A Comparative Study of the Detection of Cardiovascular Shunts by Oxygen Analysis and Indicator Dilution Methods

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Abstract
Advances in cardiovascular surgery have indicated the necessity for precise identification of cardiovascular shunts. Inadequacies of the oxygen method for catheterization have led to incomplete surgical correction or even to needless thoracotomy. In 117 patients with actual or suspected shunts, catheterization was performed using the oxygen method together with the double catheter dye dilution, the hydrogen-platinum method, or both. A step-up of 2.5 volumes per 100 ml between the cava and atrium, 1 volume per 100 ml between atrium and ventricle, or 0.5 volumes per 100 ml between ventricle and pulmonary artery was required to indicate arteriovenous shunting by the oxygen method. Intra-thoracic detection of shunted indicator-labeled blood before systemic detection of non-shunted labeled blood demonstrated arteriovenous shunting. Veno-arterial shunting was localized with dye by the systemic "double hump" contour. When hydrogen was used, the shunting was detected systemically after intrathoracic injection of hydrogen-saline. Discrepancies between oxygen and indicator techniques were found in 23% of the patients. The oxygen method failed to detect or localize left to right shunts in 18%, and right to left shunts in 5%. The oxygen method falsely revealed arteriovenous shunts in 5%. Indocyanine dye usually failed to indicate large right to left shunts which the hydrogen-platinum system readily detected. Failure to administer 100% oxygen, in studying right to left shunts, results in larger errors.