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We read with interest the work of Male et al on perception of breathlessness in acute asthma. They studied 27 children with acute asthma, 12 of whom were hypoxic at presentation with SaO2...
We read with interest the work of Male et al on perception of breathlessness in acute asthma. They studied 27 children with acute asthma, 12 of whom were hypoxic at presentation with SaO2 <_92. children="children" presenting="presenting" with="with" significant="significant" hypoxia="hypoxia" sao292="sao292" are="are" considered="considered" as="as" a="a" group="group" who="who" report="report" late="late" to="to" hospital="hospital" and="and" risk="risk" death="death" from="from" asthma="asthma" presenters="presenters" those="those" sao2="sao2"/>92% (early presenters). Perception of breathlessness was measured by what the children reported as the amount of puff they had (HMP score). This was measured on a six-point scale using the concept of blowing up a balloon. Spirometric criteria of respiratory function were measured at admission and at various points during recovery. The authors found lower HMP scores in the hypoxic population, (4 vs 3, p=0.062). They further showed higher HMP/FEV1 ratios in children presenting with hypoxia. They concluded that those with lower SaO2 at presentation perceived breathlessness poorly. This could in some children, contribute to their late presentation and/or death from asthma. At the same value of FEV1 the late presenter reported a higher puff. The result of a high value of HMP/FEV1 in children presenting with significant hypoxia is a remarkable finding from the study.
But the physiological relation of low FEV1 with hypoxia and the possibility of different permutations of FEV1 and HMP score capable of yielding the same ratio preclude the use of this ratio alone as an identifier of the late presenter. The authors acknowledging this handicap went on to examine change in HMP score (from the time of admission to 72 hours), per unit change in FEV1 (deltaHMP/deltaFEV1) per percent of predicted value, against initial SaO2. The hypoxic population was found to have significantly lower dHMP/dFEV1 ratios (median 0.021%-1 vs 0.073%-1 with a p=0.0081).
One child for instance, with SaO2 of 84% at presentation had a dHMP/dFEV1 of 0.04,whereas another with SaO2 of 98% at presentation had a dHMP/dFEV1 of 0.08 (figure 5). The authors conclude, that because the former was reporting a lower improvement than what he had actually undergone, his perception was faulty. This child, they state was at risk of dying because he would stay back home longer, continuing to deteriorate.
There is another way of looking at the data. The child reporting a lower improvement, is essentially a whiner, or the one who genuinely feels so much worse, or, tolerates so little breathlessness. If he were to behave similarly at home as he was in hospital -reporting himself more breathless for his airway obstruction, he would be the one to come so much earlier to medical attention. It is not clear, how the authors assume that the vociferous whiner in improvement, would be a silent sufferer (not perceiving a critical compromise in his lung functions), during worsening.
A high HMP/FEV1 at presentation correctly identifies the faulty perceiver, who reports himself better than his pulmonary parameters. It reflects truthfully the changes in perception and worsening obstruction, in the period immediately preceding presentation. But, a low dHMP/dFEV1, measured in the course of improvement, confounded by presumably more aggressive treatment including oxygen administration for lower SaO2, does not seem a logical parameter to identify those at risk of death from late presentation. Further research is required to identify other characteristics of the subpopulation of asthmatics, who are at a greater risk of late presentation and death from asthma, and also, whether faulty perception of improvement, identified by a low dHMP/dFEV1 is, one of their traits.
(1) Barnes P. Blunted perception and death from asthma. N Eng J Med 1994;330:1383-4.
(2) Kikuchi Y, Okabe S, Tamura G, et al. Chemosensitivity and perception of dyspnea in patients with a history of near fatal asthma. N Eng J Med 1994;330;1329-34.
(3) Male I, Seddon P. The measurement of breathlessness in children with asthma. Am J Resp Crit Care Med 1996;153:A557.