Respiratory Failure

Question 1

What is respiratory failure?

Answer 1

Respiratory failure occurs when pulmonary gas exchange is sufficiently impaired to cause hypoxaemia with or without hypercarbia. In practical terms, respiratory failure is present when the PaO2 is <8 kPa (60 mmHg) or the PaCO2 is >7 kPa (55 mmHg). It can be divided into:

• Type I respiratory failure - PaO2 is low and the PaCO2 is normal or low
• Type II respiratory failure - PaO2 is low and the PaCO2 is high.

Question 2

What is type I respiratory failure?

Answer 2

“Acute hypoxaemic” respiratory failure - occurs with diseases that damage lung tissue. Hypoxaemia is due to right-to-left shunts or V̇/Q̇ mismatch.

Question 3

What are causes of type I respiratory failure?

Answer 3

• Pneumonia
• Pulmonary oedema
• PE
• Asthma
• Empyema
• Pulmonary fibrosis
• ARDS

Question 4

What are features of acute hypoxia?

Answer 4

• Dyspnoea
• Restlessness
• Agitation
• Confusion
• Central cyanosis

Question 5

What are features of chronic hypoxia?

Answer 5

• Polycythaemia
• Pulmonary hypertension
• Cor Pulmonale

Question 6

What is type II respiratory failure?

Answer 6

Ventilatory failure - occurs when alveolar ventilation is insufficient to excrete the volume of carbon dioxide being produced by tissue metabolism. Inadequate alveolar ventilation is due to reduced ventilatory effort, inability to overcome an increased resistance to ventilation, failure to compensate for an increase in deadspace and/or carbon dioxide production, or a combination of these factors.

Question 7

What is type II respiratory failure defined as?

Answer 7

• PaO2 < 8kPa
• PaCO2 > 6.0kPa

Question 8

What are neuromuscular causes of type II respiratory failure?

Answer 8

• Cervical cord lesion
• Diaphragmatic paralysis
• Poliomyelitis
• Myasthenia gravis
• Guillain-Barre syndrome

Question 9

What are respiratory causes of type II respiratory failure?

Answer 9

• Asthma
• COPD
• Pneumonia
• End-stage pulmnary fibrosis
• Obstructive sleep apnoea
• Sedative drugs
• CNS tumour
• Trauma - flail chest
• Kyphoscoliosis

Question 10

What are features of hypercapnia?

Answer 10

• Headache
• Peripheral vasodilatation
• Tachycardia
• Bounding pulse
• Tremor/flap
• Papiloedema
• Confusion
• Drowsiness
• Coma

Question 11

How would you investigate someone with suspected respiratory failure?

Answer 11

• Blood tests - FBC, U+Es, CRP, ABG
• Radiology - CXR
• Microbiology - Sputum and BCs
• Spirometry

Question 12

How would you manage someone with type I respiratory failure?

Answer 12

• Treat the cause
• Give O2 - 25-60% by facemask
• Assisted ventilation if PaO2 < 8kPa

Question 13

How would you manage type II respiratory failure?

Answer 13

• Treat underlying cause
• Controlled O2 - start at 24%
• Recheck ABG
• Consider ventilation