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Effects of increasing airway pressure and PEEP on the assessment of cardiac preload.

BACKGROUND
Cardiac preload is most commonly assessed by pulmonary artery wedge pressure. It was postulated that the right ventricular end-diastolic volume index (RVEDVI) derived by thermodilution would be a better predictor of preload in trauma patients with high airway pressures associated with positive pressure ventilation and positive end-expiratory pressure.


METHODS
Volumetric thermodilution catheters were placed in 52 mechanically ventilated trauma patients. Regression analysis was performed on 986 sets of hemodynamic data comparing pulmonary artery wedge pressure and RVEDVI to cardiac index (CI) at various airway pressures.


RESULTS
There was much better correlation between RVEDVI and CI (r = 0.41) than with pulmonary artery wedge pressure and CI (r = -0.06). This was true of all levels of airway pressure tested. When analyzed by the degree of right ventricular dysfunction, as indexed by right ventricular ejection fraction, the strongest correlation between RVEDVI and CI was noted when right ventricular ejection fraction was > 30%.


CONCLUSIONS
Unlike the pulmonary artery wedge pressure, RVEDVI is as reliable indicator of preload in the mechanically ventilated trauma patient. This is especially true when the right ventricular ejection fraction is not severely depressed.