10.2 Pathophysiological Mechanisms Underlying Renal Failure (Part 1)

Question 1

Define hypotensive shock. How can it arise?

Answer 1

• Hypotensive shock describes a severe drop in blood pressure, leading to inadequate perfusion of vital organs
• Can be caused by hypovolaemia (2° to bleeding, dehydration, burns etc.), sepsis (so-called “septic shock”), anaphylaxis (“anaphylactic shock”), or cardiogenic

Question 2

What is a main chemical mediator released during anaphylaxis? How can anaphylaxis cause shock?

Answer 2

• Large amounts of histamine (and other inflammatory mediators) are released in response to an allergen
• This causes systemic inflammation, increased vascular permeability, mass vasodilation, and swelling, which can cause hypovolaemia (and therefore can progress to shock)

Question 3

Outline a clinical approach to treating hypotensive shock

Answer 3

• Address underlying cause (allergy = antihistamines,
• Fluid resuscitation (meaning fluid and electrolytes)
• Vasocative meds (such as adrenaline) to increase cardiac output
• Dialysis may be required if kidney function has been impaired

Question 4

How can hypertension damage the kidneys? How can this cause a positive feedback loop?

Answer 4

• Hypertension can constrict, narrow, and damage blood vessels, such as those in the kidneys
• This reduces the ability of the kidneys to recieve (and filter blood), meaning more products stay in the blood, and - since the macula densa detects less stuff - RAAS overactivation also occurs, worsening hypertension
• This can lead to hypertensive nephrosclerosis and chronic renal failure

Question 5

What are the MAP boundaries of renal autoregulation?

Answer 5

80mmHg to 180mmHg

Question 6

Outline the 3 grades of hypertension

Answer 6

Grade 1: S 140-159 OR D 90-99mmHg
Grade 2: 160-179 OR D 100-109mmHg
Grade 3: S 180mmHg + OR D 110mmHg+

Question 7

Outline 4 main types of causes of hypertension

Answer 7

• Essential (most common)
• Endocrine (hypo/hyperthyroidism, diabetes, adrenal tumours)
• Illicit substances (e.g. coke)
• Pregnancy (such as in preeclampsia

Question 8

What is malignant hypertension? Does it always involve a past hx of HTN?

Answer 8

• Severe high blood pressure that develops rapidly (over weeks or months). Sometiems defined as 180/120mmHg or above
• Does not always involve HTN hx - patient may now have known they had HTN

Question 9

What are 4 complications of malignant hypertension, and why do they arise?

Answer 9

1. Kidney damage (damage renal vessels; can cause acute renal failure)
2. Cardiac damage (because it’s acute, can cause arrhythmias, aortic dissection, or heart failure)
3. Cerebrovascular injury (vascular damage in the brain; strokes, cerebral oedema, seizures)
4. Eye damege damage to orbital vasculature; papilloedema)

Question 10

List 3 ways in which sepsis can damage the kidneys

Answer 10

1. Toxins from pathogen can damage kidneys
2. Ischaemia 2° to shock can hypoperfuse kidneys
3. Inflammatory damage to renal vasculature

Question 11

Why can renal/urinary outlet obstruction damage the kidneys?

Answer 11

• Pressure buildup since urine flow is obstructed
• Can cause hydronephrosis, infection (stasis), scarring, and loss of nephrons

Question 12

How can hypovolaemia cause renal failure?

Answer 12

• Hypovolaemia means less perfusion to the kidneys
• This decreases the ability of the kidneys to filter blood, and can lead to renal ischaemia

Question 13

Why can shock cause metabolic disturbance? What are the end results of this

Answer 13

• Continued anaerobic metabolism increases systemic acidity
• Leads to dysfunctioun of ion channels, enzymes, and other proteins
• Can cause multi-organ failure and death

Question 14

Define obstructive and distributive shock

Answer 14

Obstructive: something obstructing the flow of blood (such as a thrombus)
Distributive: systemic vasodilation causes sudden drop in BP