title: Non-invasive estimation of cardiac output in critical care patients.
abstract: OBJECTIVE
  This study was carried out to compare cardiac output measurements determined by thermodilution and by Portapres, a non-invasive system.
  
  
  METHODS
  Eighty-seven non-invasive blood pressure measurements were performed in 46 patients in our critical care unit utilising the new, non-invasive Portapres system. Cardiac output values were obtained from these blood pressure values using an aortic impedance model and compared to cardiac output values estimated by the thermodilution technique.
  
  
  RESULTS
  Statistically significant (p < 0.01) differences (2.3 l/min; limits of agreement +/-5 l/min) were noted between invasive and non-invasive cardiac output measurements. Differences in measured cardiac outputs increased for patients receiving catecholamine therapy, in patients with hemodynamic instability (e.g., sepsis and cardiac insufficiency), in patients with artificial ventilation, in patients with long duration of intensive care, in younger (<60 yr) patients and in women. We found no influence of the body mass index (BMI) on the accuracy of Portapres results. In only one single subgroup, 10 patients with pulmonary diseases, Portapres measurements were not statistically significant different from reference results.
  
  
  CONCLUSIONS
  To date, Portapres measurements cannot replace thermodilution cardiac output estimations. Fluctuations of finger arterial perfusion due to hemodynamic instability, hypothermia and catecholamines may be responsible for problems of Portapres use in critically ill patients.
authors.affiliation: Department of Internal Medicine, University of Münster, Germany.
authors.forename: U M
authors.initials: UM
authors.lastname: Gerhardt
authors.forename: C
authors.initials: C
authors.lastname: Schöller
authors.forename: D
authors.initials: D
authors.lastname: Böcker
authors.forename: H
authors.initials: H
authors.lastname: Hohage
mesh_terms: D000368:Aged; D001011:Aorta / Q000502:physiology; D001794:Blood Pressure; D015992:Body Mass Index; D002302:Cardiac Output; D002395:Catecholamines / Q000494:pharmacology / Q000627:therapeutic use; D003422:Critical Care; D017097:Electric Impedance; D005260:Female; D006439:Hemodynamics; D006801:Humans; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000379:methods; D012121:Respiration, Artificial; D012680:Sensitivity and Specificity; D013815:Thermodilution / Q000295:instrumentation / Q000379:methods
chemical_list: D002395:Catecholamines