Relation between CKD and hypertension Flashcards
Give a simple definition of CKD
CKD is defined as the presence of structural or functional abnormalities of one or both kidneys for an extended period (usaually longer than 3 months)
Various factors have been implicated that could contribute to the initiation of CKD
- ageing
- ischaemia
- dietary factors
- routine vaccination
What is the most frequent histopathologic lesion found in CKD cats
Non-specific renal lesions characterized by chronic tubulointerstitial inflammation and fibrosis
What is the most common underlying cause of systemic hypertension
CKD is one of the most common causes of systemic hypertension in cats
- 75% of cats presenting with hypertensive target organ damage have evidence of abnormal renal function
What is the current ACVIM consensus cut-off for normotension in cats
cut-off of < 140 mm Hg
What are the major body systems involved in maintaining systolic blood pressure in a relatively narrow optimal range
The kidney via:
- direct control of circulating fluid volume
- indirect neurohormonal effects on systemic vascular resistance
The cardiovascular system via:
- alterations in heart rate and force of contraction
The cardiovascular system has traditionally been thought of as responsible for minute-to-minute control of blood pressure, whereas the kidney is viewed as primarily responsible for longer term regulation
What is the mechanism of action of the renin-angiotensin-aldosterone system
The RAAS acts as a sodium-conserving system, which is activated when renal blood flow is reduced, as when low flow in the macula densa is sensed
The initial step in activation of the RAAS is the release of renin from juxtaglomerular cells located in the walls of the afferent arteriole
Renine cleaves the prohormone angiotensinogen to form angiotensin I, which is then converted by angiotensin-converted enzyme to angiotensin II, the major bioactive product of the system
In turn, angiotensin II stimulates the release of aldosterone from the adrenal medulla
What are the biological effects of angiotensin II and Aldosterone
Angiotensin II has direct effects:
- on the proximal tubule to increase sodium retention
- on vascular smooth muscle to cause vasoconstriction
- potentiates the sympathetic nervous system
Aldosterone acts on:
- the distal tubule to increase sodium retention
- is a potent vasoconstrictor
The overall effect of RAAS activation is therefore:
- to increase circulating fluid volume
- to raise total peripheral resistance
- to increase venous return
Thereby increasing systemic blood pressure
Describe the pathophysiology of hypertension in CKd
Activation of the RAAS, increased sympathetic tone and disruption of endothelial cell function represent the most significant contributors to blood pressure dysregulation
Increased RAAS activation is an expected physiological compensatory response to progressive loss of nephrons during CKD, as angiotensin II works to increase single nephron glomerular filtration rate via preferential constriction of the efferent arteriole
- in CKD this response is thought to become maladaptative, resulting in proteinuria and potentially driving disease progression and the development of hypertension
Explain why the kidney is a target of end organ damage in hypertension
In CKD there is a loss of functioning nephrons, which results in afferent arteriolar vasodilation, thereby exposing the glomerular capillaries to increased arterial pressures
The consequence of this glomerular capillary hypertension is increased protein loss across the glomerular filtration barrier
- increased protein in the filtrate is thought to be toxic to renal tubular epithelial cells, driving inflammation and further loss of functional nephrons
What are the organs most vulnerable to hypertensive target organ damage
Eyes
- blindness due to hyphema or retinal detachment
Brain
- signs secondary to hypertensive encephalopathy or due to vascular accidents
- seizures
- vestibular disease
- acute spinal cord disease
Heart
- left ventricular hypertrophy, altering diastolic and systolic myocardial function
- increase the risk of cardiovascular complications in patients with pre-existing heart disease
Kidneys
Which point is important in chosing cuff width for blood pressure measurement
The cuff width should be 30-40% of the circumference of the extremity on which it is placed
When is it recommended to treat systemic hypertension
Current ACVIM guidelines recommend to treat:
- when hypertensive TOD is noted
- in those patients where SBP is persistently > 160 mmHg
Give the ACVIM guidelines for the classification of hypertension based upon risk of TOD
< 140 mmHg: normotensive (minimal risk)
140-159 mmHg: prehypertensive (low)
160-179 mmHg: hypertensive (moderate)
> 180 mmHg: severely hypertensive (high)
When is it recommended to treat with an antiproteinuric drug in a CKD cat
Antiproteinuric therapy is recommended in cats
- with overt proteinuria (UPC > 0.4)
- with persistent borderline proteinuria (UPC 0.2-0.4)
What is the goal of antihypertensive therapy
The goal of antihypertensive therapy is:
- to reduce SBP to below 160 mmHg in order to prevent the occurence of TOD
- to attempt to minimize, or reverse, TOD when it is already evident
