Oxygen therapy Flashcards
What signs do you see in someone with hypoxia
- Altered mental state
* Dyspnoea, cyanosis, tachypnoea, arrhythmias, coma
At what level of kPa does - hyperventilation - loss of consciousness - death happen?
- Hyperventilation when PaO2 <5.3kPa (saturation <72%)
- Loss of consciousness ~ 4.3 kPa (saturation ~56%)
- Death approximately 2.7 kPa
What are the indications of oxygen therapy
- Known hypoxaemia
- acutely unwell patients with hypoxaemia is likely
How do you define hypoxaemia
low PO2 or partial pressure of oxygen in the arterial blood (PaO2) defined as <8 kPa
How do you define hypoxia
= occurs when oxygen supplies are insufficient to meet oxygen demands at the tissue level.
How do you define type 1 respiratory failure
Type 1 respiratory failure is defined as PaO2 < 8kPa with a normal or low CO2 level and is due to hypoxaemic hypoxia (hypoxia caused by hypoxaemia)
tissue hypoxia can be caused in …
Tissue hypoxia can be caused in several ways one of which is hypoxaemia.
What can cause hypoxaemia
- When at high altitudes (partial pressure of oxygen is less in the atmosphere at higher altitudes)
- Secondary to right-to-left shunts
- Ventilation–perfusion (V/Q) mismatch
- Alveolar hypoventilation
- Diffusion impairment
What is anaemic hypoxia
results from low haemoglobin levels available for oxygen transport. The patient may not be hypoxaemic (with a normal PaO2 and SpO2), but the reduced oxygen content of the blood may lead to tissue hypoxia.
What is stagnant hypoxia
a low level of oxygen in the tissues due to inadequate blood flow (either globally or regionally). This can occur in the body extremities if a person in subject to hypothermia for a prolonged time. It is the cause of gangrene in tissue that is deprived of blood in severe peripheral vascular disease. Stagnant hypoxia may occur in low cardiac output states.
How can you identify hypoxaemia
- Cyanosis
- Blood gases - PaO2 and SaO2
- Oxygen saturation - SpO2 oxygen saturation measured by pulse oximeter
What is oxygen delivery to the tissues determined by
1) Concentration of oxygen reaching the alveoli
2) Pulmonary perfusion
3) Adequacy of pulmonary gas exchange
4) Capacity of blood to carry oxygen (factors affecting haemoglobin)
5) Delivery of oxygen to the tissues
How does oxygen therapy work
Oxygen therapy works by increasing the PAO2 (the partial pressure of oxygen in the alveoli) and therefore can only work when there is adequate ventilation and when gas exchange can occur at the alveolar capillary units in the lungs.
What is ventilation
the exchange of air between the lungs and the atmosphere.
Can you think of any conditions which could cause impairment of gas exchange at the alveolar capillary membrane?
In conditions which result in thickening of the membrane such as fibrotic lung disease, there is a limitation of diffusion of oxygen from the alveoli across the membrane into the pulmonary capillaries. This is also true in conditions such as pulmonary oedema where the excess fluid in the alveoli impairs diffusion. Increasing the PAO2 in these patients however results in an increased rate of diffusion across the capillary membrane by increasing the concentration gradient.
