Evaluation of an oscillometric blood pressure monitor for use in anesthetized sheep.

OBJECTIVE

To determine the accuracy of an oscillometric blood pressure monitor in anesthetized sheep.

STUDY DESIGN

Prospective study.

ANIMALS

Twenty healthy adult sheep, 11 males and nine females, weighing 63.6 ± 8.6 kg.

METHODS

After premedication with buprenorphine or transdermal fentanyl, anesthesia was induced with ketamine-midazolam and maintained with isoflurane and ketamine, 1.2 mg kg(-1) hour(-1), ± lidocaine, 3 mg kg(-1) hour(-1). Invasive blood pressure measurements were obtained from an auricular arterial catheter and noninvasive measurements were from a cuff on the metatarsus or antebrachium. Simultaneous invasive and noninvasive measurements were recorded over a range (55-111 mmHg) of mean arterial pressures (MAP). Isoflurane concentration was increased to decrease MAP and decreasing the isoflurane concentration and infusing dobutamine achieved higher pressures. Invasive and noninvasive measurements were compared.

RESULTS

Correlation (R(2)) was good between the two methods of measurement (average of three consecutive readings) for systolic (SAP) (0.87), diastolic (DAP) (0.86), and mean (0.90) arterial pressures (p < 0.001). Bias ± SD between noninvasive and invasive measurements for SAP was 3 ± 8 mmHg, for DAP was -10 ± 7 mmHg, and MAP was -7 ± 6 mmHg. There was no significant difference between the average of three measurements and use of the first measurement. Correlations using the first measurement were SAP (0.82), DAP (0.84), and MAP (0.89). Bias ± SD for SAP was 3 ±10 mmHg, for DAP was -11 ± 7 mmHg, and MAP was -7 ± 6 mmHg. The oscillometric monitor slightly overestimated SAP and underestimated DAP and MAP for both average values and the first reading.

CONCLUSIONS AND CLINICAL RELEVANCE

This oscillometric model provided MAP measurements that were acceptable by ACVIM standards. MAP measurements with this monitor were lower than those found with the invasive technique so a clinical diagnosis of hypotension may be made in sheep that are not hypotensive.