A 28-year-old female (55-kg IBW) is being mechanically ventilated ...

[Medesa]

A 28-year-old female (55-kg IBW) is being mechanically ventilated with VC-CMV, f = 14/min, VT = 700 mL. The patient has no history of pulmonary disease. The resulting ABG values are: pH 7.55, PaCO2 27 mm Hg, HCO3 23 mEq/L.
 
  The most appropriate action to take is which of the following?
  a. Decrease VT to 600 mL.
  b. Decrease VT to 450 mL.
  c. Decrease f to 12/min.
  d. Decrease f to 10/min.

Question 2

A male patient (83-kg IBW) is intubated and ventilated with PC-CMV, f = 12/min, set PIP = 28 cm H2O, resulting in a VT of 430 mL.
 
  The ABG results on this setting are: pH 7.35, PaCO2 45 mm Hg, and HCO3 23 mEq/L. For-ty-eight hours later on the same settings, the ABG results are: pH 7.54, PaCO2 27 mm Hg, and HCO3 21 mEq/L with an exhaled VT of 800 mL. The most appropriate action at this time is which of the following?
  a. Decrease PIP to 25 cm H2O.
  b. Decrease PIP to 19 cm H2O.
  c. Decrease f to 10/min.
  d. Decrease f to 8/min.

[miss.ashley]

Answer to Question 1

ANS: B
The original volume setting exceeded the maximum VT for this patient. The VT should be set between 275 and 440 mL to achieve 5-8 mL/kg IBW. Therefore, the VT must be reduced to avoid overdistention. Using the formula:

Desired VT Known PaCO2 Known VT / Desired PaCO2
Desired VT = 473 mL

The VT of 450 mL is closest to the desired VT and is more in line with the acceptable range.

Answer to Question 2

ANS: B
At first the patient responded appropriately to the PC-CMV settings. At that point the Cs was 15 mL/cm H2O. After 48 hours, the patient's lungs improved and the same pressure, 28 cm H2O, resulted in a VT of 800 mL. The patient's Cs now is 28.5 mL/cm H2O, and the combination of Cs and PIP is resulting in respiratory alkalosis. The acceptable VT range for this patient is 415-664 mL (5-8 mL/kg IBW). Because the exhaled tidal volume now exceeds this range, the volume needs to be reduced. This is accomplished by reducing the set PIP using the following formulas:

Desired VT = and set PIP = VT/CS = 19 cm H2O.

[Medesa]

TYSM

[Viet Thy]

Excellent