Volumetric capnography to detect ventilation inhomogeneity in children and adolescents with controlled persistent asthma

Abstract

Objectives: To study changes in the variables of volumetric capnography in children and adolescents with asthma compared with a control group and to investigate their changes with the use of bronchodilators and bronchial provocation test with methacholine. Methods:One hundred and three patients with controlled persistent asthma and 40 healthy volunteers participated in the study. All of them underwent volumetric capnography and spirometry. All asthmatics repeated the tests after bronchodilator use. Among 103 asthma patients, 33 underwent methacholine challenge test, and measures were recorded on three occasions: before and after methacholine and after bronchodilator use. Results:Compared with the control group, asthmatics had an increase in the slope of phase III normalized by tidal volume and decreases in tidal volume, forced expiratory volume in one second, forced vital capacity, rate of obstruction and forced expiratory flow between 25 to 75% of forced vital capacity. After bronchodilator use, there was an increase in spirometric variables, volume of anatomic dead space, and decrease in the slope of phase II normalized by tidal volume, but the slope of phase III normalized by tidal volume did not change. After methacholine, there was an increase in this variable, which decreased after bronchodilator use. Conclusions:The increase in the slope of phase III normalized by tidal volume in asthma patients suggests that these patients have ventilation inhomogeneity in the distal air spaces, which may reflect chronic structural disorders or reversible acute changes seen on the bronchial provocation test.J Pediatr (Rio J). 2011;87(2):163-168: Capnography, spirometry, pediatrics, asthma. ResumoObjetivos: Estudar alterações nas variáveis de capnografia volumétrica em crianças e adolescentes asmáticos comparados com grupocontrole e investigar suas mudanças com o uso do broncodilatador e do teste de broncoprovocação com metacolina. Métodos:Cento e três pacientes com asma persistente controlada e 40 voluntários saudáveis participaram do estudo. Todos realizaram exames de capnografia volumétrica e espirometria. Todos os asmáticos repetiram os exames após uso do broncodilatador. Dos 103 asmáticos, 33 realizaram teste de broncoprovocação com metacolina, e foram registradas as medidas em três momentos: antes e após metacolina e após broncodilatador. Resultados:Comparados ao grupo-controle, os asmáticos apresentaram aumento do slope da fase III normalizado pelo volume corrente e diminuição do volume corrente, do volume expiratório forçado no primeiro segundo, da capacidade vital forçada, do índice de obstrução e do fluxo expiratório forçado entre 25 a 75% da capacidade vital forçada. Após o broncodilatador, houve aumento das variáveis espirométricas, do volume espaço morto anatômico e diminuição do slope da fase II normalizado pelo volume corrente; porém não houve alteração do slope da fase III normalizado pelo volume corrente. Após a metacolina, houve aumento dessa variável, com diminuição após broncodilatador. Conclus...

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“…According to Almeida et al, (9) the increase in the phase III slope normalized to tidal volume in asthma patients suggests that these patients have ventilation inhomogeneity in the distal air spaces. The authors speculated that this reflects chronic structural disorders or reversible acute changes seen on the bronchial provocation test.…”

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“…asthma [8], may still exist to some degree in healthy subjects [9]. Seventeen healthy volunteers (11 male/6 female) were recruited.…”

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“…Changes in the morphology of the capnogram indicate ventilation disturbances, and several indices based upon the geometry of the curve were developed in order to quantify ventilation homogeneity distribution. [9][10][11] Moreover, capnography provides an assessment of ventilation/perfusion ratio (V /Q ) mismatch through measurements of end-tidal CO 2 (P ETCO 2 ). The difference between P aCO 2 and P ETCO 2 in healthy subjects is very small, so P ETCO 2 may reflect P aCO 2 .…”

“…The volumetric capnogram, besides quantitative monitoring of the P ETCO 2 , provides extensive physiological information about production, transportation, and elimination of CO 2 within the lungs through waveform patterns. [9][10][11]14 Volumetric capnography, unlike time-based capnography, allows identification of CO 2 from sequential emptying of alveoli, and anatomic V D measures, and evaluation of V D in each breath. Time-based capnography requires simpler equipment than does volumetric capnography, which involves a pneumotachometer attached to a capnograph, making it a more expensive apparatus.…”

“…24,25 Furthermore, volumetric capnography can discriminate healthy individuals from those with lung disease, such as cystic fibrosis, bronchiectasis, COPD, lung fibrosis, and asthma, which presents a steeper slope of phase 3 of the capnogram. [9][10][11] In this issue of RESPIRATORY CARE, Bhalla et al 26 The interpretation of capnography must take into account the stability of physiologic variables, such as minute ventilation, V T , cardiac output, and CO 2 body storage. As a result, the evaluation and interpretation of capnographic data in children should be cautious, particularly in a critical care setting.…”