Indocyanine Green-enhanced Fluorescence to Assess Bowel Perfusion During Robotic-assisted Rectal Surgery

Colorectal cancer (CRC) is the third most common cancer diagnosed among both males and females in the United States, following prostate cancer in men, breast cancer in women, and lung cancer in both sexes. Approximately 41% of all CRCs occur in the proximal colon, with approximately 22% involving the distal colon and 28% involving the rectum.^[1] Although the incidence of CRCs has been increasing annually, the oncological outcomes have improved due to the advancements in the management approach of affected patients. However, despite improvements in surgical techniques and postoperative care, anastomotic complications are still observed in 10−20% of cases.^[2–5]

Anastomotic leakage (AL) represents one of the most feared complications following colorectal surgery. In 2010, the International Study Group of Rectal Cancer defined AL in anterior rectal resections as “a defect of the intestinal wall at the anastomotic site leading to a communication between the intraluminal and extraluminal compartments.” Furthermore, they recommended considering the presence of a pelvic abscess in proximity of the anastomosis as an AL. AL is associated with a significant rate of morbidity and mortality, including the potential need for a permanent stoma, increased duration of hospital stay,^[6] increased local recurrence rate,^[7] and significant financial implications on the healthcare system. Risk factors for AL include male sex, body mass index (BMI) greater than 35 kg/m², preoperative use of chemoradiation therapy, tumor  larger than 5 cm in size or within 7 cm of the anal verge, excessive tension, and insufficient blood supply to the site of anastomosis.^[8–10]

When the anastomosis is performed in an area with insufficient blood flow, the resulting acute ischemia may lead to colon necrosis, AL, and sepsis. Patients who develop chronic ischemic conditions may not demonstrate symptoms of peritonitis, but rather present with anastomotic stenosis or strictures that may require eventual reoperation and long-term hospitalization.^[11,12] Poor vascular anastomotic perfusion is a known risk factor for complications and thus, warrants objective assessment. Intraoperative assessment of anastomotic integrity is commonly used in practice, whether using an air leak test, endoscopy, intraoperative dye test, or laser fluorescence angiography. Perfusion status of the colon resection site has traditionally been determined subjectively by color, temperature, peristalsis of the colonic surface, as well as pulsatility and hemorrhaging of marginal vessels.^[7] However, these methods are subjective and not always accurate. Furthermore, detection of minor changes at the microcirculation level is challenging. Gross visualization of blood flow is especially difficult in patients with visceral obesity because they tend to have excess fat tissue in the mesentery and colon wall. Moreover, the ability to determine the perfusion status of ischemic colon segments requires expertise that may be lacking in young or newly graduating surgeons.^[13–15]

The essentials for any bowel anastomosis are adequate perfusion, tension-free, accurate tissue apposition, and minimal local spillage. The newly developed fluorescence camera system using indocyanine green (ICG) can be used to easily observe the perfusion status of the anastomosis during robotic or laparoscopic surgery. ICG is a water-soluble tricarbocyanine dye with a molecular mass of 775 Daltons, often mixed with less than 5% sodium iodide to ensure solubility when used in medical diagnostics. The half-life of ICG is 150 to 180 seconds and it is excreted in the bile within 10−15 minutes. There are no known metabolites. The usual dose for standard clinical use is 0.1–0.5 mg/mL/kg, which becomes completely protein-bound (98%) following intravenous injection. It has peak spectral absorption at about 800 nm. In one of 42,000 cases, side effects occur in the form of sore throat and hot flushes. Anaphylactic shock, hypotension, tachycardia, dyspnea, and urticaria have only been reported as individual case reports, although the risk of severe side effects is higher among patients with chronic kidney impairment. Since its approval as a fluorescent contrast agent by the Food and Drug Administration (US FDA) in 1959, it has been used in various clinical settings ranging from residual liver function tests to cardiac output measurements, as well as ophthalmic angiography. Furthermore, ICG-enhanced fluorescence is an innovative technique to evaluate the anastomotic perfusion during colorectal surgery. In previous studies, the effects of using ICG fluorescence to prevent anastomotic complications have not been demonstrated.^[16–19]

In this study, we aimed to evaluate the efficacy and usefulness of intraoperative assessment of vascular anastomotic perfusion in robotic low anterior resection (LAR) using ICG fluorescence angiography (FA). We compared two groups of patients who underwent robotic resection with and without intraoperative use of ICG dye and hypothesized a reduction in the AL rate in the former group.

This study was conducted after receiving the approval of the institutional review board (IRB No. 4-2018-0967) of the Severance Hospital of Yonsei University. Written informed consent was obtained from all patients included in the study. The study cohort included all consecutive patients who underwent robotic surgery for CRC between March 2017 and February 2019 at the Severance Hospital, Yonsei University, Seoul, Korea. The control group included all consecutive patients who underwent surgical intervention between March 2017 and April 2018, before implementation of ICG-FA into practice at our institute. Those who underwent surgery between April 2018 and February 2019 following the introduction of ICG-FA into standard practice were considered the ICG group. All consecutive patients who underwent surgery and met the criteria were included until reaching a sample size similar to that in the control group. The study population included patients older than 18 years diagnosed with rectal cancer who underwent LAR with primary anastomosis with or without diverting ileostomy on an elective basis. The exclusion criteria were hemodynamic instability, emergent surgery, no anastomosis, pregnancy, and history of allergy or adverse reactions to either the contrast agent for computed tomography (CT) or drugs containing iodine.

Bowel perfusion was subjectively assessed following intravenous injection of 10 mg ICG (divided into two 5-mg doses) in all patients in the ICG group. The anastomosis and margins were inspected using FA 2−3 minutes following resection and completion of the anastomosis.

Descriptive statistics were used to express numbers and percentages for all categorical variables and mean and standard deviation were used to express all continuous variables. Chi-square and t tests were used to evaluate the correlation between clinical factors and anastomotic complications. We used two-sided independent samples t tests for continuous variables of perfusion factors to identify risk factors of anastomotic complications. SPSS 23.0 (Statistical Package for Social Sciences Version 23.0; IBM Corp., Armonk, NY) was used for statistical analyses, and the significance level was set at p < 0.05.

A total of 96 patients were included in the final population: 48 each in the control group (non-ICG group) and ICG group. Most patients in the ICG group were male (64.5%), and the control group included an equal number of male and female patients. The mean age and mean BMI were similar in both groups. Patient demographics are presented in Table 1.

The tumor was located at a mean distance of 6.5 cm from the anal verge in the ICG group and 7.3 cm in the non-ICG group (p = 0.25). Most patients in both groups had stage IIIC disease. In the ICG group, 58.3% of patients had received preoperative chemoradiotherapy compared with 62.5% of patients in the non-ICG group. LAR was the most common procedure performed in both groups (ICG group, 58.3%; non-ICG group, 54.16%). The remaining patients (45.84%) in the non-ICG group underwent Ultra LAR; in the ICG group, 31.25% underwent Ultra LAR and 10.5% underwent Ultra LAR with inter-sphincteric resection. Low ligation of the inferior mesenteric vessels was performed more commonly than high ligation in both groups. In the ICG group, 70.8% of the patients underwent total mesorectal excision (TME) with circular stapled anastomosis, compared with hand-sewn coloanal anastomosis in 29.2% of patients. In the non-ICG group, 54.16% of patients underwent TME with circular stapled anastomosis and 45.84% of patients underwent hand-sewn coloanal anastomosis. In one patient in the ICG group, the surgeon subjectively decided to modify the planned anastomosis of the descending colon due to hypoperfusion in a distal segment. Postoperative AL was confirmed clinically and radiologically in one patient (2.8%) in the ICG group compared with two patients (4.16%) in the non-ICG group (p = 1). All the patients who developed AL were treated by diversion ileostomy and conservative treatment. No adverse events related to FA were recorded. Tumor characteristics and operative variables are shown in Table 2.

Among 96 patients undergoing surgery for rectal cancer, postoperative AL was confirmed clinically and radiologically in one patient (2.8%) in the ICG group compared with two patients (4.16%) in the control group.

Although improvements in surgical techniques and optimized care protocols have greatly impacted the short and intermediate postoperative outcomes, anastomotic complications, especially early postoperative AL, remain unpredictable and are often difficult to manage. The risk of AL is associated with a higher risk of local recurrence. Thus, to prevent or reduce the risk of AL following colorectal surgery, it is important to identify all preoperative, intraoperative, and postoperative risk factors. These include sex, BMI, preoperative chemoradiotherapy, anastomosis level, tumor size, surgical techniques, multiple stapler firings, precompression before stapler firings, use of transanal tube, and operative time.^[20] Intraoperatively, the mechanical integrity of the anastomosis can be checked by testing for air-tightness using air or methylene blue, or by endoscopic visualization of the anastomosis.^[7]

Moreover, adequate perfusion is a well-recognized prerequisite for complete healing of a gastrointestinal anastomosis. The colonic blood flow or vasculature can be evaluated via Doppler ultrasound, laser Doppler flowmetry, angiography, and oxygen spectroscopy, among others, which are not frequently used in the surgery because of the price of equipment, technical challenges, and difficulty in reproducibility.^[21] ICG-FA is an innovative technique used to evaluate anastomotic perfusion during colorectal surgery through evaluation of the vascular microcirculation. ICG-FA may identify the need for a change in the surgical plan, whether it comprises extending resection margins or requiring revision and re-anastomosis.^[22] Moreover, special cameras required for ICG-FA can be incorporated in open, laparoscopic, and robotic surgery, which makes it easy to adopt ICG-FA assessment to existing surgical procedures.^[23] Real-time angiography is considered a safe technique; no complications were observed in our study, and the only contraindications to the procedure are allergy to ICG. Furthermore, it is an affordable and quick method that can provide information regarding the perfusion status within seconds of administration. In comparison, ischemic demarcation of the bowel is visible to standard light more than 10 minutes away from vessel division.^[24] However, the disadvantage of ICG-FA is that the assessment of fluorescence intensity is subjective.

Most studies on the use of ICG in colorectal surgery have been dependent on subjective methods used by the operating surgeon. Son et al^[25] suggested an objective measurement of ICG in laparoscopic colorectal surgery through video analysis and modeling tools to create a standardized method of assessment. They argued that venous ischemia may be present despite adequate perfusion by ICG, which was confirmed using a quantitative analysis of ICG perfusion patterns using times ratio and fluorescence intensity reaction that can detect segments of poor perfusion, thereby reducing anastomotic complications during laparoscopic colorectal surgery.^[25] The Clinical Assessment Score proposed by Sherwinter et al^[26] describes the evaluation of bowel appearance with ICG uptake, ranging from 1, dusky appearance that correlates with no fluorescence uptake, to 5, pink-appearing bowel, pulsatility of mesenteric vessels, and bleeding from cut edge of bowel, which is consistent with isofluorescence of all segments. Score 2 was represented by patchy fluorescence and patchy appearance clinically, and 3 and 4 showed homogeneous but hypofluorescent and somewhat hypofluorescent, respectively. Both had pink appearance clinically but without bleeding cut edge in 4, and without pulsatility or bleeding cut edge in score 3.^[26]

The intensity of fluorescence is influenced by several factors, including distance between the detector and subject as well as surrounding lighting conditions.^[27] Controlling these factors should be optimized to ensure standardization and reduce bias. Intra-abdominal fluorescence evaluation lacks significant variation in distance because of the confined space. Moreover, the fluorescence lighting of the near-infrared (NIR) camera is fixed. However, variability in lighting and distance may increase if the fluorescence imaging is used outside the abdomen. Therefore, we believe that the most reproducible and reliable data are obtained intra-abdominally during the early phase of fluorescence visibility. The “quenching effect” is also important to consider. If the ICG concentration is adequately low, the relationship between the intensity and concentration remains proportional^[27]; however, if the concentration exceeds a certain level, the proportional relationship is lost, a phenomenon that is known as quenching. This effect cannot be controlled; therefore, it is preferable to maintain low-level concentrations.

Kudszus et al^[28] first reported that fluorescence imaging in colorectal surgery resulted in a proximal change of the initially planned transection line in 13.9% patients (28 of 201), and a reduction in AL by 4% compared with that in the control group (7.5 vs 3.5%). Sherwinter^[29] evaluated 20 patients undergoing LAR with an endoscopic NIR imaging system. Following anastomosis creation, ICG injection was administered and the NIR endoscopic camera was inserted transanally through an introducer for evaluation of the anastomosis mucosa. Abnormal ICG angiogram was observed in four patients, two of whom had a protective loop ileostomy created and did not show signs of breakdown; however, the other two patients developed AL. The authors suggested that transanal ICG-FA is feasible and provides information on mucosal and anastomotic blood flow.

Jafari et al^[30] used a retrospective case-control study to describe the use of fluorescence imaging in robotic rectal surgery. They compared LAR with and without fluorescence imaging to measure its impact on the assessment of bowel perfusion. The authors reported a change in the proximal transection point in 3 of 16 patients (19%) and a leak rate of 6% compared with 18% in the control group.

To improve surgical decision making and oncological outcomes, the property of the ICG uptake in the lymphatic system has appealed to surgeons in recent years. Cahill et al^[31] showed that 4 of 18 patients had involved lymph nodes outside the planned resection margins, in the pelvic sidewalls or periaortic region. A recent study by Chand et al^[32] demonstrated the feasibility of fluorescence for lymphatic mapping, with 2 of 10 patients having involved lymph nodes outside the planned resection margins; this was also confirmed histopathologically. In a meta-analysis that included 12 studies on the detection of metastatic lymph nodes in colorectal cancer using ICG NIR fluorescence, the median sensitivity was 73.7% and the specificity was as high as 100%.^[33]

The high ICG uptake by colorectal peritoneal metastases was recently studied in an attempt to detect additional metastases during surgery, which were otherwise overlooked. The use of ICG facilitated identification of additional metastases in 29% of patients undergoing cytoreductive surgery for peritoneal carcinomatosis from colorectal cancer.^[34] Further, Liberale et al^[35] showed that although the data are scarce, the use of ICG might help in the detection of small hepatic lymph nodes and peritoneal metastatic deposits. Notably, to increase sensitivity and specificity of lymph node detection by ICG-enhanced NIR fluorescence-guided imaging, this technique requires small-dose injections at peritumoral subserosal sites under the guidance of colonoscopy the night of surgery to allow lymphatic uptake of the dye.^[36] We believe that this novel technique could improve intraoperative surgical staging and ultimately lead to improved oncological outcome.

There are several limitations to this study. Fluorescence intensity measurement was based on the subjective evaluation of the surgeon. Another limitation was performing protective ileostomy in patients with a clinical risk of anastomotic complications, such as being male, history of preoperative chemoradiation therapy, or low anastomotic levels. This, among other aspects, may be considered confounding factors in this series. Finally, the study was conducted in a retrospective manner and included a small sample size. Thus, a large-scale prospective multicenter trial is needed to confirm the effectiveness of perfusion assessment using ICG-FA, and its usefulness in preventing anastomotic complications.

Based on our results, one case was diagnosed with AL in the ICG group compared with two patients in the non-ICG group. ICG-FA as an enhanced fluorescence technique appears to be a promising intraoperative tool to assess vascular perfusion during colorectal surgery and may aid in identifying the need for altering the site of resection and/or anastomosis, possibly affecting the rate of AL. A larger randomized prospective trial with objective measurement may be useful in validating this new technique.

This project was presented as a poster presentation at the American Society of Colon and Rectal Surgeons annual meeting held in June 2019 in Cleveland, Ohio.