Acute Kidney Injury

Question 1

define acute kidney injury

Answer 1

an abrupt (within hours) decrease in kidney function, which encompasses both injury (structural damage) and impairment (loss of function)

-the rapid decline in renal function is often identified as a decrease in GFR

-range from subclinical to severe dysfunction

-often associated with retention or uremic wastes, deranged fluid status, electrolyte imbalances, and acid-based disorders

Question 2

describe pathophysiology of AKI

Answer 2

metabolically active, relatively hypotoxic

diseased kidneys even more susceptible (acute on chronic)

straight portion of proximal tubule (S3) and medullary thick ascending limb most susceptible

Question 3

what does acute kidney injury encompass?

Answer 3

prerenal changes in GFR (insufficient blood flow to kidneys)
-severe dehydration
-hypovolemia
-hypotension
-decreased effective circulating volume
-shock
-heatstroke

acute kidney damage: a kidney disorder involving damage to the kidneys
-ischemic
-nephrotoxicants
-inflammatory/immune-mediated
-infectious
-neoplasia
-prolonged urinary obstruction

postrenal changes in GFR or urinary tract rupture
-obstruction in the urethra, both ureters, or one ureter with a solitary functional kidney (uroliths, masses, feline idiopathic cystitis)
-uroabdomen

Question 4

describe the phases of AKI

Answer 4

initiation: starts with the insult itself, early intervention may prevent progression

extension: ischemia, hypoxia, and inflammation propagate damage

initiation and extension last days, usually less than 48 hours

maintenance:
-ongoing damage and simultaneous repair
-damage peaks and GFR maintained at lowest point
-azotemia and/or uremia usually present
-urine output may be increases of decreases and urine resembles ultrafiltrate
-lasts days to weeks

recovery:
-ongoing repair and reorganization
-progressively improving function
–variable return to function
–permanent loss of nephrons and fibrosis if severe damage
–compensation by remaining nephrons can contribute to function
-lasts weeks to months

Question 5

describe animals that recover from AKI

Answer 5

presume to have CKD, even if serum creatinine returns to normal

remember that recovery from AKI takes months, so don’t stage CKD prematurely

Question 6

describe AKI risk factors

Answer 6

1. dehydration
2. advanced age
3. nephrotoxic drug administration
4. decreased CO
5. anesthesia
6. sepsis
7. multiple organ dysfunction
8. pre-existing chronic kidney disease

Question 7

describe diagnosis of acute kidney injury

Answer 7

1. markers of kidney function: relatively late indicators of injury
2. markers of active kidney injury (earlier indicators!); leaked tubular markers in urine or serum
   -urinary cystatin B
   -urinary clusterin
   -urinary gamma-glutamyl transferase
   -urine or serum neutrophil gelatinase associated lipocalin (NGAL)
   -urine kidney injury molecule (KIM-1)
   -urine microscopy (casts)

Question 8

why is it important to distinguish between AKI and CKD?

Answer 8

for acute kidney injury:
-rapid onset, potentially reversible
-repair processes are ongoing
-compensatory mechanism are just beginnin

for CKD:
-irreversible and slowly progressive
-exhausted compensatory mechanisms

for the same level of azotemia, the long-term prognosis is better than AKI!!
-if you can keep them alive, overall survival rate in dogs and cats is approx 50%

Question 9

how is AKI subgraded?

Answer 9

1. non-oliguric (NO) versus oligo-anuric (O)
   -very important for prognosis!! very hard to keep an animal that cannot pee alive
   -oligo-anuria means urine product <1ml/kg/hr
2. requirement for renal replacement therapy

Question 10

describe AKI grading

Answer 10

1: nonazotemic:
-documented AKI
-progressive nonazotemic increase in creatinine within 48 hours (<1.6)
-measured oliguria or anuria over 6hrs

2. mild AKI:
   -documented AKI and static or progressive azotemia
   -progressive increase in creatinine within 48hrs or volume responsiveness (higher than stage 1, 1.7-2.5)
   -measured oliguria or anuria over 6hrs

3-5: moderate to severe AKI
-documented AKI and increasing severities of azotemia and functional renal failure
3: 2.6-5
4: 5.1-10
5: >10

grading is a MOMENT in the disease course, it can worsen or improve, AKI is very dynamic ad can even be regraded every time you do labwork

Question 11

describe the process of AKI grading

Answer 11

1. establish diagnosis of AKI
2. assign a grade on serum creatinine concentration
3. assign a subgrade based on urinary output
4. assign a subgrade based on the need for renal replacement therapy
5. reassign grades/subgrades as the disease evolves (for better or worse)