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Flashcards in acid base 2 Deck (14):

describe base excess

- is a calculated parameter
- it is the amount of acid or base needed to restore pH to 7.4 (assuming normal pCO2)

positive = metabolic alkalosis
negative = metabolic acidosis


describe anion gap

cations - anions
=(Na + K) - (Cl + bicarb)

normal AG reflects mainly protein anions


what does an increased anion gap indicate and how

presence of unmeasured anions e.g. lactate

the presence of more protein and lactate consequently means less bicarbonate will be present, therefore AG goes down
*remember AG doesnt measure protein etc


when is the anion gap useful

only in metabolic acidosis


what is the approach to metabolic acidosis

1. confirm metabolic acidosis:
- low pH with a low HCO3-

2. check serum AG
- high = AG acidosis
- normal = non-anion gap acidosis

3. if normal serum AG, check urine AG


what are the causes of acidosis with increased anion gap


K- ketoacidosis (diabetic)
U- uremic (end stage renal failure)
L- lactic acidosis
T- toxins


describe the delta ratio and how it is calculated

used to determine if a mixed acid-base disorder is present
increased [AG] / decreased [bicarbonate]


non-renal causes for a normal AG acidosis

(loss of HCO3- outside of kidney but normal renal acidification)
- diarrhoea
- GI ureteral connections, ileostomy
- external loss of pancreatic or biliary secretion


renal causes for a normal AG acidosis

(failure of renal acidification)
- proximal renal tubular acidosis
- hypokalemic distal RTA
- hyperkalemic distal RTA
- RTA of chronic kidney disease


describe renal tubular acidosis

defects in acid excretion: urine pH >5.5 (should be low) and urine ammonium not increased when it should be


if the metabolic acidosis is identified what is the next step?

perform a urine test to confirm if the cause is renal or non-renal (pH <5.5 & ammonium >100mmol/L)
- if urine pH is not low then the cause is due to a renal failure e.g. renal tubular acidosis


why do some patients experience hyperchloremia with normal anion gap acidosis

- when bicarbonate is low, extra Cl needs to be reabsorbed to maintain electroneutrality with Na+ reabsorption


describe the association between K+ and acid-base
and the exception to these rules

acidosis = hyperkalemia
alkalosis = hypokalemia

- diarrhoea
- renal tubular acidosis


artefacts associated with blood gas

air in blood-gas syringe
-falsely low pCO2
-falsely appear as resp alkalosis

delayed separation of plasma from RBCs (therefore get to lab quickly)