4. Hypoxia Flashcards
What is hypoxia?
O2 deficiency at tissue level.
What is hypoxiaemia?
O2 deficiency in the blood.
What is the transport chain of O2 from the air to the tissues?
Airways, alveoli, pulmonary capillary, alveolar capillary membrane, bound to Hb, pulmonary veins, left heart, cardiac output, aorta, regional arteries, capillary blood.
What causes poor regional perfusion?
Arterial narrowing or occlusion due to atheromas.
What are the symptoms of poor regional perfusion?
Claudication, angina, neurological deficit.
What is the presentation of claudication?
Pain on exercise, relieved by rest, weak/absent peripheral pulses.
What is the cause of global poor perfusion?
Shock.
What are the types of shock?
Hypovolaemic, cardiogenic, mechanical, distributive.
What is the pathophysiology of hypovolaemic shock?
Loss of volume -> low venous return -> low preload -> low CO -> fall in arterial pressure -> baroreceptor mediated sympathetic reflexes -> venoconstriction and autotransfusion.
What is the pathophysiology of cardiogenic shock?
Damage to myocardium -> heart pumps too little -> arterial pressure falls -> baroreceptors stimulate sympathetic outflow -> reduced perfusion -> skin is cold, pale and clammy, tachycardia.
What is the pathophysiology of septicaemia?
Endotoxins released by bacteria -> overwhelming vasodilatation -> dramatic fall in TPR -> CO can’t keep up.
What is the pathophysiology of anaphylactic shock?
Release of histamine from mast cells -> overwhelming vasodilatation -> dramatic fall in TPR -> drop in blood pressure.
What are the consequences of poor perfusion in shock?
Tissue damage - lactic acid produced from anaerobic metabolism, tissues begin to die, release vasodilator mediators, circulatory collapse, multiorgan failure.
What are the causes of poor oxygen carrying capacity?
Anaemia, CO poisoning.
How can blood oxygenation be measured?
Pulse oximeter, arterial blood gas analysis.
Which type of respiratory failure does ventilatory failure cause?
Type 2.
How does ventilatory failure cause type 2 respiratory failure?
Not enough O2 enters alveoli, not enough CO2 leaves so pO2 is low and pCO2 is high.
What are the causes of ventilatory failure?
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.
How does the body respond to chronic CO2 retention?
CSF acidity corrected by choroid plexus and central chemoreceptors ‘reset’ to higher CO2 levels, persisting hypoxia.
What are the effects of hypoxia on pulmonary arterioles?
Pulmonary hypertension, right heart failure, cor pulmonale.
Which type of respiratory failure does poor diffusion across the alveolar membrane cause and why?
Type 1 - O2 diffusion affected by CO2 is so soluble that its diffusion isn’t affected.
What can cause poor diffusion across the alveolar membrane?
Fibrotic lung disease, pulmonary oedema, emphysema.
What are the causes of diffuse lung fibrosis?
Fibrosing alveolitis, asbestosis, extrinsic allergic alveolitis, pneumoconiosis.
Which type of respiratory failure does ventilation perfusion mismatch lead to?
Type 1.
