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.
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.
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