The therapist is mechanically ventilating a lung parenchyma injury patient with ARDS at an I:E ratio of 1:1 with a respiratory rate of 18 breaths/minute. What condition is likely to occur from this situation?
A. alveolar overdistention
B. dynamic hyperinflation
C. parenchymal lung injury
D. ventilator induced diaphragmatic dysfunction
ANS: B
A. Incorrect response: See explanation B.
B. Correct response: The ventilatory rate controls the Paco2. A reasonable starting point for a mechanically ventilated patient is a frequency between 12 and 20 breaths/minute. Increasing the frequency increases the minute ventilation and generally increases CO2 clearance (hyperventilation). If the respiratory rate is too high, at some point; however, air trapping or dynamic hyperinflation may develop because of inadequate expiratory time. Generally, hyperinflation begins to happen in parenchymal lung injuries at breathing rates exceeding 30 to 35 breaths/minute. Nonetheless, it can occur at much lower frequencies if the I:E ratio is high or when the time constant for lung emptying is high.
C. Incorrect response: See explanation B.
D. Incorrect response: See explanation B.?
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