Validation of non-invasive oscillometric blood pressure measurement at the tongue against invasive arterial blood pressure in anaesthetised horses
Arterial blood pressure is one of the most important variables monitored during general anaesthesia, since both hypotension and hypertension can compromise the perfusion of vital organs. The reference method, direct (invasive) measurement through an arterial catheter, is not always feasible in clinical patients, so anaesthetists rely on non-invasive oscillometric devices. The reliability of these measurements depends strongly on the cuff site, and any new site must be validated against the invasive reference before it can be recommended for clinical use.
With the financial support of the UniBern Forschungsstiftung, we were able to acquire a SunTech Vet25e veterinary monitor (Fig. 1), which measures non-invasive blood pressure (NIBP) using oscillometric technology. An appropriately sized cuff (manchette) can be positioned at several body sites; in this project we evaluated the tongue (Fig. 2), a site that is easily accessible in the intubated, anaesthetised horses.
The aim of the study is to validate NIBP measured at the tongue against simultaneously recorded invasive arterial blood pressure, following the recommendations of the American College of Veterinary Internal Medicine (ACVIM) for the validation of indirect blood-pressure devices. In horses under general anaesthesia in which an arterial catheter was placed for clinical reasons, paired tongue-NIBP and invasive readings were recorded at the same moment (Fig. 3) across a wide range of pressures. Systolic, mean and diastolic values were compared using Bland–Altman analysis (bias and limits of agreement), and the agreement was assessed against the ACVIM targets.
A preliminary analysis of 78 paired measurements from 14 horses — spanning invasive systolic pressures of 78–156 mmHg, from hypotension to hypertension — has been performed. Relative to the invasive reference, tongue-NIBP showed a mean bias (± SD) of −6.4 ± 16.4 mmHg for systolic, −2.9 ± 12.7 mmHg for mean and +3.1 ± 11.3 mmHg for diastolic arterial pressure, with 95% limits of agreement of −38.5 to +25.8, −27.8 to +22.0 and −18.9 to +25.2 mmHg, respectively. These early results suggest that the tongue is a feasible non-invasive measurement site — most reliable for mean and diastolic pressure — when conventional cuff positions are not accessible.
Med. vet. Andrei Berbecaru, DVM, MSc
Anaesthesiology and Pain Therapy Section
Vetsuisse Faculty, University of Bern
