ABG's

Question 1

ABG

Answer 1

gives info about the acid-base balance, blood gases (o2 and co2)

pH, PaO2 and PaCO2 are directly measured
HCO3, BE and SaO2 are derived

Question 2

normal values

Answer 2

pH 7.35-7.45
Pa02 10.7-13.3kPa
PaCO2 (carbon dioxide in the blood) 4.7 – 6.0 kPa
HCO3 (bicarbonate) 22 – 26 mmol/L
Base excess -2 – +2
Lactate 0.5 – 1 mmol/L

Question 3

respiratory failure

Answer 3

first step is to determine whether the pt is hypoxic

1. determine the adequacy of oxygen: look at PaO2 (partial pressure of oxygen i.e the amount of o2 dissolved in the blood). normal range is 80-100mmHg / 10.6-13.3kPa. low pao2 = hypoxia
2. check the FiO2: fraction of inhaled oxygen
3. determine the pH status: check the acid-base balance (<7.35 acidosis, 7.35-7.45 normal, >7.45 alkalosis)
4. determine the respiratory component (PaCO2)
5. determine if it’s resp/metabolic acidosis/akalosis

Question 4

FiO2

Answer 4

FiO2 is the fraction of inhaled oxygen. room air has a FiO2 of 21% which means that the concentration of oxygen in room air is 21%. a ventuir mask can be used to control the FiO2

Question 5

types of respiratory failure

Answer 5

Low PaO2 indicates hypoxia and respiratory failure

Normal pCO2 with low PaO2 indicates type 1 respiratory failure (only one is affected)

Raised pCO2 with low PaO2 indicates type 2 respiratory failure (two are affected)

Question 6

respiratory acidosis

Answer 6

ROME
respiratory opposite, metabolic equal.

i.e a low Ph but a high CO2

co2 makes the blood acidotic by breaking it down into carbonic acid (H2CO3)

a low pH with a raised PaCO2 indicates a respiratory acidosis. the pt is acutely retaining co2 and their blood has therefore become acidotic.

Question 7

respiratory acidosis with metabolic alkalosis compensation

Answer 7

acidic pH (low)
high CO2
high HCO3

HCO3 is produced by the kidneys to work as a buffer to neutralise acid in the blood in order to maintain a normal pH. this can take a while for the kidneys to produce and in acute episode of resp acidosis (high co2) the HCO3 cannot be produced fast enough to compensate. therefore, a raised HCO3 indicates a chronic retention of CO2 i.e COPD

Question 8

respiratory alkalosis

Answer 8

ROME
high pH, low CO2

occurs when the patient has a raised respiratory rate and ‘blows off’ too much co2 (high pH and low PaCO2) i.e hyperventilation syndrome in anxiety, PE

in hyperventilation syndrome, the pt will also have a high PaO2 whereas a PE will cause a low PaO2

Question 9

metabolic acidosis

Answer 9

ROME
respiratory opposite, metabolic equal

low pH
low HCO3

causes:
Raised lactate – lactate is released during anaerobic respiration (indicating tissue hypoxia)
Raised ketones – typically in diabetic ketoacidosis
Increased hydrogen ions – due to renal failure, type 1 renal tubular acidosis or rhabdomyolysis
Reduced bicarbonate – due to diarrhoea (stools contain bicarbonate), renal failure or type 2 renal tubular acidosis

Question 10

metabolic alkalosis

Answer 10

ROME - metabolic equal

high pH (alkalosis)
high HCO3 (bicarbonate)

causes:
loss of H+ hydrogen ions i.e from Gastrointestinal tract – due to vomiting (the stomach produces hydrochloric acid)
Kidneys – usually due to increased activity of aldosterone, which results in hydrogen ion excretion

reasons for increased aldosterone activity:
Conn’s syndrome (primary hyperaldosteronism)
Liver cirrhosis
Heart failure
Loop diuretics
Thiazide diuretics

Question 11

pH <7.35 (acidosis)

Answer 11

Acidosis is an abnormal process that increases the serum hydrogen ion concentration, lowers the pH and results in acidaemi

Question 12

pH >7.45 (alkalosis)

Answer 12

Alkalosis is an abnormal process that decreases the hydrogen ion concentration and results in alkalaemia.

Question 13

full or partial compensation

or uncompensated

Answer 13

whether the pH has returned to a normal level (but can still remain at the high or low end of normal)

Question 14

ABG ninja

Answer 14

useful website for practice ABG questions :)