ChemPath: Assessment of Renal Function 2 Flashcards
(40 cards)
Define AKI.
Rapid reduction in kidney function, leading to inability to maintain electrolyte, acid-base and fluid homeostasis.
What are the three stages of AKI and what is the name of the classification used?
KDIGO classification
Stage 1: increase in serum creatinine by 1.5-1.9 times baseline
or UO <0.5ml/kg/hr for 6-12h
Stage 2: increase in serum creatinine by 2-2.9 times baseline
or UO <0.5ml/kg/hr for >12h
Stage 3: increase in serum creatinine by >3 times baseline
or UO <0.3ml/kg/hr for >24h
What is pre-renal AKI?
AKI caused by reduced renal perfusion
Describe the normal response to reduced circulating volume.
- Activation of central baroreceptors and renin-angiotensin system
- Release of vasopressin
- Activation of sympathetic system
- Results in vasoconstriction, increased cardiac output and renal sodium retention
Name and describe the two mechanisms that maintain renal blood flow despite changes in systemic blood pressure.
- Myogenic stretch - if the afferent arteriole gets stretched due to high pressure, it will constrict to reduce the transmission of that pressure to the glomerulus
- Tubuloglomerular Feedback - high chloride concentration in the early distal tubule (suggestive of high GFR) stimulates constriction of the afferent arteriole which lowers GFR and, hence, chloride concentration
List some causes of pre-renal AKI.
- True volume depletion
- Hypotension
- Oedematous state
- Selective renal ischaemia (e.g. renal artery stenosis)
- Drugs
List some drugs that cause AKI and briefly state how they affect renal blood flow
- ACE inhibitors - preferential dilation of efferent arteriole
- NSAIDs - increased afferent constriction
- Calcineurin inhibitors - same as above
- Diuretics - affect tubular function and decrease preload
What is a consequence of prolonged pre-renal AKI?
Acute tubular necrosis (ATN)
This does NOT respond to fluid restoration (compared to pre-renal AKI which does respond)
What might be seen on urine microscopy in a patient with ATN?
Epithelial cell casts
What causes post-renal AKI?
Physical obstruction of urine flow
List some sites of urine obstruction.
- Intra-renal
- Ureteric
- Prostatic/urethral
- Blocked urinary catheter
Outline the pathophysiology of post-renal AKI.
- GFR is dependent on a hydraulic pressure gradient
- Obstruction results in increased tubular pressure
- This results in an immediated decline in GFR
What are some consequences of prolonged renal obstruction?
- Glomerular ischaemia
- Tubular damage
- Long-term interstitial scarring
List the possible sites of disease in intrinsic AKI.
- Vascular (e.g. vasculitis)
- Glomerular (e.g. glomerulonephritis)
- Tubular (e.g. ATN)
- Interstitial (e.g. AIN)
Causes of intrinsic renal AKI:
1. Direct tubular injury - what can cause this?
- Ischaemia (MOST COMMON)
- Endoengous toxins (e.g. myoglobin from rhabdo, immunoglobulin)
- Exogenous toxins (e.g. aminoglycosides, amphotericin, aciclovir)
Causes of intrinsic renal AKI:
2. Immune dysfunction - what can cause this?
Immune dysfunction -> renal inflammation
- Glomerulonephritis
- Vasculitis
(40yo presenting with systemic purpura + AKI)
Causes of intrinsic renal AKI:
3. Infiltration/abnormal protein deposition - what can cause this?
- Amyloidosis (associated with nephrotic syndrome)
- Lymphoma
- Myeloma
List the possible outcomes of AKI.
- Partial recovery of renal function
- Discharged with increased serum creatinine
- Discharged requiring chronic dialysis
- Death
What are the biochemical definitions of AKI?
- Increase in serum creatinine > 26.5µmol/L within 48 hours
- Increase in serum creatinine > 1.5 times baseline within the previous 7 days
- Urine volume < 0.5 ml/kg/hr for 6 hours
What are the four processes of acute wound healing?
- Haemostasis
- Inflammation
- Proliferation
- Remodelling
What are the stages of CKD?
- Stage 1: >90
- Stage 2: 60-89
- Stage 3: 30-59
- Stage 4: 15-29
- Stage 5 (end stage): <15
List some causes of CKD.
- **Diabetes mellitus ** *
- ** Hypertension** *
- Chronic glomerulnephritis
- Atherosclerotic renal disease
- Infective or obstructive uropathy
- Polycystic kidney disease
What are the normal roles of the kidney?
- Excretion of water-soluble waste
- Water balance
- Electrolyte balance
- Acid-base homeostasis
- Endocrine (EPO, RAS, vitamin D)
Outline the consequences of CKD.
- Progressive failure of homeostatic function (acidosis, hyperkalaemia)
- Progressive failure of hormonal function (anaemia, renal bone disease)
- Cardiovascular disease (vascular calcifiction, uraemic cardiomyopathy)
- Uraemia and death
