Cardiac Output and Circulating Blood Volume Analysis by Pulse Dye-densitometry

Objective: Pulse dye-densitometry (PDD) is a newly developed method for monitoring the indocyanine green (ICG) concentration in an artery with which cardiac output (CO) and circulating blood volume (CBV) can be determined. We evaluated its accuracy for clinical use.

Methods: In 7 patients under general anesthesia, ICG-sensitive optical probes (805 and 890 nm) were attached to a finger. Following injection of ICG, the arterial concentration of dye was recorded optically by the non-invasive test instrument and sampled arterial blood ICG concentration was also measured photometrically for comparison. In order to validate the PDD analysis, CO was also measured by both the dye dilution cuvette method and by thermodilution in 8 patients scheduled for coronary artery bypass grafting. In 30 other patients, CBV assessed by PDD was compared with its value estimated from body size.

Results: The blood dye concentration correlated well with the values obtained by PDD (r = 0.953, p < 0.01). Mean bias for the test PDD CO was +0.15 +/- 0.72 min l-1 (not significant (n.s.)) compared with the cuvette method while the mean bias of the thermodilution method vs the cuvette method was +0.79 +/- 0.84 min l-1 (p < 0.0001.). The average value of CBV obtained by PDD was 3.81 +/- 1.39 L compared with that estimated value, 3.72 +/- 0.77 L (n.s.).

Conclusions: CO determined by PDD agrees well with cuvette densitometry, and somewhat less well with CO by thermodilution. The new method, by not requiring a pulmonary arterial catheter, is less invasive than either older method, and yields in addition a value of CBV.