The human esophagus: Investigation of its suitability for monitoring SpO/sub 2/

Pulse oximeter probes placed peripherally may fail to give accurate values of arterial blood oxygen saturation (SpO/sub 2/) when peripheral perfusion is poor. Since central blood flow may be preferentially preserved, the esophagus was investigated as an alternative monitoring site. A new esophageal photoplethysmographic (PPG) probe and a signal processing system were developed. Esophageal PPG signals and standard ECG traces were obtained from 13 anesthetized patients and displayed on a laptop computer. PPGs with good signal-to-noise ratio were recorded from five esophageal depths. The mid to lower esophagus appeared to be the optimal site for monitoring SpO/sub 2/. The pulse transit times (PTT) to the esophagus were 95/spl plusmn/36 ms.