Respiratory Failure ✅ Flashcards
When is respiratory failure said to be present?
When there is a major abnormality of gas exchange
What are the determinants of oxygenation?
- Mean airway pressure
- FiO2
What are the determinants of CO2 elimination?
- Tidal volume
- Rate
What is the PaO2 in adults?
> 8kPa
What pO2 is usually required to maintain saturations over 90% in a newborn?
5.3-8kPa
What does the PaO2 required to maintain saturations over 90% depend on in neonates?
- Proportion of fetal haemoglobin
- Arterial pH
Is it better to define respiratory failure in terms of arterial oxygen tension or oxygen saturations?
Arterial oxygen tension
Why is it better to define respiratory failure in terms of arterial oxygen tension in neonates?
Because the left shift of the oxyhemoglobin dissociation curve due to 70% HbF is eliminated by a 0.2 drop in pH
??? don’t understand this
What can hypoxaemia in newborn infants result from?
- Ventilation perfusion mismatch
- Extrapulmonary (right-to-left) shunts
- Tissue hypoxia
How can ventilation-perfusion mismatch be identified?
A good response to supplemental oxygen
Why is there a good response to supplemental oxygen in ventilation-perfusion mismatch?
Due to intrapulmonary shunting
What is the problem in ventilation-perfusion mismatch?
There is an increase in physiologic dead space
What causes ventilation-perfusion mismatch?
Parenchymal lung disease
Give 4 parenchymal lung diseases that can cause ventilation-perfusion mismatch
- Respiratory distress syndrome
- Pneumonia
- Meconium aspiration syndrome
- Bronchopulmonary dysplasia
Is there improvement with supplemental oxygen in respiratory failure caused by extrapulmonary shunts?
Relatively little
Give 2 examples of causes of extrapulmonary shunting leading to respiratory failure
- Pulmonary hypertension
- Cyanotic congenital heart disease
When does tissue hypoxia occur, in terms of oxygenation?
When oxygen transport is reduced below a critical level, i.e. below the metabolic demand
What happens when oxygen demands of tissues are not met?
Metabolism must be maintained anaerobically, or the tissue metabolic rate must be reduced
How can tissue oxygenation be evaluated?
- Mixed venous saturation
- Blood lactate levels
- Fractional oxygen extraction
What is the use of mixed venous saturations when evaluating tissue oxygenation?
It identifies global tissue hypoxia
What is the limitation of mixed venous saturation as a measure of tissue oxygenation?
Local tissue hypoxia can exist with normal mixed venous saturation
What is the limitation of blood lactate levels in the evaluation of tissue oxygenation?
It may be elevated in the absence of tissue hypoxia, e.g. sepsis
When does fractional oxygen extraction increase?
When there is compromised oxygen transport to organs and tissues
How can fractional oxygen extraction be measured?
Using near-infrared spectroscopy (NIRS)
