Transesophageal versus surface pulse oximetry in intensive care unit patients

To compare oximetric readings from the esophagus (STEO2) and the skin (finger, SSO2) with those obtained from arterial blood samples (SaO). In addition, to compare the influences of mean arterial pressure (MAP) and body temperature to the accuracy of STEO2 and SSO2 readings.

Prospective, single-center study.

Surgical intensive care unit of an academic, teaching, and community hospital in Austria.

A total of 40 consecutive, severely traumatized or diseased, intensive care unit patients requiring mechanical ventilatory support and deep analgosedation. Patients had to be nonpregnant, > or =19 yrs of age, and without a disease or a trauma of the esophagus.

Placement of an esophageal and a finger-pulse oximetry probe and a radial artery catheter.

STEO2, SSO2, MAP, and esophageal temperature were recorded continuously during a 4-hr period, and SaO2 was measured every 30 mins. The first outcome variable was the deviation of STEO2 and SSO2 from SaO2. The second outcome variable was the influence of MAP and body temperature on STEO2 and SSO2 regression analysis and repeated measures. Analysis of variance was used for statistics (p < .05 was accepted as significant). In patients with a MAP ranging from 29 to 111 mm Hg and a temperature ranging from 33.4 degrees C (92.1 degrees to 39.2 degrees C (102.6 degrees F), SSO2 measurements underestimate SaO2 by 2% to 4%. Whereas STEO2 matches SaO2, STEO2 was not dependent on MAP or temperature, but increased temperature or low MAP were associated with falsely low SSO2 readings.

Assuming correct positioning of the probe, readings from the esophagus are more consistent with arterial oxygen saturation than readings from surface pulse oximetry. MAP or temperature changes do not influence STEO2, but they do affect SSO2. In critically ill patients, STEO2 appears to be a more reliable variable than SSO2.