Cerebral oxygenation during warming after cardiopulmonary bypass

Objectives: To evaluate jugular venous oxygen saturation (Sjv̄o₂), measured with a fiberoptic oximetry catheter, and brain tissue oxygen saturation, measured by near-infrared spectroscopy (NIRSO₂), as monitors of cerebral oxygenation during cardiopulmonary bypass surgery. Design: Prospective, clinical study. Setting: Operating room of a Veterans Administration Hospital. Patients: Nineteen patients undergoing moderate hypothermic cardiopulmonary bypass surgery. Interventions: Sjv̄o₂ and NIRSO₂ were monitored in the patients during the surgical procedure. Measurements and Main Results: Moderate hypothermic cardiopulmonary bypass surgery had two distinct cerebral hemodynamic phases. While the patients were hypothermic, Sjv̄o₂ averaged 80 ± 7% and none of the patients had an increase in cerebral lactate production. During the rewarming period, however, reductions in Sjv̄o₂ to <50% occurred in 16 (84%) patients and increased cerebral anaerobic metabolism developed in 11 (58%) patients. Sjv̄o₂ during rewarming was dependent on mean arterial pressure, with 60 mm Hg appearing to be a critical value. Two other factors appeared to also contribute to the jugular desaturation, a low hematocrit and a rapid warming time. The Sjv̄o₂ catheter hue excellent performance during the surgery. The average difference between paired measurements of Sjv̄o₂ by the catheter and in blood samples was -0.4 ± 4.25%, and the correlation between the two measurements was highly significant (r² = .93; p< .001). The NIRSO₂ trended with the Sjv̄o₂ in most patients (r² = .63; p < .001). Conclusions: The study confirms other studies showing that jugular venous desaturation can occur during rewarming after cardiopulmonary bypass surgery. Presently, Sjv̄o₂ appears to be a better monitor of cerebral oxygenation than NIRSO₂. However, NIRSO₂ has promise as a noninvasive monitor of cerebral oxygenation if future developments allow more quantitative measurements of oxygen saturation.