Measurement of tissue oxygen saturation levels using portable near-infrared spectroscopy in clinically healthy dogs

Objective: To establish a reference interval for tissue oxygen saturation (StO₂) levels measured by a portable near-infrared spectroscope and determine site(s) for reproducibly measuring StO₂ levels in dogs. Design Prospective experimental study. Setting Veterinary teaching hospital. Animals Seventy-eight healthy dogs. Measurements and Main Results: A portable device that quantitatively measures StO₂ levels directly in muscle tissue using near-infrared spectroscopy (NIRS) was topically applied to shaved sites over 4 muscle bodies. Readings from the sartorius muscle were obtained 100% of the time. The digital extensors and biceps femoris muscles provided similar readings, but less consistently obtained StO₂ values (70% and 67%, respectively). Mean StO₂ levels measured over these 3 sites were not statistically different from one another. When readings from these 3 sites were combined, a mean ±1 SD of 92.9±7.4% was obtained. The epaxial muscles produced a significantly lower mean ±1 SD (68.5±22.4%), and readings were obtained only 60% of the time. Conclusions In dogs, a mean ±1 SD of 92.9±7.4% can be used to investigate clinical applications of NIRS. The sartorius muscle most consistently allows for detection of StO₂ levels (100%). The epaxial muscles are not consistent or reliable for obtaining StO₂ readings and are not recommended for clinical application of near-infrared spectroscope. Sex does not significantly affect StO₂ readings at any site. Body condition score only affects readings obtained from the sartorius muscle.