I had a patient the other day that was on 2 mcg/min of levophed with b/p of 110/50. His blood pressure 2 hours into the shift drops into the 60/40. I increased my levophed to 10 mcg/min and his blood pressure responded to 115/50. When I alerted the resisdent to this rapid increase in levophed he asked for a CVP. I measured a cvp of 12 (pt on vent with peep of 5) After informing him of the CVP, he states that b/c the CVP is adequate no fluid bolus is needed for the blood pressure drop(lasix drip on pt and urine output 50ml/hr). My question is if increasing my levophed causes an increase in CVP because of the increase peripheral vascular resistance(increasing central venous blood return). This would make the cvp measurement after the increase in levophed an inacurate measure of fluid volume staus. Can someone help me with a sound physiologic type answer?