Page 325 - Feline Cardiology

334 Section I: Systemic Hypertension

should be part of the upkeep of BP monitoring reduce the artifact of environmental stimulation (white
equipment. coat effect).
Arterial BP may be measured on a cat’s forelimb,
Differential Diagnosis for Causes of Systemic hindlimb, or tail. A 2 × 2 cm area of skin that lies over
Hypertension the palmar metacarpal, metatarsal, or coccygeal artery,
The disorders that most commonly are associated with respectively, is clipped of hair; typically a band of 1 cm
systemic hypertension in the cat are chronic kidney or so of unclipped hair separates the clipped area from
disease (commonly causes hypertension), hyperthyroid­ the metatarsal pad, whereas the clipped area of hair
ism (commonly causes hypertension), pheochromocy­ reaches completely to the metacarpal pad (see Figure
toma (commonly causes hypertension, but rare disease 21.10). For the tail, the area that is clipped is on the
in cats), hyperaldosteronism (commonly causes hyper­ ventral surface of the tail as close to the base of the tail
tension, but rare disease in cats), and essential hyperten­ as possible, factoring in the width of the sphygmoma­
sion (rare condition in cats; diagnosis of exclusion). nometer cuff, which will need to be interposed between
Diabetes mellitus (reported as causing systemic hyper­ the Doppler probe and the tail base. The hairless area is
tension in only 2 cats) (Maggio et al. 2000) and obesity lightly moistened with isopropyl alcohol and then
are conspicuous in their lack of association with sys­ smeared with a small amount of ultrasound coupling
temic hypertension in cats. gel. A sphygmomanometer cuff is then chosen. The
width (not circumference) of the cuff should be approx­
DIAGNOSTIC TESTING imately 40% of the circumference of the limb or tail
around which it will be wrapped. Most cats use a 2 or
When should BP be measured in a cat? The measure­ 2.5 cm cuff, and a tape measure is useful for optimal
ment of a cat’s BP is indicated when 1) overt signs sug­ measurement (see Figure 21.10). The cuff is wrapped
Systemic Hypertension problems) are identified, 2) a cat is found to have a can be applied to the cuff to prevent the cuff from
gesting target organ damage (ocular, intracranial
around the limb or tail and additional white clinic tape
disease that is recognized commonly to be associated
opening midmeasurement. The limb should be posi­
with systemic hypertension (chronic kidney disease,
tioned so the point of measurement (Doppler probe) is
hyperthyroidism), or 3) as part of the evaluation of a
approximately at the same vertical level/height as the
patient with abnormalities suspected of arising from
systemic hypertension (left ventricular hypertrophy,
and the Doppler probe is placed, concave surface to the
retinal lesions, proteinuria, epistaxis). Continuous BP right atrium. The cuff is maintained in full deflation,
patient, lightly but entirely on the clipped area. It is
monitoring is also useful in cats under general anesthe­ important not to press firmly on the Doppler probe,
sia and in critically ill/unconscious cats. because doing so can reduce or obliterate the pulse, pro­
In cats, the clinical gold standard for measurement ducing false BP readings. Small movements of the probe
of arterial blood pressure uses Doppler ultrasonography on the patient’s skin are often necessary to find the loca­
for identification of the arterial pulse and a manually tion for optimal transmission of the Doppler signal.
inflated cuff connected to a spring­loaded sphygmoma­ Once this location is found, the cuff may be inflated
nometer (Figure 21.10). Systolic blood pressure readings carefully, 10–30 mm Hg at a time, rather than all at once
obtained by this technique more closely correlate with which can startle a cat and in turn increase the white
measurements from a direct arterial catheter than do coat effect. The pressure is increased until the Doppler
measurements obtained using an oscillometric instru­ signal is no longer audible, approximately 20 mm Hg
ment, particularly at higher BP where oscillometry greater than the point at which the pulse was still audible.
reports artifactually high BP in cats (Binns et al. 1995). The release valve on the sphygmomanometer is gently
activated to gradually deflate the cuff (1–5 mm Hg/
Technique for Measuring BP second). The first reappearance of the sound of the pulse
A room or area that is quiet and free of traffic is chosen. (first Korotkoff sound) corresponds to the systolic pres­
Many clinicians prefer to measure a cat’s BP in the pres­ sure, and this is noted in the cat’s medical record.
ence of his/her owner, which can be useful for limiting Occasionally, with ongoing release of cuff pressure, a
the white coat effect. A table with a padded surface is transition from brief, choppy pulse sounds to fuller,
recommended for the cat’s comfort. longer­lasting sounds is noted. This corresponds to the
Two individuals are usually needed: one to perform emergence of the diastolic pressure, and its presence is
the procedure, the other to hold the patient. The person unpredictable using this technique in cats. The proce­
providing the restraint should be willing to talk dure is repeated a total of 5 times, with a 30 sec to 1 min
softly and reassuringly to the cat, again in order to rest period between each, because momentary variation