Fluorescence in Colorectal Surgery
Fluorescence-guided surgery represents an evolution in the intraoperative assessment of physiology and anatomy during precision surgery. Fluorophores with known light excitation and emission profiles are used to specifically target tissues or pharmacologi
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Fluorescence in Colorectal Surgery António S. Soares and Manish Chand
Fluorophores Optical and haptic cues have been the main tools used by surgeons to assess disease intraoperatively since the advent of modern surgery. Fluorescence-guided surgery is an evolution of intraoperative assessment of patient anatomy and physiology. This technology has the potential to radically change current practice and enhance precision surgery [1– 3]. A fluorophore is a substance that emits energy as fluorescence after being excited by light at a specific wavelength [4]. This enables detection of the distribution of the fluorophore not only if the tissue is isolated but also through variable thickness of overlying tissues, ranging from 5 to 10 mm [5–7]. By allowing a better anatomical resolution, fluorescence-guided surgery enhances the surgeon’s ability to discriminate different tissues. The optimal wavelengths for intraoperative use are the near infrared spectra (650– 900 nm). Wavelengths shorter than this interval lead to natural haemoglobin fluorescence and therefore make detection of other fluorophores difficult. For wavelengths above 900 nm, it is the water’s fluorescence that represents an obstacle. There are several different clinically approved fluorophores available in the market [8]. Each one has a specific wavelength for excitation and for emitted fluorescence to which the devices must be adapted or be adaptable.
Indocyanine Green Indocyanine green (ICG) is the most commonly used fluorophore in clinical practice. It is a heptamethine cyanine fluorophore and has a peak excitation wavelength of
A. S. Soares · M. Chand (*) Division of Surgery and Interventional Sciences, University College Hospital, London, UK e-mail: [email protected]; [email protected]
807 nm and a peak emission wavelength of 822 nm. It is a hydrophobic molecule, and therefore, after intravenous injection, it binds to albumin and is confined to the intravascular space. This characteristic makes this an ideal fluorophore for perfusion assessment through fluorescence angiography [8]. Its half-life in plasma is around 3–5 min and is eliminated via hepatic excretion. This pharmacokinetic profile allied to rapid distribution makes ICG ideal for repeated intraoperative administrations. The hepatic excretion allows hepatic lesion identification. Tumours have a disorganised capillary network that enables the socalled enhanced permeability and retention effect (EPR). This is caused by preferential leakage of intravascular contents in the areas of neoplastic tissue [9]. This effect can be used to non-specifically detect cancers such as ovarian cancer and metastases, pancreatic cancer or peritoneal metastases. ICG has historically been used in clinical practice for ophthalmologic angiography, cardiac output measurement and functional liver assessment with a great safety and very favourable adverse effect profile [10, 11]. Care must however be exercised in patients allergic to iodine or iodine-based contrasts, as the commercially available formulati
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