[The use of helium-oxygen mixture in the ventilation study of children with chronic obstructive lung disease]

OBJECTIVE: To study the distribution of Tc-99m DTPA radioaerosol when heliox or oxygen are used in the nebulization of children and adolescents with chronic obstructive pulmonary disease during pulmonary ventilation scintigraphy. MATERIAL AND METHODS: Clinical randomized and controlled trial. Patients with chronic obstructive pulmonary disease (5 to 18 years old) who required pulmonary scintigraphy between March 1996 and September 1998 were included. Obstruction of the lower airway was measured by spirometry. Patients were randomized into two groups according to the gas used for nebulization during scintigraphy: heliox (80% helium and 20% oxygen) or oxygen. Scintigraphy studies were expressed as slope of the cumulative pulmonary radioactivity uptake curve and as the maximal cumulative radioactivity in the lung. The mean diameter of the Tc-99m DTPA particles generated by heliox and oxygen was measured by laser diffraction. RESULTS: Ten patients were allocated in each group. There were no statistical differences (P>0.05) in terms of gender, main diagnosis, signs of malnutrition, mean values of weight, height, body area, or spirometry results. The mean slope in the heliox group (5,039-/+1,652) was significantly different (P=0.018) from the mean slope of the oxygen group (3,410-/+1,100). The mean slope of patients with severe airflow obstruction in the heliox group was statically different (P=0.017) from the mean slope of patients with airflow obstruction in the oxygen group. In both groups, patients without evidence of airflow obstruction were similar in terms of mean slopes (P=0.507) and mean cumulative radiation in the lung (P=0.507). The mean diameter of heliox-generated Tc-99m DTPA particles was 2.13 m (-/+0.62). This was statistically different (P=0.004) from the mean diameter of oxygen-generated particles (0.88-/+0.99 m). CONCLUSIONS: Nebulization with heliox was more efficacious than nebulization with oxygen for distribution and dispersion of Tc-99m DTPA radioaerosol in the lungs of children and adolescents with chronic obstructive pulmonary disease submitted to ventilation scintigraphy. The benefits of heliox over oxygen are more evident in the presence of lower airway obstruction. Without airway obstruction, we did not observe any difference in the distribution and dispersion of radioaerosol in the lungs. Although the mean diameter of the Tc-99m DTPA particles generated by heliox and oxygen was significantly different, the particles generated by both gases were still within the recommended range (between 1 and 5 m). Therefore, this difference does not account for the effects of heliox observed in this study.