The first case of PPC was reported in 1967 by Edwards [1]. Although approximately 50% of patients need to convert to hemodialysis, most patients still need to continue CAPD for social reasons [2], and they require non-surgical or surgical treatment. As the surgical procedures to treat PPC, resection, direct suturing, and reinforcement of the responsible lesion of the diaphragm are performed, and these techniques are used either singly or in combination. In 1996, Di Bisceglie reported the first case of VATS for a PPC [3]. For identification of the communication between the peritoneal and pleural cavities, scintigraphy, the dye method (indigo carmine [6] and ICG [7]), and the CO2 method [8] have been reported.
In our previous case, we used indigo carmine to identify the communicating lesion of the diaphragm [9]. However, a small lesion was difficult to detect because of poor visibility so we think ICG-HSA method is good for detecting the communication site. ICG is a water-soluble amphiphilic molecule with a molecular weight of 774.96 Da. Its hydrodynamic diameter is 1.2 nm, rendering it an excellent vascular and lymphatic contrast agent if injected intravenously and into the lymphatic system (for example by subcutaneous injection), respectively. After intravenous injection, 95% of ICG will bind to serum macromolecules such as albumin and lipoprotein [10], generating fluorescence in the near-infrared (center wavelength of 845 nm) with illumination by light of wavelength of 750–800 nm as the excitation light. In blood vessels, ICG binds lipoprotein in the blood and is easy to detect with an NIR camera.
Previous preclinical and clinical work has demonstrated that adsorption of ICG to human serum albumin increases the fluorescence intensity compared with ICG alone [11, 12]. In the present study, fluorescence was not detected without albumin, but it was well detected with a small amount of albumin (Fig. 3).
Kawakita first reported the use of ICG fluorescence imaging combined with pneumoperitoneum for the detection of a diaphragmatic defect in a patient with hepatic hydrothorax [13]. Hepatic ascites often contains a high level of albumin, and it may adsorb ICG, but, in the peritoneal cavity, the amount of albumin or lipoprotein is usually extremely low. Therefore, we used a dialysate mixture with ICG:HSA, as reported by Troyan and Mieog [12, 14]. ICG:HSA has about sixfold higher fluorescence intensity than ICG alone at a fluorophore concentration of 30uM in phosphate-buffered saline[11].
There are at least two advantages of the ICG:HSA fluorescence method during VATS. First, this method can easily identify not only leakage sites but also thinner parts of the diaphragm. Second, the fluorescence color facilitates finding the communication from the peritoneum to the pleura.
Limitations
As expected, there are limitations of this method. There was a difference between the preoperative scintigraphy and intraoperative ICG fluorescence method findings. Initially, during surgery, intrathoracic pressure is not negative because of one-lung ventilation. Second, the intraoperative position of the patient was usually the lateral decubitus position, and abdominal pressure was not affected. These factors might cause a difference in the findings between before and during surgery. Third, ICG toxicity is low, but it does contain sodium iodide. Therefore, it should be used with caution in patients with a history of allergy to iodides. Moreover, albumin is a blood product and administration should be minimized in terms of diminishing use. In case of hepatic hydrothorax, communication sites may identify with ICG alone because ascites contains large amount of albumin [13, 15].