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Blood pressure: a critical factor (Proceedings)


It has been stated that: "Systemic hypertension associated with kidney disease is a very real problem, and has been diagnosed in over 60% of cats with chronic renal disease. Hypertension can have multi-systemic effects if left untreated, including left ventricular hypertrophy and cardiac failure, retinal detachment and blindness, cerebrovascular hemorrhage, and progression of renal dysfunction." (Rosemary Henik, DVM, MS, DACVIM) While this is true, let's look at the applicability of measuring blood pressure, methods of assessment and the interpretation of results in clinical practice. These notes review the literature from 1990 up until the end of 2004. The interested reader is strongly urged to read the ACVIM Consensus Statement from 2007 entitled: Guidelines for the Identification, Evaluation, and Management of Systemic Hypertension in Dogs and Cats.

Keypoints

1. Systemic arterial pressure is the pressure within the arteries and arterioles
2. Systolic pressure refers to the pressure when the aortic valve is open and the heart is ejecting blood (120 mmHg)
3. Diastolic pressure refers to the pressure when the aortic valve is closed and the heart is resting (80 mmHg)
4. Mean arterial pressure is closer to diastolic as the heart spends most of its time resting in diastole (90 mmHg)
5. Excitation, stress and pain can *transiently* raise the values, but as there are mechanisms in place to limit the elevations, consistent systolic values exceeding 170 mm Hg (range 168-180) are accepted as reflecting hypertension
6. To minimize the effects of "white coat syndrome", allow the patient to acclimate to the environment for ten minutes before measuring BP. Measure BP before performing any other evaluations (TPR, examination, etc.) Take measurements over several minutes until a series of five values are obtained that vary by no more than 10 mm Hg.
7. A mean arterial pressure of >60 mmHg are necessary to maintain perfusion to the brain, heart and kidneys.
8. Doppler measurement of systolic pressure underestimates values obtained by direct invasive measurement of arterial pressure. This may be corrected by the equation: Doppler + 14 mm Hg = direct systolic pressure.

Whose blood pressure should we measure?

Non-invasive, indirect arterial measurements of blood pressure should be made in all anaesthetized, critical or high-risk patients to detect and monitor management of hypotension. This technique should be used widely as a screening method for the pre-clinical detection of hypertension in patients with renal disease, hyperthyroidism, ocular changes consistent with hypertension, a cardiac murmur, or left ventricular hypertrophy, neurological dysfunction and all cats over eight years of age.