Noninvasive oximetry in the rat

To aid in the development of rodent models of respiratory dysfunction, the authors evaluated the ability of noninvasive pulse oximetry (SpO2) to continuously monitor oxygen saturation (SaO2) in the rat. In initial studies, a pulse oxyimeter (Nellcor N-100) detected a fall in SaO2 during hypoxia induced by hypobaric decompression or decreasing fractions of inspired oxygen (FIO2). The disposable sensor was placed proximally on the tail. To assess the accuracy of pulse oximetry, arterial blood samples (86 samples from 25 animals) were obtained via a femoral arterial catheter while the FIO2 was varied between 0.08 and 0.40. The blood samples were analyzed with an IL 282 CO-Oximeter for SaO2 and then compared with pulse oximeter values of SaO2. Between saturations of 75% and 95%, the standard deviation (SD) for the difference between the CO-Oximeter and pulse oximeter measurements of SaO2 was +/-5.7%; however, below 70%, mean pulse oximeter estimates were higher than arterial values and the SD for the difference increased. It is concluded that pulse oximetry can detect trends in oxygenation over time in anesthetized and unanesthetized rats and that the accuracy of pulse oximetry is such that between 75% and 95% SaO2 agreement between pulse oximetry and arterial blood sample values of SaO2 is acceptable.