Analysis of pO2 in Malignant Ascites of Patients with Peritoneal Dissemination of Gastric Cancer

63 Background: Peritoneal metastasis is considered to develop from carcinoma cells detached from the serosal surface of the primary site and dispersed in the peritoneal cavity. And oxygen is one of the most important environmental factors for tumor development. To investigate the oxygenation condition in the abdominal cavity, that is largely unknown, we collected ascitic fluid from patients with peritoneal dissemination of gastric cancer and measured pO2 of it. METHODS In 19 patients with peritoneal dissemination of gastric cancer, who had a considerable amount of ascites and was receiving systemic and/or intraperitoneal chemotherapy, ascitic fluid was collected at the bedside in room air, and its pH, pCO2 and pO2 were measured using a blood gas analyzer immediately. RESULTS In 19 patients, pH of malignant ascites was significantly lower than that of arterial blood (7.39 ± 0.069 vs 7.44 ± 0.025 mmHg, p < 0.05). pCO2 tended to be higher in ascites than in arterial blood. Unexpectedly, pO2 in malignant ascites showed relatively high values (85.47 ± 23.31 mmHg), which were mostly the same as that of arterial blood (97.19 ± 10.40 mmHg, p = 0.149), and appeared to be higher than that in solid tumor tissue. CONCLUSIONS Malignant ascites in gastric cancer patients showed an unexpectedly high oxygen tension, which was almost the same as that of arterial blood. The hyperpermeability condition may enable efficient oxygen delivery to peritoneal fluid via the microvessels lining the peritoneal cavity. Since the oxygen level critically affects the sensitivity of tumor cells to chemotherapeutic agents through metabolic transformation, aerobic conditions may be beneficial for the progression of peritoneal metastasis and also clinically important in considering the efficacy of chemotherapy. No significant financial relationships to disclose.