acid base 2

Question 1

describe base excess

Answer 1

• 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

Question 2

describe anion gap

Answer 2

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

normal AG reflects mainly protein anions

Question 3

what does an increased anion gap indicate and how

Answer 3

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

Question 4

when is the anion gap useful

Answer 4

only in metabolic acidosis

Question 5

what is the approach to metabolic acidosis

Answer 5

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

Question 6

what are the causes of acidosis with increased anion gap

Answer 6

KULT

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

Question 7

describe the delta ratio and how it is calculated

Answer 7

used to determine if a mixed acid-base disorder is present

increased [AG] / decreased [bicarbonate]

Question 8

non-renal causes for a normal AG acidosis

Answer 8

(loss of HCO3- outside of kidney but normal renal acidification)

• diarrhoea
• GI ureteral connections, ileostomy
• external loss of pancreatic or biliary secretion

Question 9

renal causes for a normal AG acidosis

Answer 9

(failure of renal acidification)

• proximal renal tubular acidosis
• hypokalemic distal RTA
• hyperkalemic distal RTA
• RTA of chronic kidney disease

Question 10

describe renal tubular acidosis

Answer 10

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

Question 11

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

Answer 11

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

Question 12

why do some patients experience hyperchloremia with normal anion gap acidosis

Answer 12

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

Question 13

describe the association between K+ and acid-base

and the exception to these rules

Answer 13

acidosis = hyperkalemia
alkalosis = hypokalemia

exception:

• diarrhoea
• renal tubular acidosis

Question 14

artefacts associated with blood gas

Answer 14

air in blood-gas syringe

 - falsely low pCO2
 - falsely appear as resp alkalosis

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