Relationships between volume and pressure measurements and stroke volume in critically ill patients

Objective:
To evaluate the relationships between the changes in stroke volume
index (SVI), measured in both the aorta and the pulmonary artery, and the
changes in intrathoracic blood volume index (ITBVI), as well as the
relationship between changes in aortic SVI and changes in the pulmonary artery
wedge pressure (PAWP).

      Design:
      Prospective study with measurements at predetermined
            intervals.


      Setting:
      Medical intensive care unit of a university hospital.


      Patients and methods:
      One hundred and fifty-four measurements were taken in 45
            critically ill patients with varying underlying disorders. Aortic SVI and
            pulmonary arterial SVI were determined with thermodilution. PAWP was measured
            using a pulmonary artery catheter. ITBVI was determined with thermal-dye
            dilution, using a commercially available computer system.


      Results:
      A good correlation was found between changes in ITBVI and changes
            in aortic SVI. However, this correlation weakened when changes in ITBVI were
            plotted against changes in pulmonary arterial SVI, which was in part probably
            due to mathematical coupling between ITBVI and aortic SVI. A good correlation
            between changes in ITBVI and changes in aortic SVI could also be established in
            most of the individual patients. No correlation was found between changes in
            PAWP and changes in aortic SVI.


      Conclusion:
      ITBVI seems to be a better predictor of SVI than PAWP. ITBVI may
            be more suitable than PAWP for assessing cardiac filling in clinical
            practice.