Blood Pressure Management in Small Animals: A Technician's Guide

July 2020

Ori D. Scislowicz, BS, LVT

Blood pressure in small animal patients is important to monitor, as it is commonly overlooked until target organ damage has already occurred. The organs most commonly affected by high blood pressure include the eyes, heart, kidneys and brain. High blood pressure in dogs and cats is most often due to other systemic disease such as kidney disease, Cushing's disease, or hyperthyroidism. It is important to include blood pressure readings during examinations, especially in patients with signs of target organ damage, animals diagnosed with the common underlying causes of systemic hypertension, and geriatric patients (over 8 years of age). Blood pressure is a product of cardiac output and systemic peripheral resistance. The relationship between the kidneys, autonomic nervous system, and endothelial intercellular messaging systems all contribute to a patient's blood pressure.

Methods of Blood Pressure Management

Fortunately, there are affordable and simplistic methods of monitoring blood pressure in the small animal practice. There are two methods to measuring blood pressure in small animals:

Direct Monitoring:

• More invasive, but more accurate and can be ideal in ICU patients.
• Involves placing a catheter in a peripheral artery connected to a transducer via fluid-filled tubing.
• Pressure wave is converted to an electronic signal.

Indirect Monitoring:

• Less invasive
• Can be performed via Doppler technology or with an oscillometric monitor
• Doppler
  • Tends to be more accurate especially in smaller patients.
  • Machines measure systolic blood pressure.
  • The transducer generates ultrasound waves, which are used to detect motion of the arterial wall.
  • An inflatable cuff is measured to 40% of the circumference of the limb or tail, and is inflated to a level greater than the systolic pressure, which causes the audible pulse to disappear.
  • The cuff is slowly deflated with the aneroid pressure gauge, until an audible pulse is heard again, signaling the systolic pressure reading.
• Oscillometric monitoring
  • Oscillations are created from a pulse wave traveling through the artery.
  • The cuff is selected in the same way as with the Doppler method.
  • The machine will automatically inflate and deflate the cuff slowly, and relay the systolic, mean and diastolic pressure to the operator.
  • This method can be highly inaccurate, and CVCA recommends oscillometric monitoring only in medium and large breed dogs while under anesthesia.

Technique for indirect monitoring:

• The cuff on the limb or tail should be placed at the level of the heart. This can be accomplished by laying an animal on their side and using the top limb, or by having the patient stand and using the tail.
• Technician should record cuff position, cuff size, and body position for consistency between visits.
• For initial readings, it is recommended to obtain six consecutive measurements, eliminating the first measurement as well as any outliers.
• The blood pressure should be measured prior to any physical examination, vaccinations or other treatments or diagnostics to eliminate falsely elevated readings from stress.

The room should be kept as quiet as possible, and technicians should move slowly and comfort the patient, to decrease the "white-coat effect".

Treatment

Treatment options for hypertension include dietary and medicinal intervention. In some cases where caloric intake is not a concern, a low sodium diet of <0.25% sodium on a dry-matter basis (along with adequate protein) may be recommended. Weight loss is also important in keeping blood pressure levels normal. Most patients with high blood pressure will need medical treatment. In some cases, simply treating the underlying disease (ex. Hyperthyroidism) will cause the blood pressure to return to normal.

Please refer to table 2 below for medical treatment of hypertension in small animals. In addition to the interventions listed, other therapies may include hydralazine and phenoxybenzamine. Diuretics are commonly used in treatment of human hypertension, but are not used as frequently in veterinary medicine.

Final Thoughts

Technicians should keep in mind that clinical signs in patients with hypertension often do not show until the systolic blood pressure is greater than 180mmHg, so catching lelevated blood pressure prior to actual signs is of the utmost importance. The effects of target organ damage due to uncontrolled hypertension to the heart, eyes, brain, and kidneys can be devastating and sometimes, irreversible. For hypertensive patients beginning therapy, blood pressure should be monitored weekly until in an acceptable range. Once the blood pressure is adequately controlled, it should be rechecked every 3-4 months. Bloodwork (CBC/Chem/T4/UA) should also be checked at least every 6 months.