Acid-base abnormality

Question 1

What is metabolic acidosis?

Answer 1

Metabolic acidosis is commonly classified according to the anion gap.

Question 2

What characterizes normal anion gap metabolic acidosis?

Answer 2

Normal anion gap (hyperchloraemic metabolic acidosis) can be due to gastrointestinal bicarbonate loss, renal tubular acidosis, certain drugs, and Addison’s disease.

Question 3

What are some causes of gastrointestinal bicarbonate loss?

Answer 3

Diarrhoea, ureterosigmoidostomy, and fistula.

Question 4

What drugs can cause normal anion gap metabolic acidosis?

Answer 4

Acetazolamide and ammonium chloride injection.

Question 5

What conditions lead to raised anion gap metabolic acidosis?

Answer 5

Lactate (shock, hypoxia), ketones (diabetic ketoacidosis, alcohol), urate (renal failure), and acid poisoning (salicylates, methanol).

Question 6

What is metabolic alkalosis?

Answer 6

Metabolic alkalosis may be caused by a loss of hydrogen ions or a gain of bicarbonate, mainly due to kidney or gastrointestinal tract problems.

Question 7

What are some causes of metabolic alkalosis?

Answer 7

Vomiting/aspiration, diuretics, liquorice, hypokalaemia, primary hyperaldosteronism, Cushing’s syndrome, Bartter’s syndrome, and congenital adrenal hyperplasia.

Question 8

What conditions can cause respiratory acidosis?

Answer 8

COPD, decompensation in respiratory conditions (e.g. life-threatening asthma, pulmonary oedema), and sedative drugs (benzodiazepines, opiate overdose).

Question 9

What are common causes of respiratory alkalosis?

Answer 9

Anxiety leading to hyperventilation, pulmonary embolism, salicylate poisoning, CNS disorders (stroke, subarachnoid haemorrhage, encephalitis), altitude, and pregnancy.

Question 10

What is the formula to calculate the anion gap?

Answer 10

(sodium + potassium) - (bicarbonate + chloride)

Question 11

What is a normal anion gap range?

Answer 11

8-14 mmol/L

Question 12

In which condition is the anion gap particularly useful?

Answer 12

It is useful to consider in patients with a metabolic acidosis.

Question 13

What are the causes of a normal anion gap or hyperchloraemic metabolic acidosis?

Answer 13

1. Gastrointestinal bicarbonate loss: diarrhoea, ureterosigmoidostomy, fistula
2. Renal tubular acidosis
3. Drugs: e.g. acetazolamide
4. Ammonium chloride injection
5. Addison’s disease

Question 14

What are the causes of a raised anion gap metabolic acidosis?

Answer 14

1. Lactate: shock, hypoxia
2. Ketones: diabetic ketoacidosis, alcohol
3. Urate: renal failure
4. Acid poisoning: salicylates, methanol
5. 5-oxoproline: chronic paracetamol use

Question 15

What is the first step in arterial blood gas interpretation?

Answer 15

How is the patient?

Question 16

What indicates hypoxaemia in arterial blood gas interpretation?

Answer 16

The PaO2 on air should be >10 kPa.

Question 17

What pH values indicate acidaemia or alkalaemia?

Answer 17

pH < 7.35 indicates acidaemia; pH > 7.45 indicates alkalaemia.

Question 18

What does a PaCO2 > 6.0 kPa suggest?

Answer 18

It suggests a respiratory acidosis (or respiratory compensation for a metabolic alkalosis).

Question 19

What does a PaCO2 < 4.7 kPa suggest?

Answer 19

It suggests a respiratory alkalosis (or respiratory compensation for a metabolic acidosis).

Question 20

What bicarbonate levels suggest metabolic acidosis?

Answer 20

Bicarbonate < 22 mmol/l (or a base excess < -2 mmol/l) suggests metabolic acidosis (or renal compensation for a respiratory alkalosis).

Question 21

What bicarbonate levels suggest metabolic alkalosis?

Answer 21

Bicarbonate > 26 mmol/l (or a base excess > +2 mmol/l) suggests metabolic alkalosis (or renal compensation for a respiratory acidosis).

Question 22

What does ROME stand for in arterial blood gas interpretation?

Answer 22

Respiratory = Opposite; Metabolic = Equal.

Question 23

What does low pH + high PaCO2 indicate?

Answer 23

It indicates acidosis.

Question 24

What does high pH + low PaCO2 indicate?

Answer 24

It indicates alkalosis.

Question 25

What does low pH + low bicarbonate indicate?

Answer 25

It indicates acidosis.

Question 26

What does high pH + high bicarbonate indicate?

Answer 26

It indicates alkalosis.

Question 27

Arterial blood gas interpretation - ROME

Answer 27

Question 28

What is metabolic acidosis commonly classified according to?

Answer 28

Metabolic acidosis is commonly classified according to the anion gap.

Question 29

How is the anion gap calculated?

Answer 29

The anion gap is calculated by: (Na+ + K+) - (Cl- + HCO-3).

Question 30

What is the normal range for the anion gap?

Answer 30

The normal range for the anion gap is 10-18 mmol/L.

Question 31

What is normal anion gap metabolic acidosis also known as?

Answer 31

Normal anion gap is also known as hyperchloraemic metabolic acidosis.

Question 32

What are some causes of normal anion gap metabolic acidosis?

Answer 32

Causes include gastrointestinal bicarbonate loss, prolonged diarrhoea, ureterosigmoidostomy, fistula, renal tubular acidosis, drugs like acetazolamide, ammonium chloride injection, and Addison's disease.

Question 33

What are the causes of raised anion gap metabolic acidosis?

Answer 33

Causes include lactate (shock, sepsis, hypoxia), ketones (diabetic ketoacidosis, alcohol), urate (renal failure), and acid poisoning (salicylates, methanol).

Question 34

What are the two types of lactic acidosis?

Answer 34

Lactic acidosis is subdivided into type A (sepsis, shock, hypoxia, burns) and type B (metformin).

Question 35

What is metabolic alkalosis?

Answer 35

Metabolic alkalosis may be caused by a loss of hydrogen ions or a gain of bicarbonate. It is due mainly to problems of the kidney or gastrointestinal tract.

Question 36

What are the causes of metabolic alkalosis?

Answer 36

Causes include vomiting/aspiration, diuretics, liquorice, carbenoxolone, hypokalaemia, primary hyperaldosteronism, Cushing's syndrome, and Bartter's syndrome.

Question 37

How does vomiting contribute to metabolic alkalosis?

Answer 37

Vomiting may lead to hypokalaemia and is associated with conditions like peptic ulcer leading to pyloric stenosis and nasogastric suction.

Question 38

What role does the renin-angiotensin II-aldosterone (RAA) system play in metabolic alkalosis?

Answer 38

Activation of the RAA system is a key factor; aldosterone causes reabsorption of Na+ in exchange for H+ in the distal convoluted tubule.

Question 39

What happens during ECF depletion in metabolic alkalosis?

Answer 39

ECF depletion (vomiting, diuretics) leads to Na+ and Cl- loss, activating the RAA system and raising aldosterone levels.

Question 40

How does hypokalaemia contribute to metabolic alkalosis?

Answer 40

In hypokalaemia, K+ shifts from cells to ECF, causing alkalosis due to the shift of H+ into cells to maintain neutrality.

Question 41

What is respiratory acidosis?

Answer 41

Respiratory acidosis is a condition characterized by an increase in carbon dioxide in the blood due to inadequate ventilation.

Question 42

What are some causes of respiratory acidosis?

Answer 42

Respiratory acidosis may be caused by a number of conditions: COPD, decompensation in other respiratory conditions (e.g., life-threatening asthma, pulmonary oedema), neuromuscular disease, obesity hypoventilation syndrome, and sedative drugs (e.g., benzodiazepines, opiate overdose).

Question 43

What is COPD?

Answer 43

COPD stands for Chronic Obstructive Pulmonary Disease, a progressive lung disease that obstructs airflow.

Question 44

What is neuromuscular disease?

Answer 44

Neuromuscular disease refers to a group of disorders that affect the muscles and the nerves that control them.

Question 45

What is obesity hypoventilation syndrome?

Answer 45

Obesity hypoventilation syndrome is a condition in which severely overweight individuals fail to breathe deeply, leading to low oxygen levels and high carbon dioxide levels.

Question 46

How can sedative drugs cause respiratory acidosis?

Answer 46

Sedative drugs, such as benzodiazepines and opiates, can depress the respiratory system, leading to inadequate ventilation and increased carbon dioxide levels.

Question 47

What is respiratory alkalosis?

Answer 47

A condition characterized by a decrease in carbon dioxide levels in the blood due to hyperventilation.

Question 48

What are common causes of respiratory alkalosis?

Answer 48

1. Anxiety leading to hyperventilation 2. Pulmonary embolism 3. Salicylate poisoning 4. CNS disorders: stroke, subarachnoid haemorrhage, encephalitis 5. Altitude 6. Pregnancy

Question 49

What is the effect of salicylate poisoning on respiratory alkalosis?

Answer 49

Salicylate overdose leads to a mixed respiratory alkalosis and metabolic acidosis. Early stimulation of the respiratory centre leads to a respiratory alkalosis whilst later the direct acid effects of salicylates (combined with acute renal failure) may lead to an acidosis.