Estimation of indocyanine green concentration in blood from fluorescence emission: application to hemodynamic assessment during hemodialysis

Measurement of Blood Dilution during Lancet-Free Blood Sampling

In this paper, we report on a fluorescent and colorimetric system for measuring the dilution of capillary blood released by a needle-free jet injector. Jet injection uses a high-speed liquid jet to penetrate tissue, and in the process can release capillary blood that can be collected for performing blood tests. In this way, blood sampling can be performed without the use of a lancet. However, any injectate that mixes with the collected blood dilutes the sample and may significantly impact subsequent analyses. By adding the fluorescent marker indocyanine green to the injected liquid, the fraction of injectate mixed into the collected blood can be measured. The incorporation of colorimetry allows our system to also correct for the impact of hematocrit on fluorescence. The results from this system show that it can determine the dilution of blood that has been diluted by up to 10 %, the upper limit of dilution typically observed in lancet-free blood sampling via jet injection.Clinical Relevance- Blood samples can be collected by jet injection without significant dilution, avoiding the need for lancing.

Measurement of Cardiac Output and Blood Volume During Hemodialysis with Fluorescent Dye Dilution Technique

Intradialytic hypotensive events (IDH) accompanied by deleterious decreases of the cardiac output complicate up to 25% of hemodialysis treatments. Monitoring options available to track hemodynamic changes during hemodialysis have been found ineffective to anticipate the occurrence of IDH. We have assembled opto-electronic instrumentation that uses the fluorescence of a small bolus of indocyanine green dye injected in the hemodialysis circuit to estimate cardiac output and blood volume based on indicator dilution principles in patients receiving hemodialysis. The instrument and technique were tested in 24 adult end-stage renal failure subjects during 64 hemodialysis sessions. A single calibration factor could be used across subjects and across time. Intra-subject variability of the measurements over time was <10%. Stroke volume index (SVI) (mean ± SEM = 34 ± 1 vs. 39 ± 2 mL m^-2) and central blood volume (CBV) index (783 ± 36 vs. 881 ± 33 mL m^-2) were lower at the beginning of the sessions in which IDH eventually occurred. Cardiac index, SVI, and CBV index decreased with hemodialysis in all treatment sessions but the decrease was more intense in the IDH sessions. We conclude that hemodynamic monitoring can be implemented in patients receiving hemodialysis with minimal disruption of the treatment and could help understand intradialytic hypotension.

Indocyanine green as a near-infrared fluorescent agent for identifying parathyroid glands during thyroid surgery in dogs

BACKGROUND

Surgical procedures involving the thyroid gland require identification of the parathyroid glands. Indocyanine green (ICG) is a near-infrared (NIR) fluorescent contrast agent used for a variety of procedures such as intraoperative angiography, extrahepatic cholangiography, and lymph node mapping. In this study, we used a canine model to evaluate ICG for NIR fluorescent imaging of the parathyroid gland.

METHODS

Three dogs were used for the study. The dogs were administered general anesthesia, and after surgical dissection, each dog received a series of intravenous ICG doses ranging from 12.5 to 100 µg/kg ICG. The excitation light source used to illuminate the operating field was a NIR laser (λ = 785 nm). Intravascular ICG fluorescence (λ = 835/45 nm) was recorded using a charge-coupled device that employed optical filtering to block ambient and laser light. Fluorescent imaging was assessed after injection of each dose of ICG.

RESULTS

NIR fluorescent imaging visualized the parathyroid glands. The intensity curves showing the peak and plateau of fluorescence are similar regardless of the concentration of ICG. The time to peak fluorescent intensity was 50.2 ± 2.0 s after injection of ICG. Taking into consideration background fluorescent intensity, the estimated optimal dose of ICG was 18.75 µg/kg. At 106.7 ± 5.8 s, the parathyroid glands lost much of their fluorescence, although they remained sufficiently fluorescent to be distinguishable. There was a positive correlation of fluorescent intensity with ICG dose escalation up to 25 µg/kg.

CONCLUSIONS

ICG NIR fluorescent imaging was useful in detecting the parathyroid glands of dogs. By allowing detection of parathyroid glands, the current technique shows promise for use by endocrine surgeons performing thyroidectomies.