Mechanical Ventilation- Ventilator Induced Lung Injury
There are a number of side effects associated with mechanical ventilation. However one of the biggest problems that has become evident over the years is the risk of Ventilator Induced Lung Injury (VILI).
VILI seems to be induced by high airway pressures and/or large volumes as the main causes.
So what types of injury are induced by mechanical ventilation:
- Oxygen Toxicity
Lung injury caused by excessive pressure. However the condition of the patients lung will be a deciding factor in how much pressure it will take to cause the lung injury.
If they have a very compliant lung, that is one that stretches easily with very little change in pressure then they are less likely to suffer from VILI at lower pressures.
The opposite is therefore true if they have non compliant lungs which are more likely to suffer ill effects with lower pressure ventilation.
Keeping the plateau pressure low then becomes important especially in the patient with the compromised lung e.g. the ARDS patient. Research has shown that the plateau pressure should be kept at less than 30cmH20 where possible.
There does however, seem to be evidence that it is the degree of inflation that is likely to cause more damage rather than just the pressure alone.
The quoted example of this is the trumpet player who will often create pressures of 150cm H20 without adverse effects.
Just as in experiments, if the chest wall in lab rats was restricted using strapping damage was reduced at higher pressures, then those patients with poor chest wall compliance (abdominal distension, massive fluid resuscitation, chest wall deformity, morbid obesity) are at less risk of volutrauma with high volumes.
Volutrauma then is lung parenchymal damage caused by mechanical ventilation similar to ARDS.
It manifests itself with increased permeability of the alveolar membrane, pulmonary oedema, disruption in surfactant production and a decrease in compliance of the respiratory system.
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- Lung Compliance
- Ventilation/Perfusion V/Q matching
- Ventilator Induced Lung Injury (VILI)
- Ventilator Associated Pneumonia (VAP)
- Phase variables...again...
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