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Madigan Army Medical Center Tacoma, WA
Correspondence to: Col Edward R. Carter, MD, FCCP, Department of Pediatrics, Madigan Army Medical Center, Tacoma, WA 98431; e-mail: 5Carter{at}msn.com
To the Editor:
The study by Kass and Terregino (CHEST; August 1999)1 adds to the growing body of evidence that heliox is effective in improving airflow obstruction and dyspnea in patients treated in the emergency department (ED) for acute, severe asthma. However, in the first paragraph of their discussion the authors state that "similar objective improvements have been demonstrated in children" and reference two studies, one of which was performed by my colleagues and myself.2 Using a double-blind cross-over design, we found that heliox had absolutely no effect on either FEV1 or dyspnea in 11 children who were admitted to the hospital with acute asthma. We concluded that heliox was not beneficial in our study population. While we did find that the children with less severe airway obstruction had some improvement in peak expiratory flow rate (PEFR), though not in FEV1, with heliox, those with the most severe airway obstruction had essentially the same values for PEFR and FEV1 during air and heliox breathing. PEFR is the spirometric value that is most likely to be associated with turbulent flow and, thus, is the most susceptible to improvement with heliox. I wonder whether the patients in the study by Kass and Terregino had any significant change in FEV1? As Kass and Terregino did not calibrate the peak flowmeters with heliox, we really do not know whether their two patient groups started from the same baseline. Moreover, how can we be sure that a change in PEFR with heliox using an uncalibrated peak flowmeter is equivalent to the same change in PEFR while breathing air? Nevertheless, there is substantial evidence that heliox can benefit patients presenting to the ED with acute, severe asthma. However, there are few data that confirm the benefit from heliox in the inpatient setting. Our study in children hospitalized with acute asthma found no benefit from heliox and does not support the findings by Kass and Terregino.
References
Cooper Hospital/University Medical Center UMDNJ/Robert Wood Johnson School of Medicine at Camden Camden, NJ
Correspondence to: Jonathan E. Kass, MD, FCCP, Cooper Hospital/University Medical Center, UMDNJ/Robert Wood Johnson School of Medicine at Camden, Suite 312, Three Cooper Plaza, Camden, NJ 08103
To the Editor:
Drs. Rodrigo and Rodrigo in their letter suggest that the heliox group had a more rapid onset than the oxygen group. In our study (CHEST; August 1999),1 there was a considerable overlap in duration of symptoms between the groups, which was not statistically significant (p = 0.30). Previously it had been demonstrated that patients with a duration of symptoms < 72 h had a better chance of responding successfully to heliox.2 Almost all of the oxygen group patients had a duration of symptoms <72 h, and yet only 17% had a 20% increase in peak expiratory flow (PEF) and percent predicted PEF (%PEF), while 100% of the heliox group did. They also suggest that the heliox group had more severe asthma at presentation than the oxygen group, which could have accounted for the differences found between the groups in response to the treatments. Since the intrinsic variation in PEF is large, the mean differences in PEF and %PEF between the groups of 19.1 L/min and 4.4%, respectively, are small and were not statistically significant (p = 0.27). There were trends for the heliox group to have higher dyspnea scores and vital signs. Since both groups had severe airflow obstruction with a %PEF < 31% that was not statistically significant, it is highly unlikely that these small differences in PEF and trends in dyspnea scores and vital signs between the groups biased the data such that all of the heliox group had a rapid response to treatment while only a few of the oxygen group did.
Dr. Carter alludes to the statement in our discussion that "similar objective findings have been demonstrated in children."1 He takes exception to our reference to his study supporting this statement. The objective findings that we referred to were PEF and dyspnea and not FEV1. In fact, his study did show a significant (p = 0.04) difference in %PEF between heliox and air (control) treatment arms.3 He is correct in that there were no statistically significant differences in dyspnea scores between the groups, but this may have been due to the very low baseline scores (mean 2.5 on a 0 to 10 scale). While his study did not show a significant difference between the treatments for percent predicted FEV1 (%FEV1), there was a difference in %PEF and percent predicted FEF25–75 (midexpiratory flow rate). There was also a trend (p = 0.07) for improvement in %FEV1 for heliox when compared to baseline. It is also more common to look for an improvement in FEV1 by using percent change in actual value from baseline than change in percent predicted.4 This may have improved the analysis of the response to heliox. There is also a second reference supporting the alluded-to statement, which shows a 69.4% increase in PEF and decrease in dyspnea score from 5.7 to 1.9.5 Both of these values are highly statistically significant. Dr. Carter also questions the effect of heliox on PEF with uncalibrated peak flowmeters. As we referenced in our discussion, it has been shown that heliox causes a large underestimation of PEF6 and that correcting for heliox greatly increases the improvement in PEF with heliox.
References
This article has been cited by other articles:
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  J. M. Haynes, R. J. Sargent, and E. L. Sweeney Use of Heliox to Avoid Intubation in a Child With Acute Severe Asthma and Hypercapnia Am. J. Crit. Care., January 1, 2003; 12(1): 28 - 30. [Full Text] [PDF]
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