Respiratory Failure

Question 1

What characterizes Type 1 RF?

Answer 1

Hypoxia - PaO2 less than 60
Normal or reduced PaCO2
Best reversed by PEEP to open collapsed/flooded alveoli

Causes: ARDS, cardiogenic pulmonary oedema, atelectasis, pneumonia

Question 2

What characterizes Type 2 RF?

Answer 2

Elevated CO2 greater than 45
Often have low oxygen also

Caused by alveolar hypoventilation

• decreased respiratory drive eg overdose, stroke
• neuromuscular disease
• lung disease with increased dead space + increased work of breathing (COPD, kyphoscoliosis)

Question 3

Criteria for ARDS diagnosis

Answer 3

acute onset within 1 week of insult
bilateral opacities on CXR
respiratory failure

• not explained by other pulmonary pathology

Question 4

Precipitating factors of ARDS

Answer 4

Sepsis - most common
Aspiration
Infective pneumonia
Trauma
Burns
Blood transfusion - eg TRALI
Pancreatitis
Fat embolism (post fracture)
Near drowning

Question 5

Pathology of ARDs

Answer 5

Exudative phase (first week)
 - injury to endothelial cells and pneumocytes, inflammatory infiltrate (neutrophils), hyaline membrane forms

Proliferative phase (1-3 weeks)
 - lymphocytic infiltrate, proliferation of type 2 pneumocytes

• if get high alveolar type 3 procollagen = increased progression to fibrosis and mortality

Fibrotic phase
- some patients progress to develop extensive lung fibrosis

Question 6

Treatment of ARDS

Answer 6

Supportive care - treat underlying cause
Ventilation - evidence is for low tidal volume ventilation (6ml/kg) = reduced barotrauma + mortality
No evidence for steroids/other meds

Question 7

Complications of ARDS

Answer 7

Barotrauma
Delirium
Nosocomial infection
DVT
GI bleed due to stress ulceration
Poor nutrition

Question 8

What is diaphragm innervated by?

Answer 8

C3, C4, C5 = phrenic nerve

Question 9

Causes of unilateral paralysis

Answer 9

Cardiac surgery - most common
Viral infections - polio, herpes
Cervical spondylosis
Tumours

Question 10

Diagnostic test for unilateral diaphragmatic paralysis

Answer 10

Sniff test - fluoroscopic assessment of diaphragmatic movement. Normal = diaphragm descends. Paralysed side moves up (not useful for bilateral).

Spirometry (supine and sitting)
- FVC 75-80% upright, drops further 15-25% when lying down

Question 11

Causes of bilateral diaphragm paralysis

Answer 11

Spinal cord disease
MND
Neuropathy (polio, GBS)
NMJ - myasthenia, Lambert eaton
Muscle disease - polymyositis, polymyositis, dermatomyositis, thyroid disease

Question 12

Clinical findings of diaphragmatic paralysis

Answer 12

Unilateral = often asymptomatic, can have reduced exercise tolerance

Bilateral:

• dyspnoea on immediately lying down
• symptoms of pulmonary HTN, RHF
• paradoxical abdo movement inwards on inspiration (see saw)

Question 13

Diagnosis of bilateral diaphragmatic paralysis

Answer 13

*Sniff test not useful - false appearance of diaphragm flattening

Best test is vital capacity upright and supine
- decreased FVC by 50% on lying down

Can also do MIP/EP; and trans-diaphragmatic pressure measurement

Question 14

Treatment for diaphragmatic paralysis

Answer 14

Unilateral - often don’t require tx

Bilateral - NIV, diaphragmatic pacing if intact phrenic nerve (useful in high spinal cord injury)