title: Novel continuous capnodynamic method for cardiac output assessment during mechanical ventilation.
abstract: BACKGROUND
  It is important to be able to accurately monitor cardiac output (CO) during high-risk surgery and in critically ill patients. The invasiveness of the pulmonary artery catheter (PAC) limits its use, and therefore, new minimally invasive methods for CO monitoring are needed. A potential method is estimation of CO from endogenous carbon dioxide measurements, using a differentiated Fick's principle to determine effective pulmonary blood flow (EPBF). In this study, we aimed to validate a novel capnodynamic method (COEPBF) in a wide range of clinically relevant haemodynamic conditions.
  
  
  METHODS
  COEPBF was studied in 10 pigs during changes in preload, afterload, CO increase, and bleeding. An ultrasonic flow probe around the pulmonary artery was used as reference method of CO determination. CO was also measured using a PAC thermodilution technique (COPAC). CO and other haemodynamic data were recorded before and during each intervention. Accuracy and precision and also the ability to track changes in CO were determined using Bland-Altman, four-quadrant plot and polar plot analysis.
  
  
  RESULTS
  COEPBF and COPAC showed equally good agreement, with a tendency to overestimate CO (bias 0.2 and 0.3 litre min(-1), respectively). The overall percentage error was 47% for COEPBF and 49% for COPAC. The concordance for tracking CO changes was 97 and 95% for COEPBF and COPAC, respectively, with an exclusion zone of 15% and radial limits of ±30°.
  
  
  CONCLUSIONS
  COEPBF showed reliable trending abilities, equivalent to COPAC. COEPBF and COPAC also showed low bias but high percentage errors. Further studies in animal models of lung injury and in high-risk surgery patients are warranted.
authors.affiliation: Department of Anaesthesiology, Surgical Services and Intensive Care Medicine, Karolinska University Hospital, Solna SE-171 76, Sweden.
authors.forename: C
authors.initials: C
authors.lastname: Hällsjö Sander
authors.forename: M
authors.initials: M
authors.lastname: Hallbäck
authors.forename: M
authors.initials: M
authors.lastname: Wallin
authors.forename: P
authors.initials: P
authors.lastname: Emtell
authors.forename: A
authors.initials: A
authors.lastname: Oldner
authors.forename: H
authors.initials: H
authors.lastname: Björne
mesh_terms: D000818:Animals; D001783:Blood Flow Velocity / Q000502:physiology; D019296:Capnography / Q000379:methods*; D002245:Carbon Dioxide / Q000032:analysis* / Q000378:metabolism; D002302:Cardiac Output / Q000502:physiology*; D006439:Hemodynamics / Q000502:physiology*; D023421:Models, Animal; D016343:Monitoring, Intraoperative / Q000379:methods / Q000706:statistics & numerical data; D008991:Monitoring, Physiologic / Q000379:methods* / Q000706:statistics & numerical data; D011651:Pulmonary Artery / Q000000981:diagnostic imaging / Q000502:physiology; D015203:Reproducibility of Results; D012121:Respiration, Artificial; D013552:Swine; D013815:Thermodilution / Q000379:methods / Q000706:statistics & numerical data; D014463:Ultrasonography
chemical_list: D002245:Carbon Dioxide
keywords: carbon dioxide, measurement; heart, cardiac output; measurement techniques, carbon dioxide; measurement techniques, cardiac output; measurement techniques, thermodilution