Hypertension Flashcards
What is the equation responsible for blood pressure?
It is a product of cardiac output (CO) and systemic vascular resistance (SVR)
-these variables are regulated by the sympathetic nervous system and the renin-angiotensin-aldosterone system
What happens to the blood pressure with vasodilation vs vasoconstriction?
Vasodilation–> drop in BP
Vasoconstriction–> increase in BP
Why can stress result in hypertension?
Catecholamine release directly affect smooth muscle of vessels and cause them to vasoconstrict
What downstream targets does the RAAS system affect?
Both vessel tone and blood volume
-target of a lot of drugs we use
Describe the physiology of the renin-angiotensin-aldosterone system (RAAS)
When the body is in a state of hypotension, there is decreased blood flow to the kidneys which results in production of renin
-renin goes to the bloodstream and converts angiotensinogen into angiotensin 1
-angiotensin 1 gets converted to angiotensin 2 by the action of the angiotensin converting enzyme
-angiotensin 2 then goes to act directly on blood vessels (causing vasoconstriction) and causes adrenal glands to release aldosterone which stimulates resorption of sodium/water and excretion of potassium to increase blood volume
What organ (s) are responsible for the production of Renin? Angiotensinogen? ACE? Aldosterone?
Renin- kidneys
Angiotensinogen- liver
ACE- lungs
Aldosterone- adrenal glands
What is the most basic definition of hypertension in cats and dogs?
Systolic pressure >160
(also diastolic >120)
T/F: the most common etiology of systemic hypertension in animals is idiopathic
False- this is true in people
-in animals it is usually secondary to other conditions (>80% of cases). Must look for underlying cause of what is increasing CO or impacting SVR
What are common opthalmic exam findings that accompany systemic hypertension?
-Retinal hemorrhage and retinal vessel tortuosity
-acute onset blindness
What are the main two ways to assess blood pressure?
Indirect (most common and more pratical)
- doppler: only get systolic
-Oscillometric: gives you systolic, diastolic and mean
Direct: arterial line
- most practical
- must be placed under anesthesia
Which indirect method is preferred in small dogs and cats? What about medium to large breed dogs?
Small dogs and cats: doppler
Medium to large breed dogs: oscillometric
How do you determine cuff size?
Cuff width should be 30-40% of circumference of the chosen site
- too large will falsely lower BP
-too small will falsely elevate BP
What are the preferred sites for measuring BP in small animals?
Base of tail (most used in cats)
-under metatarsal region or carpal region
Why is it important to keep animals in lateral or ventral recumbency when measuring BP?
Reduces the distance between the heart base to the cuff resulting in a more accurate reading
What are some techniques for reducing stress and falsely elevating BP in the clinical setting?
-take measurements in quiet area
-perform prior to other procedures
-allow for an acclimation period 5-10 minutes prior to the measurement
-allow the owner to be present
-use minimal restraint
How many measurements should you take to get an accurate BP reading?
Average 5-7 consecutive measurements after discarding the first measurement
-note the patient demeanor, cuff size and measurement site and stay consistent on follow up visits
What are the main organs that can be negatively affected by hypertension?
-eyes: retinal hemorrhage, acute blindness
-kidneys: presents as proteinuria or rapid progression of CKD
-brain: can have stroke like events
-heart and vasculature: left ventricular hypertrophy, new murmurs
What are the ranges for normotensive, prehypertensive, hypertensive, or severely hypertensive? When should you intervene?
Normotensive: <140 mm Hg
Prehypertensive: 140-190 mm Hg
Hypertensive: 160-179 Hg
Severely hypertensive: >180 Hg
Intervene during hypertensive phase as this is where there is moderate target organ damage risk, severe risk for TOD occurs when severely hypertensive
What are the main underlying causes of hypertension in cats?
-Chronic kidney disease*
-Hyperthyroidism*
-adrenal disorders: hyperaldosteronism (conns), pheochromocytoma, hyperadrenocorticism
-medications
*= most common
What is the mechanism of pheochromocytomas resulting in hypertension?
Adrenal tumor that causes the release of excess catecholamines which causes vasoconstriction
What medications can result in hypertension?
Corticosteroids, proin, erythropoietin agents
What are the main causes of hypertension in dogs?
-Kidney disease (acute and chronic)*
-hyperadrenocorticism (cushings)*
-diabetes mellites
-pheochromocytoma
-hyperaldosteronism (uncommon)
- = most common
What signalment factors may affect BP?
Age (older animals tend to have slightly higher) and breed (sighthounds are known to have a higher than normal resting BP)
- obesity, anxiety/stress can also affect
-all of these only increase 5-10 mmHg
When should hypertension be treated?
When it is severe (>180), when there is evidence of TOD with moderate to severe hypertension, or if there is persistent BP >160 mmHg with disease associated with hypertension
Grey zone: if there is a moderately elevated BP (160-180) with no evidence of TOD–> recheck on another day (1-2 weeks later)
What are the options for treatment of hypertension?
- Address underlying disease if possible
- Antihypertensive therapy (aimed at reducing CO, SVR or both)
- Dietary change :weight loss in obese patients and avoiding high sodium treats/diets
What is the mechanism of action of amlodipine?
Calcium channel blocker -causes relaxation of smooth muscle of vasculature
-first line of treatment in cats (reduces BP 30-50 mmHg)
-used in dogs with SEVERE hypertension (add in ACE inhibitors to block the action of RAAS)
Always recheck BP 7-10 days after starting the med
What are the two ace inhibitors frequently used in vet med? How do they work?
Benazapril and enalapril
-inhibit ACE leading to decreased production of angiotensin II
-potentially vasodilates the efferent arteriole of the glomerulus which reduces proteinuria (Can be a treatment for this as well)
-has more effect on kidney compared to amlodipine – reduces GFR and can lead to azotemia (or worsen it)
*first line of treatment in DOGS. Often use with amlodipine in severe cases. Doesn’t have much of an effect in cats (except in cases of proteinuria)
Why should you recheck kidney values 7-10 days after starting on an ace inhibitor?
In order to assess kidney function as ACE inhibitors can reduce GFR and cause worsening azotemia
What would the electrolytes look like in a patient that does not have enough aldosterone?
Hyponatremia and hyperkalemia
- can occur in patients taking ACE inhibitors long term
-try to avoid potassium going over 6–> can lead to heart problems
What is the angiotensin II receptor blocker used most commonly in vet med? How does it work?
Telmisartan
- works through blocking action of angiotensin II which inhibits RAAS
-used for moderate hypertension in cats
-alternative trt to ace inhibitors
*Best used in a cat with proteinuria in addition to hypertension
-but beware of worsening azotemia in bad kidney cats
What are the emergency treatments for severe hypertension?
Hydralazine and sodium nitroprusside
- direct arterial vasodilators that work quickly
- associated with increased risk of rebound hypotension
- only use in life threatening cases (having art line in is ideal)
What are the alpha adrenergic antagonists in vet med and when are they used?
Phenoxybenzamine and prazosin
-used for pheochromocytomas
When would you use spironolactone in a hypertension case?
In cases of hyperaldosteronism
- this is an aldosterone antagonist
What should be the goal for hypertension management?
- to reach systolic BP between 110-140 mm Hg, minimal goal <160
-want to aim for a gradual decrease rather than acute marked decrease
-if below 120, risk of hypotension, consider tapering dose of drug
What are the 3 monitoring guidelines discussed in lecture?
- If TOD is present, recheck in 3 days
- If TOD is not present, recheck in 7-10 days
- Once BP is stable, check every 3 months
