Association Between Changes in Norepinephrine Infusion Rate and Urinary Oxygen Tension After Cardiac Surgery.

Objectives: To determine if the administration of norepinephrine to patients recovering from on-pump cardiac surgery is associated with changes in urinary oxygen tension (PO ₂ ), an indirect index of renal medullary oxygenation.
Design: Single center, prospective observational study.
Setting: Surgical intensive care unit (ICU).
Participants: A nonconsecutive sample of 93 patients recovering from on-pump cardiac surgery.
Measurements and Main Results: In the ICU, norepinephrine was the most commonly used vasopressor agent (90% of patients, 84/93), with fewer patients receiving epinephrine (48%, 45/93) or vasopressin (4%, 4/93). During the 30-to-60-minute period after increasing the infused dose of norepinephrine (n = 89 instances), urinary PO ₂ decreased by (least squares mean ± SEM) 1.8 ± 0.5 mmHg from its baseline level of 25.1 ± 1.1 mmHg. Conversely, during the 30-to-60-minute period after the dose of norepinephrine was decreased (n = 134 instances), urinary PO ₂ increased by 2.6 ± 0.5 mmHg from its baseline level of 22.7 ± 1.2 mmHg. No significant change in urinary PO ₂ was detected when the dose of epinephrine was decreased (n = 21). There were insufficient observations to assess the effects of increasing the dose of epinephrine (n = 11) or of changing the dose of vasopressin (n <4).
Conclusions: In patients recovering from on-pump cardiac surgery, changes in norepinephrine dose are associated with reciprocal changes in urinary PO ₂ , potentially reflecting an effect of norepinephrine on renal medullary oxygenation.
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