Experience With Hydrogen as an Indicator of Left-to-Right Shunts

Abstract

Detection of intracardiac shunts by means of conventional oximetry, dye dilution curves, nitrous oxide, or krypton gas tests, may be hampered by lack of sensitivity of the method, cost, or complexity of equipment and unreliability of the results.The hydrogen technique proposed by Clark and Bargeron (1959a, b) and Bargeron, Clark, and McArthur (1960) seems to obviate these disadvantages. The following is a short survey of our experience with more than 450 hydrogen tests performed in 43 subjects. SUBJECTS AND METHODSOur material includes 28 patients without shunts (rheumatic heart disease, 13; essential hypertension, 4; pericarditis, 1; cor pulmonale, 1; congenital heart disease without shunt, 3; subjects without cardiovascular disease, 6), in whom 256 curves were recorded.We obtained 202 curves in 15 patients with left-to-right shunts (atrial septal defect, 7; ventricular septal defect including one case of maladie de Roger, 6; patent ductus, 1; aorto-pulmonary fistula, 1), ranging from 13 months up to 40 years of age. The shunt was demonstrated either by oximetry, or by dye curves, or by angiography.Hydrogen was administered through a face mask connected by a switch to a gas container. At a given signal, the subject was requested to take a deep breath; younger children under sedation were given the gas at the moment of inspiration. After inhalation, hydrogen gas immediately crosses the pulmonary capillary membrane and enters the arterial blood. A platinum electrode mounted on an intravascular catheter acts as a hydrogen detector; on contact with the platinum, hydrogen becomes ionized, thus creating an electrical potential which can be recorded.We used a commercially available electrode catheter* connected through a control-box (Fig. 1A) to an Electronics for Medicine recorder. Two or more curves were systematically recorded at about 30-second intervals in each of the following locations: right and/or left pulmonary artery, right ventricle, right atrium, superior vena cava. Whenever possible, curves were recorded in the left cardiac cavities in patients with septal defects. As many as 21 curves were thus obtained in a single patient with no untoward effect.A special stylet (Fig. IB) adaptable to a Seldinger arterial needle was later employed for the detection of gas at a peripheral arterial site; the usefulness of such a time reference has been underlined by Hyman et al. (1961). Recently we have started using a thinner platinum electrode probe* which can be introduced through a Cournand needle and may be advanced further up into the aorta.In the earlier studies, a nasal electrode was employed for the exact timing of inspiration; however, it was soon abandoned, the somewhat greater time accuracy being outweighed by the inconvenience caused to the patient; good approximation was obtained by manually recording the onset of inhalation.