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

ObjectiveTo evaluate the relationships between the changes in stroke volumeindex (SVI), measured in both the aorta and the pulmonary artery, and thechanges in intrathoracic blood volume index (ITBVI), as well as therelationship between changes in aortic SVI and changes in the pulmonary arterywedge pressure (PAWP).DesignProspective study with measurements at predeterminedintervals.SettingMedical intensive care unit of a university hospital.Patients and methodsOne hundred and fifty-four measurements were taken in 45critically ill patients with varying underlying disorders. Aortic SVI andpulmonary arterial SVI were determined with thermodilution. PAWP was measuredusing a pulmonary artery catheter. ITBVI was determined with thermal-dyedilution, using a commercially available computer system.ResultsA good correlation was found between changes in ITBVI and changesin aortic SVI. However, this correlation weakened when changes in ITBVI wereplotted against changes in pulmonary arterial SVI, which was in part probablydue to mathematical coupling between ITBVI and aortic SVI. A good correlationbetween changes in ITBVI and changes in aortic SVI could also be established inmost of the individual patients. No correlation was found between changes inPAWP and changes in aortic SVI.ConclusionITBVI seems to be a better predictor of SVI than PAWP. ITBVI maybe more suitable than PAWP for assessing cardiac filling in clinicalpractice.

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