ABG interpretation

Question 1

What is the normal pH of blood?

Answer 1

7.35 - 7.45

Question 2

What is a normal PaCO2?

Answer 2

4.7 – 6.0 kPa

Question 3

What is a normal PO2?

Answer 3

11 – 13 kPa

Question 4

What is a normal HCO3-?

Answer 4

22-26 mmol/l

Question 5

What is a normal base excess?

Answer 5

-2 to +2 mmol/l

Question 6

When looking at an ABG, what question should be asked first?

Answer 6

Is this patient hypoxic?

Question 7

What should the PaO2 be for a patient on room air?

Answer 7

> 10 kPa

Question 8

What should the PaO2 be for a patient on oxygen therapy?

Answer 8

10kPa less than the % inspired concentration FiO2

Question 9

What type of mask will give an accurate concentration of oxygen to the patient regardless of the oxygen flow rate?

Answer 9

venturi mask

Question 10

What % oxygen is given with

a) 1L/min?
b) 2L/min?
c) 3L/min?
d) 4L/min?

Answer 10

a) 24%
b) 28%
c) 32%
d) 36%

Question 11

Which PaO2 indicates severe hypoxiaemia and respiratory failure for a patient on room air?

Answer 11

<8 kPa

Question 12

Which type of respiratory failure has hypercapnia?

Answer 12

type 2

Question 13

Which type of respiratory failure has normocapnia?

Answer 13

type 1

Question 14

What is type 1 respiratory failure the result of?

Answer 14

V/Q mismatch

Question 15

What is V/Q mismatch?

Answer 15

a mismatch of ventilation to perfusion ie. the volume of air going into the lungs doesn’t correlate with the volume of blood flowing into the lungs

Question 16

Give some causes of type 1 respiratory failure

Answer 16

pulmonary oedema
pulmonary embolism
bronchoconstriction

Question 17

Why does type 2 respiratory failure occur?

Answer 17

alveolar hypoventilation

Question 18

Why might alveolar hypoventilation occur?

Answer 18

1. increased resistance due to airway obstruction eg. COPD
2. reduced compliance of chest wall or lung tissue eg. fracture, obesity
3. reduced muscle strength eg. MND, guillain-barre
4. drugs acting on respiratory centre eg. opiates

Question 19

An imbalance in what causes a respiratory driven acidosis/alkalosis?

Answer 19

CO2

Question 20

An imbalance in what causes a metabolism driven acidosis/alkalosis?

Answer 20

HCO3-

Question 21

What helps to rule the respiratory system in or out as the cause for the derangement in pH?

Answer 21

abnormal CO2

Question 22

What does CO2 bind with H2O to form?

Answer 22

carbonic acid (H2CO3)

Question 23

What happens to pH when CO2 is

a) retained?
b) blown off?

Answer 23

a) increase

b) decrease

Question 24

What is bicarbonate?

Answer 24

a base that helps to mop up H+

Question 25

Give the carbonic acid equation

Answer 25

CO2 + H20 ⇌ H2CO3 ⇌ HCO3- + H+

Question 26

What happens to pH when there is a) increased HCO3-? b) decreased HCO3-?

Answer 26

a) increases | b) decreases

Question 27

When the cause of the problem is respiratory, how does the body compensate?

Answer 27

adjusts HCO3-

Question 28

When the cause of the problem is metabolic, how does the body compensate?

Answer 28

blows off or retains CO2 (changes ventilation)

Question 29

In respiratory acidosis, what is the a) pH? b) CO2? c) HCO3?

Answer 29

a) decreased b) raised c) normal

Question 30

In respiratory acidosis with metabolic compensation, what is the a) pH? b) CO2? c) HCO3?

Answer 30

a) decreased or normal b) raised c) increased

Question 31

In respiratory alkalosis, what is the a) pH? b) CO2? c) HCO3?

Answer 31

a) increased b) decreased c) normal

Question 32

In respiratory alkalosis with metabolic compensation, what is the a) pH? b) CO2? c) HCO3?

Answer 32

a) high or normal b) low c) low

Question 33

In metabolic acidosis, what is the a) pH? b) CO2? c) HCO3?

Answer 33

a) low b) normal c) low

Question 34

In metabolic acidosis with respiratory compensation, what is the a) pH? b) CO2? c) HCO3?

Answer 34

a) low or normal b) low c) low

Question 35

In metabolic alkalosis, what is the a) pH? b) CO2? c) HCO3?

Answer 35

a) high b) normal c) high

Question 36

In metabolic alkalosis with respiratory compensation, what is the a) pH? b) CO2? c) HCO3?

Answer 36

a) high b) high c) high

Question 37

What does a high base excess indicate?

Answer 37

high HCO3- so primary metabolic alkalosis or a compensated respiratory acidosis

Question 38

What does a low base index indicate?

Answer 38

low HCO3- so primary metabolic acidosis or a compensated respiratory alkalosis

Question 39

How quickly does a) respiratory compensation b) metabolic compensation take to occur?

Answer 39

a) quickly | b) few days

Question 40

``` What is the a) pH b) CO2 c) HCO3- in a mixed respiratory and metabolic acidosis? ```

Answer 40

a) low b) increased c) decreased

Question 41

``` What is the a) pH b) CO2 c) HCO3- in a mixed respiratory and metabolic alkalosis? ```

Answer 41

a) high b) low c) high

Question 42

Give some causes of respiratory acidosis

Answer 42

- respiratory depression due to opiated - guillain-barre - asthma - COPD - iatrogenic (incorrect mechanical ventilation)

Question 43

Give some causes of respiratory alkalosis

Answer 43

- anxiety attack - pain - hypoxia - pulmonary embolism - iatrogenic (excess mechanical ventilation)

Question 44

What is the anion gap?

Answer 44

used to evaluate metabolic acidosis to see if its due to increased acid production or ingestion vs decreased acid excretion or loss of HCO3–

Question 45

How is the anion gap calculated?

Answer 45

Na+ - (Cl- + HCO3-)

Question 46

What is a normal anion gap?

Answer 46

4-12 mmol/L

Question 47

What does an increased anion gap indicate

Answer 47

increased production or ingestion

Question 48

Give causes of metabolic acidosis that cause an increased anion gap

Answer 48

diabetic ketoacidosis lactic acidosis aspirin overdose

Question 49

Give causes of metabolic acidosis that cause a decreased anion gap

Answer 49

GI loss of HCO3- (eg. diarrhoea, ileostomy, proximal colostomy) renal tubular acidosis addison's disease

Question 50

What does a decreased anion gap indicate?

Answer 50

decreased acid excretion or loss of HCO3-

Question 51

Give some causes of metabolic alkalosis

Answer 51

GI loss of H+ (vomiting, diarrhoea) renal loss of H+ (e.g. loop and thiazide diuretics/heart failure/nephrotic syndrome/cirrhosis/Conn’s syndrome) Iatrogenic (e.g. addition of alkali such as milk-alkali syndrome)

Question 52

How does hyperventilation lead to perioral and peripheral paresthesia?

Answer 52

hypocalcaemia Because a portion of both hydrogen ions and calcium are bound to serum albumin, when blood becomes alkalotic, the bound hydrogen ions dissociate from albumin, freeing up the albumin to bind with more calcium and thereby decreasing the freely ionized portion of total serum calcium leading to hypocalcaemia.