A patient with pulmonary fibrosis and respiratory discomfort in the pressure support mode (PSV)
Last update: Wednesday, 28 Sep 2016 at 17:10
A 79-yeard-old man with pulmonary fibrosis was admitted in the ICU for acute hypoxemic respiratory failure that required intubation and mechanical ventilation. After some clinical improvement he was lightly sedated and ventilated in the pressure support mode (PSV) with the following settings: PS:8cmH2O, cycling off of 25% of the peak inspiratory flow and PEEP:10cmH2O. The use of accessory muscles of respiration was clinically evident and the curves on the ventilator display are shown bellow.
Source: www.xlung.net
Which of the following would be the most appropriate adjustments of the PSV mode?
a) Reduction of the rise time
b) Increase of the rise time
c) Reduction of the cycling off criterion (% peak inspiratory flow)
d) Increase of the cycling off criterion (% peak inspiratory flow)
Show answer
Answer
The correct answer is option:
c) Reduction of the cycling off criterion (% peak inspiratory flow)
In this particular case the ventilator curves indicate premature cycling in the PSV mode. This type of asynchrony may happen when the deceleration of the inspiratory flow is too rapid, as it would be expected in a patient with low lung compliance due to lung fibrosis.
The figure below shows the effects of the reduction of cycling off criterion from 25 to 5% of the peak inspiratory flow. The sign of the asynchrony (arrow) disappears after this adjustment while the inspiratory time increased from about 0.90s to 0.98s.
Fonte: www.xlung.net
The Brazilian recommendations of mechanical ventilation suggests that patient-ventilator asynchronies should be looked up in a pro-active way.
For this purpose the visual inspection of the flow curves can be very helpful.
The figure above shows on the left that the ventilator's inspiratory time was shorter than the patient’s respiratory muscle inspiratory time . This is shown in the expiratory segment of the flow curve, which tends to return to baseline or to become positive as a result of the patient's inspiratory effort, which is still present (arrow). On the right the cutoff cycling point was reduced to 5%, prolonging the inspiratory time and improving synchrony.
In cases with premature cycling of PSV it is recommended a reduction of the cycling off criterion, specially in patients with restrictive lung diseases who show this sign at the flow curve1
.
References:
Comments