title: Assessment of trending ability of cardiac output monitors by polar plot methodology.
abstract: OBJECTIVE
  To develop a valid statistical method of showing acceptable cardiac output (CO) trending ability when new CO monitors are compared to a reference standard, such as thermodilution, using polar coordinates.
  
  
  METHODS
  Developing a new statistical analytic method using historic data.
  
  
  METHODS
  University Hospital Anesthesia and Intensive Care Department.
  
  
  METHODS
  Data taken from previously published CO validation studies.
  
  
  METHODS
  Cartesian data were reanalyzed, being uplifted using Data Thief 3.0 software (http://datathief.org/). Polar plots were constructed from this data. Central zone data (<0.5 L/min or <10% change) were excluded because they introduced statistical noise. Trial polar criteria were set using data from a study that compared 5 CO monitors against thermodilution. Then, these criteria were further validated using data extracted from 15 other studies. Mean (95% confidence intervals) polar angles were used.
  
  
  RESULTS
  Trial data suggest ±5° (angle) ±30° (95% confidence interval) as acceptance limits. Concordance rates (ie, >95%-90%) from 5 articles supported trending, and polar data from these studies concurred with the authors' pilot criteria. Favorable comments on trending also were found in 8 of 15 articles in which radial limits were less than ±32°. Good calibration was associated with a mean polar angle of less than ±5°.
  
  
  CONCLUSIONS
  Polar plots can be used to show the trending ability of CO monitors in comparative validation studies. They overcome the deficiencies of concordance analysis, which uses the direction of change as a statistic and ignores the magnitude of change in CO.
authors.affiliation: Department of Anaesthesia & Intensive Care, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, New Territories, Hong Kong, China. hcritchley@cuhk.edu.hk
authors.forename: Lester A
authors.initials: LA
authors.lastname: Critchley
authors.forename: Xiao X
authors.initials: XX
authors.lastname: Yang
authors.forename: Anna
authors.initials: A
authors.lastname: Lee
mesh_terms: D002302:Cardiac Output / Q000502:physiology*; D006801:Humans; D008991:Monitoring, Physiologic / Q000592:standards* / Q000706:statistics & numerical data / Q000639:trends; D015203:Reproducibility of Results; D013815:Thermodilution / Q000592:standards* / Q000706:statistics & numerical data / Q000639:trends