Maintenance of appropriate systemic arterial blood pressure is vital for survival. Because many common situations and conditions (eg, general anesthesia, renal or cardiovascular disease) place animals at risk for dangerously high or low blood pressure, blood pressure monitoring is a fundamental necessity.
In clinical practice, blood pressure is usually measured indirectly. The two most common methods of indirect blood pressure measurement are Doppler ultrasound using a sphygmomanometer and oscillometry. Both techniques use an inflatable cuff placed around an extremity. High-definition oscillometry, a newer indirect technique, is not used often in clinical practice.
Doppler Ultrasound Measurement
Doppler ultrasound measurement is likely the most common blood pressure measurement technique used in small animal practice. The procedure is straightforward, and the equipment is relatively inexpensive and reliable.
Doppler ultrasound reliably measures only systolic blood pressure in dogs and cats; it cannot be used to measure mean or diastolic blood pressure.
Standard Oscillometry Measurement
In clinical practice, oscillometers are often built into multiparameter monitors and usually have a stat feature that allows continual, repeated measurements. Thus oscillometers are commonly used for critically ill or anesthetized patients that may require more intensive monitoring.
Oscillometers report systolic, diastolic, and mean blood pressures; however, they are unreliable in patients with cardiac dysrhythmias because measurement relies on rhythmic arterial pulsations.
While actual blood pressure measurement varies between the techniques described here, some important points apply to both.
Patient Acclimation & Restraint
Ideally, blood pressure should be measured in a quiet, comfortable environment after the patient has become acclimated (ie, without disturbance) for at least a few minutes, but acclimation is rarely possible for acutely or critically ill patients.
The patient should remain still during measurements to optimize accuracy and, if necessary, can be physically restrained gently. However, some patients cannot be restrained in lateral recumbency because of agitation, respiratory distress, or other reasons. Chemical restraint should be avoided, as it often alters results.
To acquire the most accurate blood pressure values, cuff height should be as close to the level of the right atrium as possible (Step 1A). The cuff can be placed on the antebrachium, distal pelvic limb, or tail.
If the vertical distance between the cuff site and the right atrium exceeds 10 cm, a correction factor must be integrated to interpret blood pressure measurement results (see Correcting for Cuff & Right Atrium Level Disparity). When the cuff is much lower than the right atrium, pressure values are falsely high because of the weight of the blood column between the atrium and cuff site.
The first blood pressure measurement should be discarded. At least 3 additional measurements should be obtained for a minimum of 3 to 7 consecutive, consistent measurements with less than 20% variability. Once these measurements have been obtained, they should be averaged to yield the blood pressure measurement.
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