Critical Care Medicine-Neurologic Disorders>>>>>Mechanical Ventilation
Question 7#

A 75-year-old woman has been intubated for 7 days for communityacquired pneumonia. She is placed on a spontaneous breathing trial on ventilator settings of:

• pressure support of 5 cm H₂O
• PEEP of 0 cm H₂O
• FiO₂ of 0.3

What is the most accurate explanation of how breaths are cycled (initiated or terminated) on this ventilator mode?

A. Breaths are initiated based on a set respiratory rate and inspiratory:expiratory ratio
B. Breaths are terminated when inspiratory flow decreases to a set percentage of peak inspiratory flow
C. Breaths are terminated when a target volume is reached
D. Breathes are initiated based on diaphragmatic inspiratory effort
E. Breaths are terminated when a peak inspiratory flow is reached

Correct Answer is B

Comment:

Correct Answer: B

Pressure support breaths are cycled from inspiratory to expiratory when the patient’s inspiratory flow reaches a set percentage of the peak inspiratory flow, often 25% of peak inspiratory flow by default (answer B is correct). Pressure assist-control, a form of continuous mandatory ventilation, cycles based on a set inspiratory time (answer A is incorrect). Volume assist-control, a form of continuous mandatory ventilation, cycles when a breath reaches a target TV, the time for which is dictated by an inspiratory flow rate (answer C is incorrect). Neurally assisted ventilation coordinates inspiratory support with diaphragmatic muscular effort (answer D is incorrect). There are no modes that are terminated by reaching a peak inspiratory flow (answer E is incorrect).

Reference:

1. Gentile MA. Cycling of the mechanical ventilator breath. Respir Care. 2011;56(1):52-60.