Tissue and cellular oxygenation state measurement during cardiac surgery

NIR reflection measurements of hemoglobin and cytochrome aa3 in healthy tissue and tumors. Correlations to oxygen consumption: preclinical and clinical data

OBJECTIVES

A new near infrared reflectance spectroscopy based technology (MULTISCAN OS 10/30) for non-invasive measurements of tissue oxygenation allows detection of absolute tissue hemoglobin concentration and saturation values in real time.

METHODS

MULTISCAN OS 10/30 scans a tissue sector of defined geometry at 400 to 1200 nm wavelength with 0.3 nm intervals at a scan rate of up to 400 Hz in reflection mode. The newly developed algorithms are based on the entropy pattern of photons and allow the detection of absolute values of total hemoglobin (tHb), deoxy- (Hb) and oxy-hemoglobin (HbO2) in mg/ml tissue as well as tissue oxygen (saturation = tiSO2) in the range of 0 to 100% in real time. Cytochrome aa3 (Cyt) can be monitored simultaneously.

RESULTS

Physiological Stimulation. Clamping experiments at the finger of volunteers, in the intestine of a pig, in the kidney of mice and rats showed a very fast, sensitive and tissue specific reaction. Changes in breathing and/or anesthesia conditions were immediately followed by corresponding changes of tissue oxygenation (brain, finger, skin). Simultaneous measurements of oxygen (HbO2), and cytochrome showed a strong correlation between both parameters. For validation purposes parallel polarographic measurements (pO2 measurements) were performed in mice. Furthermore angiographic data of patients as well as NMR/I data were compared with the NIR spectroscopy findings. Tumor Measurements. Patients with tumors of different origins showed significantly different oxygen values. The lowest level was found in glioblastoma (< 10% sat, < 1.0 mg/ml tHb), whereas renal carcinoma showed tremendously increased values (> 90% sat, > 5.0 mg/ml tHb). In contrast the surrounding healthy kidney tissue was significantly less oxygenated and perfused compared to the tumors. Oxygen Consumption Measurements. Oxygen consumption was measured in 16 patients after ligation of the blood supply (A. and V. renalis) to the kidney affected by tumor. All tumors showed a significantly lower consumption rate compared to the healthy tissue. These findings were controlled by animal experiments of human renal carcinomas on nude mice. The same results were obtained under these experimental conditions.

CONCLUSION

MULTISCAN OS 10/30 is a new and useful tool for in vivo characterization of oxygen and cytochrome in healthy and tumor tissues. In many clinically relevant situations oxygen measurements can be helpful and support the clinical routine diagnostics.