Biochemistry

Question 1

Anion gap calculated by

Answer 1

[Na + K] - [Cl - HCO3]

Question 2

Osmolar gap

Answer 2

2[Na + K] + Urea + Glucose

Question 3

Normal osmolar gap

Answer 3

<10

Question 4

What might a large osmolar gap indicate

Answer 4

presence of high levels of e.g. ethanol

Question 5

At what levels can CO2 be said to be compensating in a metabolic acidosis?

Answer 5

<4.5 kPa

Question 6

At what level can HCO3 be said to be compensating in a respiratory acidosis?

Answer 6

> 30 mmol/L

Question 7

At what levels can CO2 be said to be compensating in a metabolic alkalosis?

Answer 7

> 6.0 kPa

Question 8

At what levels can HCO3 be said to be compensating in a respiratory alkalosis?

Answer 8

< 24 mmol/L

Question 9

Acute respiratory acidosis results

Answer 9

CO2 high and pH is low

Question 10

Chronic resp acidosis with compensation results

Answer 10

CO2 is high pH normal/ near normal. High HCO3

Question 11

Causes of hypoventilation

Answer 11

Neuromuscular disease e.g. GBS or myasthenia gravis

Lung disease e.g. COPD

Decreased central resp drive - trauma, brainstem disease, encephalitis

Question 12

Typical features of hypoventilation

Answer 12

Confusion
Peripheral vasodilation - raised ICP
Coma

Question 13

Investigations in hypoventilation

Answer 13

FBC 
U&E 
TSH 
ABG 
Toxicology 
CXR 
Lung function

Question 14

Treatment for hypoventilation

Answer 14

Treat cause and think about resp support

Question 15

Acute resp alkalosis presentation

Answer 15

CO2 low and pH high

Question 16

Chronic resp alkalosis w/ compensation presentation

Answer 16

CO2 low and pH normal / near to normal with HCO3 low

Question 17

Causes of hyperventilation

Answer 17

CNS - meningitis / stroke / anxiety / trauma

Lung - pneumothorax, pneumonia, pulmonary oedema, PE

Hypoxia - severe anaemia

Drugs - Salicyclates, catecholamines

Endocrine - pregnancy, hyperT

Other - sepsis, liver / heart failure / mechanical ventilation

Question 18

Clinical features of hyperventilation

Answer 18

numbness in hands
tingling round mouth
light headed
tachycardia

Question 19

Investigations in hyperventilation

Answer 19

ABG
U&Es
TSH

Question 20

What is the anion gap used for ?

Answer 20

To investigate if a metabolic acidosis is due to exogenous or endogenous acid

Question 21

High anion gap is …

Answer 21

> 16mmol/L

Question 22

What does a high anion gap indicate?

Answer 22

due to an exogenous acid build up e.g. ethanol / lactic acid

Question 23

Normal anion gap is ….

Answer 23

12 - 16 mmol/L

Question 24

normal anion gap indicates?

Answer 24

endogenous acid build up or bicarb loss e.g. GI / renal loss

Question 25

Causes of metabolic acidosis

Answer 25

Increased H+ - Lactic acidosis, ketoacidosis and some drugs
Failure to excrete H+ - renal failure
Loss of bicarb - GI loss or renal loss

Question 26

Investigations in metabolic acidosis

Answer 26

FBC 
ABG 
U&Es 
Lactate 
Serum osmolarity 
Glucose

Question 27

In severe causes what is given in metabolic acidosis?

Answer 27

Bicarb replacement

Question 28

Metabolic alkalosis - three causes

Answer 28

Loss of H+ - vomiting, diuretic therapy

Endocrine imbalance - cushings, hyperaldosternoism, fludrocortisone

Build up of HCO3 - ingestion

Question 29

Clinical features of metabolic alkalosis

Answer 29

Hypoventilation - due to compensation

may be hypocalcaemia symptoms

Question 30

Investigations in metabolic alkalosis

Answer 30

ABG
U&Es
Renin, aldosterone and cortisol

Question 31

Treatment of metabolic alkalosis

Answer 31

Fluid replacement
Treat the causes
Replace electrolytes - bicarb should replace itself

Question 32

Normal anion gap acidosis causes (4)

Answer 32

Hyperchloraemia
Renal tubular acidosis
Addison’s disease
Diarrhoea