A comparison of tissue oxygen saturation measurements by 2 different near-infrared spectroscopy monitors in 21 healthy dogs.

Objective: To determine whether a difference exists in tissue oxygen saturation (StO2 ) measurements between 2 near-infrared spectroscopy monitors on the sartorius muscle in healthy dogs.

Design: Prospective experimental study.

Setting: University veterinary teaching facility.

Animals: Seventeen healthy student volunteered dogs and 4 healthy veterinary medicine teaching dogs.

Interventions: An Inspectra 650 and INVOS 5100C StO2 probe were simultaneously placed on the medial right and left sartorius muscles of each dog for 2 minutes of real-time recording while standing and in left lateral recumbency. Left and right probe locations were reversed for both standing and lateral measurements. The peak value over the first 30 seconds on the Inspectra was also recorded.

Measurements And Main Results: Peak StO2 values on the Inspectra over 30 seconds yielded an average of 89.9 ± 4.8%. There was no significant difference between groups above or below 9 kg, or between male and female dogs. The 2-minute averaged mean for the Inspectra was statistically higher than the INVOS (87.7 ± 5.47% and 64.1 ± 5.51%, respectively). The linear mixed-effects model showed that there is a 1.82% decrease in StO2 when standing compared to left lateral recumbency, which was elicited on both machines. On average, the INVOS underestimated the StO2 by 23.7% compared to the Inspectra.

Conclusions: The INVOS significantly underestimates StO2 when compared to the Inspectra. Given this difference is on average 23.7%, StO2 cut off values used to guide therapy based on Inspectra readings cannot be applied to the INVOS. While there was a statistically significant difference in standing versus lateral positions on both devices, it is unlikely to be clinically significant. Studies using different devices should not be directly compared, and it is important to use the same monitor when taking serial measurements.