Agreement between arterial blood pressures measured non-invasively and invasively in anaesthetised sheep

Both invasive and non-invasive blood pressure measuring methods are used in clinical and experimental work in veterinary medicine and several studies validating these methods are published. The aim of this study was to assess the level of agreement between non-invasive and invasive arterial blood pressure measurements within a wide range of blood pressures in sheep. Six adult Texel-cross female sheep were included. Anaesthesia was induced with IV propofol (4-8 mg/kg) and maintained with sevoflurane in 50% oxygen and air. Blood pressure measurements were simultaneously obtained using both invasive methods (electronic pressure transducer (EPT) connected to the auricular and carotid arteries, and aneroid manometer connected to the auricular artery) and non-invasive methods (the oscillometric device (OD) and Doppler). Carotid artery EPT was considered the 'gold standard' to which other methods were compared. The agreement between the two methods was evaluated with the Bland-Altman method, in conditions of normotension, hypertension (MAP > 160 mmHg, induced with phenylephrine), and hypotension (MAP < 50 mmHg, induced with acepromazine). The devices were evaluated using the American College of Veterinary Internal Medicine guidelines.

Carotid MAP values ranged from 37 to 192 mmHg. Mean bias and limits of agreement were - 2.8 mmHg and - 11-5.4 mmHg for the auricular EPT MAP; 5.1 mmHg and - 12.2-22.3 mmHg for the aneroid manometer MAP; - 2.7 mmHg and - 23.9-18.6 mmHg for the OD MAP; - 1.5 mmHg and - 20.1-23.2 mmHg for the Doppler SAP; respectively. Correlation coefficients for all methods were > 0.95.

Doppler SAP and OD MAP demonstrated acceptable accuracy over a broad blood pressure range, supporting their utility for sheep as surrogate of invasive methods of measuring blood pressure. Auricular EPT was the best surrogate of central arterial pressure to be used in clinical conditions.