Week 5 - Hypoxia Flashcards
What is hypoxia?
Oxygen deficiency at tissue level
What is hypoxaemic hypoxia?
Not enough oxygen is getting into the lung and pulmonary capillaries
Poor oxygenation in lungs
Low pO2 and oxygen saturation
What is anaemic hypoxia?
Normal pO2 but insufficient haemoglobin to carry it
What is stagnant/circulatory hypoxia?
Reduced delivery of oxygen due to poor perfusion
Could be global or local
What is cytoxic hypoxia?
Oxygen delivery is adequate but tissues unable to utilise it e.g. Cyanide poisoning
What are the features of respiratory failure?
Not enough oxygen enters the blood
Not enough carbon dioxide leaves the blood
At what level of oxygen saturation does tissue damage occur?
<90% (<8 kPa pO2)
What is type 1 respiratory failure?
pO2 of arterial blood <8 kPa
Oxygen saturation <90%
pCO2 normal or low
What is type 2 respiratory failure?
pO2 in arterial blood <8 kPa
Oxygen saturation <90%
pCO2 >6.4 kPa (high)
How do we measure oxygen in blood?
Pulse oximeter
Arterial blood gas analysis
What does a pulse lximeter show?
Oxygen saturation of haemoglobin in arterial blood
What are the mechanisms of type 2 respiratory failure?
Ventilatory failure - unable to move sufficient air in and out if lungs
What are the mechanisms of type 1 respiratory failure?
Poor diffusion across alveolar membrane and/or mismatching of ventilation and perfusion
What are some causes of type 2 respiratory failure/ventilatory failure?
Opiates Trauma Myasthenia gravis Myopathy Severe obesity Pneumothorax Large pleural effusions Respiratory distress of newborn Ling fibrosis Late COPD
What is kyphoscoliosis?
Increase in anteroposterior and lateral curvature of spine
What is flail segment?
Segment of chest wall where multiple ribs are fractured in 2 places
During inspiration the segment gets sucked inwards preventing adequate lung expansion
What are the acute effects of type 2 respiratory failure?
pCO2 rises pO2 falls Central chemoreceptors stimulated Breathlessness (cant completely compensate) Respiratory acidosis
What factors effect gas exchange?
Thickness of the membrane is increased (lung fibrosis)
Available surface area reduced (emphysema)
How doe diffusion impairments affect partial pressures?
pO2 low
pCO2 normal or low because CO2 is more soluble than O2 so diffusion is less affected
What is the consequence of low pO2?
Hypoxia stimulates peripheral chemoreceptors resulting in hypoventilation which further increases CO2 removal
What is ventilation perfusion ratio?
Alveolar ventilation/lung perfusion (same as cardiac output)
Is ideally 1
What is ventilation perfusion mismatching?
Imbalance between alveolar ventilation and alveolar blood flow
What happens when ventilation perfusion ratio is <1?
Alveolar pO2 falls and pCO2 rises
