RESPIRATORY ACID-BASE DISORDERS

Question 1

What is the main cause of respiratory alkalosis? List some things that can cause this

Answer 1

Hyperventilation:

• pain
• Anxiety
• Early aspirin overdose
• Over mechanical ventilation

Question 2

How do the kidneys and RBCs acclimatise to high altitude?

Answer 2

High altitude = low oxygen

• Renal response: kidneys excrete HCO₃ so pH falls back to normal, correcting respiratory alkalosis
• Red-cell response: synthesis of 2,3-diphosphoglyceric acid

Question 3

Describe the two acid-base disorders that aspirin causes. When do they occur after ingestion?

Answer 3

• Shortly after ingestion: salicylates stimulate medulla causing hyperventilation → respiratory alkalosis
• Hours after ingestion: salicylates decrease lipolysis and citric acid cycle leading to accumulation of lactate, pyruvate, ketones → anion gap metabolic acidosis

Question 4

In someone with aspirin OD, what would you expect Winter’s formula to show?

Answer 4

An expected carbon dioxide level higher than reality, indicating a concomitant respiratory alkalosis with metabolic acidosis

Question 5

What are 4 broad reasons for a respiratory acidosis? Hint: hypoventilation

Answer 5

1. CNS drive decreased: opiates
2. Respiratory muscle disease: polio, MS, ALS
3. Impaired gas exchange: pneumonia, pulmonary oedema
4. Airway obstruction: aspiration, sleep apnoea

Question 6

Why would somebody with COPD have a chronically high HCO3 level?

Answer 6

Chronic respiratory acidosis → chronically increased CO2 → compensated with increased HCO3