An old patient with respiratory distress in PSV mode
A 65-year-old patient with Chronic Obstructive Pulmonary Disease (COPD) is on pressure support ventilation (PSV) mode. He presents respiratory distress, using the accessory muscles of breathing and showing asynchrony with the ventilator. Which adjustment would be advisable, based on the ventilation curves below?
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a) Increase PEEP b) Increase pressure support (PS) c) Increase the “rise time” d) Increase the cycling off criterion (%flow)
The correct answer is: d) Increase the cycling off criterion (% flow)
See the following curves:
Source: www.xlung.net
Note the first respiratory cycle has a delayed cycling compared to respiratory muscle effort (Pmus, pink line). Mechanical ventilator time is longer than the patient's neural time. It is a common phenomenon in patients with COPD in PSV mode.
Changing the PS cycling off criterion, from 25% to 45% (as shown in the last two cycles), reduced the inspiratory time, improving synchrony. The degree of auto PEEP and air trapping was also reduced (see flow x time and volume x time curves) due to the longer expiratory time. Another interesting or useful measure would be to reduce the PS level.
See bellow comments on the other options.
a) Increase PEEP: This setting could potentially aggravate pulmonary hyperinflation, the ventilator would not be able to reduce the inspiratory time.
b) Increase pressure support (PS): This setting could aggravate the problem by generating even higher peak inspiratory flow and VT.
c) Increase the “rise time”: This setting could make the problem even worse by reducing the pressurization rate of the airway and retarding the deceleration of flow.
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