Nephrology Flashcards
how is the anion gap calculated?
(Sodium and potassium - positive cations) - (chlorine and bicarbonate - negative anions)
what is the anion gap?
the blood serum should have a neutral charge. the number of cations (positive) should equal the number of anions (negative). the reason we have an anion gap is because we don’t calculate all the anions present in the blood stream. we only look at chlorine and bicarbonate.
there are other anions e.g. sulphate, phosphate and organic acids. when there is a big anion gap - these anions are making up a bigger proportion of the anion molecules e.g. raised lactic acid (lactate anion)
how does lactic acidosis widen the anion gap?
lactic acid dissociates to form a lactate anion and hydrogen ion. the hydrogen is buffered by the bicarbonate, lowering its numbers.
less bicarbonate and more lactate anions leads to a bigger anion gap
what are causes for a raised anion gap?
lactic acid
ketoacids
urate - renal failure
acid poisoning - methanol (formic acid) and salicylate
what happens in a normal anion gap acidosis?
the bicarbonate falls and kidney compensates for the decrease in anions by increasing the production of chlorine anions.
therefore, can also be known as a hyperchloraemic acidosis
what are causes of normal anion metabolic acidosis?
loss of bicarbonate in the GI tract = e.g. diarrhoea
renal tubular acidosis (RTA) e.g. decreased bicarb re-absorption in DCT
addissons disease
what causes metabolic alkalosis?
caused by a loss of hydrogen ions or gain of bicarb
mainly due to problems in the kidneys or GI tract
- diuretics
- vomiting/aspiration
- cushings syndrome
- primary hyperaldosteronism
- hypokalaemia
what is diabetes insipidus?
characterised by raised plasma osmolarity and low urinary osmolarity
due to a deficiency of ADH (cranial DI) or decreased sensitivity to ADH (nephrogenic DI)
what are causes of cranial DI?
idiopathic
head injury
pituitary surgery
craniopharyngomas
what are causes of nephrogenic DI?
genetic - mutations affection vasopressin receptor / aquaporin channel
electrolytes- hypercalcaemia, hypokalaemia
tubulo-interstital disease (pyelonephritis, sickle-cell, obstruction)
what are features of diabetes insipidus?
polyurea
polydipsia
high plasma osmolarity
low urine osmolarity (<700 )
what is rhabdomyolosis?
break down of muscle fibres and the release of their content into the blood stream - can cause serious complications such as renal failure
due to direct or indirect muscle injury
what is myoglobinuria?
the presence of myoglobin in the urine
usually associated with rhabdomyolosis or muscle destruction
what can cause renal tubular apoptosis?
aminoglycosides and radio contrast medium
what can cause renal tubular necrosis? ATN
myoglobinuria and haemolysis
how is an AKI defined?
an AKI is a syndrome of reduced renal function, measured by creatinine or urine output. There are a number of different aetiologies
clinically defined as:
how is AKi clinically defined?
1) creatinine rise >26 in 48 hours
2) Creatinine rise in adults by 50% + in 7 days
3) eGFR fall in children by 25% + in 7 days
3) urine output < 0.5ml/kg/h for >6 consecutive hours
what are the clinical parameters for the severity staging of AKIs?
Stage 1 = Creatining rise 1.5x baseline or Urine output <0.5 for > 6 hours
Stage 2 = Creatinine rise 2-2.9 x baseline or Urine output <0.5 for >12 hours
Stage 3 = creatinine rise >3 x baseline or urine output <0.3 for >24 hours
how are causes for AKI classified?
Pre-renal 85%
Renal 10%
Post renal 5%
what are pre-renal causes for an AKI?
anything causing decreased renal perfusion
- sepsis, shock
- haemorrhage, burns, pancreatitis, D and V
- cardiogenic shock, severe HF, MI (decreased cardiac output)
- drugs - vasodilation
- hypotension
- ACE-I, ARBs, hepatorenal syndrome, NSAIDs ( renal vasoconstriction)
- dehydration
what are renal causes for AKI?
anything damaging the actual kidney
glomerular = glomerularnephritis, acute tubular necrosis
interstitial = drug reaction, infection, infiltration
vessels = vasculitis, DIC (disseminated intravascular coagulation), TTP (Thrombotic thrombocytopenic purpura), HUS (haemolytic ureamic syndrome)
drugs - NSAIDs, ARBs, ACEi, gentamycin, radio contrast,
rhabdomyelosis
what are post-renal causes of AKI?
anything obstructing the output
- within renal tract: stone, renal tract malignancy, clot, stricture
- extrinsic pressure: retroperitoneal fibrosis, pelvic malignancy, prostatic hypertrophy
what are the most common causes of AKI?
- sepsis
- major surgery
- cardiogenic shock
- other hypovolaemias
- drugs
- hepatorenal syndrome
how does a patient with an AKI present?
dizzy, nausea, vomiting, fluid overload (orthopnea, pulmonary oedema etc), hypotension, tachycardia,