[The source and factors that influence tracheal pulse oximetry signal]

To investigate the source and factors that influence tracheal pulse oximetry signal.

The adult mongrel dog was intubated after anesthesia. The tracheal tube was modified by attaching a disposable pediatric pulse oximeter to the cuff. The chest of the dog was cut open and a red light from the tracheal oximeter was aligned with the deeper artery. The changes in tracheal pulse oxygen saturation (SptO2) signal were observed after the deeper artery was blocked temporarily. The photoplethysmography (PPG) and readings were recorded at different intracuff pressures. The influence of mechanical ventilation on the signal was also tested and compared with pulse oxygen saturation (SpO2).

The SptO2 signal disappeared after deeper artery was blocked. The SptO2 signal changed with different intracuff pressures (P < 0.001). Stronger SptO2 signal appeared under 20-60 cm H2O of intracuff pressure than under 0-10 cm H2O of intracuff pressure(P < 0.001). The PPG of SptO2 signal under a condition with mechanical ventilation differed from that without mechanical ventilation (P < 0. 01), which, was also different from SpO2 (P < 0.01).

SptO2 signal is primarily derived from deeper arteries around the trachea, not from the tracheal wall. Both intracuff pressures and mechanical ventilation can influence SptO2 signal. The SptO2 signal under 20-60 cm H2O of intracuff pressure is stronger than that under 0-10 em H2O of intracuff pressure. Mechanical ventilation mainly changes PPG.