Effect of indocyanine green dye administration on cerebral oxygen saturation.

Sir,

Near-infrared spectroscopy (NIRS) is a non-invasive continuous method of measuring regional cerebral oxygen tissue saturation (SctO2).[1] It uses a technique similar to pulse oximetry where light absorption in wavelength 600–900 nm is used.

Indocyanine green (ICG) is a water soluble and iodide containing dye that fluoresces when exposed to infrared light. This property of ICG is used for the intra-operative assessment of blood flow during aneurysm surgery. Safety of ICG usage in clinical settings has been demonstrated for determining cardiac output, hepatic function and liver blood flow and for ophthalmic angiography.[2] There have been hypotension, urticarial reaction or anaphylaxis and falsely low pulse oximetry recording during or following use of ICG.[34]

Contrary to falsely low pulse oximetry recordings, ICG administration has been shown to increase SctO2.[4] Here, we are describing the effect of ICG administration on SctO2.

A 65-year-old male patient was scheduled to undergo clipping of right supraclinoid internal carotid artery aneurysm under general anaesthesia. Apart from the routine monitoring, we placed bilateral NIRS sensors over the forehead of the patient. After administration of 10 mg of ICG, the SctO2 on both the sides suddenly increased to 100 from a baseline of about 65–75% and gradually decreased to the baseline value after about 15 min [Figure 1]. There were no associated haemodynamic changes.

Figure 1

Snap shot of near infrared spectroscopy monitor showing the graphical trend of the cerebral oxygen saturation. Furthermore, clearly seen is the sudden acute increase in saturation after injection of indocyanine green at two different time points and gradual return of the saturation to baseline

This sudden increase in SctO2 following administration of ICG can be explained by the principle applied in NIRS sensors. NIRS uses wavelengths between 700 and 850 nm to determine regional cerebral oxygen SctO2 by differentiating oxyhaemoglobin from reduced haemoglobin in the frontal lobe. Thus, any substances that absorb infrared light of the same wavelength produced by the light-emitting diodes may affect the absorption of light as they traverse the blood and tissues.[5] ICG has a characteristic absorption peak at around 805 nm and this is likely to reduce the amount of detected light in the 810 nm wavelength of the NIRS device, which would be interpreted as an increased oxyhaemoglobin concentration leading to falsely elevated SctO2 reading.[6]

The effect of this falsely elevated SctO2 on the clinical outcome of the patients is not known. Despite these changes, the remaining of the surgical procedure was uneventful or did the patient develop any new neurological deficits and patient's trachea was successfully extubated at the end of the procedure.

The anaesthesiologists and neurosurgeons must be aware of this interaction of ICG and cerebral oxygen SctO2 in the intra-operative period.

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Conflicts of interest

There are no conflicts of interest.