The investigators hypothesis is that for ICU patients with shock, the use of the vasoactive
drugs phenylephrine and vasopressin will reduce tachydysrhythmias when compared to
norepinephrine and epinephrine. To investigate this hypothesis, the investigators are
conducting a randomized double blind controlled trial comparing phenylephrine and vasopressin
vs. norepinephrine and epinephrine in ICU patients with shock that is not responsive to IV
fluids. All patients admitted to the adult intensive care units at the University of Chicago
will be screened for eligibility.