Accuracy and repeatability of blood volume measurement by pulse dye densitometry compared to the conventional method using Cr-51-labeled red blood cells

Objective:To determine the accuracy and repeatability of pulse dye densitom etry (PDD) in measuring blood volume (BV) by comparing it with the conventi onal method using Cr-51-labeled red blood cells (RI method) and by assessin g sequential measurements. Design: Prospective clinical study. Setting: University hospital. Patients and participants: Eleven adult ICU patients who received cardiac s urgery (Ist ICU day). Interventions: None. Measurements and results: After injecting indocyanine green (10 or 20 mg) i nto the right atrium, its arterial concentration was continuously monitored at the nose and finger by PDD, and BV was calculated by back extrapolating the logarithmic dye concentration on the dye elimination curve between 2.5 and 5.5 min after mean transit time to each mean transit time with the lea st squares method. These measurements were repeated in eight patients and p erformed only once in the other three, and the BV was measured concurrently by the RI method one time. The Bland-Alt-man method was used for evaluatin g differences between methods and within methods. The (percentage) biases a nd standard deviations between the PDD and RI methods and between the succe ssive measurements by PDD at the finger and nose were 0.26 +/- 0.491 (8.8 /- 15.3 %) and 0.004 +/- 0.25 1 (0.06 +/- 5.9 %) with the probe on a nostri l, and 0.16 +/- 0.56 1 (2.5 +/- 14.4 %) and 0.19 +/- 0.31 1 (4.7 +/- 7.3 %) using the finger probe. The bias between methods was less than 10%, and th e repeatability of PDD was better. Conclusions. As PDD can measure BV with good repeatability and with a small bias compared to the RI method, serial changes in BV can be evaluated at t he bedside of critically ill patients noninvasively and repeatedly.