Outline the causes, consequences and management of intrinsic PEEP.
Causes: consider increased expiratory resistance (prolonged expiratory time constant: eg. bronchospasm, narrow/kinked ETT, inspissated secretions, exhalation valves/HME/filters), increased minute ventilation (inadequate expiratory time), prolonged inspiratory time.
Consequences: consider increased intra-thoracic lung volume (with increased pressures for a given tidal volume and risks of barotrauma), increased intra-thoracic pressure (decreasing venous return, and increasing inspiratory work to trigger the ventilator).
Management: consider treatment of reversible factors (bronchospasm, secretions, expiratory devices), prolongation of expiratory time (decrease respiratory rate, increase inspiratory flow, decrease in inspiratory time) or decrease tidal volumes, application of exogenous PEEP (to 50 –85% of accurately measured intrinsic PEEP) can be used to decrease inspiratory triggering work in spontaneously breathing patients, and possibly to improve distribution of inspired gas.
Intrinsic PEEP seems to be a favourite college topic. There are numerous questions, all of which ultimately ask the same thing: what is intrinsic PEEP, and how does one detect it, and which ventilator settings does one twiddle with in order to defeat it?
So, here we go again.