Equivalence Between Invasive and Oscillometric Blood Pressure
Measurements in a Controlled Haemorrhage Model in Dorsally-Recumbent
Isoflurane-Anaesthetised Horses
Abstract
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.