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It has been shown that ventilation-induced pulse pressure variation (PPV) is a better variable than central venous pressure (CVP) or pulmonary artery occlusion pressure (PAOP) for predicting cardiac output changes after fluid administration. The plethysmographic wave form measured with a fingertip pulse is very similar to the arterial blood pressure curve.We investigated whether this widely used, noninvasive instrument could predict fluid responsiveness by conducting an observational study in 32 patients who had undergone cardiac surgery. We compared PPV, CVP, PAOP, diastolic pulmonary artery pressure, and ventilation-induced plethysmographic variation (VPV) for predicting the cardiac output change after the administration of 500 mL 6% hydroxyethylstarch.We found a good correlation between cardiac output changes and both PPV and VPV (P < 0.05). Receiver operating characteristic analysis revealed an area under the curve of 0.937 for PPV and 0.892 for VPV. The optimal thresholds were a variation of 11.3% for both PPV and VPV in predicting a 15% increase in cardiac output.This study shows that VPV, like PPV, is a more reliable predictor of fluid responsiveness than CVP and PAOP.