a. Patients can be considered for study inclusion when his/her vasopressor requirements are as follows: i. Norepinephrine 0.04-0.25 mcg/kg/min (plus or minus vasopressin) OR phenylephrine 0.2-2 mcg/kg/min (plus or minus vasopressin) AND ii. Last measured lactate value was < 4 mmol/L AND iii. The patient is on stable or decreasing doses of vasopressors for 8 hours or more. This 8 hour measurement will start at the maximum amount of vasopressor support within the range defined in i. above.