Acute kidney injury Flashcards
What does acute on chronic mean?
- an acute injury suffered in addition to pre-existing chronic renal disease
– the injury may or may not be related to the cause of pre- existing disease
3 categories of AKI
- Haemodynamic i.e. volume responsive (pre-renal azotaemia)
- Intrinsic Renal i.e. actual damage to the kidneys
- Postrenal i.e. urethral obstruction
What contributes to haemodynamic AKI?
- Anything that affects renal blood flow locally or systemic hypotension will contribute to this
- common causes being hypovolaemia, anaesthesia, use of NSAIDS (prostaglandin inhibition)
What does haemodynamic AKI cause and why?
- produces a pre-renal azotaemia due to reduced clearance that is rapidly resolved by correcting the underlying cause (often fluid therapy to restore renal perfusion)
What happens if you don’t correct haemodynamic AKI?
– progression to intrinsic renal damage occurs
– ischaemia and hypoxia
Most common causes of intrinsic renal damage
- ischaemic/hypoxic or toxic in nature
Ischaemic causes of intrinsic renal AKI
- Hypovolaemia, distributive, obstructive, cardiogenic shock*
- Deep / prolonged anaesthesia*
- Thrombosis / DIC
- Hyperviscosity / polycythaemia
- NSAIDs*
Causes of primary renal disease
- Infectious
– UTI (e.coli / gram negative most common) – pyelonephritis
– Lepto - Immune mediated e.g. glomerulonephritis, SLE
- Neoplasia e.g. lymphoma
Secondary disease that causes intrinsic renal AKI
- Infectious e.g. FIP, Leishmania
- Malignant hypertension
- Hepatorenal syndrome in cirrhosis (rare)
- Sepsis – endothelial glycocalyx damage, vascular leak, microcirculatory disruption*
–- S-AKI*
Nephrotoxins that cause intrinsic renal AKI
- NSAIDs*
- Ethylene Glycol*
- Lillies (cats)*
- Vitamin D toxicity
- Aminoglycoside antibiotics
Causes of post-renal AKI
Urinary obstruction
- Ureteral obstruction
– Ureterolithiasis is becoming more common in cats
– Iatrogenic post spey
- Urethral obstruction (blocked bladder)*
- Prolonged obstruction will lead to intrinsic renal damage
Urinary leakage
- Ureteral, bladder or proximal urethra damage leading to uroabdomen
- Distal urethra leading to tissue leakage
- If a UTI is present, septic peritonitis can develop
Resolves with treatment of the underlying problem
The 4 phases of intrinsic AKI
Phase 1 – Asymptomatic phase of the initial insult, towards the end of this phase Azotaemia begins to develop and urine output drops.
Phase 2 – hypoxia and inflammatory responses propagate renal damage, particularly proximal tubule and loop of Henle (highly metabolic cells).
Phase 3 – can last up to three weeks, urine output may be increased or decreased.
Phase 4 – recovery phase, can last weeks to months. During this period, sodium may be lost and severe polyuria – this can result in hypovolaemia, causing recurrent damage through hypoxia.
Diagnosis - history
- Presence of a predisposing factor e.g. anaesthesia, toxin exposure
- <1w history – anorexia, vomiting, PUPD, lethargy, diarrhoea.
Diagnosis - Clinical exam
- Signs associated with fluid loss
– dehydration/hypovolaemia. - Signs associated with concurrent illness e.g. sepsis
Specific signs:
- Renal pain +/- palpable enlargement
- Uremic halitosis and oral ulceration
- Jaundice - Lepto
Diagnosis - biochem
- in phase 1 these changes may be subtle
- Azotaemia
- Hyperphosphataemia (relatively marked)
- Hyperkalaemia – to a possibly dangerous level
- Hypokalaemia possible
- Hypocalcaemia
- Elevated hepatic parameters in Lepto
Diagnosis - urinalysis
- in phase 1 these changes may be subtle
- Inappropriate USG
- Proteinuria
- Glucosuria
- Get a sample for culture and sensitivity
Diagnosis - US: POCUS
- Kidneys may appear normal or enlarged
– Dogs – 5.5 - 9.1x Aortic Diameter
– Cats – 3 – 4.3cm in length - Peri-renal free fluid may be seen with Lepto in dogs, or lymphoma in cats
- Hydronephrosis – obstruction or pyelonephritis
- Allows for FNA (may allow rapid diagnosis of lymphoma on cytology) or Biopsy (risk of bleeding)
Diagnosis - Radiography/CT
- Identification of obstructions
- Intravenous contrast studies elucidate better
Problems caused by leptospirosis
- Renal damage (99.6%)
- Hepatic damage (26%)
- Dyspnoea – Leptospira pulmonary haemorrhage syndrome (LPHS)
(76.7%) - DIC (18.2%)
Leptospirosis - diagnosis
- Findings can include
thrombocytopaenia, anaemia, electrolyte disturbances. - Imaging may reveal interstitial/alveolar patterns, hepatomegaly, splenomegaly, abdominal free fluid, mild lymphadenomegaly.
- SNAP Lepto antibody test (needs antibodies to have been generated,
so early false negatives) - External lab – PCR or MAT (microscopic agglutination test)
Is lepto zoonotic?
- yes
- so any dog with a possible AKI should be tested
Fluid therapy
The goal is to maintain volume status and renal perfusion, but avoid volume overload – close monitoring is key, and regular alterations in fluid rates to maintain normal volume status in the face of either polyuria, oliguria or anuria.
Monitoring – ins/outs and body weight
Match the losses – this means in severe polyuria you may need high fluid rates, but if losses are less, titrate down to avoid volume overload as damaged kidneys can’t get rid of it– don’t go over the target weight and reassess your target weight daily.
Oliguria definition
= <1ml/kg/hr in the hydrated and perfused patient
Anuria definition
= little to no urine in the hydrated and perfused patient
