Perioperative Perfusion Measurement - a Feasibility and Usability Study

Introduction:

An optimal perfusion is essential in gastrointestinal surgery when resection of a cancerous tissue requires an anastomosis, since impaired perfusion seems to be associated with increased risk of anastomotic leakage (AL). AL is a severe complication with the risk of; prolonged hospital stay, cancer recurrence, permanent stoma in colorectal surgery, and increased short and long-term mortality. To avoid poor perfusion of an anastomosis, perfusion assessment is necessary during the operative procedure. Traditionally, perfusion is assessed visually and manually by the surgeon by judging the; color of the tissue, bleeding from the resection line, and the arterial supply pulse by palpation. These methods have earlier been shown to be unreliable and prone to observer bias. Furthermore, palpation of arterial supply is not possible in laparoscopic or robot-assisted surgery, and the increased use of staplers to divide the bowel leaves no bleeding resection lines. Therefore newer methods for perfusion assessment have been investigated, and fluorescence angiography (FA) and laser speckle contrast imaging (LSCI) has shown very promising results. In a systematic review of nonrandomized studies, the leakage rate in 916 colorectal resections was significantly lower when using FA compared to controls (3.3%, [95% CI: 1.97-4.63%] vs 8.5%, [95% CI: 4.8-12.2%], p=0.0055).

In FA, the tissue of interest is exposed to near-infrared (NIR) light simultaneously with intravenous injection of a fluorescent dye. When the dye reaches the illuminated area, it fluoresces, and a camera with a special filter can visualize the microcirculation of the tissue on a monitor. Many NIR-camera systems are on the market, combining the technique with conventional laparoscopic or robotic equipment, and several non-randomized studies have indicated that FA may reduce the anastomotic leakage rate in gastrointestinal surgery. Most surgeons are using only a visual subjective assessment of the FA, which may be prone to observer bias. Moreover, if the camera is not held at a standard distance from the tissue, or a different concentration of dye is used, a false negative or positive assessment of the perfusion may be made. Therefore, it has been argued that there is a need for an objective unbiased quantitative assessment tool in FA.

A quantification algorithm that provides a fluorescence-time curve and a quantitative parameter of perfusion, the normalized slope has previously been published, where a nearly linear correlation to regional flow was found. Until now measurements has been performed as analyses of video-recordings after the procedure.

In order to use the method in a clinical setting, development and testing of a tool that may be operated by the surgeon during the procedure to perform perioperative measurements is of high importance. A touchscreen tablet has been developed, in order to perform live perioperative quantitative perfusion assessment using FA. The tool may be used with several systems including Karl Storz fluorescence laparoscopic equipment and the daVinci SI or XI from Intuitive. This tool is essential in order to implement the technology into daily practice, as it allows the surgeon to get an immediate quantitative parameter of perfusion (normalized slope) at desired regions of interest. The interface of the tool should be easy to use and provide fluorescence-time curves to control the automated calculation of the normalized slope. In addition, a color-coded map of perfusion intensity should be provided as an overlay on the white light picture of the bowel investigated.