Microscope-integrated indocyanine green video angiography (ICG-VA) is used to assess
the completeness of clipping and cerebral vascular flow during aneurysm surgery.[1] It is a more practical and less time-consuming alternative to intraoperative digital
subtraction angiography (DSA). ICG has been reported to cause a decrease in peripheral
oxygen saturation (SpO2).[2]
[3]
[4]
We report a 48-year-old male who presented with complaints of holocranial throbbing
headache for 1 month without any history of seizures or focal neurological deficit.
The patient was a known alcoholic for the past 20 years. Liver function test showed
hyperbilirubinemia and elevated serum transaminases. Noncontrast computed tomography
brain revealed subarachnoid hemorrhage. The patient was found to have two aneurysms
in the anterior cerebral circulation, one in the anterior communicating artery and
one in the right M1 middle cerebral artery, on a DSA scan. He was scheduled for a
craniotomy and clipping of both aneurysms. ICG (Aurogreen, Aurolab, Madurai, Tamil
Nadu, India) at a dose of 0.25mg/kg was administered after the placement of a permanent
clip to ascertain the absence of residual flow through the aneurysm. The intraoperative
course was uneventful and the patient's trachea was extubated in the operating room,
after the surgery. Postoperative DSA showed a left distal anterior cerebral artery
(DACA) aneurysm, which was not detected prior to the surgery.
The patient was then scheduled for clipping of the DACA aneurysm, a week after the
first surgery. Intraoperatively, ICG was administered intravenously, in the same recommended
dose (0.25 mg/kg) after placement of the permanent clip. The SpO2 dropped to 92% from a baseline of 98%, immediately after the administration of the
dye without any change in the signal quality of the SpO2 waveform. This decrease in saturation was transient and lasted for approximately
one minute. There was no concurrent hemodynamic disturbance or change in end-tidal
carbon dioxide. There was no other significant intraoperative event and tracheal extubation
was performed in the operating room. In spite of the fact that the same SpO2 probe was used, no incidence of desaturation was noted during ICG administration
for the first surgery. However, the half-life of ICG may be substantially prolonged
in patients with liver disease.[5] Although the exact duration of the increase in elimination half-life of ICG in the
presence of liver disease has not been quantified in literature, we believe that the
cumulative effect of the residual nonmetabolized ICG from the first surgery and the
additional ICG administered during the second surgery could be a plausible explanation
for the observed desaturation during the second surgery and not the first one. Altered
liver function resulting in reduced clearance of the dye might have been responsible
for its accumulation and subsequent peripheral oxygen desaturation when it was administered
the second time. This hypothesis, however, merits larger, well-designed studies for
its investigation.
ICG is a water-soluble, inert, fluorescent dye with a very high hepatic extraction
and minimal systemic toxicity. It binds to albumin and distributes rapidly after injection.
It has no interaction with neuronal tissue rendering it pharmacodynamically inert
in the brain. ICG is exclusively metabolized by the liver and excreted unchanged into
bile without any enterohepatic re-circulation. The clearance occurs by a rapid exponential
decay of plasma levels followed by a slower prolonged decay.[6] ICG is the only Food and Drug Administration-approved near-infrared fluorophore
making it an invaluable angiographic tool in neurosurgery; especially in aneurysmal
surgeries. The recommended injectable dose of ICG for angiography is between 0.2 and
0.5 mg/kg, with a maximum dose of 5 mg/kg.[1]
The absorption spectrum of ICG ranges from 600 to 850 nm, with an absorption spectral
peak at 805 nm and an emission peak at 835 nm. However, ICG absorbs a significant
amount of red light at approximately 660 nm also, and the shift of the absorption
peak toward the red end of the spectrum appears to be dose-dependent.[4]
[7] This may result in a reduced detection of traversed red light by the photo sensor,
which may in turn be falsely attributed to an increased concentration of deoxygenated
hemoglobin in the arterial system. The short half-life of ICG (150–180 seconds) probably
accounts for the evanescent nature of this observation.[4] A transient increase in regional cerebral SpO2, measured using near infrared spectroscopy following intravenous administration of
ICG, has also been reported.[6]
[7]
[8]
Although peripheral oxygen desaturation after administration of ICG has been reported
in the literature, it is not listed as one of the adverse effects in this particular
manufacturer's pamphlet. The effect of this transient desaturation on overall patient
outcomes is not known. It is desirable that anesthesiologists be aware of this interaction
and not be unduly alarmed by this observation. However, exercising caution seems prudent
when relatively higher doses of ICG are administered, on more than one occasion, within
a short span of time, especially in the presence of liver disease.
