Pulmonary Pathophysiology - Respiratory Failure

Question 1

Physiological changes seen in hypoxaemia

Answer 1

Question 2

Causes of CO2 retention

Answer 2

Hypoventilation

Ventilation perfusion inequality

Question 3

Effects of raised CO2 on CNS

Answer 3

Cerebral vasodilation

Raised CSF pressure

Results in headache, reduced GCS, tremor

Question 4

Muscle fibres of the diaphragm

Answer 4

Striated skeletal muscle with:
- Slow twitch oxidative fibres
- Fast twitch oxidative-glycolytic fibres

Question 5

Classification / categories of respiratory failure (not Type 1 and Type 2)

Answer 5

Acute overwhelming lung disease

Neuromuscular disorders

Acute on chronic lung disease

Adult Respiratory Distress Syndrome

Infant Respiratory Distress Syndrome

Question 6

Examples of acute overwhelming lung disease

Answer 6

Any severe acute lung disease

Eg. Pneumonia, massive PE

Question 7

Categories of neuromuscular disorders causing respiratory failure

Answer 7

Respiratory centre depression

Diseases of medulla

Spinal cord

Anterior horn cell

Neural disease

Myoneural junction

Respiratory muscles

Question 8

Causes of respiratory centre depression

Answer 8

Opioids
Barbiturates

Question 9

Causes of diseases of the medulla

Answer 9

Encephalitis
Haemorrhage

Question 10

Causes of spinal cord respiratory failure

Answer 10

High spinal dislocation (C3,4,5)

Question 11

Causes of anterior horn cell disease

Answer 11

Poliomyelitis

Question 12

Causes of neural disease resulting in respiratory failure

Answer 12

Guillain-Barre syndrome

Question 13

Causes of myoneural junction disease

Answer 13

Myasthenia gravis

Question 14

Causes of respiratory muscle weakness

Answer 14

Progressive muscular dystrophies

Question 15

ARDS definition

Answer 15

End result of many pathological processes
Multi-organ failure including lung
High mortality

Question 16

ARDS pathology

Answer 16

Pulmonary oedema high in protein

Cellular debris

Atelectasis areas

May resolve but may develop fibrosis

Question 17

Clinical signs of ARDS

Answer 17

Low lung compliance
High ventilatory pressures

Question 18

IRDS features

Answer 18

Main cause is absence of pulmonary surfactant

Particularly common in premature babies (as surfactant system forms late in gestation)

Question 19

IRDS pathology

Answer 19

Pulmonary oedema with haemorrhage + protein

Patchy atelectasis

Hyaline membranes and cellular debris

Question 20

IRDS clinical signs

Answer 20

Reduced lung compliance

Late complication may develop bronchopulmonary dysplasia

Question 21

IRDS management

Answer 21

Exogenous surfactant via trachea

Question 22

Factors in tissue hypoxia

Answer 22

Arterial PO2

Hb concentration

Cardiac output

Local blood flow

Hb affinity for O2 - eg CO poisoning

Question 23

Hazards of oxygen therapy

Answer 23

CO2 retention - eg. COPD

Oxygen toxicity

Lung atelectasis

Retrolental fibroplasia

Question 24

Oxygen toxicity

Answer 24

Endothelium of pulmonary capillaries are particularly sensitive to O2

Question 25

Retrolental fibroplasia

Answer 25

Occurs in infancy Risk of fibrosis behind lens in eye with persistent high PaO2

Question 26

Effects of PEEP

Answer 26

Increases FRC Reduces atelectasis thus increasing PO2 Compresses capillaries thus increases dead space Reduces venous return Large pressures damage pulmonary capillaries