Measurement of Tissue Oximetry in Standing Unsedated and Sedated Horses

Near infrared spectroscopy (NIRS) noninvasively measures peripheral tissue oxygen saturation (StO(2)) and may be useful to detect early changes in StO(2) in anaesthetized and critically ill horses. This study aimed to identify the muscle belly that provided the highest percentage of successful StO(2) readings and the highest mean StO(2) value. Fifty adult horses were enrolled in a prospective controlled study. StO(2) was measured at six different muscles in each horse, for each intervention: hair overlying the muscle was clipped (post clipping: PC), clipped skin was cleaned with chlorhexidine (post-surgical prepping: PP) and medetomidine was administered intravenously (post medetomidine: PM). Mean StO(2) values were calculated for each muscle, and a linear effects model was used to assess the effect of muscle group and intervention on StO(2). The sartorius muscle gave the highest percentage of successful StO(2) values (p < 0.001) and the highest mean (90% CI) StO(2) values for the PC, PP and PM interventions. Surgical prepping of the skin increased the success for measurement of StO(2) values. For all muscles, administration of medetomidine was associated with lower StO(2) values (p < 0.001). In conclusion, of the muscles examined, the sartorius muscle may be the preferred muscle to measure StO(2) in horses, and clipping and cleaning of the probe placement site is recommended.