U&Es Flashcards
What in u&es points to dehydration as a cause of aki
In the bloods, urea is more than twice the normal range whilst creatinine is only just above the upper limit; this is indicative of dehydration.
In states of dehydration, ADH is secreted to increase reabsorption of water from the collecting ducts. ADH also causes reabsorption of urea from the loop of Henle and collecting duct.
what is creatinine
Creatinine is a waste product of muscle metabolism excreted entirely by the kidney.
Serum creatinine level is naturally higher in individuals with greater skeletal muscle mass (thus generally higher in males than females). However, the primary determinant of serum creatinine is the kidney’s ability to filter creatinine from the bloodstream.
Therefore, a raised creatinine level is an indicator of kidney dysfunction.
what is eGFR
The eGFR is a mathematically derived number based on a patient’s serum creatinine in conjunction with age, sex and race.
eGFR aims to estimate the glomerular filtration rate (GFR), which cannot be directly measured in humans. As the serum creatinine rises, the eGFR will decrease, indicating worsening kidney dysfunction.
how to discuss eGFR with patients
A ‘normal’ glomerular filtration rate is around 100ml/min/1.73m3.
When discussing results with patients, the eGFR can be roughly equated to a percentage of kidney function.
stages of CKD eGFR
Stage 1: eGFR >90 (normal), with other tests showing signs of kidney damage (e.g. proteinuria)
Stage 2: eGFR of 60 to 89 ml/min, with other tests showing signs of kidney damage (e.g. proteinuria)
Stage 3a: eGFR of 45 to 59 ml/min
Stage 3b: eGFR of 30 to 44 ml/min
Stage 4: eGFR of 15 to 29 ml/min
Stage 5: eGFR <15 ml/min
what is urea?
Urea is a waste product of protein breakdown produced in the liver. 3 The kidneys predominantly excrete urea, and it can be used as a surrogate marker of renal function. However, this is fairly non-specific.
causes of raised urea?
Renal dysfunction: decreased excretion of urea into the urine.
Dehydration: urea rises quickly in dehydration, even in the presence of normally functioning kidneys. This is physiologically mediated by anti-diuretic hormone (ADH), released from the posterior pituitary gland in response to intravascular volume depletion. ADH increases urea and water reabsorption in the collecting ducts.
Upper gastrointestinal bleeding: blood in the upper GI tract is broken down into proteins, which are transported to the liver via the portal vein and metabolised into urea.
causes of low sodium
Low serum urea levels are non-pathological, associated with pregnancy and those on a low-protein diet.
broad explanation of how aki be detected?
The kidneys are primarily responsible for fluid balance and maintaining homeostasis. Therefore two of the key ways AKI may be detected are:
- a reduced urine output. This is termed oliguria and is defined as a urine output of less than 0.5 ml/kg/hour
- fluid overload
- a rise in molecules that the kidney normal excretes/maintains a careful balance of. Examples include potassium, urea and creatinine
symptoms aki
Many patients with early AKI may experience no symptoms.
However, as renal failure progresses the following may be seen:
reduced urine output
pulmonary and peripheral oedema
arrhythmias (secondary to changes in potassium and acid-base balance)
features of uraemia (for example, pericarditis or encephalopathy)
criteria for diagnosing aki
Rise in creatinine of more than 25 micromol/L in 48 hours
Rise in creatinine of more than 50% in 7 days
Urine output of less than 0.5 ml/kg/hour over at least 6 hours
risk factors aki
Older age (e.g., above 65 years)
Sepsis
Chronic kidney disease
Heart failure
Diabetes
Liver disease
Cognitive impairment (leading to reduced fluid intake)
Medications (e.g., NSAIDs, gentamicin, diuretics and ACE inhibitors)
Radiocontrast agents (e.g., used during CT scans)
Causes of pre-renal aki
Pre-renal causes are the most common. Insufficient blood supply (hypoperfusion) to kidneys reduces the filtration of blood. This may be due to:
Dehydration
Shock (e.g., sepsis or acute blood loss)
Heart failure
Causes of renal aki
Acute tubular necrosis
Glomerulonephritis
Acute interstitial nephritis
Haemolytic uraemic syndrome
Rhabdomyolysis
causes of post-renal aki
Kidney stones
Tumours (e.g., retroperitoneal, bladder or prostate)
Strictures of the ureters or urethra
Benign prostatic hyperplasia (benign enlarged prostate)
Neurogenic bladder
