title: Measurement of blood concentration of indocyanine green by pulse dye densitometry--comparison with the conventional spectrophotometric method.
abstract: OBJECTIVE
  Pulse dye densitometry (PDD) uses two wavelengths (805 and 890 nm) in association with pulse oximetry to compute the arterial blood concentration ratio of indocyanine green (ICG) to hemoglobin (Hb). When Hb is measured in the usual way, this permits the PDD to compute cardiac output, plasma or blood volume, and liver blood flow following an intravenous injection of ICG. In this study, we evaluate the accuracy of the PDD calculation of dye concentration by comparing it with measurement of the dye concentration in blood (Cb) measured by the spectrophotometric cuvette method during dye clearance in patients.
  
  
  METHODS
  In 25 patients receiving major abdominal surgery, ICG (10, 20, or 40 mg) was injected into a central vein and arterial ICG concentration was continuously and simultaneously monitored at nose and finger by PDD; concurrently, ICG concentrations were measured by a spectrophotometer at 805 nm in 4 radial arterial blood samples. Repeated measures or one-way ANOVA were used for comparison of ICG concentrations and percent errors by PDD at the nose, finger, and Cb.
  
  
  RESULTS
  The percent error (bias) of calculated dye concentration and its standard deviation (precision) was -3.9 +/- 16.8% (p < 0.01) with the probe on a nostril and 3.4 +/- 12.6% using the finger probe. These errors were found to be greatest when the mean transit time of the dye was rapid (-20.7 +/- 6.8% at nose p < 0.01 and -8.5 +/- 2.5% at finger p < 0.05) due to factors other than the time delay of blood sampling.
  
  
  CONCLUSIONS
  These errors are of similar size to those associated with thermal cardiac output measurement, suggesting that PDD should be valuable clinically as a noninvasive tool especially since it provides values for blood volume and liver blood flow.
authors.affiliation: Department of Critical Care Medicine, Tokyo Medical and Dental University School of Medicine, Japan. taka.ikasika.ccm@med.tmd.ac.jp
authors.forename: T
authors.initials: T
authors.lastname: Imai
authors.forename: K
authors.initials: K
authors.lastname: Takahashi
authors.forename: F
authors.initials: F
authors.lastname: Goto
authors.forename: Y
authors.initials: Y
authors.lastname: Morishita
mesh_terms: D000368:Aged; D004396:Coloring Agents / Q000032:analysis* / Q000493:pharmacokinetics; D003720:Densitometry / Q000379:methods / Q000592:standards*; D004395:Dye Dilution Technique / Q000592:standards*; D005260:Female; D005385:Fingers; D006801:Humans; D007208:Indocyanine Green / Q000032:analysis* / Q000493:pharmacokinetics; D008297:Male; D008875:Middle Aged; D011674:Pulse; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013053:Spectrophotometry / Q000592:standards*
chemical_list: D004396:Coloring Agents; D007208:Indocyanine Green