*ABG Basics*

Question 1

Normal ranges for all values?

Answer 1

pH = 7.35-7.45
pO2 = 11-13 (>10)
pCO2 = 4.7-6.0
HCO3- = 22-26
BE = -2 to +2

Question 2

What is normal pO2 and how is it calculated in patients on administered oxygen?

Answer 2

Normal should be >10 on room air (RA)

• normal for patients on delivered oxygen is calculated as roughly 10kPa below the %oxygen being administered
• e.g. patient on 20% oxygen should be at pO2 10kPa

Question 3

What are the abnormal pO2 states defined as?

Answer 3

Hypoxaemia = pO2<10

Severe hypoxaemia/respiratory failure = pO2<8

Question 4

What are the 2 types of respiratory failure and how are they defined?

Answer 4

Type 1 - hypoxaemia (<8) with normocapnia (<6)

Type 2 - hypoxaemia with hypercapnia (>6)

Question 5

What is type 1 respiratory failure caused by and how does it form?

Answer 5

Ventilation/perfusion mismatch (V/Q mismatch)

• volume of air flowing in/out of the lungs does not match the flow of blood to the lung tissue
• as a result of the mismatch, pO2 falls and pCO2 rises (remember these are in the blood, not the lungs)
• the rise in pCO2 triggers an increase in the patients alveolar ventilation which corrects the pCO2 but not the pO2 (different dissociation curves)

Question 6

Examples of V/Q mismatch?

Answer 6

Reduced ventilation with normal perfusion = pulmonary oedema, bronchoconstriction (e.g. severe asthma)

Reduced perfusion with normal ventilation = pulmonary embolism

Question 7

What is type 2 respiratory failure caused by and how does it form?

Answer 7

Caused by alveolar hypoventilation

• patient can’t adequately oxygenate, and eliminate CO2 from, their blood
• pCO2 rises as it isn’t cleared
• pO2 falls as less is absorbed into the blood form the lungs

Question 8

What are the causes of alveolar hypoventilation (i.e. causes of type 2 respiratory failure)?

Answer 8

• Increased resistance due to airway obstruction (COPD)
• Reduced compliance of the lung tissue/chest wall (pneumonia, rib fracture, obesity)
• Reduced strength of respiratory muscles (Guillain-Barré syndrome, motor neurone disease)
• Drugs acting on the respiratory centre reducing overall ventilation (opiates)

Question 9

Evidence for source of pH derangement?

Answer 9

Imbalance in HCO3- = metabolic
Imbalance in pCO2 = respiratory
- these are the buffers the body uses to correct the pH if one of them is causing a deranged pH

Question 10

What is a typical pH, pCO2, and HCO3- appearance for respiratory acidosis with no compensation?

Answer 10

pH - decreased (acidic)
pCO2 - increased (CO2 retention)
HCO3- - normal

Question 11

What is a typical pH, pCO2, and HCO3- appearance for respiratory alkalosis with no compensation?

Answer 11

pH - increased (alkalotic)
pCO2 - decreased (hypocapnia)
HCO3- - normal

Question 12

What is a typical pH, pCO2, and HCO3- appearance for respiratory acidosis with partial/complete metabolic compensation?

Answer 12

pH - low/normal (partial/complete comp)
pCO2 - increased
HCO3 - increased

Question 13

What is a typical pH, pCO2, and HCO3- appearance for respiratory alkalosis with partial/complete metabolic compensation?

Answer 13

pH - high/normal (partial/complete comp)
pCO2 - decreased
HCO3 - decreased

Question 14

Incomplete so will come back to this but GeekyMedics quiz link on back of this and in Practice Paper 3

Answer 14

https://geekyquiz.com/learn/quiz/336440/