title: Five algorithms that calculate cardiac output from the arterial waveform: a comparison with Doppler ultrasound.
abstract: BACKGROUND
  Different mathematical approaches are used to calculate arterial pulse pressure wave analysis (PPWA) cardiac output. The CardioQ-Combi is a research oesophageal Doppler (COODM) monitor that includes these five fundamental PPWA algorithms. We compared these PPWA cardiac output readings to COODM and suprasternal USCOM Doppler (COUS) over a range of cardiac output values induced by dopamine infusion in patients undergoing major surgery. USCOM acted as a control.
  
  
  METHODS
  Serial sets of cardiac output data were recorded at regular intervals as cardiac output increased. Formulae included: cardiac output calculated form systemic vascular resistance (COMAP), pulse pressure (COPP), Liljestrand-Zander formula (COLZ), alternating current power (COAC) and systolic area with Kouchoukos correction (COSA). The reference method for comparisons was COODM. Statistical methods included: Scatter plots (correlation), Bland-Altman (agreement) and concordance (trending) and polar (trending).
  
  
  RESULTS
  From 20 patients 255 sets of cardiac output comparative data were collected. Mean cardiac output for each method ranged between 5.0 and 5.5 litre min(-1). For comparisons between COUS and the five PPWA algorithms with COODM: Correlation was best with COUS (R(2)=0.81) followed by COLZ (R(2)=0.72). Bias ranged between 0.1 and 0.5 litre min(-1). Percentage error was lowest with COUS (26.4%) followed by COLZ (35.2%), others (40.7 to 56.3%). Concordance was best with COUS (92%), followed by COLZ (71%), others (64 to 66%). Polar analysis (mean(standard deviation)) were best with COUS (-2.7 (21.1)), followed by COLZ (+4.7 (26.6).
  
  
  CONCLUSIONS
  The Liljestrand-Zander PPWA formula was most reliable compared with oesophageal Doppler in major surgical patients under general anaesthesia, but not better than USCOM.
authors.affiliation: Department of Anesthesiology, The First Affiliated Hospital of Zhengzhou University, Zhengzhou, China.
authors.forename: J
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Department of Anaesthesia and Intensive Care, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong SAR hcritchley@cuhk.edu.hk.
authors.forename: L A H
authors.initials: LA
authors.lastname: Critchley
authors.affiliation: Department of Anesthesia and Surgical Intensive Care, Peking University First Hospital, Beijing, China.
authors.forename: L
authors.initials: L
authors.lastname: Huang
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000465:Algorithms; D002302:Cardiac Output / Q000502:physiology*; D015150:Echocardiography, Doppler / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000379:methods*; D063177:Pulse Wave Analysis / Q000379:methods*
keywords: cardiac output; doppler; pulse wave analysis