Comparison of a prototype esophageal oximetry probe with two conventional digital pulse oximetry monitors in aortocoronary bypass patients

Objective. Pulse oximetry (SpO(2)) is the noninvasive standard for monitori ng arterial oxygen saturation in patients undergoing anesthesia, but is sub ject to external interference by motion artifact, peripheral vasoconstricti on, and low cardiac output. We hypothesized that oximetry signals could be acquired from the esophagus when peripheral pulse oximetry is unobtainable. Therefore, we tested an esophageal stethoscope which incorporates transver se oximetry photodetectors and emitters in patients undergoing coronary byp ass surgery. Methods. Immediately after induction of general anesthesia in 10 coronary artery bypass (CABG) patients, Criticare and Nellcor digital pr obes were positioned on the left hand, concurrent with placement of an esop hageal SpO(2) probe. A computer recorded 5,910 matched oximetry signals eve ry 15 sec during an average of 2.5 hrs. All SpO(2) measurements were before , and immediately after non-pulsatile, hypothermic cardiopulmonary bypass. Data represent the percentage (median value [range]) of the total monitored time that a SpO(2) value was displayed. Results. The Nellcor (99.8%, range 6.5-100%) and Criticare (99.7%, range 36.6-100%) acquired and displayed sa turation signals more frequently (p = 0.003) than the esophageal monitor (7 5.3%, range 42.1-95.8%). The two standard digital oximeters had a mean diff erence of 0.9%, with a standard deviation of the differences of 0.9. The es ophageal probe had a mean difference of -5.2% and -4.8%, with standard devi ation of differences of 8.0 and 7.7 (compared to the Nellcor and Criticare monitors, respectively). A second-generation prototype shielded from electr ocautery interference was tested in an additional 4 patients. The shielded prototype displayed signals more frequently (96.7%, range 68.4-100%) than t he original esophageal prototype. Conclusions. Digital pulse oximetry failu re is common in CABG patients, probably because of marginal cardiac output and peripheral vasoconstriction associated with hypothermia. Our study coul d not confirm that esophageal technology, which utilizes the esophagus as a site of transflectance oximetry, was superior to conventional digital puls e oximetry.