Effects of clonidine on cardiovascular responses to infrarenal aortic cross-clamping. Experimental study in dogs.
OBJECTIVE
Infrarenal aortic cross-clamping is associated to cardiovascular effects. Clonidine, an alpha2-agonist, determines bradycardia and hypotension. This study aimed at analyzing the effects of clonidine on the cardiovascular function of dogs submitted to infrarenal aortic cross-clamping.


METHODS
This randomized study involved 16 mixed breed dogs randomly distributed in two groups: G Control - no clonidine; and G Clon - clonidine (5 microg kg(-1)) immediately before aortic cross-clamping, followed by 2 microg min(-1) m(2) until the end of the study. All dogs were submitted to infrarenal aortic cross-clamping during 45 minutes. Hemodynamic parameters were measured at control (C), 10 (Ao10) and 25 (Ao25) minutes after aortic cross-clamping, and 10 (DAo10) and 25 (DAo25) minutes after aortic unclamping.


RESULTS
There were significant differences between groups in heart rate, mean blood pressure and cardiac index (G control > G Clon) during aortic cross-clamping. After aortic unclamping there were significant differences between groups in heart rate (G Control > G Clon), and right atrium and pulmonary capillary wedge pressures (G Clon > G Control). During aortic cross-clamping both groups have shown significant increase in right atrium pressure, pulmonary capillary wedge pressure, stroke volume index and left ventricular systolic work index, and significant decrease in pulmonary vascular resistance index. There has been significant increase in mean blood pressure, pulmonary artery pressure, cardiac index and right ventricular systolic work index in the G Control. The clonidine group has shown significant heart rate decrease. After aortic unclamping, both groups have shown significant heart rate and mean blood pressure decrease, while right atrium pressure and stroke volume index remained high. Right ventricular systolic work index remained high in the control group, while cardiac index values returned to close to baseline values. In the clonidine group, right atrium pressure, pulmonary wedge pressure and systolic index remained significantly high.


CONCLUSIONS
In dogs under our experimental conditions, continuous intravenous clonidine has attenuated cardiovascular responses to infrarenal aortic cross-clamping.
Achôa
Renato Viccário
RV
CET/SBA do Departamento de Anestesiologia da Faculdade de Medicina de Botucatu (FMB-UNESP), Botucatu, SP.
Vane
Luiz Antonio
LA
Braz
José Reinaldo Cerqueira
JR