title: The qualitative detection of decreases in cardiac output.
abstract: BACKGROUND
  Cardiac output is a major factor in the maintenance of physiological homeostasis and is difficult to measure with accuracy. This study describes an evidence-based technique, based on physiological changes, which may indicate small changes in cardiac output that cannot be measured by current techniques.
  
  
  METHODS
  Synchronous changes in blood pressure, heart rate, pulse amplitude and end-tidal carbon dioxide are analysed using runs analysis and a normalisation technique. An evidence-based algorithm was used to detect possible changes in cardiac output and data extracts from 31 consenting patients are presented as examples.
  
  
  RESULTS
  The decrease in end-tidal carbon dioxide, during steady state ventilation, was greater in those events notified as hypovolaemia associated with a fall in cardiac output than those events notified as hypovolaemia alone. The difference in end-tidal carbon dioxide between the two groups was -0.25 kPa (CI -0.42 to -0.09) p<0.003.
  
  
  CONCLUSIONS
  Runs analysis can detect trends in EtCO2 that during steady state ventilation may indicate a decrease in cardiac output. It is a safe technique; no additional hardware is required and the generated alerts only notify the clinician of the possibility of an adverse change. Determination of the rate of clinically significant false positives and negatives requires further work.
authors.affiliation: Department of Surgery and Anaesthesia, University of Otago Medical School (Wellington), 23A Mein St. 6021, Wellington, New Zealand. Electronic address: michael.harrison@otago.ac.nz.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Harrison
authors.affiliation: Dunedin Hospital, Dunedin, New Zealand.
authors.forename: Ross
authors.initials: R
authors.lastname: Scott-Weekly
authors.affiliation: Dunedin Hospital & Dunedin School of Medicine, Dunedin, New Zealand.
authors.forename: Mathew
authors.initials: M
authors.lastname: Zacharias
mesh_terms: D000758:Anesthesia; D001794:Blood Pressure / Q000502:physiology*; D002245:Carbon Dioxide / Q000032:analysis; D002302:Cardiac Output / Q000502:physiology*; D019295:Computational Biology; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008991:Monitoring, Physiologic; D013990:Tidal Volume / Q000502:physiology
chemical_list: D002245:Carbon Dioxide
keywords: Anaesthesia; Cardiac output; End-tidal carbon dioxide; Non-invasive monitoring