IN-VIVO MEASUREMENT OF TUMOR BLOOD OXYGENATION BY NEAR-INFRARED SPECTROSCOPY - IMMEDIATE EFFECTS OF PENTOBARBITAL OVERDOSE OR CARMUSTINE TREATMENT

Near-infrared (NIR) spectroscopy was used to measure blood oxygen satu ration (SO2) in vivo, in normal rat brain and in subcutaneously-implan ted rat 9L gliosarcoma. Changes in cranial and tumor blood SO2 were me asured during lethal pentobarbital overdose. After sacrifice, SO2 of c ranial blood fell rapidly to a mean of 5.0% of the pre-sacrifice value s, whereas SO2 of tumor blood stabilized at a mean of 72.4% of the pre -sacrifice values. This suggests that oxygen consumption by tumor is v ery low compared to brain. Cranial blood had a higher SO2 than tumor b lood before sacrifice (p = 0.03), and a lower SO2 after sacrifice (p = 0.02). The magnitude of the change in SO2 after sacrifice was greater in normal brain than in tumor (p = 0.02), showing that brain tissue u ses a greater proportion of the oxygen in ischemic blood than does tum or tissue. To determine the effect of carmustine (BCNU) treatment on t umor and cranial blood SO2, we compared BCNU-treated rats with sham-tr eated rats. Continuous NIR measurements before and immediately followi ng treatment (ie. over 30-60 min) showed that tumor blood SO2 tended t o increase after BCNU treatment, whereas SO2 tended to decrease follow ing sham-treatment. The difference in SO2 between treated and control tumors was significant at 60 min (p = 0.02). Thus BCNU treatment can p otentially result in immediate increases in tumor oxygenation. The inc rease in treated tumor blood SO2 occurred despite the fact that there was no change in cranial blood SO2 even at day 4 following treatment. Tumor blood SO2 was inversely correlated with tumor size (p = 0.001), confirming that blood is more poorly oxygenated in large tumors.