Abstract
BackgroundClonidine 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.MethodsAfter 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.ResultsHbcrit 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.).ConclusionAnaemia tolerance was not affected by clonidine induced sympathicolysis. Consequently, perioperative clonidine administration probably has not to be omitted in view of acute anaemia.
Highlights
Clonidine effectively decreases perioperative mortality by reducing sympathetic tone
The significantly higher Systemic vascular resistance (SVRI), LVPsys, and LVPedp were not maintained during the progression to Hbcrit
This is reflected in identical critical haemoglobin concentrations and exchangeable blood volumes observed in both study groups
Summary
Clonidine effectively decreases perioperative mortality by reducing sympathetic tone. One pillar of modern patient blood management concepts is to decrease the number of perioperative blood transfusions by accepting low intraoperative haemoglobin concentrations without endangering tissue oxygenation This decline of oxygen carrying capacity has to be compensated for by an increase of cardiac output, organ perfusion, and oxygen extraction ratio [1,2,3]. Perioperative α2-adrenergic agonists decrease global oxygen consumption [6] and improve perioperative myocardial morbidity and mortality [7, 8] by increasing coronary perfusion especially in ischemic heart disease [9], by improving coronary reserve, and by decreasing oxygen consumption [6, 10] They are widely used for postoperative sedation in the ICU [11]
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