The effect of tidal volume and intravascular volume state on systolic pressure variation in ventilated dogs

Both tidal volume and effective blood volume may affect the variation in the arterial pressure waveform during mechanical ventilation. The systolic pressure variation (SPV), which is the difference between the maximal and minimal systolic pressure values following one positive pressure breath was analyzed in 10 anesthetized and ventilated dogs, during ventilation with tidal volumes of 15 and 25 ml/kg. The dogs were studied during normovolemia, hypovolemia (after bleeding of 30% of estimated blood volume) and hypervolemia (after retransfusion of shed blood with additional 50 ml/kg of plasma expander). The SPV reflected hemodynamic changes and was maximal during hypovolemia and minimal during hypervolemia. Unlike all other hemodynamic parameters it was also affected by the tidal volume and significantly increased at higher tidal volumes during each volume state. We conclude that the SPV and its components are useful parameters in evaluating the intravascular volume state. They also reflect the magnitude of the tidal volume employed.