Comparison of arterial blood pressure measurements obtained invasively or oscillometrically using a Datex S/5 Compact monitor in anaesthetised adult horses

Objective

To assess agreement between noninvasive blood pressure (NIBP) oscillometrically-derived values from a multiparameter monitor (Datex Ohmeda S/5 Compact) with those obtained by invasive blood pressure (IBP) measurement in anaesthetised horses undergoing elective surgery.

Study design

Prospective clinical study.

Animals

A total of 40 healthy adult horses.

Methods

Horses were anaesthetised with various anaesthetic protocols (based on clinical requirements). Depending on positioning, cannulation of the facial or lateral metatarsal artery was performed for IBP measurement. The cannula was connected via a transducer to the monitor. An appropriately sized NIBP cuff was placed around the tail base and connected to the same monitor. Systolic (SAP), mean (MAP) and diastolic (DAP) arterial blood pressures were continuously recorded from the invasive system, and at 3 minute intervals from the oscillometric system, throughout the surgical procedure using a Datex iCollect program. An appropriate arithmetic correction factor was applied to the oscillometric results where the cuff was not level with the heart. Assessment of the degree of agreement between invasive and noninvasive readings at each time point was performed using a modified Bland-Altman analysis.

Results

While in many horses there was relatively close correlation between the values obtained over time, there was substantial variability in individual animals which resulted in wide Bland-Altman limits of agreement. The oscillometric device over-reads by approximately 32, 23 and 22 mmHg, and under-reads by 26, 17 and 19 mmHg for SAP, MAP and DAP, respectively, compared with the IBP values. However, using the mean difference and standard deviation, the device conforms to American College of Veterinary Internal Medicine (ACVIM) standards.

Conclusions and clinical relevance

Oscillometric blood pressure measurement using the Datex Ohmeda S/5 Compact multiparameter monitor conforms to ACVIM standards when the NIBP cuff is placed on the tail. However, because of the wide variability in measurements, we cannot recommend this technique to guide therapy in anaesthetised adult horses.