Cerebral oxygenation during warming after cardiopulmonary bypass

Objectives: To evaluate jugular venous oxygen saturation (Sj(v) over bar o(2)), 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: Sj(v) over bar o(2) 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, Sj(v) over bar o(2) averaged 80 +/- 7% and none of the patients had an increase in cerebral lactate production. During the rewarming period, however, reductions in Sj(v) over bar o(2) to <50% occurred in 16 (84%) patients and increased cerebral anaerobic metabolism developed in 11 (58%) patients. Sj(v) over bar o(2) 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 Sj(v) over bar o(2) catheter had excellent performance during the surgery. The average difference between paired measurements of Sj(v) over bar o(2) by the catheter and in blood samples was -0.4 +/- 4.25%, and the correlation between the two measurements was highly significant (r(2)=.93; P<.001). The NIRSO2 trended with the Sjvo(2) in most patients (r(2)=.63; P<.001), Conclusions: The study confirms other studies showing that jugular venous desaturation can occur during rewarming after cardiopulmonary bypass surgery. Presently, Sj(v) over bar o(2) appears to be a better monitor of cerebral oxygenation than NIRSO2. However, NIRSO, has promise as a noninvasive monitor of cerebral oxygenation if future developments allow more quantitative measurements of oxygen saturation.