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.