Comparison of reflection and transmission pulse oximetry after open-heart surgery

To determine if there was a difference between reflection and transmission pulse oximeters in their ability to regain data display after hypothermia in patients recovering from open-heart surgery.

Prospective, randomized, controlled study.

Nineteen adult patients scheduled for open-heart surgery were studied immediately after surgery in the ICU.

Transmission and reflection sensors were used in random order in two simultaneously monitoring identical oximeters and probes. The time difference at the start of display between the oximeters was measured and the skin temperatures in the region of the probes, cardiac index, systolic BP, pulse pressure, and systemic vascular resistance index were recorded.

The mean skin temperatures at the probe sites differed significantly (p = .001) at the moment of data acquisition. The mean forehead, ear lobe, and fingertip temperatures (simultaneously measured) were 33.9 degrees C, 31.8 degrees C, and 28.8 degrees C, respectively. The hemodynamic variables were comparable at the moment when the oximeters resumed display. The reflection probe was the first to resume function in 12 patients and the transmission probe was the first to resume function in four patients (p less than .02). The bias of the reflection probe was 1.4% (SD 2.2) and that of the transmission probe was -0.4% (SD 2.7). All the patients were normoxic throughout the study.

The forehead reflection probe regained signal detection earlier than the transmission probe on the ear lobe in patients with compromised peripheral blood flow and cool periphery. This finding may be due to higher skin temperature at the reflection probe site, since the systemic hemodynamic conditions were equal at the time of the data acquisition of both sensors.