Page 239 - Small Animal Internal Medicine, 6th Edition

CHAPTER 11
VetBooks.ir

Systemic Arterial

Hypertension

GENERAL CONSIDERATIONS is associated with BPs between 160 and 179 mm Hg systolic
and 100 and 119 mm Hg diastolic. Arterial pressures greater
Systemic hypertension refers to the sustained elevation of than 180/120 mm Hg indicate severe hypertension, with
systemic arterial blood pressure (BP). Over time, marked severe risk for target organ damage (Category IV). An addi-
increase in arterial BP can cause serious clinical conse- tional 20 mm Hg is allowed for specific breed differences
quences. Multiple studies have attempted to define BP levels (e.g., for sighthounds).
in normal dogs and cats; the largest studies suggest average Animals with mild hypertension (Category II) usually are
systolic BP of approximately 130 mm Hg in dogs and not given antihypertensive therapy, although any underlying
120 mm Hg in cats. However, various factors influence disease should be addressed. Some surveys of normal animals
values obtained for systolic, diastolic, and mean arterial BP show BPs in this range, and it is likely that anxiety (“white-
in healthy, as well as diseased, animals. Variations related to coat” hypertension) plays a role in mild BP elevation.
age, sex, reproductive status, and other factors might con- Animals with moderate hypertension (Category III) could
tribute minimally, whereas breed differences in normal benefit from specific antihypertensive therapy, especially if
values can be more pronounced. For example, BP can be 10 there is evidence for target organ damage or treatment for
to 20 mm Hg higher in normal Greyhounds and some other underlying disease does not normalize BP. However, animals
sighthounds compared with mixed-breed dogs, although with BP closer to 160 mm Hg or where the white-coat effect
this could reflect an increased and sustained level of anxiety is thought likely usually are not treated unless the clinician’s
in the hospital setting (“white-coat” effect). Lesser differ- assessment of the case dictates otherwise. Patients with
ences in normal BPs have been reported for some other dog severe hypertension (Category IV) should be treated to
breeds as well. Variation in measured BP could be related to prevent or reduce target-organ damage. When possible, BP
technique (direct and various noninvasive methods) and measurement is repeated to confirm presence of severe
patient anxiety. Use of a consistent protocol for BP measure- hypertension. On occasion, marked patient anxiety or tech-
ment in the clinic can help reduce variability related to envi- nical error in BP recording can produce this degree of BP
ronmental factors and technique. The demarcation between elevation, although this is uncommon. Some animals require
acceptable and “abnormally high” arterial BP is not clear-cut. urgent antihypertensive therapy because of rapidly progress-
Furthermore, although some dogs and cats clearly have clini- ing signs (see p. 213). When antihypertensive therapy is
cal disease caused by hypertension, many with “abnormally used, close monitoring for efficacy, adverse effects, and dete-
high” BP have no evidence of related pathology. In addition, rioration of underlying conditions is warranted. In all cases,
systolic BP can exceed 180 mm Hg in some stressed normal predisposing disease should be treated, as possible.
animals. Repeated BP measurements over time along with
careful clinical evaluation are indicated when considering a Etiology
diagnosis of hypertension. Hypertension in dogs and cats usually is associated with
Classification of abnormal BP in dogs and cats is based other diseases (Box 11.1) rather than being a primary condi-
on risk for damage to so-called target organs (see p. 212). tion (idiopathic or essential hypertension). The most
Animals with BP less than 150/95 mm Hg (systolic/diastolic) common associations in cats are chronic kidney disease
have minimal risk (Risk Category I). In general, this level is (CKD) and hyperthyroidism. Reported prevalence of hyper-
the therapeutic goal for patients receiving antihypertensive tension in these disease conditions ranges from 25% to 75%.
medications. Repeatable BP measurements of 150 to 159 mm In dogs, the most common conditions associated with
Hg systolic and 95 to 99 mm Hg diastolic constitute mild hypertension are renal disease (especially glomerular disease)
hypertension, as well as mild risk for future target organ and hyperadrenocorticism, with prevalence of hypertension
disease (Category II). Moderate hypertension (Category III) reported to be up to 30% to 80% for each disease. Diabetes

211