Comparison of direct and Doppler blood pressure measurements in rabbits during isoflurane anaesthesia

Objective To measure the level of agreement between Doppler measured (DOP) arterial blood pressure (ABP) in the forelimb and directly measured (DIR) auricular systolic ABP (SAP) and mean ABP (MAP) in isoflurane-anaesthetized rabbits. Study design Prospective clinical study. Animals Data were analysed from 17 of 24 healthy rabbits, weighing 1.3-2.8 kg. Methods Rabbits were anaesthetized for neutering using a standardized protocol. A 26G catheter placed in an auricular artery was connected via heparinised saline filled non-compliant tubing (regularly flushed) to a calibrated pressure transducer (zeroed level with the thoracic inlet) to obtain DIR ABP. A cuff was placed proximal to the carpus (approximately level with the thoracic inlet) and a Doppler transducer sited over the dorsal carpal branch of the radial artery to obtain DOP ABP. Simultaneous DIR and DOP ABP recordings were made every 5-10 minutes during anaesthesia. Agreement was assessed as described by Bland JM & Altman (2007). Results Mean +/- SD cuff width: limb circumference ratio was 0.50 +/- 0.04. Mean between-method differences +/- SD, DIR SAP-DOP and DIR MAP-DOP, were +1 +/- 8 and -13 +/- 8 mmHg respectively. The 95% limits of agreement between DIR SAP and DOP and between DIRMAP and DOP were -14 to +17 and -28 to +2 mmHg respectively. Differences between DIR SAP and DOP were <= 10 mmHg 85% of the time. Defining hypotension as either DIR SAP < 80 mmHg or DIR MAP < 60 mmHg, and taking DOP ABP of < 80 mmHg to indicate hypotension, sensitivity and specificity were 92% and 67% respectively. Conclusions Good agreement was found between DIR SAP and DOP. Doppler measurements below 80 mmHg are a reliable indicator of arterial hypotension. Clinical relevance DOP is acceptable for monitoring ABP in isoflurane-anaesthetized rabbits and is useful for detection of hypotension. Clinical relevance DOP is acceptable for monitoring ABP in isoflurane-anaesthetized rabbits and is useful for detection of hypotension.