title: Continuous measurement of cardiac output by the Fick principle: clinical validation in intensive care.
abstract: OBJECTIVE
  To compare continuous measurement of cardiac output by the Fick principle with the thermodilution cardiac output technique in hemodynamically unstable patients.
  
  
  METHODS
  An open comparison of two methods.
  
  
  METHODS
  Multidisciplinary ICU in a university hospital.
  
  
  METHODS
  Eight patients after coronary bypass surgery and 13 patients with hyperdynamic septic shock. All patients were mechanically ventilated.
  
  
  RESULTS
  The continuous Fick cardiac output technique was compared with the thermodilution cardiac output using both warm and cold injection in the coronary artery bypass surgery patients and using warm injection only in the patients with hyperdynamic septic shock. The mean difference between the continuous cardiac output technique and all thermodilution measurements (n = 201) was 0.6 +/- 19%. There was a good correlation between the continuous cardiac output and the warm thermodilution technique (n = 125, r2 = .79; p less than .001). When consecutive measurements with warm and cold thermodilution were compared with the respective Fick-derived values (n = 76), the mean differences between the Fick-derived and the warm and cold thermodilution cardiac output values were 0.2 +/- 1.0 L/min and 0.3 +/- 1.0 L/min, respectively. The relationship between Fick-derived and both methods of thermodilution-derived cardiac output was relatively constant during different modes of ventilatory support. The correlation between the thermodilution measurements with cold and room temperature injectate was weak (r2 = .36; p less than .001), whereas a good correlation was observed between the respective Fick-derived values (r2 = .73; p less than .001). The mean difference between the warm and cold thermodilution cardiac output measurements was 0.1 +/- 1.1 L/min and between the corresponding Fick-derived measurements was 0.01 +/- 0.7 L/min.
  
  
  CONCLUSIONS
  Continuous measurement of cardiac output by the Fick principle offers a convenient, reproducible method for hemodynamic monitoring of unstable patients. The variation between the two tested thermodilution techniques is likely to reflect relatively rapid dynamic variation of cardiac output, which is filtered in the 1-min average of cardiac output obtained by the continuous Fick technique.
authors.affiliation: Department of Intensive Care, Kuopio University Hospital, Finland.
authors.forename: O
authors.initials: O
authors.lastname: Keinänen
authors.forename: J
authors.initials: J
authors.lastname: Takala
authors.forename: A
authors.initials: A
authors.lastname: Kari
mesh_terms: D000328:Adult; D001784:Blood Gas Analysis; D001794:Blood Pressure; D002153:Calorimetry, Indirect; D002302:Cardiac Output; D001026:Coronary Artery Bypass; D003422:Critical Care / Q000379:methods*; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic; D010101:Oxygen Consumption; D011184:Postoperative Period; D012121:Respiration, Artificial; D012772:Shock, Septic / Q000503:physiopathology; D013815:Thermodilution / Q000379:methods