Hydrogen inhalation for detecting intracardiac left-to-right shunting in adults

The hydrogen inhalation technique is easily performed and exquisitely sensitive for detecting intracardiac left-to-right shunting. Previous studies of this technique relied heavily on data from infants and children, and the distinction between "normal" and "abnormal" was imprecise and somewhat arbitrary. The present study was done to assess the results of hydrogen inhalation in adults with and without intracardiac left-to-right shunting. In 45 adult subjects (15 men, 30 women, aged 18 to 72 years) (18 without and 27 with intracardiac left-to-right shunting), the elapsed time from hydrogen inhalation to its appearance in the pulmonary artery was measured. The 18 patients without shunting had an appearance time of 12 +/- 3 (mean +/- SD) seconds, and it was > or = 9 seconds in all. In contrast, the 27 subjects with shunting had an appearance time of 1.5 +/- 0.7 second, with only 1 of 27 being > or = 3 seconds. There was no relation between the magnitude of left-to-right shunting and the hydrogen appearance time. Thus, the hydrogen inhalation technique easily and reliably separates adult subjects with and without intracardiac left-to-right shunting, with no overlap between the 2 groups.