Adrenergic drugs alter both the fluid kinetics and the hemodynamic responses to volume expansion in sheep.
BACKGROUND
Plasma volume expansion is often performed during adrenergic therapy in the intensive care unit, but little is known about their combined effects.


METHODS
The influence of three adrenergic drugs (50 microg/kg/min of dopamine, 0.1 microg/kg/min of isoprenaline, or 3 microg/kg/min of phenylephrine) on the relationship between plasma dilution (an index of volume expansion) and the central hemodynamic responses to volume loading with 24 ml/kg of 0.9% saline were evaluated in 6 adult sheep. Kinetic analysis was also applied to the data on plasma dilution and the urinary excretion measured during and after volume loading.


RESULTS
The adrenergic agents markedly changed the baseline values for all hemodynamic parameters. The kinetic analysis showed that phenylephrine, which is an alpha-adrenergic receptor agonist, promoted renal excretion of infused fluid at the expense of fluid distribution to the periphery (P < 0.05 versus controls). Isoprenaline, which stimulates adrenergic beta-receptors, had the opposite effect. During volume expansion, cardiac atrial pressures increased by 25 to 90%, cardiac output by 13-80% and the arterial pressures by 2 to 22%. Plasma dilution during and after volume loading correlated, in a linear fashion, with these hemodynamic responses. The correlations were strong (r > 0.80) in the control and phenylephrine groups, but weaker in the dopamine and isoprenaline groups. Dopamine was associated with the most variable hemodynamic responses overall.


CONCLUSIONS
Adrenergic drugs altered the hemodynamics at baseline (direct effects), changed the distribution and elimination of infused 0.9% saline (indirect effects) and, finally, modified most hemodynamic responses to plasma dilution (interaction effects).
Ewaldsson
Carl-Arne
CA
Department of Anesthesiology, South Hospital, Stockholm, Sweden.
Vane
Luiz A
LA
Kramer
George C
GC
Hahn
Robert G
RG
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D004298:Dopamine / Q000494:pharmacology*; D015259:Dopamine Agents / Q000494:pharmacology*; D005260:Female; D006439:Hemodynamics; D007545:Isoproterenol / Q000494:pharmacology*; D007700:Kinetics; D010656:Phenylephrine / Q000494:pharmacology*; D010953:Plasma Volume; D012756:Sheep; D014882:Water-Electrolyte Balance / Q000187:drug effects* / Q000502:physiology*
D000316:Adrenergic alpha-Agonists; D000318:Adrenergic beta-Agonists; D015259:Dopamine Agents; D010656:Phenylephrine; D007545:Isoproterenol; D004298:Dopamine