arf
acute renal failure (ARF)
introduction
ARF is a common finding in the ED patient and one of the clinician's tasks is to decide on whether it is pre-renal, renal or post-renal.
exclusion of urinary retention by checking with a bladder scanner is a simple first step
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investigations to help determine pre-renal vs post-renal causes
index | pre-renal ARF | renal ARF |
blood urea : creatinine ratio (in mM) | >40:1 | < 40:1 |
specific gravity urine | >1.013 | <1.013 |
urinary sodium concentration (mM) | <10 | >10 |
urine osmolality | >500 | <350 |
urine:plasma osmolar ratio | >1.2 | <1.2 |
Fe Na % | <1 | >3 |
renal failure index | <1 | >4 |
urinary sodium indices
urinary sodium concentration provides information on the integrity of tubular reabsorptive function
normally urimary sodium concentration parallels sodium intake
low urinary sodium thus indicates not only intact tubular reabsoptive mechanism but also the presence of a stimulus to conserve sodium
urinary sodium concentration (and fractional excretion of sodium (FENa)) helps distinguish between the two most common causes of ARF: pre-renal azotaemia and ATN.
urinary indices are most helpful in oliguric patients. In euvolaemic individuals who are in sodium balance, & who have a normal sodium intake and normal renal function will have urinary sodium concentration < 20mEq/L & FENa < 1%
UNa < 20mEq/L, FENa < 1%
normal individuals
oliguric pts:
pre-renal azotaemia
acute glomerulonephritis (check urine microscopy for red cell casts)
acute obstruction
some cases of contrast-induced ATN
some cases of rhabdomyolysis-associated ATN
early sepsis
10% of cases of oliguric ATN
UNa 20-40mEq/L:
UNa > 40mEq/L, FENa > 1%
pre-renal causes of ARF
general features
aetiology
volume loss:
GIT: vomiting, diarrhoea, NG drainage
renal: diuresis
blood loss
insensible losses
third space sequestration
pancreatitis
peritonitis
trauma
burns
cardiac:
AMI, valvular disease, cardiomyopathy
decreased effective arterial volume:
antihypertensive drugs
nitrates
"neurogenic":
sepsis
anaphylactic
hypoalbuminaemia
nephrotic syndrome
liver disease
impaired intrarenal blood flow:
renal causes of ARF
vascular:
large vessel:
small & medium vessel:
scleroderma
malignant HT:
severe HT with headaches, cardiac failure, retinopathy, CNS dysfn, papilloedema
RBC casts; LVH on ECG with resolution on control of BP
HUS, TTP:
compatible clinical Hx - diarrhoea; cyclosporin; anovulants;
fever, pallor, ecchymoses, neurological abnormalities
anaemia, thrombocytopenia, schistocytes, LDH, renal Bx
glomerular
systemic diseases:
SLE, infective endocarditis, systemic vasculitis (PAN, Wegener's), HSP, cryoglobulinaemia
Goodpasture's syndrome
primary renal disease:
tubulointerstitial:
infections: acute bilateral pyelonephritis
allergic interstitial nephritis:
recent ingestion of drug - b lactams, NSAIDs, diuretics, proton pump inhibitors, sulphonamides, allopurinol, rifampicin
LOW, malaise, fever, rash or arthralgias
classic triad uncommon: fever, rash and eosinophilia
WBC casts (often eosinophils); RBCs; proteinuria (occas. nephrotic)
eosinophilia; skin Bx of rash (leukocytoclastic vasculitis);
renal Bx - mononuclear infiltrates of lymphocytes, plasma cells & eosinophils +/- histiocytes
drugs/toxins (many):
multiple myeloma:
acute tubular necrosis (ATN)
ischaemia:
nephrotoxins:
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the fungal mycotoxin, Ochratoxin A (OTA), a secondary metabolite produced by several fungal species, in particular from Aspergillus ochraceus and Penicillium verrucosum which may contaminate foods such as cereals
pigments:
myoglobinuria:
haemoglobinuria:
crystals:
post-renal causes of ARF
in the absence of infection, full renal recovery from post-renal ARF is said to be possible even after 1-2 weeks full obstruction, although serum CRN may not return to baseline for several weeks
as the onset of irreversible loss of renal function with obstruction appears to be gradual, a few days delay in diagnosis generally is considered acceptable, although common sense dictates that obstructions should be detected and relieved as expeditiously as possible.
intrarenal & ureteral:
kidney stone
sloughed papilla (esp. if sudden deterioration of renal fn in diabetes, analgesic nephropathy or HbS)
malignancy
retroperitoneal fibrosis
crystal precipitation - uric acid (eg. with tumour lysis), oxalic acid, sulphonamide
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surgical misadventure
bladder:
urethra:
clinical features and complications of ARF
cardiovascular:
pulmonary oedema
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pericardial effusion
AMI
PE
neurologic:
asterixis
NM irritability
mental state changes
somnolence
coma
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GIT:
nausea, vomiting
gastritis
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GIT bleeding
malnutrition
haematologic
infectious:
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septicaemia
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wound infection
arf.txt · Last modified: 2020/01/07 21:15 (external edit)