Indocyanine green clearance and estimation of plasma volume in the normal horse.

The study aims at determining the effectiveness of using the Indocyanine green (ICG) dye in estimating the plasma volume of horses during cardiovascular testing and recording its pharmacokinetics for reference in hepatic function testing.

Study Rationale

• The research revolves around equine exercise physiology and how it impacts cardiovascular functions in horses. The researchers want to develop a new and effective way to measure plasma volume during exercise testing regimes.
• The team opts to explore Indocyanine green (ICG) as a replacement for Evans blue dye. Evans blue dye was a widely used element in plasma volume estimation but is no longer easily accessible for clinical use.

Choice of Indocyanine Green (ICG)

• The ICG dye has shown promise in cardiovascular studies in humans and is similarly bound to protein (essentially albumin) upon intravenous injection. This binding means that it is basically limited to the vascular space.
• Previous studies on dogs demonstrated that plasma volume measured with both dyes were not significantly different, hinting at the potential of ICG to replace Evans blue for plasma volume estimation in horses.
• The additional advantage of ICG is that it can also be employed to evaluate hepatic function—an attribute making it even more interesting to the researchers.

Research Aim

• The goal of the study is to establish recommendations on the use of the ICG dye for measuring plasma volume (PV) in horses.
• Another aspect of the research involves documenting the pharmacokinetics of the ICG dye’s elimination from blood. This information will be used to provide reference values for hepatic function testing of horses in future studies.

The Importance of the Study

• The successful use of ICG in measuring plasma volume could replace the no longer readily available Evans blue dye technique. It would enable more accurate and reliable exercise testing on horses, ensuring optimum physiological adaptations to athletic performance.