4. Hypoxia Flashcards Preview

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Flashcards in 4. Hypoxia Deck (26)
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1
Q

What is hypoxia?

A

O2 deficiency at tissue level.

2
Q

What is hypoxiaemia?

A

O2 deficiency in the blood.

3
Q

What is the transport chain of O2 from the air to the tissues?

A

Airways, alveoli, pulmonary capillary, alveolar capillary membrane, bound to Hb, pulmonary veins, left heart, cardiac output, aorta, regional arteries, capillary blood.

4
Q

What causes poor regional perfusion?

A

Arterial narrowing or occlusion due to atheromas.

5
Q

What are the symptoms of poor regional perfusion?

A

Claudication, angina, neurological deficit.

6
Q

What is the presentation of claudication?

A

Pain on exercise, relieved by rest, weak/absent peripheral pulses.

7
Q

What is the cause of global poor perfusion?

A

Shock.

8
Q

What are the types of shock?

A

Hypovolaemic, cardiogenic, mechanical, distributive.

9
Q

What is the pathophysiology of hypovolaemic shock?

A

Loss of volume -> low venous return -> low preload -> low CO -> fall in arterial pressure -> baroreceptor mediated sympathetic reflexes -> venoconstriction and autotransfusion.

10
Q

What is the pathophysiology of cardiogenic shock?

A

Damage to myocardium -> heart pumps too little -> arterial pressure falls -> baroreceptors stimulate sympathetic outflow -> reduced perfusion -> skin is cold, pale and clammy, tachycardia.

11
Q

What is the pathophysiology of septicaemia?

A

Endotoxins released by bacteria -> overwhelming vasodilatation -> dramatic fall in TPR -> CO can’t keep up.

12
Q

What is the pathophysiology of anaphylactic shock?

A

Release of histamine from mast cells -> overwhelming vasodilatation -> dramatic fall in TPR -> drop in blood pressure.

13
Q

What are the consequences of poor perfusion in shock?

A

Tissue damage - lactic acid produced from anaerobic metabolism, tissues begin to die, release vasodilator mediators, circulatory collapse, multiorgan failure.

14
Q

What are the causes of poor oxygen carrying capacity?

A

Anaemia, CO poisoning.

15
Q

How can blood oxygenation be measured?

A

Pulse oximeter, arterial blood gas analysis.

16
Q

Which type of respiratory failure does ventilatory failure cause?

A

Type 2.

17
Q

How does ventilatory failure cause type 2 respiratory failure?

A

Not enough O2 enters alveoli, not enough CO2 leaves so pO2 is low and pCO2 is high.

18
Q

What are the causes of ventilatory failure?

A

Poor respiratory effort - respiratory centre depression, muscle weakness; chest wall problems - scoliosis/kyphosis, trauma, pneumothorax; stiff lungs - severe fibrosis; hard to ventilate lungs - high airway resistance in late stages of COPD and severe asthma.

19
Q

How does the body respond to chronic CO2 retention?

A

CSF acidity corrected by choroid plexus and central chemoreceptors ‘reset’ to higher CO2 levels, persisting hypoxia.

20
Q

What are the effects of hypoxia on pulmonary arterioles?

A

Pulmonary hypertension, right heart failure, cor pulmonale.

21
Q

Which type of respiratory failure does poor diffusion across the alveolar membrane cause and why?

A

Type 1 - O2 diffusion affected by CO2 is so soluble that its diffusion isn’t affected.

22
Q

What can cause poor diffusion across the alveolar membrane?

A

Fibrotic lung disease, pulmonary oedema, emphysema.

23
Q

What are the causes of diffuse lung fibrosis?

A

Fibrosing alveolitis, asbestosis, extrinsic allergic alveolitis, pneumoconiosis.

24
Q

Which type of respiratory failure does ventilation perfusion mismatch lead to?

A

Type 1.

25
Q

What can cause V/Q mismatch?

A

Pneumonia, acute asthma, RDS of newborn; pulmonary embolism.

26
Q

How do pulmonary embolisms cause V/Q mismatch?

A

Blood is redirected to other parts of the lung, ventilation of affected parts is wasted, resulting hypoxia.