arf
Table of Contents
acute kidney injury (AKI) / acute renal failure (ARF)
see also:
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
- patients in clinical the shocked hypotensive patient will obviously need this addressed ASAP.
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 |
- fractional excretion of sodium (Fe Na %):
- = [(UNa / PNa) / (UCr / PCr)]x100
- this reflects the fraction of filtered sodium that escapes reabsorption & is excreted in urine
- note that urine & plasma levels of sodium & creatinine must be taken simultaneously
- renal failure index (RFI)
- 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:
- non-discriminatory as may be either pre-renal, mild ATN or diuretic use, etc
- UNa > 40mEq/L, FENa > 1%
- 90% of cases of ATN
- chronic obstruction
- diuretic drugs
- osmotic diuresis
- underlying chronic renal failure
pre-renal causes of ARF
general features
- usually have:
- BUN:CRN ratio (in mM) > 100
- FE Na < 1% & urinary sodium < 20 mEq/dL
- if it is severe & prolonged, may result in ATN
- NB. “renal dose” dopamine does not effect clinical outcomes in pts with ARF (Ann Int Med April 2005)
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:
- ACE inhibitors
- NSAIDs (generally reversible):
- inhibit the normal renal vasodilator PG's which are critical in maintaining glomerular perfusion in pts with diminished renal blood flow such as:
- elevated renin/AGII levels as in CCF, CRF & cirrhosis
- elderly, diuretic use, renovascular disease, diabetes
renal causes of ARF
- most patients with Covid-19 AKI had at least mild chronic changes due to diabetic glomerulosclerosis or hypertensive nephroangiosclerosis 1)
- pathophysiology of COVID-19 kidney injury involves both direct effects of COVID-19 on the kidneys as well as mechanisms resulting from:
- a) systemic consequences of the inflammatory response to the viral infection on hemodynamic stability (hypovolemia, sepsis);
- b) effects of the virus on distant organs (organ crosstalk);
- c) therapeutic interventions to manage critical COVID-19 disease (mechanical ventilation, nephrotoxins, inadequate correction of volume depletion)
- Covid-19 vaccination has rarely been implicated as a cause of AKI but some have occurred including Acute Tubulointerstitial Nephritis after mRNA vaccines 2)
vascular:
- large vessel:
- renal artery thrombosis or stenosis:
- Hx of AF/recent AMI; AAA; N/V/flank pain;LDH; renal arteriogram;
- renal vein thrombosis:
- evidence of nephrotic synd. or PE; flank pain; haematuria; IVCgram;
- atheroembolic disease:
- usually age>50;recent aortic procedure;retinal plaques;s/c nodules;palpable purpura; livedo reticularis; vasculopathy; HT; eosinophilia; hypocomplementaemia; skin Bx; renal Bx
- 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:
- COVID-19 coronavirus (2019-nCoV / SARS-CoV-2) - micro-clots
- collapsing glomerulopathy mostly observed in black patients, and was associated with high-risk APOL1 genotypes
- focal segmental glomerulosclerosis - mainly non-ICU patients
- SLE, infective endocarditis, systemic vasculitis (PAN, Wegener's), HSP, cryoglobulinaemia
- Goodpasture's syndrome
- primary renal disease:
- post-strept. & other post-infectious GN
- rapidly progressive GN
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):
- heavy metals, ethylene glycol, etc
- multiple myeloma:
- bone pain; dipstick neg. proteinuria; circ. or urinary paraprotein;
- acute tubular necrosis (ATN)
- ischaemia:
- shock
- sepsis
- all causes of severe pre-renal azotaemia
- nephrotoxins:
- antibiotics, non-steroidal anti-inflammatory drugs (NSAIDs), radiographic contrast agents
- 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:
- rhabdomyolysis (this may also occur in patients with mild Covid-19 kidney damage), vigorous exercise, status epilepticus, myonecrosis, heat illness and heat stroke
- myopathy
- urine supernatant tests +ve for heme;
- haemoglobinuria:
- haemolytic anaemias
- urine supernatant pink & tests +ve for heme;
- pink plasma +ve for Hb
- crystals:
- uric acid:
- tumour lysis (chemotherapy); urate crystals on micro.;
- oxalate:
- ethylene glycol ingestion; oxalate crystals on micro; tox. screen; acidosis; osmolal gap;
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
- methotrexate, aciclovir or Bence Jones protein precipitation
- surgical misadventure
bladder:
- acute urinary retention
- chronic urinary retention
- kidney stone
- blood clot
- prostatic hypertrophy
- bladder carcinoma
- neurogenic bladder
urethra:
- phimosis
- stricture
clinical features and complications of ARF
cardiovascular:
- pulmonary oedema
- arrhythmia due to hyperkalaemia
- pericardial effusion
- AMI
- PE
metabolic:
- decreased serum levels of:
- increased serum levels of:
- acids
- phophate
- uric acid
neurologic:
- asterixis
- NM irritability
- mental state changes
- somnolence
- coma
GIT:
- nausea, vomiting
- gastritis
- GIT bleeding
- malnutrition
haematologic
- haemorrhagic diathesis
infectious:
- septicaemia
- wound infection
arf.txt · Last modified: 2023/07/12 01:53 by gary1