Acid-Base Disorders

Question 1

What is the normal pH range?

Answer 1

7.35-7.45

Question 2

Where do we get acid from?

Answer 2

CO2 production

Acid production - diet

Question 3

How long does respiratory compensation take?

Answer 3

12-24 hours

Question 4

How long does metabolic compensation take?

Answer 4

2-4 days

Question 5

What is the approach to interpreting blood gas results?

Answer 5

1. ACIDOSIS or ALKALOSIS (look at pH)
2. RESPIRATORY or METABOLIC (look at bicarb and CO2)
3. Is compensation appropriate? (look at tables)
4. If acidosis, is there an anion gap? (calculate)
5. Is more than one disorder present?

Question 6

What are the causes of metabolic acidosis?

categorise before giving answer

Answer 6

Increased H+ load 
- ketoacidosis 
- lactic acidosis 
- drugs e.g. salicylates
- methanol, ethanol 
- ethylene glycol (antifreeze)
Decrease H+ secretion 
- renal failure 
- renal tubular acidosis 
- mineralocorticoid deficiency 
Loss of HCO3
- GIT --> diarrhoea 
- Renal --> renal tubular acidosis

Question 7

What are the causes of metabolic alkalosis?

categorise before giving answer

Answer 7

Loss of H+ load 
- GIT --> vomiting 
- Renal --> mineralocaroitid excess, severe K+ deficiency (kidneys secrete H+ to preserve K+)
Excessive HCO3 intake 
- oral or IV therapy

Question 8

What are the causes of respiratory acidosis?

categorise before giving answer

Answer 8

Lung disease 
- emphysema 
- bronchitis 
- asthma 
Neuromuscular 
- guillain barre syndrome
CNS 
- trauma 
- infection 
- tumours
Drugs 
- sedatives 
- anaesthesia 
Mechanical ventilation

Question 9

What are the causes of respiratory alkalosis?

categorise before giving answer

Answer 9

Always hyperventilation!
Pulmonary
- pneumonia, asthma, CCF, embolism, mechanical ventilation
Central
- trauma, infection, tumours, septicaemia, liver failure, salicylates, hysterical

Question 10

What is the anion gap and why is it useful?

Answer 10

• Calcuates if the acidosis is caused by H+ or another acid
• Helps identify cause of acidosis
• See big anionic gap in salicylic acid, antifreeze, ketoacidosis