ABSTRACT

Objective:

Systolic pressure variation results from cyclical fluctuation in the intra-thoracic pressure associated with mechanical ventilation and has been used as a measure of relative hypovolemia in mechanically ventilated patients. The impact of the magnitude of the tidal volume and airway pressure on systolic pressure variation, however, has not been examined in mechanically ventilated patients.

Methods:

Two patients underwent monitoring following elective cardiac surgery. Tidal volume was randomly varied between 3 and 11 mL/kg over a two minute interval, and the corresponding airway pressure was monitored, as were the effects on the systolic pressure variation of the systemic and pulmonary circulations.

Results:

There was a strong correlation between increasing tidal volume and peak airway pressure (p<0.0001). In addition, peak airway pressure strongly correlated with the systolic pressure variation of both the systemic and pulmonary circulations (p<0.0001). The increase in diastolic pulmonary arterial pressure induced by insufflation correlated well with the associated increase in systolic blood pressure (p<0.0001). Similarly, the increase in systolic pulmonary artery pressure (PAP) correlated with the associated decrease in systolic blood pressure induced by insufflation (p<0.0001).

Conclusions:

Systolic pressure variation in the systemic and pulmonary circulations is affected by tidal volume and peak airway pressure. This should be considered when using systolic pressure variation as a marker of intravascular volume status. Our findings regarding the correlations between changes in the pulmonary arterial pressure and the systemic arterial pressure induced by mechanical ventilation are consistent with the proposed physiological mechanisms of systolic pressure variation. (Critical Care and Resuscitation 2004; 6: 167-174)

Key words:

Systolic pressure variation, pulmonary artery pressure variation, plateau pressure, tidal volume, peak airway pressure

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