title: Validation of continuous thermodilution cardiac output in critically ill patients with analysis of systematic errors.
abstract: OBJECTIVE
  Bolus thermodilution cardiac output (BCO) measurements are affected by variations in injectate volume, rate, and temperature. These variations are eliminated when CO is measured by a continuous automated thermal technique (CCO). Further, CCO eliminates the need for fluid boluses, reduces contamination risk, requires no operator, and provides a continuous CO trend. We prospectively evaluated CCO versus BCO in a population of critically ill adults with low, normal, and high CO states. We sought to discern any systematic effects of temperature fluctuations or signal-to-noise-ratios (SNR) on disparities between BCO and CCO measurements and also sought to assess the relative cost effectiveness of the CCO system.
  
  
  METHODS
  Pulmonary artery catheterizations were performed in a convenience sample of 20 patients over 6 months. BCO data were obtained using a standardized protocol. Three bolus injections of 5% dextrose were given when each CO was within 10% of the median before averaging; otherwise five boluses were given, with the high and low values eliminated before averaging. Injectates were administered randomly through the respiratory cycle and at 1-minute intervals. CCO measurements were recorded from a Vigilance monitor pre and post BCO measurements, yielding an average CCO value. Also recorded were pre- and post-core temperatures and SNR during the first CCO measurement. Cost data included estimates of operator time for BCO determinations as well as costs of Intellicath (Baxter-Edwards, Irvine, CA) pulmonary artery catheters, Vigilance (Baxter-Edwards, Irvine, CA) monitors, conventional catheters, and injectates.
  
  
  RESULTS
  Of the 20 patients, 15 were mechanically ventilated. A total of 306 paired CO values were obtained for analysis. CCO ranged from 2.5 to 14.4 L/min and BCO from 2.4 to 13.3 L/min. Absolute differences between CCO and BCO measurements increased with increasing CO, but percentage differences did not. Of the paired values, 77% were within 1 L/min of one another. Temperature instability and SNR independently had weak correlations with CCO/BCO disparities. The Vigilance system had a slightly higher net cost than conventional BCO, although no economical value was assigned to the clinical usefulness of continuous, as opposed to intermittent, CO monitoring.
  
  
  CONCLUSIONS
  Continuous CO is a reliable and cost-effective alternative to bolus thermodilution CO for critically ill patients in low, normal, and high CO states.
authors.affiliation: Critical Care Medicine Department of the Warren G. Magnuson Clinical Center, National Institutes of Health, Bethesda, MD 20892-1662, USA.
authors.forename: D L
authors.initials: DL
authors.lastname: Medin
authors.forename: D T
authors.initials: DT
authors.lastname: Brown
authors.forename: R
authors.initials: R
authors.lastname: Wesley
authors.forename: R E
authors.initials: RE
authors.lastname: Cunnion
authors.forename: F P
authors.initials: FP
authors.lastname: Ognibene
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D016477:Artifacts; D015982:Bias; D002302:Cardiac Output; D002407:Catheterization, Swan-Ganz; D003362:Cost-Benefit Analysis; D016638:Critical Illness; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic / Q000191:economics / Q000295:instrumentation / Q000379:methods; D011446:Prospective Studies; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted; D013696:Temperature; D013815:Thermodilution / Q000191:economics / Q000295:instrumentation / Q000379:methods*