Respiratory Failure

Question 1

Define respiratory failure/

Answer 1

Respiratory failure occurs when gas exchange is inadequate, resulting in hypoxia. It is defined as PaO2 <8kPa and subdivided into 2 types according to PaCO2 levels

Question 2

What are the clinical features of respiratory failure?

Answer 2

Hypoxia:

• confusion
• dyspnoea
• restlessness
• agitation
• central cyanosis.

Long-standing hypoxia:

• polycythaemia
• pulmonary hypertension
• cor pulmonale.

Hypercapnia:

• headache
• peripheral vasodilation
• tachycardia
• bound pulse
• tremor/flap
• Papilloedema
• Confusion
• Drowsiness
• Coma

Question 3

What causes type I respiratory failure?

Answer 3

Type I respiratory failure is defined as hypoxia (PaO2 <8kPa) with a normal or low PaCO2. This is caused primarily by ventilation/perfusion (V/Q) mismatch. Causes include:
•	Pneumonia
•	Pulmonary oedema
•	PE
•	Asthma
•	Emphysema
•	Pulmonary fibrosis
•	ARDS

Question 4

How do you manage type I respiratory failure?

Answer 4

1. Treat underlying cause
2. Give oxygen (35-60%) by facemask
3. Assisted ventilation (i.e. CPAP) if PaO2 <8kPa despite 60% O2

Question 5

What causes type II respiratory failure?

Answer 5

Type II respiratory failure is defined as hypoxia (PaO2 <8kPa) with hypercapnia (PaCO2 >6kPa). This is caused by alveolar hypoventilation, with or without V/Q mismatch. Causes include:

Pulmonary disease: asthma, COPD, pneumonia, end-stage pulmonary fibrosis, obstructive sleep apnoea

Reduced respiratory drive: sedative drugs, CNS tumour or trauma

Neuromuscular disease: cervical cord lesion, diaphragmatic paralysis, poliomyelitis, myasthenia gravis, Guillain-Barre syndrome, progressive MND

Thoracic wall disease: flail chest, kyphoscoliosis

Question 6

How is type II respiratory failure managed?

Answer 6

Important to note that the respiratory centre may be relatively insensitive to CO2 and respiration could be driven by hypoxia.

1. Treat underlying cause
2. Controlled oxygen therapy (give 24% initially)
3. Recheck ABG after 20mins. If PaCO2 is steady or lower, increase O2 concentrations to 28%. If PaCO2 has risen >1.5kPa, and the patient is still hypoxic, consider Non-invasive Ventilation (NIV)
4. If this fails, consider intubation and ventilation if appropriate