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Failure to Ventilate due to outflow obstruction: the
patient is attempting to ventilate at high lung volumes where the lungs
are least compliant.
This patient has severe
outflow obstruction and gas trapping. Due to the high resistance to
ventilation, air is slow to exit the lungs, and the patient feels
uncomfortable, he attempts to actively exhale and this causes dynamic
airways collapse, causing further airway closure. Some airways may remain
closed during the entire ventilatory cycle, and oxygen is not replenished
– and there is a ventilation-perfusion mismatch. This man is exhibiting
signs of acute gas trapping (auto PEEP) and hypercarbia, indicating
worrisome loss of physiological reserve.
He needs to be intubated and PEEP applied to his airway in excess of the
auto-peep generated (the waterfall effect see figure below): he should be
treated with pressure support ventilation: this mode provides limitless
flow to match the patient's demands.
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