Degree of peripheral vasodilation induced by dexmedetomidine and midazolam in patients undergoing lower extremity surgery

Objective To evaluate the degree of peripheral vasodilation induced by dexmedetomidine and midazolam in the patients undergoing lower extremity surgery. Methods One hundred patients of both sexes, aged 27-64 yr, with body mass index of 20-30 kg/m2, of American Society of Anesthesiologists physical status Ⅰ or Ⅱ, undergoing elective lower extremity surgery under epidural anesthesia, were randomly divided into 4 groups(n=25 each): dexmedetomidine group(group D), compensatory volume expansion+ dexmedetomidine group(group CVE+ D), midazolam group(group M), and compensatory volume expansion + midazolam group(group CVE+ M). In D and CVE+ D groups, dexmedetomidine was infused over 5 min in a loading dose of 0.5 μg/kg, followed by an infusion of 0.3-0.6 μg·kg-1·h-1 until Observer's Assessment of Alertness/Sedation (OAA/S)score reached 3.In M and CVE+ M groups, midazolam was injected over 5 min in a dose of 0.05 mg/kg, followed by an infusion of 0.03-0.10 μg·kg-1·h-1 until OAA/S score reached 3.In CVE+ D and CVE+ M groups, compensatory volume expansion was performed at the same time as dexmedetomidine and midazolam were infused, 6% hydroxyethyl starch 130/0.4 and sodium chloride solution was infused intravenously at a rate of 0.5 ml·kg-1·min-1, and the total volume infused was 7 ml/kg.Before injection of dexmedetomidine or midazolam, and when OAA/S score reached 3, arterial blood samples were collected to determine the blood glucose concentration.Then 50% glucose 10 ml was injected intravenously, and 3 min later, arterial blood samples were collected again to determine the blood glucose concentration.According to the initial distribution volume of glucose, the degree of glucose dilution was determined to reflect the degree of peripheral vasodilation. Results The degree of peripheral vasodilation was(8.5±0.5)%, (8.4±0.4)%, (0.9±0.5)% and(0.8±0.5)% in D, CVE+ D, M and CVE+ M groups, respectively.There was no significant difference in the degree of peripheral vasodilation between D and CVE+ D groups, and between M and CVE+ M groups. Conclusion The degree of peripheral vasodilation induced by dexmedetomidine is about 8.5%, and by midazolam is only about 0.9% in the patients undergoing lower extremity surgery. Key words: Dexmedetomidine; Midazolam; Conscious sedation; Peripheral vasodilation