Page 47 - Basic Monitoring in Canine and Feline Emergency Patients

can also reduce GFR and lead to renal damage. function or maintenance of vascular tone as
Combination therapy appears safer for the kidneys detailed in Section 2.3, documentation of hypoten-
VetBooks.ir as RAAS inhibitors preferentially dilate the efferent sion in anesthetized patients is also quite common;
anesthetic hypotension has been documented in
glomerular arteriole and the joined effect of both
afferent and efferent glomerular arteriole dilation
The body’s autoregulation of the cardiovascular
will ideally spare the glomerulus exposure to >25% cats and dogs in various studies.
increased hydrostatic pressures. Even so, any patient system suggests that a relatively constant delivery
receiving CCB even with RAAS inhibition should of blood to the organs exists with a MAP between
have renal values monitored. Amlodipine is the most roughly 60–160 mmHg in awake otherwise healthy
commonly prescribed CCB used to treat hyperten- animals. However, in disease or anesthetic states,
sion in dogs and cats. the body’s normal autoregulatory processes may
Cats receiving CCB therapy alone have not been not be fully maintained. Hypertensive cases typi-
shown to suffer the same ill effects on the glomeru- cally focus on the systolic blood pressure to assess
lus that have been documented in dogs. Therefore, the risk of TOD (dependent on degree of blood
the first-line treatment of hypertensive cats is gen- pressure elevation or rate of change in blood pres-
erally amlodipine. Telmisartan (ARB) has been sure elevation). However, as the perfusion pressure
shown to be efficacious as single-agent therapy in is more closely related to the MAP than the systolic
hypertensive cats, although the efficacy has not blood pressure, in hypotensive patients there may
been studied in severely hypertensive cats. In cats, be a greater focus on the MAP than the systolic
ACEi are not recommended as first-line therapy as blood pressure. Although MAP is more associated
the reduction in systolic blood pressure is usually with perfusion pressure, assessment of the MAP in
minimal (~10 mmHg) with those drugs. a small and/or hypotensive patient may not be eas-
The reader is referred to the Further Reading sec- ily achieved, so degrees of hypotension are still
tion for more detail on dosing and specific moni- often described in terms of the systolic blood pres-
toring regiments for dogs and cats being treated for sure. The degree of hypotension may be classified
hypertension. as outlined in Table 2.4.
Rarely, a hypertensive crisis may become evident If hypotension is convincingly documented, steps
in a patient leading to acute severe TOD. Some should be pursued immediately to correct this con-
potential causes for a hypertensive crisis include dition as it can lead to death. The initial step, with
sudden catecholamine release from a tumor (e.g. rare exceptions (e.g. conditions marked by poor
pheochromocytoma), drug or toxin exposure (e.g. cardiac contractility such as dilated cardiomyopa-
methylxanthines, phenylpropanolamine), or glo- thy), is additional fluid support. Usually the first
merulonephritis. Retinal detachment or acute cen- fluid administered is an intravenous crystalloid
tral neurologic effects may be related to severe and/ delivered as a fluid bolus. Multiple crystalloid
or acute hypertension. In such cases, 24-hour care boluses are often performed if the patient fails to
is often necessary to control and monitor the show an appreciable or acceptable response.
hypertension using parenteral treatment titrated to Colloid bolus(es) may subsequently be adminis-
affect. Precise recommendations for therapy do not tered to a persistently hypotensive patient. Please
exist at this time, but considerations include see the Further Reading section for more detail
fenoldopam, labetolol, hydralazine, nitroprusside, related to fluid therapy in hypotensive patients.
and phentolamine. Please see the Further Reading Laboratory and routine examination and moni-
section for more detail on parenteral treatment of toring are also critical in the hypotensive patient to
hypertensive crises.

Table 2.4. Categories of hypotension in dogs and cats.
Hypotension
Mild Moderate Severe
Decreased blood pressure, or hypotension, is the hypotension hypotension hypotension
other extreme of blood pressure measurement.
Hypotension is commonly appreciated during the Systolic 80–90 60–80 <60
evaluation of patients with varying causes of shock blood
or in critically ill patients. Due to the potential effects pressure
of anesthetic medications on either myocardial (mmHg)

Blood Pressure Monitoring 39