Cardiovascular reflex responses to temporal reduction in arterial pressure during dexmedetomidine infusion: a double-blind, randomized, and placebo-controlled study.

BACKGROUND The low and moderate doses of dexmedetomidine reduce arterial pressure and heart rate (HR), suggesting attenuation of sympathetic activity and dominance of cardiac-vagal activity. These autonomic responses under dexmedetomidine sedation may attenuate cardiovascular reflex responses to temporal reduction in arterial pressure, inducing a severe hypotension. We therefore investigated the effects of dexmedetomidine on cardiovascular reflex responses to temporal reduction in arterial pressure induced by the thigh cuff method. METHODS Twelve healthy men received placebo, low-dose (loading 3 microg kg(-1) h(-1) for 10 min; maintenance 0.2 microg kg(-1) h(-1) for 60 min), and moderate-dose (loading 6 microg kg(-1) h(-1) for 10 min; maintenance 0.4 microg kg(-1) h(-1) for 60 min) dexmedetomidine infusions in a randomized, double-blind, crossover study. After 70 min of drug infusion, systolic arterial pressure (SAP) and HR responses after thigh cuff deflation were evaluated as indices of cardiovascular reflex. RESULTS Reduction in SAP (Delta SAP) [placebo 8 (4), low 12 (4), moderate 19 (5) mm Hg] after thigh cuff deflation was significantly greater in dexmedetomidine than placebo infusions, in a dose-dependent manner. The change in HR (Delta HR), Delta HR/Delta SAP, and the percentage restoration of SAP were lower with dexmedetomidine compared with placebo. CONCLUSIONS The present results indicated that dexmedetomidine weakens arterial pressure preservation and HR responses after thigh cuff deflation, suggesting attenuated cardiovascular reflexes. Therefore, it must be cautioned that dexmedetomidine can lead to further and sustained reduction in arterial pressure during transient hypotension induced by postural changes, haemorrhage, and/or other stresses.