Data Interpretation

Question 1

pH: 7.2 (7.35-7.45)
PaCO2: 9.6 (4.7-6.5)
PaO2: 9.2 (10.5-13.5)
HCO3- : 26 (22-26)

What abnormality is shown?
a - Metabolic Alkalosis
b - Respiratory Alkalosis
c - Metabolic Acidosis
d - Respiratory Acidosis

Answer 1

D - respiratory acidosis

- pH is low + pCO2 is high with normal HCO3- (acute respiratory acidosis)

Question 2

pH: 7.55 (7.35-7.45)
PaCO2: 3.0 (4.7-6.5)
PaO2: 13.6 (10.5-13.5)
HCO3-: 24 (22-26)

What abnormality is shown?
a - Metabolic Alkalosis without compensation
b - Metabolic Alkalosis with compensation
c - Respiratory Alkalosis without compensation
d - Respiratory Alkalosis with compensation

Answer 2

c - respiratory alkalosis without compensation

- high pH with low pCO2 + high pO2 + normal HCO3- (acute respiratory alkalosis - hyperventilation)

Question 3

Which of these is a common cause of respiratory alkalosis?

a) Opiates
b) Anxiety
c) COPD
d) Norovirus
e) Atelectasis

Answer 3

b - anxiety

- hyperventilation leads to excess removal of CO2 from the blood causing it to become more alkalotic

Question 4

pH: 7.5 (7.35-7.45)
PaCO2: 6.6 (4.7-6.5)
PaO2: 11.0 (10.5-13.5)
HCO3-: 28 (22-26)

What abnormality is shown?

a) Metabolic Alkalosis without compensation
b) Metabolic Alkalosis with compensation
c) Respiratory Alkalosis without compensation
d) Respiratory Alkalosis with compensation

Answer 4

b - metabolic alkalosis with compensation

• pH is high, pCO2 is high but HCO3- is also high
• pCO2 would be low in respiratory alkalosis so is compensating here for raised HCO3-

Question 5

pH: 7.32 (7.35-7.45)
PaCO2: 7.1 (4.7-6.5)
PaO2: 10.8 (10.5-13.5)
HCO3-: 30 (22-26)

What abnormality is shown?
A) Metabolic Acidosis without compensation
B) Metabolic Acidosis with compensation
C) Respiratory Acidosis without compensation
D) Respiratory Acidosis with compensation

Answer 5

D) respiratory acidosis with compensation

- pH is low, pCO2 is high, HCO3- is high (compensation)

Question 6

pH: 7.21 (7.35-7.45)
PaCO2: 3.7 (4.7-6.5)
PaO2: 12.9 (10.5-13.5)
HCO3-: 15 (22-26)

What abnormality is shown?
A) Metabolic Acidosis without compensation
B) Metabolic Acidosis with compensation
C) Respiratory Acidosis without compensation
D) Respiratory Acidosis with compensation

Answer 6

B) Metabolic acidosis with compensation

- low pH, low HCO3- + low pCO2

Question 7

What happens if sodium is replaced too quickly in a hyponatraemic patient?

A) Cardiac arrhythmia
B) Central pontine myelinolysis
C) Tonsillar herniation
D) Anaphylaxis
E) Cerebral oedema

Answer 7

B) Central pontine myelinolysis

- main point is that sodium replacement should be done slowly

Question 8

Patty Bouvier is a 42 year old female who has bipolar disorder. She successfully manages her condition using the mood stabiliser, Lithium. After a routine blood test, her doctor suspects she has diabetes insipidus.

Which of the following describes the effect of diabetes insipidus of blood sodium?

A) Normonatraemic
B) Hypovolaemic hyponatraemia
C) Euvolaemic hyponatraemia
D) Hypervolaemic hyponatraemia
E) Hypernatraemia

Answer 8

E) Hypernatraemia
- diabetes insipidus likely here (lithium as nephrogenic DI cause). The dilute urine = more water lost than sodium = hypernatraemia (high conc)

Question 9

A patient’s has been admitted to hospital. She is given oxygen and ABG and basic observations are taken:

pH: 7.19 (7.35-7.45)
PaCO2: 6.9 (4.7-6.5)
PaO2: 14.2 (10.5-13.5)
HCO3-: 24 (22-26)
Temp: 38.1°C
HR: 109 bpm
BP: 94/66
RR: 30
SaO2: 100% on 15L O2

What abnormality is shown?
A) Metabolic Acidosis
B) Metabolic Alkalosis
C) Respiratory Acidosis 
D) Respiratory Alkalosis

Answer 9

C) Respiratory acidosis

• low pH, high pCO2, normal HCO3-
• high pO2 may be due to oxygen therapy

Question 10

The patient is Selma Bouvier, a 42 year old female. She has been a chronic heavy smoker since her teenage years. She is admitted to hospital confused, her observations and lab results are as follows:

Na: 128
K: 4.4
Urea: 9
Creatinine: 109
Temp: 38.1°C
HR: 109 bpm
BP: 94/66
RR: 30
SaO2: 100% on 15L O2

What is the likely underlying diagnosis?
A) Small cell lung cancer
B) Pneumonia 
C) Heart failure
D) Diarrhoeal illness
E) AKI

Answer 10

B) Pneumonia
- euvolaemic hyponatraemia can be due to SIADH secondary to pneumonia. confusion likely due to hyponatraemia

• a) chronic malignany is a cause of euvolaemic hyponatraemia but no insidious features
• c) HF causes hyponatraemia but not respiratory acidosis
• d) diarrhoeal illness causes hypovolaemic hyponatraemia but wouldn’t cause respiratory acidosis
• e) AKI causes hypervolaemic hypernatraemia, not hyponatraemia, and wouldn’t cause respiratory acidosis
  (Respiratory acidosis refers to the ABG part of this question in another SBA)