MANUSCRIPT
The equine perioperative mortality rate is disproportionately larger than that reported for humans, dogs, and cats.1Hypotension, and its association with decreased tissue perfusion, is one factor implicated in this disparity. In addition to its pivotal role in cerebral and renal autoregulation, mean arterial blood pressure (MAP) targets greater than 70 mmHg in the horse have been championed to reduce the severity of postanesthetic myopathy and anaesthetic recovery duration.2,3 Accurate blood pressure measurement is essential for appropriate monitoring to guide clinical interventions in equine anaesthesia.
Numerous studies evaluating noninvasive blood pressure measurements using oscillometry in comparison to invasive techniques in peripheral arteries using the limbs,4-6 a cuff-width-to-circumference ratio of 0.4-0.6,4,7-9 or under normotensive or standing conditions have failed to prove equivalence.8,10 Two studies, one in normotensive, laterally recumbent anaesthetised horses and another in laterally recumbent, anaesthetised ponies, demonstrated equivalence between noninvasive oscillometry and an invasive technique measured at the transverse facial artery or metatarsal artery only when a cuff width-to-circumference ratio of 0.25 was applied at the tail base, whereas all other cuff sizes and placement sites were not equivalent.11,12 An additional study in standing and anaesthetized horses in dorsal and lateral recumbency (unknown number in each recumbency) found that a cuff-width-to-tail circumference ratio of 0.2 was optimal for oscillometric measurements to correlate with invasive pressure measurements obtained at the metatarsal artery.13 However, the lack of demonstration of equivalence between oscillometric and invasive techniques, no determination of clinically relevant endpoints such as sensitivity and specificity, and the use of a single artery for invasive pressure measurements are important limitations of that study. The present study aimed to evaluate MAP equivalence between oscillometry and three peripheral arterial sites in dorsally-recumbent, anaesthetised horses over hypotensive and normotensive conditions, and determine clinically relevant endpoints such as sensitivity and specificity of the oscillometric method. A second aim was to describe the variability of the differences between MAP invasive measured in the three peripheral locations in relation to that measured centrally in the thoracic aorta, seeking to gain insight into whether or not there is an ideal or preferred peripheral site for invasive measurement of arterial blood pressure in anaesthetised horses in dorsal recumbency and to which the oscillometric method should be compared.