The therapist is about to determine the respiratory system ...

[oliviahorn72]

The therapist is about to determine the respiratory system compliance of a patient receiving mechanical ventilation. The patient's tidal volume is 700 ml. Based on the pressure-time scalar presented below, which of the following pressures or pressure gradients does the therapist need to use in this calculation?
 
  A. The pressure reading at f needs to be used.
  B. The pressure gradient from g to f must be selected.
  C. The g-h pressure gradient must be chosen.
  D. The pressure measured at point g needs to be taken.

Question 2

While monitoring a mechanically ventilated patient, the therapist performs an expiratory hold maneuver to ascertain the presence of auto-PEEP. During that maneuver, the therapist notes that the pressure indicates 0 cm H2O. How should the therapist interpret this finding? I. The patient has no auto-PEEP. II. Airway pressure at this time equals alveolar pressure. III. The patient's static compliance has increased. IV. The patient's lungs have not completely emptied.
 
  A. I only
  B. IV only
  C. I, II only
  D. II, III only

[choc0chan]

Answer to Question 1

ANS: C
A. Incorrect response: Label f on the pressure-time tracing represents the peak inspiratory pressure. This pressure is used in the denominator (minus total PEEP) of the formula used to calculate the dynamic compliance.
B. Incorrect response: The pressure gradient f minus g is the pressure generated during VT delivery required to overcome airway resistance. Specifically, these labels signify the difference between the peak inspiratory pressure minus the plateau pressure.
C. Correct response: The pressure gradient required for the calculation of respiratory system compliance is plateau pressure minus total PEEP. On the pressure-time scalar here, the gradient is g minus h.
D. Incorrect response: The pressure measure at g is the plateau pressure. The plateau pressure is used in the denominator (minus total PEEP) of the formula used to calculate the static compliance.

Answer to Question 2

ANS: C
A. Incorrect response: See explanation C.
B. Incorrect response: See explanation C.
C. Correct response: During an expiratory hold maneuver, the flow during the expiratory phase is held at zero. When no gas flows at this time, alveolar pressure equilibrates with airway pressure. Therefore, if the reading during an expiratory hold is 0 cm H2O, the conclusion is that auto-PEEP is absent. Similarly, if this pressure measurement indicates some level of positive pressure, then auto-PEEP is present, assuming that the measured pressure exceeds any applied PEEP. In other words, if applied PEEP is 5 cm H2O, and the measured pressure during an expiratory hold is 10 cm H2O, 5 cm H2O of auto-PEEP is present.
D. Incorrect response: See explanation C.