Author Question: A patient is receiving PC-CMV with a target tidal volume of at 750 ml. The average peak inspiratory ... (Read 78 times)

tingc95 · **on:** Jul 16, 2018

A patient is receiving PC-CMV with a target tidal volume of at 750 ml. The average peak inspiratory pressure is 30 cm H2O, and the compliance factor for the breathing circuit is 3 ml/cm H2O. Calculate the volume compressed in the ventilator tubing.

A. 250 ml
B. 90 ml
C. 25 ml
D. 10 ml

Question 2

Based on the volume and flow waveforms depicted below, determine the cycle and limit variables.

A. limit variables: pressure and volume; cycle variable: flow
B. limit variables: volume and flow; cycle variable: time
C. limit variables: volume and time; cycle variable: flow
D. limit variables: volume and flow; cycle variable: volume

TheDev123 · **Reply #1 on:** Jul 16, 2018

Answer to Question 1

ANS: BA. Incorrect response: See the calculation associated with choice B.
B. Correct response: The compressible volume is defined as the volume that remains in the patient's breathing circuit at the end of inspiration. This compressed volume can be calculated as follows:
compressed volume = peak inspiratory pressure tubing compliance factor
Vcompressed = PIP Ctubing
Vcompressed = 30 cm H2O 3 ml/cm H2O
Vcompressed = 90 ml
C. Incorrect response: See explanation associated with choice B.
D. Incorrect response: See explanation associated with choice B

Answer to Question 2

ANS: BA. Incorrect response: The flow waveform cannot be the cycle variable because the flow is held constant throughout inspiration. Flow does not terminate when it reaches a preset limit. It maintains that preset limit throughout the inspiratory phase.
B. Correct response: Notice how both the volume and flow waveforms reach a limit and plateau at that level while inspiration continues. Based on that fact, the variable time serves as the cycle variable (i.e., the variable responsible for terminating inspiration).
C. Incorrect response: Limit variables include (1) flow, (2), volume, and (3) pressure. Time is not a limit variable, but can be a cycle variable (terminates inspiration).
D. Incorrect response: Both volume and flow are limit variables in this example because they both plateau during inspiration when they achieve their peak levels. Because volume is a limit variable, it cannot be a cycle variable. Because volume is held constant for a period during inspiration, it cannot cause inspiration to terminate.