Comparison of direct and Doppler arterial 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 DIR MAP 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.