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.