ABGs

Question 1

6 step approach

Answer 1

1. assess oxygenation
2. determine acid-base status
3. determine the respiratory component (PaCO2) and does this explain acid-base status
4. determine HCO3-, and does this explain the acid-base status
5. which is the primary problem?
6. is there any compensation (v rarely completely restores pH to normal range)

Question 2

respiratory acidosis

Answer 2

any cause of hypoventilation:
CNS depression
neuromuscular disease
acute or chronic lung disease
cardiac arrest 
ventilator malfunction
drugs

Question 3

respiratory alkalosis

Answer 3

any cause of hyperventilation:
hypoxia
acute lung conditions
anxiety
fever
pregnancy
hepatic failure
some CNS lesions

Question 4

hepatic failure

Answer 4

causes resp alkalosis, because progesterone, which is normally metabolized in the liver, increases the rate of breathing through its action on progesterone receptors

Question 5

metabolic acidosis

Answer 5

increased anion gap (added acid) caused by:
renal failure
ketoacidosis
lactic acidosis
salicylate/tricyclic overdose
decreased anion gap (loss of bicarbonate) caused by:
renal tubular acidosis
diarrhoea
carbonic anhydrase inhibitors
ureteral diversion
chloride administration

Question 6

metabolic alkalosis

Answer 6

loss of acid or gaining of alkali by:
vomitting
diarrhoea
diuretics
hypokalaemia
ingestion of alkali