Evaluation of an indirect oscillometric blood pressure monitor in normotensive and hypotensive anesthetized dogs

Objective – To determine the accuracy and precision of an oscillometric noninvasive blood pressure device as a predictor of invasive direct blood pressure in healthy anesthetized hypotensive and normotensive dogs. Design – Prospective observational study. Setting – University teaching hospital. Animals – Eight crossbred adult dogs. Interventions – Anesthesia was induced with propofol and maintained with isoflurane. A catheter was placed in the dorsal pedal artery to record systolic, mean, and diastolic arterial blood pressures (aSAP, aMAP, and aDAP, respectively). The noninvasive blood pressure device cuff was placed around the contralateral front limb to record noninvasive systolic, mean, and diastolic blood pressure (nSAP, nMAP, and nDAP). Two states of blood pressure (BP) were studied: baseline state was established by keeping end-tidal isoflurane concentration at 1.2±0.1%. The hypotensive state was achieved by maintaining the same isoflurane concentration while withdrawing approximately 40% of the animal's blood volume until aMAP was stable at approximately 40 mm Hg. At the end of the study, blood was returned to the animal and it was allowed to recover from anesthesia. Measurements and Main Results – Agreement between the direct and indirect BP measurements was determined by the Bland-Altman method. The SAP and MAP but not DAP bias varied significantly between each BP state. Normotensive absolute biases (mean [SD]) for SAP, MAP, and DAP were −14.7 mm Hg (15.5 mm Hg), −16.4 mm Hg (12.1 mm Hg), and −14.1 mm Hg (15.8 mm Hg), respectively. Absolute biases during the hypotensive state for SAP, MAP, and DAP were −32 mm Hg (22.6 mm Hg), −24.2 mm Hg (19.5 mm Hg), and −16.8 mm Hg (17.2 mm Hg), respectively. Conclusion – The oscillometric device was not reliably predictive of intra-arterial BP during hypotension associated with acute hemorrhage.