Application of a new dye for near‐infrared fluorescence laparoscopy of the ureters marked laparoscopic fluorescence imaging systems cannot yet visualize methylene blue though. Furthermore, methylene blue sometimes causes severe adverse reactions, such as methemoglobinaemia or anaphylaxis. Intravenous methylene blue interferes with the ability of the oximeter to measure the saturation of peripheral oxygen (SpO2), resulting in a transient, marked decrease in SpO2, potentially lasting up to several minutes12. The pre‐clinical near‐infrared dye CW800‐CA has fluorescent characteristics at similar wavelengths as indocyanine green (ICG), for which laparoscopic imaging systems are already available8,13. Intravenously administered ICG is not useful for ureteral fluorescence imaging, because it is rapidly cleared by the liver and has no detectable urinary excretion12. In contrast, CW800‐CA can provide bright visualization of ureters by renal clearance7,12. Visualization of the ureters can be rapidly obtained following intravenous injection as shown in this small feasibility study in pigs. In these experiments no influence of the intravenously injected CW800‐CA on SpO2 monitoring was observed. No adverse effects to the administered dye were observed in the present study. Moreover, a single‐dose intravenous toxicity study of CW800‐CA in rats, concluded that a dose of up to 20 mg/kg did not result in adverse reactions following intravenous administration of the dye14. This constitutes a much higher dose than was used in the present study. In the same toxicity study, clearance half‐life of CW800‐CA following intravenous injection was determined to be 35.7 minutes14. This seems sufficient for the described application, as the ureters are normally identified early during the surgical procedure. CW800‐CA dosage in the first experiment of this study was based on the report by Tanaka et al.7. A dose of 7.5 g/kg bodyweight appeared not to be sufficient for laparoscopic fluorescence detection of the ureters in pigs. With a significantly higher dose (85 g/kg) of injected dye, clear visualization of the course of both ureters was obtained. Preinjection of a diuretic (furosemide) has been investigated for its potential to increase near‐infrared fluorescence signal of the intravenously administered dye (in this case methylene blue). However, neither a qualitative nor quantitative improvement was found10. Therefore no furosemide was given before CW800‐CA injection in the present study. With the present commercially available system, the surgeon is able to switch in a split second from the conventional to the fluorescence camera mode and back, using a foot pedal. Unfortunately, direct fluorescence image‐overlay on the conventional anatomical image is not yet possible with the current imaging systems. Although this study only reports on a small sample size and a large difference in dosage of CW800‐CA, the concept of fluorescence visualization of the ureters using CW800‐CA 83
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