INDICATOR‑DILUTION STUDIES: IC‑GREEN™ permits recording of the indicator‑dilution curves for both diagnostic and research purpose independently of fluctuations in oxygen saturation. In the performance of dye dilution curves, a known amount of dye is usually injected as a single bolus as rapidly as possible via a cardiac catheter into selected sites in the vascular system. A recording instrument (oximeter or densitometer) is attached to a needle or catheter for sampling of the dye-blood mixture from a systemic arterial sampling site. 

Under sterile conditions, the IC‑GREEN™ powder should be dissolved with the Aqueous Solvent provided for this product, and the solution used within 6 hours after it is prepared. If a precipitate is present, discard the solution. The amount of solvent to be used can be calculated from the dosage form which follows. It is recommended that the syringe used for injection of the dye be rinsed with this diluent. Isotonic saline should be used to flush the residual dye from the cardiac catheter into the circulation so as to avoid hemolysis. With the exception of the rinsing of the dye injection syringe, saline is used in all other parts of the catheterization procedure. 

This matter of rinsing the dye syringe with distilled water may not be critical, since it is known that an amount of sodium chloride sufficient to make an isotonic solution may be added to dye that has first been dissolved in distilled water. This procedure has been used for constant-rate injection techniques without precipitation of the dye. 

The usual doses of IC‑GREEN™ which have been used for dilution curves are as follows: 

    Adults – 5.0 mg 
    Children - 2.5 mg 
    Infants - 1.25 mg 

These doses of the dye are usually injected in a mL volume. An average of five dilution curves are required in the performance of a diagnostic cardiac catheterization. The total dose of dye injected should be kept below 2 mg/kg. 

Calibrating Dye Curves: To quantitate the dilution curves, standard dilutions of IC GREEN™ in whole blood are made as follows. It is strongly recommended that the same dye that was used for the injections be used in the preparation of these standard dilutions. The most concentrated dye solution is made by accurately diluting 1 mL of the 5 mg/mL dye with 7 mL of distilled water. This concentration is then successively halved by diluting 4 mL of the previous concentration with 4 mL of distilled water. (If a 2.5 mg/mL concentration was used for the dilution curves, 1 mL of the 2.5 mg/mL dye is added to 3 mL of distilled water to make the most concentrated "standard" solution. This concentration is then successively halved by diluting 2 mL of the previous concentration with 2 mL of distilled water.) Then 0.2 mL portions (accurately measured from a calibrated syringe) of these dye solutions are added to 5 mL aliquots of the subject's blood, giving final concentrations of the dye in blood beginning with 24.0 mg/liter, approximately (actual concentration depends on the exact volume of dye added). This concentration is, of course, successively halved in the succeeding aliquots of the subject's blood. These aliquots of blood containing known amounts of dye, as well as a blank sample of which 0.2 mL of saline containing no dye has been added, are then passed through the detecting instrument and a calibration curve is constructed from the deflections recorded. 

HEPATIC FUNCTION STUDIES: Due to its absorption spectrum, changing concentrations of IC‑GREEN™ (indocyanine green for injection) in the blood can be monitored by ear densitometry or by obtaining blood specimens at timed intervals. The technique for both methods is as follows. 

The patient should be studied in a fasting, basal state. The patient should be weighed and the dosage calculated on the basis of 0.5 mg/kg of body weight. 

Under sterile conditions, the IC‑GREEN™ powder should be dissolved with the Aqueous Solvent provided. Exactly 5 mL of aqueous solvent should be added to the 25 mg vial giving 5 mg of dye per mL of solution. 

Inject the correct amount of dye into the lumen of an arm vein as rapidly as possible, without allowing the dye to escape outside the vein. (If the photometric method is used, prior to injecting IC‑GREEN™, withdraw 6 mL of venous blood from the patient's arm for serum blank and standard curve construction, and through the same needle, inject the correct amount of dye.)

Ear Densitometry: Ear oximetry has also been used and makes it possible to monitor the appearance and disappearance of IC‑GREEN™ without the necessity of withdrawal and spectrophotometric analysis of blood samples for calibration. An ear densitometer which has a compensatory photo-electric cell to correct for changes in blood volume and hematocrit, and a detection photocell which registers levels has been described. This device permits simultaneous measurement of cardiac output, blood volume and hepatic clearance of IC‑GREEN™* and was found to provide a reliable index of plasma removal kinetics after single injections or continuous intrusions of IC‑GREEN™. This technique was employed in newborn infants, healthy adults and in children and adults with liver disease. The normal subject has a removal rate of 18‑24% per minute. Due to the absence of extra‑hepatic removal, IC‑GREEN™ was found to be ideally suited for serial study of severe chronic liver disease and to provide a stable measurement of hepatic blood flow. In larger doses, IC‑GREEN™ has proven to be particularly valuable in detecting drug‑induced alterations of hepatic function and in the detection of mild liver injury. 

Using the ear densitometer, a dosage of 0.5 mg/kg in normal subjects gives the following clearance pattern. 

*Dichromatic earpiece densitometer supplied by The Waters Company, Rochester, Minnesota.