Vol. III: The Measurement of Blood Pressure

Before Doppler and oscillometric monitors were used in veterinary medicine, palpating the peripheral artery was the only means of noninvasively assessing blood pressure. This assessment of pulse quality is called pulse pressure. Pulse pressure is the difference between systolic and diastolic blood pressure. However, it does not really measure pressure and has been proven to be an unreliable and fairly inaccurate technique.

Modern Methods for Blood Pressure Measurement

There are three methods available to veterinary staff that continue to improve and provide reliable blood pressure measurements: oscillometric technology, Doppler instrumentation (indirect methods), and the direct method of blood pressure measurement.

Oscillometric Technology

Oscillometric technology involves simply placing a cuff around a leg or tail and connecting the cuff to a computerized monitor. The width of the cuff should be approximately 40% of the circumference of the leg or tail to which it is applied.

Oscillometers measure blood pressure by detecting pressure oscillations within the cuff bladder. A pump inflates the cuff, and a computer measures the changes in intracuff pressure caused by pulse wave pressure as the cuff is slowly deflated. The system then calculates the systolic, mean, and diastolic pressures from these cuff pressure changes. Many of the monitors in use are designed to veterinary specifications.

Doppler Instrumentation

Using Doppler instrumentation (e.g., Parks Medical Electronics, Aloha, OR) is a bit more labor-intensive but yields accurate results.

The hair over the dorsal pedal, coccygeal, or metacarpal artery is first clipped, and the piezoelectric crystal is placed directly over the artery. The probe is taped in place, and the flow of blood is converted into an audible sound. As with oscillometric measurement, an appropriately sized cuff is placed above the Doppler probe, and the cuff tubing with a manometer and bulb are attached.

The Doppler is then turned on, and the cuff is inflated until no sound is heard. The pressure is slowly released from the cuff, and the first sound heard indicates the systolic blood pressure.

Direct Blood Pressure Measurement

Direct blood pressure measurement involves placing a catheter into an artery via percutaneous or cut-down methods. While this technique requires a skilled technician or anesthetist, the arterial blood pressure readings obtained with direct measurement are more accurate and continuous compared to indirect methods.

The most commonly used arteries for percutaneous catheterization in dogs and cats are the dorsal pedal (metatarsal) artery or the lingual artery. Once the catheter has been placed, it can be connected to a commercial transducer and recording system, which allows for continuous systolic, mean, and diastolic pressure readings.