Changes in stroke volume variation (SVV) and pulse pressure variation (PPV) in response to fluid infusion were experimentally evaluated during vecuronium infusion and sevoflurane anesthesia in 5 adult, mechanically ventilated, euvolemic, beagle dogs. Sequential increases in central venous pressure (CVP; 3-7[baseline], 8-12, 13-17, 18-22 and 23-27 mmHg) were produced by infusing lactated Ringer's solution and 6% hydroxyethyl starch solution. Heart rate (beats/min), right atrial pressure (RAP, mmHg), pulmonary arterial pressure (PAP, mmHg), pulmonary capillary wedge pressure (PCWP, mmHg), transpulmonary thermodilution cardiac output (TPTDCO, l/min), stroke volume (SV, ml/beat), arterial blood pressure (ABP, mmHg), extravascular lung water (EVLW, ml), pulmonary vascular permeability index (PVPI, calculated), SVV (%), PPV (%) and systemic vascular resistance (SVR, dynes/sec/cm(5)) were determined at each predetermined CVP range. Heart rate (P=0.019), RAP (P < 0.001), PAP (P < 0.001), PCWP (P < 0.001), TPTDCO (P=0.009) and SV (P=0.04) increased and SVR (P < 0.001), SVV (P < 0.001) and PPV (P < 0.001) decreased associated with each stepwise increase in CVP. Arterial blood pressure, EVLW, PVPI and the arterial partial pressures of oxygen and carbon dioxide did not change. The changes in SVV and PPV directly reflected the fluid load and the minimum threshold values for detecting fluid responsiveness were SVV >= 11% and PPV >= 7% in dogs.