Objective: To determine whether catecholamines with different adrenergic receptor affinities are characterized by individual relationships between cardiac output (Q) and oxygen consumption (VO2).
Design: Comparison of the dose-effect relationships and Q/VO2 relationships of four different catecholamines in the same awake dogs.
Setting: University research department of experimental anesthesiology.
Subjects: Ten trained, healthy dogs in the basal metabolic state with chronically implanted ultrasonic flow transducers around the pulmonary artery for the continuous measurement of cardiac output.
Interventions: Increasing doses of norepinephrine, epinephrine, dobutamine, or dopexamine were infused in a randomly varied sequence on separate days until VO2 and Q reached a maximum.
Measurements and main results: VO2 was measured by indirect calorimetry, and Q was measured via the pulmonary artery by ultrasonic flowmetry. In healthy dogs, catecholamines increased both VO2 and Q in a dose-dependent manner until a plateau was reached when VO2 had doubled and Q had quadrupled compared with baseline conditions. Regardless of the catecholamine, the resulting Q/VO2 relationships were linear up to the maximal effects, but their slopes (s) differed significantly between agents (p < .05, paired sign test) and increased approximately three-fold in the order norepinephrine (s = 34), epinephrine (s = 54), dobutamine (s = 86), and dopexamine (s = 105). Except for norepinephrine, the catecholamines also increased oxygen delivery more than VO2, so that O2 extraction decreased to 40% below baseline.
Conclusions: Catecholamines are characterized by linear Q/VO2 relationships with drug-specific slopes. All agents (except norepinephrine) increased oxygen delivery more than oxygen demand. For the practice of catecholamine therapy, our experiments imply that synthetic agents such as dobutamine and particularly dopexamine may be preferred in the treatment of low cardiac output states because they increase Q with the least metabolic effects.