small animal med- acute kidney injury

what is acute kidney injury (AKI)?

abrupt failure of the kidneys to carryout normal functions

-sudden accumulation of uremic toxins

-dysregulation of fluid, electrolytes and acid-base balance

can AKIs only occur in animals with normal kidney function?

no, can occur with normal kidney function or in patients with pre-existing CKD (acute on chronic kidney disease)

how severe are AKIs?

can range from injuries that are clinically non-detectable to severe dysfunction and acute renal failure

what is the most severe stage of AKI?

acute renal failure

what can detection of AKI at earlier stagies lead to?

improved outcomes (the earlier it is caught and treated, the better the outcome)

what are the phases in the pathogenesis of AKIs?

1. initiation (immediately following insult and lasts <48 hours)

2. extension

3. maintenance (azotemia lasts days to weeks)

after maintenance, can either:

-recover

-death (due to permanent damage)

what are the clinical signs of AKIs?

nonspecific- lethargy, vomiting, diarrhea, PU/PD

what history questions should you ask owners with animals presenting for suspected AKI?

-inciting cause (toxin exposure, travel history, vaccine history, recent anesthesia)

-is the dog/cat urinating

-previous medical history (history of CKD, UTI, uroliths)

how can the physical exam help make a diagnosis of AKI?

-renal and bladder palpation (size, pain)

-hydration status (usually dehydrated)

-fever (points to infectious etiology if present)

-cardiovascular status

-rectal exam, look for melena

-oral exam, examine MMs, oral ulcers (uremia)

-respiratory status (pulmonary edema, ARDS, pleural effusion)

what minimum diagnostic testing is needed to diagnose AKI?

-CBC

-chem profile

-urinalysis

-urine culture

-blood pressure (w/ fundic exam)

-imaging (abdominal U/S, rads)

what CBC abnormalities may be seen in patients with an AKI?

-anemia (look for underlying CKD if anemic)

-hemoconentration (dehydration)

-thrombocytopenia

what chemistry panel abnormalities may be seen in patients with an AKI?

-azotemia

-hyperphosphatemia

-hyperkalemia

-metabolic acidosis

- +/- hypoalbuminemia

- +/- hyperbilirubinemia and elevated liver enzymes

what urinalysis changes can be seen in animals with an AKI?

UA supports renal azotemia:

-isosthenuria

-proteinuria

-hematuria

-pyuria

-bacteriuria

-glucosuria

-epithelial cells

-casts

what is urine microscopy used for when diagnosing AKI?

detects presence of active tubular injury/damage

correlates with severity of outcomes

what are markers of AKI/tubular injury seen with urine microscopy?

-free renal tubular epithelial cells

-renal tubular epithelial cells

-granular casts

-RBC casts

may also see glucosuria without hyperglycemia

how effective is imaging when diagnosing AKI?

can support a diagnosis but cannot exclude AKI

what ultrasonographic changes may be seen in animals with AKI?

ultrasound can be normal, but may also see:

-medullary rim sign

-renal enlargement

-renal pelvic and ureteral dilation

-retroperitoneal fluid

-renal abscess

-renal mass (lymphoma, other neoplasia)

how can urine output/production be used to diagnose AKI?

oliguria (UOP <1ml/kg/hr) or anuria (no urine) for over 6 hours after fluid resuscitation supports AKI

have to first rule out pre-renal and post-renal causes

what does polyuria indicate when seen with AKI patients?

polyuria (UOP >2ml/kg/hr) indicates beginning of repair phase or indicative of less severe insult

polyuria in AKI= great sign

what is the IRIS grading system for AKIs?

AKI grade 1-5 (grade changes as progresses from maintenance to recovery)

subgrades:

-non-oliguric or oligo-anuric

-requiring renal replacement therapy

is renal function recovery seen in AKI and CKD?

AKI: renal function recovery is possible

CKD: renal function recovery is not possible

what is the duration of illness in AKI vs CKD?

AKI: acute onset

CKD: gradual and progressive (but can have acute exacerbation)

what is the hematocrit in AKI vs CKD?

AKI: normal HCT

CKD: anemic

how do the kidneys palpate with AKI vs CKD?

AKI: normal to enlarged (often painful)

CKD: normal to small, irregular

what are the serum potassium levels in AKI vs CKD?

AKI: normal to increased

CKD: variable

can casts/glucosuria be seen on UA in AKI and CKD?

AKI: may have casts, may have renal glucosuria

CKD: no casts or glucosuria

how will the kidneys appear on ultrasound in AKI vs CKD?

AKI: peri-renal fluid, +/- renomegaly

CKD: irregular margins, cortical cysts, +/- small kidneys

what are the 3 general causes of AKI? which is most common?

1. prerenal (hemodynamic-most common)

2. renal parenchymal

3. postrenal

what pre-renal causes of AKI?

any condition that decreases renal blood flow:

-vasoconstriction

-reduced renal perfusion (hypovolemia, heart failure)

-thromboembolic injury

what are renal parenchymal causes of AKI?

any disease or toxin directly affecting kidneys

-infection, toxin, immune-mediated, systemic disease w/ renal manifestation

what are postrenal causes of AKI?

any condition that obstructs urine flow anywhere along urinary tract

-ureteral or urethral obstruction

what are common causes of AKIs in dogs?

-grapes/raisin toxicity

-leptospirosis

-lyme nephritis

what are common causes of AKIs in cats?

-lily toxicity

-ureteral obstruction

-renal lymphoma

-FIP

what are common causes of AKIs seen in both dogs and cats?

-pyelonephritis

-hemodynamic instability (hypo/hypertension)

-acute pancreatitis

-drugs (aminoglycosides, amphotericin, NSAIDs, ace inhibitor)

-ethylene glycol toxicity

what endocrine disease can present similar to an AKI?

addison's disease

how to differ: an addisionian crisis is very responsive to fluid resuscitation

what are the categories of treatment for AKIs?

1. assess hydration status

2. provide nutrition

3. treat oliguria/anuria

4. hyperkalemia

5. metabolic acidosis

6. hypertension

7. renal replacement therapy

what hydration status can animals with AKI present with?

1. dehydrated/hypovolemic patients (most commonly)

2. euhydrated patients

3. overhydrated patient (after IV fluids)

what is the goal for dehydrated/hypovolemic patients?

correct dehydration and restore renal perfusion (without flooding kidneys)

what is the treatment for correcting dehydration in AKI patients?

-bolus IV replacement crystalloids (plasmalyte, LRS) as indicated until stable (10-20ml/kg bolus over 15-30 minutes)

-calculate fluid prescription (deficit, maintenance (2-3ml/kg/hr), ongoing losses)

***reassess***

are fluids necessary in a euhydrated AKI patient?

IVF prescription necessary to maintain hydration until the pet is eating

may need urinary catheter to calculate UOP (match ins/outs)

ideally, providing water by mouth/feeding tube is the best option

what is the treatment for an overhydrated AKI patient?

discontinue fluids if overhydrated

risk of respiratory compromise, non-responsive hypertension, and renal parenchymal edema with overhydration

which AKI patients is overhydration a higher risk in?

in AKI patients with oliguria/anuria

how is hydration status monitored in AKI patients?

-repeat PEs

-body weight

-respiratory rate

-PCV/TP

-blood pressure

-urinary output

how often should hydration status in AKI patients be monitored?

continual re-evaluation of patient and hydration status every 3-6 hours

what is indicated if an AKI patient is anorexic for over 2 days?

need to place a feeding tube (NE/NG tube)

allows delivery of nutrition, medications, and free water administration

what food/diets should be given to AKI patients?

focus on caloric intake while in-hospital

-if concern for pancreatitis, start with low fat/highly digestible diet

-long term: renal therapeutic diet (once home and stable)

what are pre-renal causes of oliguria/anuria?

dehydration- rehydrate these animals before raising concern for oliguria/anuria

what are renal causes of oliguria/anuria?

-tubular swelling

-inflammation/necrosis

-cast deposition within tubules

-altered renal blood flow

what are post-renal causes of oliguria/anuria?

urinary tract obstruction (upper or lower)

what is the treatment for oliguria/anuria?

-ensure adequate hydration (give IVF to treat dehydration)

-furosemide CRI (concurrently with fluids)

-hemodialysis

-surgical intervention for urinary tract obstructions

if anuria is still present after fluid resuscitation, should you continue IV fluids?

no- discontinue fluids if anuria persists after fluid resuscitation

what is the treatment for hyperkalemia in AKI patients?

1. may spontaneously resolve with diuresis

2. initiate treatment if over 6.0mEq/L

-dextrose

-regular insulin with dextrose

-sodium bicarbonate

how can dextrose administration treat hyperkalemia in AKI patients?

causes endogenous insulin secretion to drive potassium into the cells

how can dextrose with insulin administration treat hyperkalemia in AKI patients?

causes intracellular potassium movement

supplemental dextrose is needed to prevent hypoglycemia

what does sodium bicarbonate administration treat hyperkalemia in AKI patients?

promotes intracellular potassium movement

can also help treat acidosis (potassium moves into cells in exchange for H+)

what are causes of metabolic acidosis in AKI patients?

-increased production of acidic uremic toxins

-decreased bicarbonate production by kidney

-dehydration leading to lactic acidosis

what is the treatment for metabolic acidosis?

1. correct hypovolemia to correct lactic acidosis

2. sodium bicarbonate administration (avoid in patients with respiratory dz and hypercapnia due to increased CO2)

what is the treatment for hypertension in AKI patients?

-start amlodipine

-avoid RAAS inhibition in high grade AKI (avoid ace inhibitors and angiotensin receptor blockers — telmisartan, enalapril)

if refractory to amlodipine: hydralazine +/- beta blocker for reflex tachycardia, acepromazine

how is hemodialysis performed?

-uses dialyzer membrane and dialysate fluid

-blood and dialysate separated by membrane

-dialysate composition dictates diffusion of substances from the blood into the dialysate and vice versa

-given continuously in hospital 2-3 times weekly until recovery

what are indications for hemodialysis?

patient with AKI and one or more of the following:

-significant fluid overload with oliguria and anuria

-uncontrollable hyperkalemia

-severe azotemia (creat >5) and clinical signs despite fluid resuscitation

does hemodialysis treat underlying conditions of AKI?

no, does not treat underlying condition

only treats sequelae of disease