Hypertension Flashcards
What is systemic hypertension? What are other factors to consider with systemic hypertension?
- persistently elevated systemic bp
Extremely dependant circumstances
- fear or excitement
- typically requires more than just 1 abnormal reading
- drugs (fluid therapy, steroids, cyclosporin A, phenylpropanolamine)
Guidelines
- systolic >160mmHg warrants further investigation
- diastolic >100mmHg warrants further investigation
- age (possible 1-3mmHg/year after 8y)
- breed (sighthounds have 10-20mmHg higher BP
- obesity (small increase)
What does systemic hypertension diagnosis need to be supported by?
- underlying condition
- end organ damage producing CS
BP formula
BP = CO x PVR
PVR = peripheral vascular resistance
CO = SV x HR
Pathophysiology of systemic hypertension
Initiating causes
- chronic fluid accumulation
- persistently increased HR
- chronic vasoconstriction
Perpetuating causes
- small arteries changes:
– extravasation of plasma into the vessel wall (hyaline arteriosclerosis)
– vascular smooth muscle hypertrophy
- renal dz
Renal dz:
- BP can’t remain persistently elevated without abnormal sodium handling (chronic renal failure / insufficiency)
- kidney dz of any type results in areas of ischaemia that lead to activation of the RAAS
- kidney dz leads to dilation of the afferent arteriole and constriction of the efferent arteriole resulting in dramatic raises in glomerular pressures which leads to renal damage and proteinuria
What is the most common cause of increased bp?
- increase in peripheral vascular resistance
Aetiology of systemic hypertension
Artefact
- stress induced
Primary (idiopathic)
- no underlying dz detected
– common in humans (diet & lifestyle related)
– rare in veterinary spp
Secondary
- underlying dz detected
- most common in vet pts (>80%)
Aetiology of secondary systemic hypertension
Renal dz
- 30-40% of dogs with CRF have hypertension
- disturbance in neuroendocrine factors and body fluid balance
Hyperadrenocorticism (dog)
- increases renal retention of salt & water
- overproduction of renin: vasoconstriction
Hyperthyroidism (cat)
- increases sensitivity of myocardium to catecholamines
Diabetes mellitus (dog & cat)
- volume expansion due to hyperglycaemia
- overproduction of renin: vasoconstriction
Phaechromocytoma
- rare
- tumour of the adrenal medulla -> so get overproduction of catecholamines
Hyperaldosteronism
- rare
Drug therapy
- steroids, NSAIDs, cyclosporin A, phenylpropanolamine
Diet
- not as significant as in humans
Clinical signs
None at the initial phases
- pts perception (humans: headaches, general unease)
- aging - depression
Only present with end organ damage
- >180mmHg r if 30mmHg rise within 48h
Ocular (hypertensive retinopathy)
- acute blindness, retinal detachment
- intraocular haemorrhage
CNS (hypertensive encephalopathy)
- disorientation, ataxia, stupor
- seizures, strokes
Renal (proteinuria)
- PUPD
Cardiac (left ventricular hypertrophy)
- murmur, arrhythmias
- CHF
Measuring bp
Direction
- invasive (requires arterial catheter)
- intra-op
- ICU
Indirect
- non-invasive (compressive cuff)
- commonly used in clinics
Methods of indirect bp measurement
Doppler
- manual
- requires more training
- more user variability
- faster
- only systolic BP
Oscillometric (high definition oscillometric)
- automatic
- straightforward
- time consuming
- systolic, diastolic & mean
Protocol for measuring bp
- cuff width size should measure 40% of the cuff site circumference
- cuff placed on a limb (cats) or tail (dogs)
- the pt should remain calm and motionless
- cuff should be maintained at the same level as the heart
- 1st measurement should be discarded and an average of 3-7 consecutive measurements should be obtained
Treatment - when to?
Risk end organ damage
Underlying dz identified
- CS: low to moderate risk to end organ damage (systolic >160mmHg)
- no CS: moderate to high risk of end organ damage (systolic >180mmHg)
Risk categories & their tx
BP <150mmHg
- risk of TOD: minimal
- tx: none
- risk category 1
BP 150-159mmHg
- risk of TOD: mild risk
- tx: none
- risk category II
BP 160-179mmHg
- risk of TOD: moderate
- tx: treat if repeatable findings of evidence of TOD
- risk category III
BP >180mmHg
- risk of TOD: severe
- tx: aggressively tx - if no CS repeat measurement prior to tx
- risk category IV
Treatment options
- lifestyle
- diet (salt restriction)
– 1st line in humans, not used in veterinary - diuretics (volume depletion)
– frequently used in humans
– only in emergency setting in vet pts - beta blockers
- ACEi
- Ca channel blockers
- combination of the above
Beta blockers - use, examples
Reduce HR and contractility
Atenolol (beta-1 selective)
- dogs: 0.2-1mg/kg BID
- cats: 6.25-12.5mg/cat SID or BID
Propanolol (non-selective)
- dogs: 0.2-1.0mg/kg TID
- cats: 2.5-5mg/cat TID
- NOT TO ASTHMATIC
Is the tx of choice in hyperthyroid cats (increased sensitivity to catecholamines so good for this)
Poor results as a single agent in other conditions
ACE inhibitors - use, examples
Block RAAS
Benazepril, Enalapril, Imidapril
- dogs & cats: 0.5mg/kg SID or BID
Better in pathologies that lead to elevated renin levels
- renal failure, Cushing’s & diabetes
1st choice In dogs and pts with proteinuria
- good effect on intra-glomerular pressure, therefore good for proteinuria
Frequently insufficient as a single agent but should always be considered
Calcium channel blockers - use, examples
Vasodilators
Inhibit calcium influx into the cell
Amlodipine
- dogs & cats: 0.1-0.25mg/kg SID
1st choice in cats (proven efficacy)
Commonly added to ACEi in dogs for significant results
Rapid onset (emergency)
Angiotensin II receptor blocker - use, examples
Potent vasoconstrictor
Telmisartan
- 1mg/kg BW (0.25ml/kg BW)
Reduction of proteinuria associated with CKD in cats
Seminar is an oral solution and is well accepted by most cats
Treatment goals
- reduce bp (<150/95mmHg, >120mmHg)
- reduce EOD risk
- decrease proteinuria
- alleviate CS
- prevent further deterioration of organ function
- depends on underlying dz
- minimise hospitalisation
- O compliance
- monitor for hypotension
