Systemic Hypertension Flashcards
What 2 things determine systemic blood pressure?
Cardiac output & systemic vascular resistance
*Remember BP = CO x SVR
Describe how the SNS regulates systemic blood pressure.
The SNS is activated when baroreceptors in blood vessels & the heart sense a decrease in blood pressure
-> Catecholamines (norepinephrine & epinephrine) are released
-> CO & SVR are increased
Systemic blood pressure is regulated by what 2 things?
- Sympathetic nervous system
- RAAS
Describe how RAAS regulates blood pressure
Decreased renal perfusion causes release of renin from kidneys -> converts angiotensinogen (produced by liver) to angiotensin I
-> ACE converts angiotensin I to angiotensin II
-> Angiotensin II causes contraction of smooth m. in vasculature -> inc. SVR
-> Angiotensin II also causes release of aldosterone from adrenals -> stimulates reabsorption of Na & H2O to inc. blood volume -> inc. CO
Angiotensin II also causes excretion of K+
Define systemic hypertension
Persistent elevation of systemic blood pressure (systolic > 160mmHg)
What 2 things determine cardiac ouput?
Heart rate & stroke volume
*Remember CO = HR x SV
What are the 2 general causes of systemic hypertension in dogs & cats?
- Primary idiopathic
- Secondary to other conditions that increase CO +/- SVR
Of direct and indirect methods to measure blood pressure, which is the gold standard & which is most practical?
Indirect = most practical
Direct = gold standard
Which method of measuring blood pressure is preferred in cats and small dogs?
Doppler
What are the 2 indirect methods used to measure blood pressure in dogs & cats?
Doppler & Oscillometric
Describe how doppler method works to measure systemic blood pressure
Arterial blood flow is occluded by inflating a cuff & then deflating it until the flow goes back to normal.
How do you know what size cuff to use when measuring blood pressure in dogs and cats?
Cuff width should be 30-40% of the circumference of the chosen site (limb or tail)
If the cuff you have chosen is too big, it could falsely increase/decrease (choose one) blood pressure.
Decrease
If the cuff you have chosen is too small, it could falsely increase/decrease (choose one) blood pressure.
Increase
Why should you gently restrain the dog/cat in lateral or ventral recumbency when measuring blood pressure?
To limit vertical distance from the heart base to the cuff
What are the 4 potential locations you may use to obtain an indirect blood pressure in dogs & cats?
- Underside of carpus
- Underside of metatarsus
- On top of the medial aspect of the metatarsus between the long bones of digits 2 & 3 on top of the back of the foot
- Underside base of tail (cats)
What are 4 possible areas of target organ damage from systemic hypertension?
- Eyes (retinopathy, blindness)
- Kidneys (proteinuria, progression of CKD)
- Brain (encephalopathy, stroke)
- Heart/blood vessels (left ventricular hypertrophy, arrhythmias, CHF, etc.)
What systemic blood pressure range is considered to be normotensive & has minimal TOD risk?
< 140mmHg
What systemic blood pressure range is considered to be hypertensive & has moderate TOD risk?
160-170mmHg
What systemic blood pressure range is considered to be prehypertensive and has low TOD risk?
140-159mmHg
What systemic blood pressure range is considered to be severely hypertensive and has a high TOD risk?
180mmHg or greater
Is primary or secondary systemic hypertension more common in dogs & cats?
Secondary causes
What are the 2 most common secondary causes of systemic hypertension in cats?
Only looking for most common, but feel free to list more for bonus points
- CKD
- Hyperthyroidism
Other (less common) causes include adrenal disorders (Hyperaldosteronism, Pheochromocytoma, Hyperadrenocorticism), and medications
What are 4 examples of medications that are associated with causing hypertension?
- Glucocorticoids
- Mineralocorticoids
- Phenylpropanolamine (Proin)
- Erythropoietin
How does renal disease lead to hyperthyroidism?
Looking for 5 things here
- Activation of RAAS & impaired Na+ excretion -> inc. intravascular volume
- Stimulation of SNS
- Endothelial dysfunction
- Decreased vasodilator production (Nitric oxide)
- Increased production of vasoconstrictors (endothelin)
How does hyperthyroidism cause hypertension in cats?
Increased sympathetic activity -> increased SV & HR -> increased CO
What are 5 secondary causes of hypertension in dogs?
- Kidney dz (acute or chronic)
- Cushing’s
- Diabetes
- Pheochromocytoma
- Hyperaldosteronism (uncommon)
What are 3 cases in which you should definitely treat a patient for hypertension?
- Severe hypertension
- Evidence of TOD w/ moderate to severe hypertension
- Persistent BP > 160mmHg w/ dz associated w/ hypertension
When is treatment for systemic hypertension not recommended? What should you do instead?
- Tx not recommended w/ prehypertension w/ no clinical signs
- Monitor BP during future visits
Why is it controversial to recommend a sodium restricted diet in cats & dogs with hypertension?
- Not as effective as in humans
- Usually doesn’t substantially decrease BP (may actually increase BP by activating RAAS)
What is the first line of treatment for systemic hypertension in cats?
Amlodipine (calcium channel blocker)
Describe the mechanism of action of calcium channel blockers
Relax vascular smooth muscle -> vasodilation -> decrease SVR
What is the first line of treatment of systemic hypertension in dogs?
ACE Inhibitor (Benazepril, Enalapril)
Bonus points if you said + Amlodipine in dogs w/ severe hypertension (180-200mmHg)
Why can ACE inhibitors be used as a treatment for proteinuria?
They preferentially dilate the EFFERENT arteriole of the glomerulus
How can ACE inhibitors cause azotemia?
They preferentially dilate the EFFERENT arteriole of the glomerulus (decreased pressure within the glomerulus), which can reduce GFR -> azotemia
Amlodipine can decrease BP by how much in cats?
30-50mmHg
Why is Amlodipine not used as a sole treatment for dogs with severe hypertension?
Amlodipine preferentially dilates renal AFFERENT arterioles, potentially exposing glomerulus to damaging increases in glomerular capillary hydrostatic pressure
aka can lead to increased proteinuria if BP not significantly decreased
You have just started a dog on an ACE Inhibitor. When do you tell the client you would like to see the dog again, and what are you going to do at that visit?
Evaluate renal values & electrolytes 7-10 days after starting tx or increasing dose
*Ace inhibitors block the production of Aldosterone, so they can look like an Addisonian patient (hyperkalemia & hyponatremia)
Why are ACE inhibitors not the first line of treatment for systemic hypertension in cats?
Only has a ~10mmHg reduction in BP in cats
What drug class is Telmisartan, and when is it used?
Angiotensin II receptor blocker;
used for moderate hypertension & proteinuria in cats (& dogs as an alternative tx to ACE inhibitors)
You have started a cat on Telmisartan. When do you tell the owner you would like to see the cat again, and what are you going to do at that visit?
Recheck renal values & electrolytes 7-10 days after starting or increasing dose
Can reduce GFR like ACE inhibitors, but has stronger effect on kidneys so use caution in cat that is already azotemic
What emergency drugs are used to treat severe life-threatening hypertension?
Direct arterial vasodilators (Hydralazine, Sodium nitroprusside)
Have greater risk for hypotension, so rarely used unless absolute emergency
When are alpha adrenergic antagonists used to treat systemic hypertension?
Give 2 examples of drugs in this class.
- Used for treating hypertension caused by pheochromocytomas (excess catecholamine production)
- Phenoxybenzamine & Prazosin
What diuretic can be used in treatment of systemic hypertension, specifically in cases of hyperaldosteronism?
Spironolactone (act as an aldosterone antagonist -> reduces sodium & water reabsorption)
A patient you started on Enalapril presents to you one month after starting tx for hypertension. The patient is QAR, tachycardic, and the owner reports the patient seems weak at home & described an episode of syncope. BP in hospital was 110mmHg. What do you do?
Concerned for hypotension -> decrease dose
Patients with a BP <120 & showing the clinical signs described in the case are consistent with hypotension
*Our goal is to keep systolic BP <140mmHg
A patient has an elevated BP, and there are signs of TOD. When should you recheck BP?
3 days
A patient has an elevated BP, but there are not signs of TOD. When should you recheck BP?
7-10 days
Once a patient’s BP is stable with treatment, how often should you recheck BP?
Every 3 months