Central venous pulsations associated with a falsely low oxygen saturation measured by pulse oximetry

Venous pulsations are thought, but to our knowledge have never been demonstrated, to result in underestimation of oxygen saturation measured by pulse oximetry (SpO2); however, to our knowledge, this has never been demonstrated. A patient with ischemic cardiomyopathy requiring intra-aortic balloon counterpulsation (IABC) had to withstand a temporary cessation of IABC (period I), during which she had marked central venous pulsations and a pulse oximeter bias of -18%. After IABC was reinstituted (period II), the venous pulsations disappeared and the bias was reduced to 0%. Cardiac output, systemic vascular resistance, and temperature during both periods were comparable. Pulmonary vascular resistance, however, was much lower during period II. We postulate that the bias was caused by venous pulsations significantly contributing to the AC, or variable component, of light absorption.