Page 45 - Basic Monitoring in Canine and Feline Emergency Patients

Table 2.2. Conditions known to be associated with stroke volume and blood pressure (Fig. 2.3).
secondary hypertension in dogs and cats. Animals with cardiogenic shock experience
VetBooks.ir Associated conditions Examples decreased forward flow from the left ventricle and
also have a decreased stroke volume/blood pressure
(Fig. 2.3), while patients in hypovolemic shock
Kidney disease
Chronic kidney disease
Acute kidney injury have a decreased circulating blood volume which,
Glomerular disease when sufficiently diminished, leads to a decreased
Endocrinopathy Diabetes mellitus venous return to the heart (preload) and a subse-
Hyperadrenocorticism quent drop in stroke volume and blood pressure
(dogs) (Fig. 2.3). Animals suffering from septic shock fre-
Hyperthyroidism (cats) quently exhibit multiple forms of shock as their
Neoplasia Primary hyperaldosteronism illness likely leads to some measure of hypovolemia
Pheochromocytoma while the systemic inflammatory response may eas-
Drugs Glucocorticoids ily have a depressive effect on both cardiac function
Mineralocorticoids (inotropy) and maintenance of vascular tone.
Phenylpropanolamine Anesthesia can also be associated with hypoten-
Toceranib phosphate sion for numerous reasons, necessitating blood
Erythropoiesis-stimulating pressure monitoring. Many anesthetic drugs cause
agents cardiopulmonary depression (decreased heart rate
Ephedrine/pseudoephedrine or inotropy) or affect vasomotor tone leading to
Miscellaneous Obesity decreased SVR (Fig. 2.3). Positive pressure ventila-
Brachycephalic airway tion during anesthesia may lead to decreased
disease (dogs) venous return to the heart by compressing the vena
cava or other components of the venous system, in
turn decreasing preload and negatively affecting
also have a blood pressure measurement performed. stroke volume (Fig. 2.3). Hypoxemia during anes-
Furthermore, some drugs (e.g. phenylpropanolamine) thesia can deplete energy reserves and lead to
are known to cause hypertension. Patients receiving peripheral vasodilation as individual tissues make
such drugs should have their blood pressure routinely efforts to preserve oxygen delivery. At a local level,
monitored before starting and while taking the medi- such responses to tissue hypoxia are advantageous;
cation. Dogs or cats receiving medication aimed at however, if tissue hypoxia is more global, wide-
lowering blood pressure should also have their blood spread peripheral vasodilation can contribute to
pressure monitored after starting therapy. hypotension. Moreover, hypercapnia occurring
under anesthesia causes global smooth muscle
relaxation as a direct effect of carbon dioxide on
Hypotension
the smooth muscle of the vasculature. For many of
Hypotension usually occurs in more critically ill these reasons, mild hypotension is frequently noted
animals. Patients suffering from various forms of even in healthy animals undergoing anesthesia, and
shock are at risk for hypotension and warrant unhealthy animals are even more likely to display
blood pressure monitoring. Major presentations of hypotension.
shock include hypovolemic shock (e.g. marked
blood loss either through external hemorrhage or 2.4 Interpretation of the Findings
internal/cavitary hemorrhage), distributive shock
(e.g. anaphylaxis with diffuse vasodilation), A blood pressure measurement may be interpreted
obstructive shock (e.g. gastric dilatation-volvulus as either elevated (hypertension), normal, or low
placing pressure on the vena cava and occluding (hypotension).
the venous blood supply), cardiogenic shock (e.g.
dilated cardiomyopathy leading to markedly
reduced forward blood flow from the left ventri- Hypertension
cle), and septic shock. Animals with obstructive or When considering the potentially hypertensive
distributive shock have a diminished venous return patient, a reading <140 mmHg is generally considered
to the heart, which in turn leads to a decreased to be normal. The vast majority (>80%) of hypertensive

Blood Pressure Monitoring 37