title: Predictors of the accuracy of pulse-contour cardiac index and suggestion of a calibration-index: a prospective evaluation and validation study.
abstract: BACKGROUND
  Cardiac Index (CI) is a key-parameter of hemodynamic monitoring. Indicator-dilution is considered as gold standard and can be obtained by pulmonary arterial catheter or transpulmonary thermodilution (TPTD; CItd). Furthermore, CI can be estimated by Pulse-Contour-Analysis (PCA) using arterial wave-form analysis (CIpc). Obviously, adjustment of CIpc to CItd initially improves the accuracy of CIpc. Despite uncertainty after which time accuracy of CIpc might be inappropriate, recalibration by TPTD is suggested after a maximum of 8 h. We hypothesized that accuracy of CIpc might not only depend on time to last TPTD, but also on changes of the arterial wave curve detectable by PCA itself. Therefore, we tried to prospectively characterize predictors of accuracy and precision of CIpc (primary outcome). In addition to "time to last TPTD" we evaluated potential predictors detectable solely by pulse-contour-analysis. Finally, the study aimed to develop a pulse-contour-derived "calibration-index" suggesting recalibration and to validate these results in an independent collective.
  
  
  METHODS
  In 28 intensive-care-patients with PiCCO-monitoring (Pulsion Medical-Systems, Germany) 56 datasets were recorded. CIpc-values at baseline and after intervals of 1 h, 2 h, 4 h, 6 h and 8 h were compared to CItd derived from immediately subsequent TPTD. Results from this evaluation-collective were validated in an independent validation-collective (49 patients, 67 datasets).
  
  
  RESULTS
  Mean bias values CItd-CIpc after different intervals ranged between -0.248 and 0.112 L/min/m(2). Percentage-error after different intervals to last TPTD ranged between 18.6% (evaluation, 2 h-interval) and 40.3% (validation, 6 h-interval). In the merged data, percentage-error was below 30% after 1 h, 2 h, 4 h and 8 h, and exceeded 30% only after 6 h. "Time to last calibration" was neither associated to accuracy nor to precision of CIpc in any uni- or multivariate analysis. By contrast, the height of CIpc and particularly changes in CIpc compared to last thermodilution-derived CItd(base) univariately and independently predicted the bias CItd-CIpc in both collectives. Relative changes of CIpc compared to CItd(base) exceeding thresholds derived from the evaluation-collective (-11.6% < CIpc-CItd(base)/CItd(base) < 7.4%) were confirmed as significant predictors of a bias |CItd-CIpc| ≥ 20% in the validation-collective.
  
  
  CONCLUSIONS
  Recalibration triggered by changes of CIpc compared to CItd(base) derived from last calibration should be preferred to fixed intervals.
authors: II. Medizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, Ismaninger Strasse 22, D-81675 Munich, Germany.
authors: Wolfgang
authors: W
authors: Huber
authors: II. Medizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, Ismaninger Strasse 22, D-81675 Munich, Germany.
authors: Jonas
authors: J
authors: Koenig
authors: II. Medizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, Ismaninger Strasse 22, D-81675 Munich, Germany.
authors: Sebastian
authors: S
authors: Mair
authors: Institut für Medizinische Statistik und Epidemiologie, Klinikum Rechts der Isar; Technische Universität München, Ismaninger Strasse 22, D-81675 Munich, Germany.
authors: Tibor
authors: T
authors: Schuster
authors: II. Medizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, Ismaninger Strasse 22, D-81675 Munich, Germany.
authors: Bernd
authors: B
authors: Saugel
authors: Toxikologische Abteilung, II. Medizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, Ismaninger Strasse 22, D-81675 Munich, Germany.
authors: Florian
authors: F
authors: Eyer
authors: II. Medizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, Ismaninger Strasse 22, D-81675 Munich, Germany.
authors: Veit
authors: V
authors: Phillip
authors: II. Medizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, Ismaninger Strasse 22, D-81675 Munich, Germany.
authors: Caroline
authors: C
authors: Schultheiss
authors: II. Medizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, Ismaninger Strasse 22, D-81675 Munich, Germany.
authors: Philipp
authors: P
authors: Thies
authors: II. Medizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, Ismaninger Strasse 22, D-81675 Munich, Germany.
authors: Ulrich
authors: U
authors: Mayr
authors: II. Medizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, Ismaninger Strasse 22, D-81675 Munich, Germany.
authors: Henrik
authors: H
authors: Einwächter
authors: II. Medizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, Ismaninger Strasse 22, D-81675 Munich, Germany.
authors: Matthias
authors: M
authors: Treiber
authors: II. Medizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, Ismaninger Strasse 22, D-81675 Munich, Germany.
authors: Josef
authors: J
authors: Hoellthaler
authors: II. Medizinische Klinik und Poliklinik, Klinikum rechts der Isar, Technische Universität München, Ismaninger Strasse 22, D-81675 Munich, Germany.
authors: Roland M
authors: RM
authors: Schmid
mesh_terms: D000465:Algorithms; D001794:Blood Pressure / Q000502:physiology; D002138:Calibration; D002302:Cardiac Output / Q000502:physiology*; D003422:Critical Care; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic; D011446:Prospective Studies; D011674:Pulse / Q000592:standards*; D012680:Sensitivity and Specificity; D013815:Thermodilution / Q000379:methods; D014655:Vascular Resistance / Q000502:physiology
keywords: Accuracy; Calibration; Cardiac index; Cardiac output; Hemodynamic monitoring; Precision; Pulse contour analysis; Transpulmonary thermodilution