Support of mean arterial pressure during tepid cardiopulmonary bypass: Effects of phenylephrine and pump flow on systemic oxygen supply and demand

Objective: To examine the effects of phenylephrine infusion and increases i n pump flow on systemic oxygen supply and demand when they are used to supp ort mean arterial pressure (MAP) during cardiopulmonary bypass (CPB). Design: Prospective, unblinded study. Setting: The animal cardiopulmonary laboratory at the Mayo Foundation (Roch ester, MN). Participants: Twelve pigs. Interventions:Twelve pigs had systemic oxygen delivery ((D) over dot O-2) a nd consumption ((V) over dot O-2) measured before CPB and then underwent CP B at 35 degrees C. During CPB, measurements of (D) over dot O-2 and (V) ove r dot O-2 were obtained at an MAP of approximately 50 mmHg and a pump flow of 2.2 L/min/m(2). Thereafter, MAP was elevated to 70 mmHg either by increa ses in pump flow or by a phenylephrine infusion, and the balance between sy stemic oxygen supply and demand was reassessed. Measurements and Main Results: Before CPB, (D) over dot O-2 was 375 +/- 83 mL/min/m(2) and decreased with the onset of CPB mainly because of the effec ts of hemodilution. During CPB, with a pump flow of 2.2 L/min/m(2) and an M AP of 53 mmHg, (D) over dot O-2 was 218 +/- 40 mL/min/m(2). Increasing perf usion pressure to an MAP of 72 mmHg with phenylephrine and maintaining pump flow constant (2.2 L/min/m(2)) did not change (D) over dot O-2 (222 +/- 37 mL/min/m(2)), and the oxygen extraction ratio (OER) was increased relative to pre-CPB levels. In contrast, increasing MAP to 71 mmHg by increasing pu mp flow to 3.2 L/min/m(2) resulted in a significantly greater (D) over dot O-2 and the OER normalized to the pre-CPB value. Conclusions: During CPB with conventional flow rates, (D) over dot O-2 is d ecreased. supporting MAP with increases in pump flow better maintains (D) o ver dot O-2 than the administration of an alpha-agonist. Copyright (C) 1999 by W.B. Saunders Company.