Influence of clonidine induced sympathicolysis on anaemia tolerance in anaesthetized pigs

BACKGROUND Clonidine effectively decreases perioperative mortality by reducing sympathetic tone. However, application of clonidine might also restrict anaemia tolerance due to impairment of compensatory mechanisms. Therefore, the influence of clonidine induced, short-term sympathicolysis on anaemia tolerance was assessed in anaesthetized pigs. We measured the effect of clonidine on anaemia tolerance and of the potential for macrohemodynamic alterations to constrain the acute anaemia compensatory mechanisms. METHODS After governmental approval, 14 anaesthetized pigs of either gender (Deutsche Landrasse, weight (mean ± SD) 24.1 ± 2.4 kg) were randomly assigned to intravenous saline or clonidine treatment (bolus: 20 μg · kg-1, continuous infusion: 15 μg · kg-1 · h-1). Thereafter, the animals were hemodiluted by exchange of whole blood for 6 % hydroxyethyl starch (MW 130.000/0.4) until the individual critical haemoglobin concentration (Hbcrit) was reached. Primary outcome parameters were Hbcrit and the exchangeable blood volume (EBV) until Hbcrit was reached. RESULTS Hbcrit did not differ between both groups (values are median [interquartile range]: saline: 2.2 (2.0-2.5) g · dL-1 vs. clonidine: 2.1 (2.1-2.4) g · dL-1; n.s.). Furthermore, there was no difference in exchangeable blood volume (EBV) between both groups (saline: 88 (76-106) mL · kg-1 vs. clonidine: 92 (85-95) mL · kg-1; n.s.). CONCLUSION Anaemia tolerance was not affected by clonidine induced sympathicolysis. Consequently, perioperative clonidine administration probably has not to be omitted in view of acute anaemia.