SUMMARY
Background: Defining the reliability of oscillometry
(NIBP) for measuring mean arterial pressure (MAP) during normotension
and hypovolemic hypotension could help with cardiovascular monitoring in
horses anaesthetised in dorsal recumbency.
Objectives: To assess equivalence between NIBP and invasive MAP
during normotension and hypovolemic hypotension in dorsally recumbent,
anaesthetised horses.
Study Design: Prospective experimental study using 9
cardiovascularly healthy mature horses.
Methods: Under isoflurane anaesthesia, blood was removed every
10 minutes at 5 ml/kg bwt increments up to 25 ml/kg bwt and returned.
Paired NIBP and invasive MAP measurements (facial, transverse facial,
and metatarsal arteries; FA, TFA, MT) were obtained prior to and during
blood removal/return and tested for equivalence using linear
mixed-effects model. Sensitivity and specificity of NIBP to detect
hypotension (MAP < 70 mmHg) were calculated, and an optimum
NIBP MAP cut-off for hypotension was estimated.
Results: A total of 257 paired NIBP and invasive MAP were
compared. NIBP was equivalent to invasive MAP measured at the FA
(p = 0.3; M = -1, 95% CI [-3, 0.5]), with 88% sensitivity
and 73% specificity to detect hypotension (defined as MAP <
70 mmHg in the FA). NIBP and MAP measurements from the FA remained
equivalent when a standard 27 mmHg heart level correction was used
(p = 0.4; M = 1, 95% CI [-1, 3]). NIBP MAP < 80
mmHg using a heart level correction of 27 mmHg (or MAP < 107
mmHg without correction) is the optimum value defining hypotension (best
balance between sensitivity, 95%, and specificity, 65%).
Main limitations: Only adult horses in dorsal recumbency were
studied.
Conclusions: NIBP, as studied here, was equivalent to invasive
MAP in the FA under normotension and hypovolemic hypotension. A NIBP MAP
< 80 mmHg after 27 mmHg heart level correction appears to be
the optimum value defining hypotension.