A localized pulmonary bulla is sometimes difficult to detect clearly on thoracoscopy, especially in a deflated lung. VATS has already been accepted for wedge resection of lung bullae or emphysema and partially for lobectomy or segmentectomy of lung cancer or infectious diseases of the lung[
3,
4]. Under VATS, inflation of the lung makes the operation difficult because a large part of the chest cavity is occupied. To address this issue, Gotoh et al. used ICG to detect bullae of pneumothorax by infrared thoracoscopy[
5]. Their infrared camera was very useful because it was a two-color infrared camera that showed the tissue with ICG as blue and that without ICG as white. However, they used ICG 3.0 mg/kg, which is much more than the volume of ICG used for liver function testing[
5]. According to toxicity studies, a 5.0 mg/kg ICG intravenous injection is safe and tolerable[
6], and another report described it as safe enough, as there were only three (0.15%) mild adverse reactions, four (0.2%) moderate reactions, and one (0.05%) severe reaction in 1226 consecutive patients[
7]. However, some reports noted that ICG dye has a dose-dependent toxic effect on the retina[
8], and in our experience, prolonged vomiting or fever has occurred postoperatively in some cases. It is clear that a smaller volume of ICG than they used is much better.
The PDE imaging system contains a charge-coupled device camera that filters out light with a wavelength of less than 820 nm, as well as 36 light-emitting diodes with a wavelength of 760 nm. It shows clearly that the tissue with ICG is white and that without ICG is black[
9]. The advantage of the PDE system is high sensitivity for ICG, which allows a lower dose of ICG (0.5 mg/kg) to be used. Since even ICG at 0.5 mg/kg can show the contrast clearly, it may be possible to reduce the ICG dose further. Another advantage of this approach includes the ability to see the border clearly as a black and white line and to be able to use normal thoracoscopy from another 10-mm port to see the normal color lung at the same time. This means that it is possible to use electrocautery to mark the border using normal thoracoscopy and the PDE system concurrently. The black and white contrast lasted for about 30 seconds, and then gradually the bullous lesion turned white; this is not long, but it is enough to see the border and mark it by electric cautery. Furthermore, because the color is lost about 15 minutes after injection, the segment line can be used one more time during cutting. On the other hand, a disadvantage is the large size of the system, having a diameter of 8 cm, which requires a large incision to be used. However, in our experience, it is possible to use at least a 4-cm incision because the part of the charged-coupled device (CCD) camera except for the infrared light-emitting diode (LED) is 3.2 cm in diameter.
In conclusion, the procedure using the PDE system with ICG injection to perform surgery for pulmonary bullous emphysema is safe and can be quickly completed, with minimal drug-related side effects. This approach is cost-effective because the PDE system can be used in other operations, and ICG is inexpensive. ICG fluorescence for lung operations promises to be useful.