PBL 2 - blood gas primer

Question 1

what is the partial pressure of a gas in solution proportional to?

Answer 1

the conc of that gas in solution (ie. not bound to any carrier)

Question 2

what is another way of saying/thinking about the partial pressure of gas in solution?

Answer 2

the conc of gas in solution

Question 3

what are the normal range of values of blood gases (breathing air)?

Answer 3

measured:

Hb: 13.3 - 17.7 g/dl
pH: 7.37 - 7.45 units
PCO2: 4.7 - 6.4 kPa (35-48mm Hg)
PO2: over 10.7 kPa (80mmHg)

calculated:

base excess: -2 to +2 mmol/l

Question 4

what is the dissociation equation in blood?

Answer 4

CO2 + H2O H2CO3 H+ + HCO3-

Question 5

what is the equation linking pH and [H+]?

Answer 5

pH = -log[H+]

Question 6

describe type 1 respiratory failure

Answer 6

• hypoxaemic failure
• low PaO2
• normal (or low) PaCO2
• disturbance of the relationship of ventilation to perfusion — overall level of ventilation remains normal or may be increased
• mismatch of regional perfusion and ventilation — areas of lung are poorly ventilated — disturbance

Question 7

describe type 2 respiratory failure

Answer 7

• ventilatory failure
• low PaO2 and raised PaCO2
• alveolar ventilation is reduced

Question 8

what is it called if type 1 and type 2 respiratory failure are present at the same time?

Answer 8

mixed respiratory failure

Question 9

what does low PCO2 cause?

Answer 9

alkalosis = high pH

Question 10

the log relationship between pH and [H+] means that a unit change in pH reflects how much of a change in [H+]?

Answer 10

10x change in [H+]

Question 11

PA vs Pa?

Answer 11

Pa = arterial pressure 
PA = alveolar pressure

Question 12

what should SaO2 be?

Answer 12

above 95%

Question 13

what is type 1 respiratory failure due to?

Answer 13

lung damage

Question 14

name some things that can cause type 1 respiratory failure

Answer 14

pulmonary embolism,pneumothorax, pneumonia

Question 15

what can cause type 2 respiratory failure?

Answer 15

COPD, asthma

Question 16

what does a high base excess indicate and result in?

Answer 16

• due to an increase in renal excretion of acid of ingestion or the administration of base
• may also be dye to loss of acid from vomiting
• result is metabolic alkalosis

Question 17

which does a low base excess indicate and result in?

Answer 17

• the overproduction of metabolic acids (eg.lactic acid) or the ingestion of acid
• may also be dye to a reduction in, or failure of, acid excretion by the kidney or to excessive loss of alkali from the intestine with diarrhoea
• result is metabolic acidosis