Norepinephrine and ephedrine do not counteract the increase in cutaneous microcirculation induced by spinal anaesthesia

Neuraxial anaesthesia improves tissue perfusion and tissue oxygen tension. Vasodilation induced by this technique may result in hypotension requiring the administration of vasoactive drugs. The use of peripheral vasoconstrictors might counteract the improved tissue perfusion and its potentially beneficial effects. We therefore investigated the effect of i.v. norepinephrine and ephedrine on skin perfusion using laser-Doppler flowmetry (LDF) in patients during spinal anaesthesia.Skin blood flow expressed in perfusion units (PU) provided by LDF was measured simultaneously at the foot and the manubrium levels in 44 patients during spinal anaesthesia with a sensory level below T5. Norepinephrine infusion was then titrated to normalize mean arterial pressure (MAP) in 23 patients (Group NOR). Ephedrine (max. 10 mg) was administered in 21 patients (Group EPH). Changes in relative PU were compared between the two sites of measurements in each group during drug administration. The same doses of norepinephrine were assessed in 11 normal volunteers to assure comparable vasoreactivity at the foot and manubrium levels.Spinal anaesthesia resulted in a 10% decrease in MAP (P0.001), an increase in relative PU values at the foot level (P0.001), and a decrease at the sternum level (P0.05). Norepinephrine and ephedrine produced a significant increase in relative PU values at the foot level when compared with the sternum level (NOR: P=0.02; EPH: P=0.0035). In volunteers, norepinephrine decreased cutaneous perfusion similarly at the manubrium and foot levels.Improved skin perfusion induced by spinal anaesthesia was not counteracted by the use of norepinephrine or ephedrine.