Tissue oxygen levels in sedated horses examined in Australian study

Study team sought to identify the muscles that provide the highest percentage of successful tissue oxygen saturation readings and highest average values.
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Many people will be familiar with a pulse oximeter, the little device a doctor or nurse may clip on a finger to determine the oxygen saturation of the blood.

This is important patient information for a medical professional, and it’s the same with veterinarians, especially for anaesthetized and critically ill horses.

Researchers at the University of Queensland set out in a just-published study to measure peripheral tissue oxygen saturation in standing unsedated and sedated horses.

They used noninvasive technology — near-infrared spectroscopy, which operates in a similar way to pulse oximetry. Near-infrared spectroscopy uses the increased permeability of skin and tissue to near-infrared light and allows for the determination of oxygen saturation at greater depths than pulse oximetry.

Nicholas Cowling and his fellow researchers, writing in the journal Veterinary Sciences, said measuring tissue oxygen saturation may be useful to detect early changes in oxygen levels in anaesthetized and critically ill horses.

This study team sought to identify the muscles that provided the highest percentage of successful tissue oxygen saturation readings and the highest average values.

Fifty healthy adult horses owned by the University of Queensland were enrolled in the study. Oxygen saturation in the horses was measured at six different muscles in each horse, while sedated and unsedated.

In all cases, hair overlying the muscle was clipped and the skin cleaned with chlorhexidine, with readings taken before and after cleaning.

The muscles tested in the study were the sartorius, biceps brachii, semimembranosus, extensor digitorum longus, brachiocephalicus and the extensor carpi radialis. They were selected on the basis of success in other species, potential ease of access, and presumed thin skin that may allow for more successful readings.

Medetomidine was used for sedation.

The researchers found that the sartorius muscle, which runs down from the pelvis towards the stifle, gave the highest percentage of successful oxygen saturation values and the highest mean oxygen saturation values after clipping, after cleaning, and after sedation.

However, as accessing this muscle in the standing horse is not practical, the authors recommend the use of the extensor carpi radialis or brachiocephalicus muscle.

They found that the cleaning of the skin increased the success of taking measurements.

For all the muscles measured in the study, the administration of medetomidine was associated with lower oxygen saturation values.

The researchers said future studies in horses should consider the use of a five-wavelength monitor to counteract skin pigmentation, which can confound readings.

While the monitor used in their study was able to obtain oxygen saturation levels from horses of a variety of colours and sexes, it was postulated that pigmentation likely reduced the ability of this two-wavelength monitor to attain values.

“Furthermore, studies should consider the potential for near-infrared spectroscopy’s application for anaesthetized patients and critical care patients such as acute abdomen equine colic cases and other equine anaesthesia.”

The establishment of an intervention point for tissue oxygen saturation would also be valuable, they said. For example, a level below 35% would represent a significant decrease and would necessitate the need for treatment. This would allow for the development of treatment algorithms for managing decreased oxygen levels.

The study team comprised Cowling, Solomon Woldeyohannes, Albert Sole Guitart and Wendy Goodwin.

Cowling, N.; Woldeyohannes, S.; Sole Guitart, A.; Goodwin, W. Measurement of Tissue Oximetry in Standing Unsedated and Sedated Horses. Vet. Sci. 2021, 8, 202. https://doi.org/10.3390/vetsci8100202

The study, published under a Creative Commons License, can be read here.


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