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IR light monitors bypass operations

25 May 2004

Optical measurements of the heart’s oxygen consumption show whether bypass operations have been successful.

Optical monitoring of the heart’s oxygen consumption during bypass surgery can help clinicians judge if the operation has been successful, according to Dutch firm Avantes. The spectrometer specialist is currently working with clinicians from University Hospital, Basel in Switzerland to test the technique on 20 patients.

“The aim of the current project is to determine metabolic changes in the heart muscle during ‘beating heart surgery’,” Benno Oderkerk, technical director of Avantes, told Optics.org. “The bypasses are being performed on a heart that is still beating. There is no necessity for an external blood flow through a heart-lung machine. This saves time and money and reduces the risk of contamination or infection of the blood.”

Oderkerk and his Basel colleagues determine the oxygen consumption of the heart muscle by measuring deoxygenized and oxygenized haemoglobin. They believe that this is an essential measurement in beating heart surgery. Oderkerk adds that the approach also complements current monitoring techniques such as measuring blood pressure and electrocardiograms.

The technique uses a halogen light source, Avantes’ AvaSpec-2048 spectrometer and a special reflection probe which is built in to a standard heart catheter. The catheter is inserted into the coronary artery in the heart.

The reflection probe contains seven fibers, six of which are used for illumination while the seventh carries reflected light back to the spectrometer. “Near infrared light is scattered by the blood and reflections are gathered by the probe,” explained Oderkerk. “The absorption path length increases with decreasing back-reflected light. The typical absorption wavelengths we are analyzing are around 630-650 nm and 760 nm.”

When the catheter is inserted into the heart, the team acquires a reference spectrum. Absorption spectra are taken at different stages throughout the operation and are compared to the reference to judge if bypasses have been successful. “The success of a bypass can be seen directly from the spectrum,” said Oderkerk. “The lack of ischemia [inadequate blood flow] means the operation was successful.”

The team now hopes to expand its research to other organs where intravascular near-infrared spectroscopy could be a valuable tool.

Jacqueline Hewett is technology editor on Optics.org and Opto & Laser Europe magazine.

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