Overview
Definition:
Indocyanine green (ICG) fluorescence is a technique utilizing near-infrared (NIR) fluorescent dye injected intravenously to assess tissue perfusion and vascular integrity in real-time during surgical procedures
ICG, when excited by NIR light, emits fluorescence that can be visualized using a specialized camera system, allowing surgeons to evaluate blood flow to organs and identify potential vascular compromise.
Epidemiology:
The application of ICG fluorescence is widespread across various surgical specialties, including gastrointestinal, hepatobiliary, cardiothoracic, vascular, and oncologic surgery
Its use is increasing as technology advances and its benefits in improving surgical outcomes become more evident.
Clinical Significance:
Accurate assessment of tissue perfusion is critical for preventing intraoperative complications such as ischemia, necrosis, and anastomotic leaks
ICG fluorescence provides an objective, real-time method to confirm adequate blood supply to organs and reconstruction sites, guiding surgical decisions, identifying aberrant vasculature, and reducing the risk of postoperative morbidity
This is particularly vital in complex reconstructive surgeries or in patients with compromised vascular health.
Indications
Gastrointestinal Surgery:
Assessing perfusion of the bowel during resections and reconstructions (e.g., colectomy, gastrectomy)
identifying the viability of intestinal segments before anastomosis.
Hepatobiliary Surgery:
Evaluating liver segment or lobe perfusion during hepatectomy
assessing biliary tree patency and identifying aberrant vessels around the bile ducts.
Cardiothoracic Surgery:
Assessing myocardial perfusion during cardiac surgery
evaluating pulmonary perfusion and bronchial artery flow.
Vascular Surgery:
Assessing the patency of bypass grafts and vascular reconstructions
evaluating peripheral perfusion in limb revascularization procedures.
Oncologic Surgery:
Mapping lymphatics for sentinel lymph node biopsy
assessing tumor vascularity or perfusion of flaps used in reconstruction.
Urology And Gynecology:
Assessing ureteral or pelvic organ perfusion during radical resections or reconstructive procedures.
Technique And Interpretation
Icg Administration:
A sterile solution of ICG (typically 2.5-5 mg/mL) is prepared and injected intravenously, usually through a peripheral venous line
The dose varies based on patient weight and the specific procedure, but commonly ranges from 0.5-5 mg.
Imaging System:
A dedicated NIR fluorescence imaging system equipped with an excitation light source (typically in the NIR spectrum) and a sensitive camera capable of detecting the emitted fluorescence is used
Modern systems often have dual modes, allowing visualization of both normal anatomy (white light) and fluorescence overlay.
Timing Of Imaging:
Imaging is performed at different time points after ICG injection: immediate (arterial phase), shortly after (capillary phase), and later (venous phase)
The interpretation depends on the expected vascular supply and drainage patterns of the target tissue.
Interpretation Of Fluorescence:
Adequate perfusion is indicated by homogeneous and rapid fluorescence uptake and washout
Poor perfusion is characterized by patchy fluorescence, delayed uptake, prolonged retention, or absence of fluorescence
Discrepancies between expected and observed patterns warrant further investigation and potential surgical modification.
Surgical Applications
Bowel Anastomosis:
Confirming adequate blood supply to the bowel ends before performing an anastomosis, reducing the risk of leak
Segments with poor perfusion may require revision or wider resection.
Organ Viability:
Determining the viability of an organ or a portion of an organ, such as in liver resections or reconstructive flaps, ensuring adequate blood flow is maintained.
Lymphatic Mapping:
Visualizing lymphatic channels and identifying sentinel lymph nodes in oncologic surgery, aiding in accurate staging and guiding dissection.
Biliary Surgery:
Visualizing the biliary tree to identify leaks or strictures and assess patency of reconstructions, particularly in complex hepatobiliary procedures.
Detection Of Leaks:
Identifying unintended leaks from hollow organs or vascular structures that might not be apparent with conventional methods.
Advantages
Real Time Assessment:
Provides immediate, dynamic visualization of perfusion, allowing for timely intraoperative adjustments.
Objective Data:
Offers quantitative and qualitative data on blood flow, reducing subjective assessment reliance.
Improved Safety:
Helps prevent complications related to inadequate perfusion, such as anastomotic leaks and tissue necrosis.
Versatility:
Applicable across a wide range of surgical specialties and procedures.
Minimal Invasiveness:
A simple intravenous injection requires no additional incisions or invasive maneuvers.
Limitations And Considerations
Allergy:
Rare allergic reactions to ICG can occur, though generally mild
Pre-procedure screening is advisable.
Renal And Hepatic Impairment:
Severe renal or hepatic impairment can affect ICG clearance, potentially prolonging its presence and affecting interpretation.
Dye Concentration And Imaging Quality:
The quality of the fluorescence image depends heavily on the concentration of the dye, imaging equipment capabilities, and ambient light conditions.
Interpretation Variability:
While objective, subtle findings may require experienced interpretation
Anatomic variations or previous surgeries can influence expected patterns.
Cost:
The specialized imaging equipment represents a significant capital investment, though the cost of ICG itself is relatively low.
Key Points
Exam Focus:
Understand the principles of ICG fluorescence, its indications in common surgical procedures (e.g., bowel anastomosis, hepatectomy), and how to interpret the fluorescence patterns
Know the advantages and limitations.
Clinical Pearls:
Always use a sterile technique for ICG preparation and administration
Corroborate fluorescence findings with other clinical parameters and surgical judgment
Consider patient factors like renal/hepatic function
Standardize your imaging protocols for consistent interpretation.
Common Mistakes:
Misinterpreting patchy fluorescence due to dye aggregation or poor injection technique
Over-reliance on fluorescence alone without considering macroscopic signs of perfusion
Not accounting for potential allergic reactions
Inadequate training in interpreting subtle fluorescence patterns.