TYK80
Which of the following clinical situations is likely to INCREASE pulmonary vascular resistance (PVR)?
A. PEEP of 4 cm H20
B. Tidal volume of 6-8 cc/kg
C. Metabolic alkalosis
D. Respiratory alkalosis
E. Respiratory acidosis
Answer
The answer is E.
PVR is noted to be lowest at normal tidal volumes. At low tidal volumes (<4 cc/kg) and high tidal volumes (>12 cc/kg) capillary vessels would likely be compressed due to atelectasis or alveolar distention respectively. This is the same argument for PEEP in a patient with pulmonary hypertension. PVR will usually be improved with some PEEP (read physiologic) because PVR is LOWEST at FRC. FRC is most well maintained with physiologic PEEP. Of course, this depends on the patient's lung disease, but is most readily done with PEEP of 4-5. PEEP can be deleterious if it causes over-distention of the alveoli more than preventing atelectasis. So a PEEP of > 8-10 is probably bad for PHTN. Any acidosis (respiratory or metabolic) raises PVR while any alkalosis lowers it.
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