much longer duration of action. Cambonie et al used the same score as others (2;3) - the modified Wood’s clinical asthma score (m-WCAS). However, they used their own devised assessment tool to score respiratory distress. The validity of extrapolation of a visual-analogue scale (VAS) from “pain” into the area of “assessment of respiratory effort” may be questioned since the two areas are unrelated. Furthermore, the VAS used was originally designed for the patients to describe their own pain and not for external observers to make that judgement (4). Gas delivery and blinding remain major challenges in designing trials of heliox therapy. Cambonie et al correctly identify that “the hood may not be optimal for heliox delivery because the helium tends to concentrate at the top of it, which potentially increases the density of the mixture inhaled by the infant”, consistent with the findings of Stillwell et al (5). This “layering effect” gives rise to our concern that, by placing the oxygen analyser at the top of the hood, it is likely to give an underestimate of the FiO2 in the entire chamber. The calibration of the flow meters for gas A and B appears to have been done with air. If so, that is not a valid method since heliox has a lower density and therefore at the set flow rate of 7 L/min the amount of heliox being delivered would have been much greater (approximately 12.6 L/min). Therefore the total flow into the oxyhoods would have been considerably greater for patients receiving gas B. This would have had a potentially significant effect on patient comfort and entrainment of room air. It is possible to manufacture visually identical but functionally different flow meters for trials of heliox therapy (6). The obvious advantages of this are, ‘blinding’ whilst ensuring identical gas flow rates of heliox or airox. The choice of treatment ‘end point’ and the weaning criteria in the study are interesting. The patients’ gas therapy (gas A or B) was discontinued after 60 minutes and then restarted if, 15 minutes later, the score was higher than the value at time 0 + 60 min. The authors stated that the heliox treated group required a significantly longer time to wean. The duration of gas mixture administration was reported as 3.6 ± 1.8 h in the airox group versus 13.0 ± 3.8 h in the heliox group (p < 0.05), yet the authors make no comment on this paradoxical finding. Cambonie et al have shown that heliox improved the respiratory distress score of infants with moderate to severe Bronchiolitis, but the significance of their finding must be accepted with some degree of caution. The m-WCAS at 60 minutes was significantly lower in the heliox group compared to airox group but the time to successful wean was much longer in the heliox group. We agree with Cambonie et al that further studies are needed to examine the possible benefits of heliox inhalation using clinical endpoints such as prevention of endotracheal intubation and improvement in patient outcome in young infants with acute RSV bronchiolitis. A randomised, double blind, controlled, multi-centre trial of heliox therapy in infants with bronchiolitis is therefore underway (6). In conclusion, the authors have attempted to address an important area of research and clinical care. However, until we have evidence from large-scale, prospective, double-blinded, randomised controlled trials, the true efficacy of heliox cannot be conclusively determined. REFERENCES (1) Cambonie G, Milesi C, Fournier-Favre S, Counil F, Jaber S, Picaud JC, et al. Clinical effects of heliox administration for acute bronchiolitis in young infants. Chest 2006 Mar;129(3):676-82. (2) Hollman G, Shen G, Zeng L, Yngsdal-Krenz R, Perloff W, Zimmerman J, et al. Helium-oxygen improves Clinical Asthma Scores in children with acute bronchiolitis. Crit Care Med 1998 Oct;26(10):1731-6. (3) Martinon-Torres F, Rodriguez-Nunez A, Martinon-Sanchez JM. Heliox Therapy in Infants With Acute Bronchiolitis. Pediatrics 2002 Jan 1;109(1):68-73. (4) Coll AM, Ameen JRM, Mead D. Postoperative pain assessment tools in day surgery: literature review. Journal of Advanced Nursing 2004;46(2):124-33. (5) Stillwell PC, Quick JD, Munro PR, Mallory GB, Jr. Effectiveness of open-circuit and oxyhood delivery of helium-oxygen. Chest 1989 Jun;95(6):1222-4. (6) Chowdhury M, Habibi P, et al. Bronchiolitis RCT: Emergency Assisted Therapy - an Evaluation (The BREATHE Study). Current Controlled Trials Register (www.controlled- trials.com/isrctn/trial/BRONCHIOLITIS/0/18238432.html). 27-9-2005. |
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